Minimize Copernicus: Sentinel-1

Copernicus: Sentinel-1 — The SAR Imaging Constellation for Land and Ocean Services

Spacecraft    Launch    Mission Status    Sensor Complement    Ground Segment    References

Sentinel-1 is the European Radar Observatory, representing the first new space component of the GMES (Global Monitoring for Environment and Security) satellite family, designed and developed by ESA and funded by the EC (European Commission). The Copernicus missions (Sentinel-1, -2, and -3) represent the EU contribution to GEOSS (Global Earth Observation System of Systems). Sentinel-1 is composed of a constellation of two satellites, Sentinel-1A and Sentinel-1B, sharing the same orbital plane with a 180° orbital phasing difference. The mission provides an independent operational capability for continuous radar mapping of the Earth with enhanced revisit frequency, coverage, timeliness and reliability for operational services and applications requiring long time series.

Copernicus is the new name of the European Commission's Earth Observation Programme, previously known as GMES (Global Monitoring for Environment and Security). The new name was announced on December 11, 2012, by EC (European Commission) Vice-President Antonio Tajani during the Competitiveness Council.

In the words of Antonio Tajani: "By changing the name from GMES to Copernicus, we are paying homage to a great European scientist and observer: Nicolaus Copernicus (1473-1543). As he was the catalyst in the 16th century to better understand our world, so the European Earth Observation Programme gives us a thorough understanding of our changing planet, enabling concrete actions to improve the quality of life of the citizens. Copernicus has now reached maturity as a programme and all its services will enter soon into the operational phase. Thanks to greater data availability user take-up will increase, thus contributing to that growth that we so dearly need today."

Table 1: Copernicus is the new name of the former GMES program 1)

The overall objective of the Sentinel-1 mission is to provide continuity of C-band SAR operational applications and services in Europe. Special emphasis is placed on services identified in ESA's GSE (GMES Service Element) program. Additional inputs come from on-going GMES projects funded by ESA, the EU, and ESA/EU member states. The Sentinel-1 mission is expected to enable the development of new applications and meet the evolving needs of GMES, such as in the area of climate change and associated monitoring. 2) 3) 4)

The Sentinel-1 mission represents a completely new approach to SAR mission design by ESA in direct response to the operational needs for SAR data expressed under the EU-ESA GMES (Global Monitoring for Environment and Security) program. The mission ensures continuity of C-band SAR data to applications and builds on ESA's heritage and experience with the ERS and Envisat SAR instruments, notably in maintaining key instrument characteristics such as stability and accurate well-calibrated data products.

The key mission parameters are revisit time, coverage, timeliness combined with frequency band, polarization, resolution and other image quality parameters. Short revisit time demands for an appropriate orbit selection and large swath widths.

The baseline mission concept under development is a two-satellite constellation, with four nominal operational modes on each spacecraft designed for maximum compliance with user requirements. 5) 6) 7) 8) 9) 10)

• Orbit: Sun-synchronous near-polar orbit, repeat cycle of 12 days, cycle length of 175 days

• Operational modes:

- Stripmap mode (SM): 80 km swath, 5 m x 5 m resolution, single-look

- Interferometric Wide Swath mode (IWS): 240 km swath, 5 m x 20 m resolution, single-look

- Extra Wide Swath mode (EWS): 400 km swath, single-look

- Interferometric Wide Swath mode (IWS): 240 km swath, 25 m x 80 m resolution, 3-looks

- Wave mode (WM): 20 km x 20 km, 20 m x 5 m resolution, single-look

• Polarization: Dual polarization for all modes VV+VH or HH+HV

• Operations:

- Consistent, reliable and conflict free mission operations

- Near real-time delivery of data within 3 hours (worst case) with 1 hour as goal

- Data delivery from archive within 24 hours

• Sensitivity: NESZ (Noise Equivalent Sigma Zero), σo = -25 dB

• Radiometry:

- Stability = 0.5 dB

- Accuracy = 1.0 dB

• Ambiguity ratio: DTAR (Distributed Target Ambiguity Ratio) = -25 dB

In April 2007, ESA selected TAS-I (Thales Alenia Space Italia) as prime contractor for the Sentinel-1 spacecraft (overall satellite design & integration at system and subsystem level, including the design of the SAR antenna's transmit/receive modules). ESA awarded the contract to TAS-I on June 18, 2007 at the Paris International Air Show. EADS Astrium GmbH of Friedrichshafen, was in turn awarded a contract by TAS-I to build the radar imaging payload for Sentinel-1, including the central radar electronics subsystem developed by Astrium UK. The objective of Sentinel-1 is to assure C-band SAR data continuity for the user community currently provided by Envisat and ERS-2. 11)

Three priorities (fast-track services) for the mission have been identified by user consultation working groups of the European Union: Marine Core Services, Land Monitoring and Emergency Services. These cover applications such as: 12)

• Monitoring sea ice zones and the arctic environment

• Surveillance of marine environment

• Monitoring land surface motion risks

• Mapping of land surfaces: forest, water and soil, agriculture

• Mapping in support of humanitarian aid in crisis situations.

Unlike its more experimental predecessors ERS-1, ERS-2 and Envisat that supply data on a best effort basis, operational satellites like Sentinel-1 are required to satisfy user requirements and to supply information in a reliable fashion with the data provider accepting legal responsibility for the delivery of information.

In March 2010, ESA and TAS-I signed a contract to build the second Sentinel-1 (Sentinel-1B) and Sentinel-3 (Sentinel-3B) satellites, marking another significant step in the Copernicus program. 13)

As part of the Copernicus space component, the Sentinel-1 (S1) mission is implemented through a constellation of two satellites (A and B units) each carrying an imaging C-band SAR instrument (5.405 GHz) providing data continuity of ERS and Envisat SAR types of mission. Each Sentinel-1 satellite is designed for an operations lifetime of 7 years with consumables for 12 years. The S-1 satellites will fly in a near polar, sun-synchronized (dawn-dusk) orbit at 693 km altitude. 14)

The Sentinel-1 mission, including both S-1A and S-1B satellites, is specifically designed to acquire systematically and provide routinely data and information products to Copernicus Ocean, Land and Emergency as well as to national user services. These services focus on operational applications such as the observation of the marine environment, including oil spill detection and Arctic/Antarctic sea-ice monitoring, the surveillance of maritime transport zones (e.g. European and North Atlantic zones), as well as the mapping of land surfaces including vegetation cover (e.g. forest), and mapping in support of crisis situations such as natural disasters (e.g. flooding and earthquakes) and humanitarian aid.

In addition, the 12-day repeat orbit cycle of each Sentinel-1 satellite along with small orbital baselines will enable SAR interferometry (InSAR) coherent change detection applications such as the monitoring of surface deformations (e.g. subsidence due to permafrost melt) and cryosphere dynamics (e.g. glacier flow).

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Figure 1: Artist's view of the deployed Sentinel-1 spacecraft (image credit: ESA, TAS-I)


Spacecraft:

The spacecraft is based on the PRIMA (Piattaforma Italiana Multi Applicativa) bus of TAS-I, of COSMO-SkyMed and RADARSAT-2 heritage, with a mission-specific payload module. Attitude stabilization: 3-axis, attitude accuracy = 0.01º (each axis), orbital knowledge = 10 m (each axis, 3σ using GPS).

The spacecraft structure provides the accommodation for all platform and payload units. A box type structure has been adopted using external aluminum sandwich material, with a central structure in CFRP (Carbon Fiber Reinforced Plastic). A modular approach has been taken whereby the payload is mounted to a dedicated part of the structure, allowing separate integration & test of the payload before integration to the main part of the structure carrying the platform units. This has many advantages for the overall AIT (Assembly, Integration and Test) process. 15) 16) 17) 18) 19) 20)

The PRIMA platform comprises three main modules, which are structurally and functionally decoupled to allow for a parallel module integration and testing up to the satellite final integration. The modules are: 21)

1) SVM (Service Module), carrying all the bus units apart from the propulsion ones

2) PPM (Propulsion Module), carrying all the propulsion items connected by tubing and connectors

3) PLM (Payload Module), carrying all the payload equipment including the SAR Instrument antenna.

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Figure 2: 3D exploded view of the Sentinel-1 platform (image credit: TAS-I)

TCS (Thermal Control Subsystem): The TCS provides control of the thermal characteristics and environment of the Satellite units throughout all phases of the mission. In general the TCS is passive, with the control provided by means of standard techniques such as heat pipes, radiators and MLI (Multi-Layered Insulation). Survival heaters are provided to prevent units becoming too cold during non-operative phases.

EPS (Electric Power Subsystem): The EPS uses two solar array wings for power generation. Each wing consists of 5 sandwich panels using GaAs triple junction solar cells. The average onboard power is 4.8 kW (EOL), the Li-ion battery has a capacity of 324 Ah. The PCDU (Power Control and Distribution Unit) is designed to provide adequate grounding, bonding & protection for the overall electrical system (e.g. by use of fuses) and must also be integrated into the satellite FDIR concept to ensure that adequate power resources and management are available in the event of on-board failures. Li-Ion battery technology has been selected for the batteries in view of the large benefits offered in terms of mass and energy efficiency.

The spacecraft dimensions in stowed configuration are: 3.4m x 1.3 m x 1.3 m. The Sentinel-1 spacecraft has a launch mass of ~2,200 kg, the design life is 7.25 years (consumables for up to 12 years). 22) 23)

Since the B2 Phase of Sentinel-1, a commonality approach with Sentinel-2 and Sentinel-3 was introduced and deeply investigated, to optimize and minimize as much as possible new developments, HW procurement and operations costs. Besides the differences among payload instruments and their relative required performances, each of these three satellites have its own orbital parameters, as well its own specific requirements. 24) 25)

Parameter

Sentinel-1

Sentinel-2

Sentinel-3

Launch date

April 03, 2014 of S1-A
April 22, 2016 of S1-B

June 23, 2015 of S2-A
Expected in 2016 of S2-B

2016 of S3-A
Expected in 2017 of S3-B

Orbit type

SSO (Sun-synchronous Orbit) 12 day repeat cycle LTAN = 18:00 hours

SSO 10 day repeat cycle LTDN = 10:30 hours

SSO 27 day repeat cycle LTDN = 10:00 hours

Orbital altitude

693 km

786 km

814.5 km

Sensor complement

C-SAR (C-band Synthetic Aperture Radar)

MSI (Multi Spectral Instrument)

SRAL (Sentinel-3 Radar Altimeter) MWR (MicroWave Radiometer) OLCI (Ocean and Land Color Instrument) SLSTR (Sea and Land Surface Temperature Radiometer)

Spacecraft mass Spacecraft size Spacecraft power

2300 kg 3.4 m x 1.3 m x 1.3 m 4.8 kW (EOL)

1140 kg 3.0 m x 1.7 m x 2.2 m 1.7 kW (EOL)

1250 kg 3.9 m x 2.2 m x 2.2 m 2.05 kW (EOL)

Downlink X-band data rate

520 Mbit/s

520 Mbit/s

520 Mbit/s

TT&C S-band

64 kbit/s uplink 128 kbit/s or 2 Mbit/s downlink

64 kbit/s uplink 128 kbit/s or 2 Mbit/s downlink

64 kbit/s uplink 128 kbit/s or 2 Mbit/s downlink

Science data storage

1.4 Tbit (EOL)

2 Tbit (EOL)

300 Gbit (EOL)

Required data quality

BER (Bit Error Rate): < 10-9

FER (Frame Error Rate): < 10-8

FER (Frame Error Rate): < 10-7

Operational autonomy

8 days

14 days

27 days

Prime contractor

TAS-I (Thales Alenia Space-Italy)

EADS Astrium GmbH, Germany

TAS-F (Thales Alenia Space-France)

Baseline launcher

Soyuz (Kourou)

Vega (Kourou)

Rockot vehicle of Eurockot Launch Services

Table 2: List of some Sentinel-1, -2, -3 characteristics and key requirements impacting on end-to-end performance 26)

The Sentinel-1 spacecraft design is characterized by a single C-band SAR (Synthetic Aperture Radar) instrument with selectable dual polarization, a deployable solar array, large on-board science data storage, a very high X-band downlink rate, and stringent requirements on attitude accuracy and data-take timing. In addition, the spacecraft will embark the LCT (Laser Communication Terminal) unit allowing downlink of recorded data via the EDRS (European Data Relay Satellite). 27) 28)

Spacecraft stabilization

3-axis stabilized

Attitude accuracy, knowledge

≤ 0.01º for each axis, < 0.003º for each axis

Nominal flight attitude, attitude profile

Right side looking geometry, geocentric and geodetic

Orbit knowledge

10 m (each axis, 3 sigma) using GPS (dual frequency receiver)

Operative autonomy of spacecraft

96 hours

Spacecraft availability

0.998

Spacecraft structure

Box of aluminum sandwich panels + CFRP central structure

Spacecraft body dimensions

3.4 m x 1.3 m x 1.3 m

Spacecraft envelope dimensions

3.9 m x 2.6 m x 2.5 m

Spacecraft launch mass

2157 kg (inclusive 154 kg of monopropellant fuel)

Spacecraft design life

7.25 years (consumables for 12 years)

EPS (Electric Power Subsystem)

4800 W average (End-of-Life), GaAs triple junction solar cells, 2 solar array wings, each wing of 5 sandwich panels

Battery (for eclipse operation) Battery assembly mass

Li-ion technology, capacity = 324 Ah, max discharge power ≥ 1950 W ≤ 130 kg

Onboard science data storage capacity

1410 Gbit (End-of-Life)

S-band TT&C data rates

4 kbit/s TC (telecommand); 16/128/512 kbit/s TM (programmable)

X-band science data telemetry rate

600 Mbit/s

Propulsion subsystem (orbit maintenance)

Monopropellant hydrazine system, 14 thrusters, 6 (orbit control)+8 (attitude)

Thermal control

Mainly passive, standard techniques

Table 3: Main parameters of the Sentinel-1 spacecraft

AVS (Avionics Subsystem): The AVS performs both Data Handling & Attitude/Orbit Control functions. This is realized through the concept of an integrated control system that performs the control of the platform and payload. The AVS performs all data management & storage functions for the satellite, including TM/TC reception and generation, subsystem & unit monitoring, autonomous switching actions and synchronization. The AVS includes the AOCS processing and the interfaces to the AOCS sensors Star trackers, fine sun sensors, and fine gyroscope and actuators, 4 reaction wheels, 3 torque rods, 14 thrusters, 2 solar array drive mechanism. 29)

The AOCS comprises all means to perform transfer- and on-orbit control maneuvers and to control all necessary satellite attitude and antenna pointing states during all mission phases, starting at separation from the launcher until de-orbiting of the satellite at end of life. This includes the attitude steering of the LEO satellite to provide both yaw and roll steering capability. At present, a dedicated precise orbit predictor is implemented within the AOCS, in addition to making use of the data uploaded to the payload by the GPS constellation. The AOCS (Attitude and Orbit Control Subsystem) is able to perform some functions autonomously and it is supported by a very reliable FDIR scheme (Ref. 15). Telecommand data will be received from the TT&C subsystem and will be decoded and deformatted in the AVS.

AOCS consists of the following sensors and actuators: fine sun sensors, magnetometers, gyroscopes, star trackers, GPS receivers, magnetic torquers, a reaction wheels assembly and a monopropellant (hydrazine) propulsion system. The propulsion system has 3 pairs of 1 N orbit control thrusters and 4 pairs of reaction control thrusters for attitude correction. Every pair is made up of a prime and a redundant component. The attitude control thrusters are fired when the spacecraft enters RDM (Rate Damping Mode) after separation, damping any residual rotation left by the launcher upper stage and achieving a spacecraft pitch rotation of -8 times the orbital period. In the subsequent AOCS mode, called SHM (Safe Hold Mode), magnetotorquers and reaction wheels maintain the attitude and reduce the pitch rotation rate to twice the orbital period.

The periodic behavior of the Earth's magnetic field in a polar orbit and the polarization of the angular momentum with the loading of the reaction wheels allow the magnetotorquers to maintain this pitch rate while aligning the spacecraft –Y axis with the orbit normal, which in a dusk-dawn orbit coincides with the direction to the Sun (Figure 3). When the appendages deployment commences, the effect of the gravity gradient torque dominates over the magnetic torque, resulting in the alignment of the S/C X axis (appendages axis) with the nadir direction, maintaining thus a pitch rate equal to the orbital period. Upon ground telecommand, a transition into the NPM (Normal Pointing Mode) occurs, where the spacecraft performs a fine attitude control based on the use of reaction wheels in close loop with star trackers, gyroscopes and GPS, and magnetotorquers for wheel unloading (Ref. 20).

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Figure 3: Sentinel-1A stowed representation (in RDM and SHM). +X S/C axis points towards the flight direction. S/C Y axis is aligned with the Sun direction. Solar Array –Y illuminated when stowed (image credit: ESA, Ref. 20)

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Figure 4: Architecture of the avionics subsystem (image credit: TAS-I)

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Table 4: Sentinel-1 attitude steering modes (Ref. 216)

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Figure 5: Spacecraft power generation and distribution (image credit: TAS-I)

PDHT (Payload Data Handling & Transmission) subsystem (Ref. 24):

The commonality process is driving the spacecraft design with the objective to satisfy the needs of three different missions within the same product. This involves several Sentinels subsystems: in particular, TAS-I was selected to coordinate the common design of two assemblies: 30)

• TXA (Telemetry X-band transmission Assembly) 31)

• XBAA (X-Band Antenna Assembly)

The objective of the PDHT subsystem is to provide the services of data acquisition, storage and transmission to the ground in X-band. After having acquired observation data from the DSHA (Data Storage and Handling Assembly), the TXA executes encoding, modulation, up-conversion, amplification and filtering; the X-band signal provided at the TXA output is then transmitted by an isoflux, wide coverage antenna, included in the XBAA.

To summarize, the performance requirements on TXA specification took into account the different needs of the Sentinels, allowing a fully recurrent units approach: beside a specific TXA layout due to accommodation needs, the modulator, TWTA, and RF filter are exactly the same for the three Sentinels.

After the selection of the TXA & XBAA suppliers (TAS-España and TAS-I IUEL respectively), an agreement was reached between ESA and the Sentinel prime contractors on the way to handle the common design and procurement for TXA and XBAA.

Besides strong efforts to manage different needs coming from different missions, the commonality activities performed in the frame of Copernicus Sentinels enable an effective optimization of costs and development time for those subsystems selected for a common design.

To provide flexibility in the downlink operation, the PDHT is designed with two X-band independent links. The PDHT provides an overall input/output throughput of about 1950 Mbit/s, with a payload input data rate of 2 x 640 Mbit/s (multi-polarization acquisition) or 1 x 1280 Mbit/s (single-polarization acquisition) and a transmitted symbol rate of 2 x 112 Msample/s. The data storage capacity is > 1410 Gbit at EOL.

The provided antenna isoflux coverage zone is about ±64º with respect to nadir to allow link establishment with the ground starting from the ground antenna elevation angle of 5º above the horizon.

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Figure 6: The PDHT (Payload Data Handling & Transmission) subsystem (image credit: TAS-I)

Legend of Figure 6:

• DSHA (Data Storage & Handling Assembly)

• TXA (Telemetry X-band transmission Assembly)

• XBAA (X-band Antenna Assembly)

Mass memory capacity of SAR data (EOL)

> 1400 Gbit (SD-RAM based cubes)

Mass memory capacity of HK/GNSS/POD data (EOL)

32 Gbit

PDHT overall throughput

1950 Mbit/s

Encryption

AES (Advanced Encryption Standard)

Coding

RS (255,223)

Information data rate (on each link)

300 Mbit/s

Bandwidth (on each link, without baseband shaping)

280 MHz

Modulation scheme

O-QPSK

Frequency carrier

8180 MHz

EIRP (on each channel)

> 18.45 dBW

Antenna gain (at 4.5º w.r.t. boresight)

> 20 dB

Polarization

RHCP and LHCP

Antenna pointing mechanism speed

2º/s

Maximum power consumption (10% of contingency)

450 W

Table 5: Main performance characteristics of the PDHT

The TXA architecture provides two redundant X-band channels with the same output power (16 dBW) and useful data rate (260 Mbit/s). Cold redundancy is implemented at channel level. The main elements of the assembly are:

- X-band modulators, developed by TAS-F, are fully compliant with ECSS and modulation standard

- TWTA (Traveling Wave Tube Amplifiers), provided by TAS-B (ETCA), deliver up to 60 W RF power

- OMUX (Optical Multiplexer), developed by TAS-F, filters and combines both channels and provides out of band rejection.

To achieve good spectral confinement and especially to ensure that the emission levels in the adjacent deep space band (8400 to 8450 MHz) are respected, both baseband filtering with a roll-off of 0.35 (0.35-SRRC) and filtering techniques have been applied. In addition, 6-pole channel band pass filters have been implemented in the OMUX. The 6-pole solution provides two main advantages in front of other less selective solutions, such as 4-pole:

- It filters our more efficiently the regrowth of baseband filtered 8PSK carrier due to the gain nonlinearity of the TWTA, thus allowing for a better overall DC efficiency

- It is compatible with data rates up to 300 Mbit/s per channel by adjusting the frequency plan (increase of frequency spacing between channels).

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Figure 7: Architecture of the TXA (image credit: TAS)

Parameter

Performance

Remarks

Frequency plan

F1 = 8095 MHz, F2 = 8260 MHz

 

Occupied bandwidth

< 295 -2.1/+1.8 MHz for 112 MS/s

< 130 MHz per channel

Modulation scheme

8PSK

 

Inner coding

TCM 5/6 encoding rate

 

Downlink useful data rate

280 Mbit/s per channel at modulator input

260 Mbit/s channel at RS decoder output

RF losses

< 1.1 dB

Between TWTA output and TXA output I/F

RF output power level

> 15.3 dBW per channel

At OMUX output flange

Transmission technological degradation (at FER <10-7)

< 1.4 dB

Both channels active

Power consumption, dissipation

< 280 W, < 195 W

Both channels active

Mass of device

< 24.7 kg

Panel excluded

Table 6: Summary of the key performances of the Sentinel TXA

PRP (Propulsion Subsystem): The PRP is based on 14 RCTs (Reaction Control Thrusters) located in 4 different sides of the spacecraft, provides the means to make orbit corrections to maintain the requested tight orbit control throughout the mission. Initially, corrections are required to reach the final orbit position after separation from the launcher. During the mission, some infrequent corrections to the orbit are necessary to maintain the requirements upon the relative and absolute positioning of individual satellite. The thrusters located on the –Z side of the satellite are specifically dedicated to attitude control during the safe mode.

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Figure 8: Sentinel-1 satellite block diagram (TAS-I, ESA, Ref. 15)

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Figure 9: Stowed satellite views (image credit: TAS-I)

RF communications: Onboard source data storage volume of 900 Gbit (EOL). TT&C communications in S-band at 4 kbit/s in uplink and 16, 128, or 512 kbit/s in downlink (programmable). Payload downlink in X-band at a data rate of 2 x 260 Mbit/s.

The Copernicus Sentinel spacecraft are the first ESA Earth Observation spacecraft to implement communications security on the command link. It has been decided to secure the spacecraft from unauthorised command access by adding a security trailer to the command segments which are sent to the spacecraft. The trailer is composed of a Logical Authentication Counter and a Message Authentication Code. The latter is obtained by performing cryptographic encryption of the hash value of the command segment and the Logical Authentication Counter. Only parties in possession of the right key can perform this operation in a way that the command segment is accepted by the spacecraft. The concept applies to all Copernicus Sentinel spacecraft. 32)

Science data compression: Currently, the most promising solution seems to be the FDBAQ (Flexible Dynamic Block Adaptive Quantization) approach as proposed by ESA; 3 output bits would be sufficient for most of "typical" acquisitions over various targets, while few high reflectivity scenes would need 4 bits, making the expected average output bit rate little higher then 3 bits, thus lower then the estimated 3.7 bits for the ECBAQ (Entropy-Constrained Block Adaptive Quantization) compression. 33) 34) 35) 36)

Data delivery: Sentinel-1 will provide a high level of service reliability with near-realtime delivery of data within 1 hour after reception by the ground station, and with data delivery from archive within 24 hours.

OCP (Optical Communication Payload): In parallel to the RF communications, an optical LEO-GEO communications link using the LCT (Laser Communication Terminal) of Tesat-Spacecom (Backnang, Germany) will be provided on the Sentinel spacecraft. The LCT is based on a heritage design (TerraSAR-X) with a transmit power of 2.2 W and a telescope of 135 mm aperture to meet the requirement of the larger link distance. The GEO LCT will be accommodated on AlphaSat of ESA/industry (launch 2012) and later on the EDRS (European Data Relay Satellite) system of ESA. The GEO relay consists of an optical 2.8 Gbit/s (1.8 Gbit/s user data) communication link from the LEO to the GEO satellite and of a 600 Mbit/s Ka-band communication link from the GEO satellite to the ground. 37)

Since the Ka-band downlink is the bottleneck for the whole GEO relay system, an optical ground station for a 5.625 Gbit/s LEO-to-ground and a 2.8 Gbit/s GEO-to-ground communication link is under development.

LCT

1st Generation

2nd Generation

3rd Generation

Link type

LEO-LEO

LEO-GEO

LEO-LEO, LEO-GEO, UAS-GEO

Mission

NFIRE, TerraSAR-X

Sentinel 1 & 2, AlphaSat, ERDS

Euro Hawk, Global Hawk

Lifetime

2-5 years

15 years

Mission depending

Data rate

5.625 Gbit/s

1.800 Gbit/s

1.800 - 5.625 Gbit/s

Range

1000 - 5100 km

< 45,000 km

1000 - 45,000 km

Target BER

1 x 10-8

1 x 10-8

Better than 1 x 10-8

Tx power

0.7 W

2.2-5.0 W

< 5 W

Telescope diameter

125 mm

135 mm

< 125 mm

Instrument mass

~33 kg

~53 kg

< 45 kg

Power consumption

~ 120 W

~160 W

120 - 180 W

Instrument volume

~ 0.5 m x 0.5 m x 0.6 m

~ 0.6 m x 0.6 m x 0.74 m

3-box design (TBD)

Technology Readiness Level

TRL9

TRL5

TBD

Table 7: Technical data of the LCT generations 38)

Ground segment: Spacecraft operations is provided by ESOC, Darmstadt, while the payload data processing and archiving functions (including the planning for SAR data acquisitions) are provided by ESRIN, Frascati. Options are being provided to permit some functions to be outscored to other operating entities.

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Figure 10: Isometric views of the deployed satellite (image credit: TAS-I)

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Figure 11: SAR antenna deployment test supported by zero gravity deployment device (solar array in stowed position), image credit: TAS-I, (Ref. 21)

Figure 12 shows the fully integrated Sentinel-1A spacecraft with the SAR antenna and the solar array wings in stowed position. The figure shows the Sentinel-1 spacecraft already mounted on the shaker and ready for sine vibration testing after it has successfully passed the Mass Properties measurements (namely center of mass and inertia moments). Successful completion of vibration and acoustic testing has been followed by the deployment tests of both the SAR antenna and the solar array. Each solar array is tied down on four hold down points by dedicated Kevlar cables. Wing deployment is purely passive, driven by springs, and actuated upon activation of specific thermal knives devices. The time to complete deployment of one wing lasts about 3.5 minutes since the last cable cut. In the end position, the solar array panels are mechanically latched.

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Figure 12: Photo of the Sentinel-1A spacecraft during functional tests in Cannes, France (image credit: TAS) 39)

• Prior to shipment to the launch site in late February 2014, the Sentinel-1 spacecraft has spent the last couple of months at Thales Alenia Space in Cannes, France, being put through a last set of stringent tests. This included suspending the satellite from a structure to simulate weightlessness and carefully unfolding the two 10 m-long solar wings and the 12 m-long radar antenna. 40)

• The first satellite dedicated to Europe's Copernicus environmental monitoring program arrived at Cayenne in French Guiana on 24 February 2014. Sentinel-1A is scheduled to be launched from Europe's spaceport in Kourou on 3 April. By delivering timely information for numerous operational services, from monitoring ice in polar oceans to tracking land subsidence, Sentinel-1 is set to play a vital role in the largest civil Earth observation programme ever conceived. 41)

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Figure 13: The Sentinel-1A radar satellite has arrived at Europe's Spaceport in French Guiana to be prepared over the coming weeks for launch in April (image credit: ESA,M. Shafiq) 42)

 

Launch of S-1A: The Sentinel-1A spacecraft was launched on April 3, 2014 (21:02 UTC) on a Soyuz-STB Fregat vehicle from Kourou, French Guiana (the launch is designated as VS07 by the launch provider Arianespace). After a 617 second burn, the Fregat upper stage delivered Sentinel-1A into a Sun-synchronous orbit at 693 km altitude. The satellite separated from the upper stage 23 min 24 sec after liftoff. 43)

 

Launch of S-1B: The Sentinel-1B spacecraft, a twin sister of Sentinel-1A, was launched on April 25, 2016 (21:02:13 GMT) into the same orbital plane of Sentinel-1A (phased by 180º). The launcher was a Soyuz-STA/Fregat vehicle (VS 14) of Arianespace and the launch site was Kourou. 44) 45)

The contract between ESA and Arianespace to launch the Sentinel-1B satellite was signed on July 17, 2014 by ESA's Director of Earth Observation Programs, Volker Liebig, and CEO of Arianespace, Stéphane Israël, at ESA headquarters in Paris, France. As part of the Copernicus program, Sentinel-1B will round out the initial capacity offered by Sentinel-1A to offer a comprehensive response to the need for environmental and security monitoring via spaceborne radar systems. 46) 47) 48)

On March 22, 2016, the Sentinel-1B satellite has arrived in French Guiana to be prepared for liftoff on 22 April. 49)

Secondary payloads of Sentinel-1B: 50)

• MicroSCOPE, a minisatellite (303 kg) of CNES (French Space Agency) which will test the universality of free fall (equivalence principle for inertial and gravitational mass as stated by Albert Einstein).

• AAUSAT4, a 1U CubeSat of the University of Aalborg, Denmark to demonstrate an AIS (Automatic Identification System), identifying and locating ships sailing offshore in coastal regions.

• e-st@r-II (Educational SaTellite @ politecnico di toRino-II), a 1U CubeSat from the Polytechnic of Turin, Italy.

• OUFTI-1 (Orbital Utility for Telecommunication Innovation), a 1U CubeSat of the University of Liège, Belgium, a demonstrator for the D-STAR communications protocol.

Tyvak International installed the three CubeSats in the orbital deployer. The three CubeSats are part of ESA's FYS (Fly Your Satellite) student program.

 

Orbit: Sun-synchronous near-circular dawn-dusk orbit, altitude = 693 km, inclination = 98.18º, orbital period = 98.6 minutes, ground track repeat cycle = 12 days (175 orbits/cycle). An exact repeat cycle is needed for InSAR (Interferometric Synthetic Aperture Radar) support. LTAN (Local Time on Ascending Node) = 18:00 hours.

Orbital tube: A stringent orbit control is required to the Sentinel-1 system. Satellites' position along the orbit needs to be very accurate, in terms of both accuracy and knowledge, together with pointing and timing/synchronization between interferometric pairs. Orbit positioning control for Sentinel-1 is defined by way of an orbital Earth fixed "tube" 50 m (rms) wide in radius around a nominal operational path (Figure 14). The satellite is kept inside such a tube for most of its operational lifetime Ref. 15). 51)

One of the challenges of the Sentinel-1 orbit control strategy is the translation of a statistical tube definition in a deterministic control strategy practically functional to the ESOC (European Space Operations Center) operations.

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Figure 14: Schematic view of the orbital tube (image credit: ESA, TAS, Ref. 15) 52)

The second obvious challenge is the very stringent tube diameter which forces the application of frequent and intense maneuvers nevertheless still compatible with S/C request for consumables of up to a 12 years lifetime.

A satellite control strategy has been specifically developed and consists in applying a strict cross-track dead-band control in the most Northern Point and in the ascending node crossing. Controlling the orbit at these 2 latitudes, the satellite is shown to remain in the tube, within the rms (root mean square) criteria, for all other latitudes.

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Figure 15: Orbital tube section (image credit: ESA, TAS, Ref. 15)

Orbit knowledge accuracy (< 3 m rms in each axis) in realtime for autonomous operations is not considered as demanding as the on-ground postprocessing requirements (< 5 cm 3D rms) for the detection of (slow) land movements and deformations through the differential interferometry technique. The latter is almost as demanding as for Sentinel-3 and requires dual-frequency receivers. 53)

As both satellites, Sentinel-1A and Sentinel-1B, will fly in the in the same orbital plane with 180º phased in orbit, and each having a 12-day repeat orbit cycle, it will facilitate the formation of SAR interferometry (InSAR) image pairs (i.e., interferograms) having time intervals of 6 days. This, along with the fact that the orbital deviation of each Sentinel-1 satellite will be maintained within a tube of ±50 m radius (rms) will enable the generation of geographically comprehensive maps of surface change such as for measuring ice velocity in the Polar regions, as well as monitoring geohazard related surface deformation caused by tectonic processes, volcanic activities, landslides, and subsidence (Ref. 238).

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Figure 16: The main Sentinel-1 mode will allow complete coverage of Earth in six days when operational with the two Sentinel-1 satellites are in orbit simultaneously (image credit: ESA/ATG medialab) 54)

Minimize Mission Status:

Mission status:

• February 1, 2019: This week's edition of the Earth from Space program features a Copernicus Sentinel-1 image over one of the areas in Iraq that suffered flooding recently. 55)

- The town of Kut is in the lower-center of the image. It lies within a sharp ‘U-bend' of the Tigris River, which can be seen meandering across the full width of the image. The image has been processed to show floods in red, and it is clear to see that much of the area was affected including agricultural fields around the town. Dark patches in the image, including the large patch in the center , however, indicate that there was no or little change between the satellite acquisitions.

- After the searing dry heat of summer, November typically signals the start of Iraq's ‘rainy season' –but November 2018 brought heavier rainstorms than usual. Many parts of the country were flooded as a result. Thousands of people had to be evacuated, and infrastructure, agricultural fields and other livelihoods were destroyed, and tragically the floods also claimed lives. Declared an emergency, the International Charter Space and Major Disasters was activated. The Charter takes advantage of observations from a multitude of satellites to aid emergency relief. Images from Copernicus Sentinel-1 contributed to this particular effort.

- The two identical Copernicus Sentinel-1 satellites carry radar instruments, which can see through clouds and rain, and in the dark, to image Earth's surface below. This capability is particularly useful for monitoring and mapping floods, as the image shows. Satellite images play an increasingly important role in responding to disaster situations, especially when lives are at risk. Also, after an event, when damage assessments are needed and plans are being made to rebuild, images from satellites are a valuable resource.

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Figure 17: This Copernicus Sentinel-1 image combines two acquisitions over the same area of eastern Iraq, one from 14 November 2018 before heavy rains fell and one from 26 November 2018 after the storms. The image reveals the extent of flash flooding in red, near the town of Kut. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

• January 10, 2019: Images acquired every six days by the European Union's Copernicus Sentinel-1 satellites are being used to map ground movement across two billion measurement sites in Norway, revealing shifts as small as one millimeter a year. 56)

- Thanks to this information, the Geological Survey of Norway, the Norwegian Water Resources and Energy Directorate, and the Norwegian Space Center have recently launched the Norwegian Ground Motion Service – InSAR Norway.

- This new service will provide the basis for strategic governmental use of interferometry in Norway. Interferometry is a technique involving multiple repeat satellite radar images over the same scene that are combined to identify slight alterations between acquisitions, thus 'spotting the difference'.

- The service will map ground deformation caused by, for example, subsidence. It will also assess the risk of landslides and monitor changes in infrastructure in urban areas. Furthermore, the service will lead to downstream commercial and public use – for instance in sectors such as big data analysis, insurance, real estate, structural engineering and transport infrastructure.

- The service will also benefit road and rail authorities, municipalities and city planners, as well as citizens.

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Figure 18: On 29 November 2018, the Geological Survey of Norway (NGU), the Norwegian Water Resources and Energy Directorate (NVE) and the Norwegian Space Center launched the Norwegian Ground Motion Service, InSAR Norway, to help monitor and measure all of Norway's ground movements, using Copernicus Sentinel-1 data. InSAR data is given at full resolution, freely and openly available to everyone from the InSAR Norway portal (image credit: ESA, the image contains modified Copernicus Sentinel data (2018)/processed by InSAR Norway and powered by KSAT-GMS)

- InSAR Norway aims to find all unstable rock slopes in Norway that could collapse catastrophically, and understand the geologic conditions of each unstable slope and rank them based upon their hazard and risk, and establishing a 24/7 early-warning system where necessary.

- John Dehls, from the Geological Survey of Norway, stated, "Setting-up such an operational ground motion service has had significant technical challenges. However, we are already seeing the first benefits. New critical areas prone to large landslides were discovered within days of the first dataset being produced. These will be followed up with fieldwork next summer. - We consider that the information provided by the InSAR Norway service will be of interest not only for public and commercial entities, but also for citizens. We have decided to provide the related data at full resolution, freely and openly to everyone. Furthermore, InSAR Norway data will be maintained and updated at regular intervals, thus creating predictability for long-term operational users".

Figure 19: The service uses images acquired every six days by the Sentinel-1 satellites of the European Union's Copernicus Program. Over 4000 images a year, in two different geometries (so-called ascending and descending orbit passes) are used, ensuring that more than two billion locations in Norway can now be measured and continuously monitored to within1mm/year. This represents an average of more than 6,000 measurement locations/km2. 57)

Legend to Figure 19: On 29 November 2018, NGU, NVE and the NSC (Norwegian Space Center) launched the operational Norwegian Ground Motion Service with InSAR subsidence data at full resolution, free and open to everyone on the InSAR Norway portal. More than 25,000 users accessed the service in the first week of operation.

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Figure 20: This 3D image map covered with InSAR measurement points showing a mountain on the move in Osmundneset, Gloppen, Norway. The dark red points correspond to subsidence of up to 2 cm/year, while green ones correspond to negligible movement. The inlet figure shows the average subsidence of 2236 points for the light grey marked polygon in the map. The average velocity of the subsidence is calculated at some 4-5 mm/year for the period 2015-2018 Image credit: ESA, the image contains modified Copernicus Sentinel data (2018)/processed by InSAR Norway and powered by KSAT-GMS)

- The Norwegian research institute, Norut, and the Dutch company PPO.Labs, have been the research and development partners for InSAR Norway, through the KSAT-GMS partnership with the Norwegian Kongsberg Satellite Services (KSAT). The official unveiling was the result of several years of intensive research and development activities, from the design phase of innovative algorithms to implementation and operationalization of the service.

- The main goal of this free service is to produce operational Interferometric Synthetic Aperture Radar (InSAR) ground deformation measurements over Norway and improve accessibility of InSAR results for public and commercial users.

- InSAR Norway will provide the basis for strategic governmental use of interferometry in Norway, by mapping ground deformation such as subsidence, assessing rock-slide risks and by monitoring infrastructure in cities. Furthermore, the service will be a tool for creating downstream commercial and public use, for instance in geotechnical, climate, big data analysis, insurance, real estate, structural engineering and transport infrastructure applications. The service will also benefit users such as road authorities, railroad authorities, municipalities and city planners, as well as citizens.

Beyond Norway: towards a European ground motion service (Ref. 57)

- "We are very proud of the state-of-the-art tools and methods our team from NGU, NSC, NVE, Norut, PPO.Labs and KSAT-GMS have been able to develop for the InSAR Norway operational ground motion service. Personally, I think this is a breakthrough for applied operational nation-wide large-scale use of InSAR."

- A European–wide Copernicus ground motion service based on Sentinel-1 data is under planning by the European Commission in partnership with the European Environment Agency and the states participating in the Copernicus Earth Observation program.

- "This is a very important and valuable development also for Europe, which we look forward to supporting, as well as collaborating with the European Commission and nations in Europe to make it happen successfully", concluded Dag Anders Moldestad and John Dehls.

• November 30, 2018: The Copernicus Sentinel-1 mission takes us over Mexico City. This huge, densely-populated capital can be seen in the top right of the image. It is home to almost nine million people, with the Greater Mexico City area recording a population of over 21 million. This makes it the largest Spanish-speaking city in the world. 58)

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Figure 21: Mexico City is located in the top right of the SAR image. This striking image has been created using three Copernicus Sentinel-1 acquisitions from 28 July, 27 August and 26 September 2018, overlaid in red, green and blue, respectively. Where we see explosions of color, changes have occurred between the different acquisitions. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

- In the left of the image, three bodies of water are shown in black: Villa Victoria, Valle de Bravo, and Tepetitlán. Water is significant to the development of Mexico City, which is thought to have been built over a lake by the Aztecs around 1325.

- Today, the city finds itself in a precarious situation in terms of water supply in spite of the regular flash floods and heavy rainfall it experiences during the wet season from June and September.

- In the top right, we can see the round structure of El Caracol meaning ‘the snail' in Spanish. Currently used as a reservoir for industrial facilities within Mexico City, there are plans for this to become a wastewater treatment plant. A 62 km-long sewer tunnel is also due to begin operating this year.

- The Cumbres del Ajusco national park is shown to the southwest of the capital, in an area of the image that shows colorful dots forming a circle. Famous for being up to almost 4000 m above sea level at its highest elevation, it is one of many national parks surrounding the capital.

- Volcanoes are also dotted around this area. Popocatépetl, to the south east of Mexico City, last erupted in September 2018.

• On 8 October 2018 at 05:28 GMT (07:28 CEST), the Copernicus Sentinel-1 mission captured its first images of the oil spill from a collision between two ships that had occurred the day before in the Mediterranean Sea, north of the French island of Corsica. This first image shows that the oil slick was about 20 km long. By the evening at 19:21 CEST, however, imagery shows that the slick had lengthened to about 35 km. And 24 hours later, on 9 October at 19:14 CEST, the slick had grown to about 60 km long. 59)

Figure 22: The Copernicus Sentinel-1 mission returns images showing how oil is spreading in the Mediterranean Sea following a collision between two ships (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO

Legend to Figure 22: The image from 9 October also shows a large black patch southeast of the oil slick – this is a result of low reflectivity of the radar signal and therefore depicts calm waters.

• October 8, 2018: The Copernicus Sentinel-1 mission has imaged the oil spill in the Mediterranean following a collision between two merchant ships on Sunday 7 October 2018. A Tunisian cargo ship is reported to have struck the hull of a Cypriot container ship in waters north of the French island of Corsica. There were no casualties, but the collision caused a fuel leak – which has resulted in an oil slick about 20 km long. Although the collision occurred in French waters, the cleanup operation is part of a joint pact between France, Italy and Monaco to address pollution accidents in the Mediterranean. 60)

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Figure 23: This image of the slick, which can be seen as a dark patch north of the tip of Corsica, was captured by the Sentinel-1A satellite on 8 October at 05:28 GMT (07:28 CEST). Sentinel-1 is a two-satellite constellation built for the European Commission's Copernicus environmental monitoring program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

• September 28, 2018: The Copernicus Sentinel-1B satellite takes us over central Italy. From the Apennine Mountains in the top right, to the fertile, former lakebed of the Avezzano plain in the center right, this bright, false-color image (Figure 24) captures the diversity and beauty of the region's landscapes. 61)

- Dual-polarization radar technology has been used, resulting in vibrant shades of green for most of the land surface shown. Built-up areas, such as Italy's capital city of Rome, appear in shades of red and pink. Meanwhile, the structure of the agricultural fields of Altopiano in the Abruzzo region is clearly reflected in a combination of blue and violet hues.

- This radar technology allows us to see the crater lake structures of the volcanic lakes of Nemi and Albano in the bottom left clearly. The same is true for Lago di Vico with the volcano and crater clearly visible in the top left of the image.

- The central region of Italy is an important one for the space industry. For example, ESA's center for Earth observation, which celebrates its 50-year anniversary this week, is located in this area.

- This region is also prone to earthquakes. In August 2016, a magnitude 6.2 earthquake struck the small towns of Amatrice, Accumoli and Pescara del Tronto. It was followed by two aftershocks. A magnitude 6.6 earthquake in Norcia followed in October the same year. The tremor of this last earthquake was felt across the country. It was the most powerful one to hit Italy since 1980.

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Figure 24: Sentinel-1B captured this image of central Italy on 6 July 2018, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

• September 14, 2018: The Copernicus Sentinel-1B satellite takes us over Semera in northeast Ethiopia. Semera is a new town with a population of just over 2600 and serves as the capital of the Afar region. The region spans an estimated 270,000 km2, from close to the border with Eritrea towards the capital of Addis Ababa (also written as Addis Abeba). 62)

- We can see the regional capital in the top right of this false-color image (Figure 25), with the larger urban center of Dubti just south of the town. Both are found in the Great Rift Valley, which lies between the Ethiopian Plateau and the Somalia Plateau.

- The landscape of the Afar region is characterized by desert shrubland and volcanoes, particularly in the north. In this image we can see differences in altitude represented in the variations in color. The left part of the image is dominated by yellow, signifying changes in vegetation found at higher altitudes. Two lakes, Hayk Lake and Hardibo Lake, are shown in the bottom left.

- South of Dubti we can see the Awash River, which flows into the northern salt lakes rather than into the sea. Salt trade is typical of the area, whilst cotton is grown in the Awash River valley. Maize, beans, papaya and bananas are also cultivated in the Afar region. It is thought that 90% of the region's population lead a pastoral life, rearing animals such as camels, sheep and donkeys.

- Dallol, to the north of Semera in Ethiopia's Danakil Depression, is frequently cited as one of the hottest inhabited places on Earth. Lying 125 m below sea level, with temperatures in the spectacular hydrothermal fields averaging 34.4 °C year-round, and the area receiving just 100–200 mm rainfall a year, conditions are thought to be amongst the most inhospitable in the world.

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Figure 25: This image of Sentinel-1B, which was captured on 5 April 2018, is of northeast Ethiopia (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO) 63)

• September 13, 2018: In July 2017, one of the largest icebergs on record calved from the Larsen C ice shelf in Antarctica. However, sea ice to the east and shallow waters to the north kept this giant berg, named A68, hemmed in. So for more than a year it wafted to and fro, but never left its parent ice shelf's side. Strong winds blowing from Larsen C have finally given it the push it was waiting for. In early September 2018, these winds pushed the southern end of the berg out into the Weddell Gyre. This clockwise drift of ocean waters and sea ice flowing north past the Larsen shelf, which can be seen in the animation as a flow from right to left, has rotated A68 out into the Weddell Sea. Here it is freer to float away and be carried further north into warmer waters. 64)

Figure 26: The animation, generated by Adrian Luckman at Swansea University (UK), uses data from the Copernicus Sentinel-1mission – a two-satellite constellation. Each satellite carries an advanced radar instrument that can image Earth's surface through cloud and rain and regardless of whether it is day or night. This is essential for monitoring the polar regions, which are shrouded in darkness during the long winter months (image credit: ESA, the image contains modified Copernicus Sentinel data (2017–18), processed by Swansea University–A. Luckman)

• August 8, 2018: Scientists with the ARIA (Advanced Rapid Imaging and Analysis) project , a collaboration between NASA's Jet Propulsion Laboratory in Pasadena, California, and Caltech, also in Pasadena, used synthetic aperture radar (SAR) data from the European Union's Copernicus Sentinel-1A and -1B satellites, operated by the European Space Agency. They generated a map of the deformation of Earth's surface caused by the Aug. 5, 2018 magnitude 6.9 earthquake under Lombok island, Indonesia (Figure 27). The deformation map is produced from automated interferometric processing of the SAR data using the JPL-Caltech ARIA data system in response to a signal received from the U.S. Geological Survey. The false-color map shows the amount of permanent surface movement that occurred almost entirely due to the quake, as viewed by the satellite, during a 6-day interval between two Sentinel-1 images acquired on July 30 and Aug. 5, 2018. 65)

- From the pattern of deformation in the map, scientists have determined that the earthquake fault slip was on a fault beneath the northwestern part of Lombok Island and caused as much as 25 cm of uplift of the ground surface. The map depicts motion towards the satellite (up and west) in the direction of the radar's line-of-sight, with contours every 5 cm. White areas are places where the radar measurement was not possible, largely due to dense forests in the middle of the islands.

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Figure 27: New satellite map shows ground deformation after Indonesian quake. The map shows that the earthquake fault was under the northwest corner of Lombok island, probably extending offshore to the west. Through these maps, NASA and its partners are contributing observations and expertise that can assist with response to earthquakes and other natural or human-produced hazards (image credit: NASA/JPL-Caltech/Copernicus/ESA, the image contains modified Copernicus Sentinel-1 data (2018) processed by ESA and NASA/JPL)

• July 30, 2018: Copernicus Sentinel-1 data are highlighting the collapse of the Xe-Pian Xe-Namnoy dam in the southeastern province of Attapeu in Laos. The collapse has led to flash floods that have claimed several lives and left many more people missing, according to local news reports. 66)

- Sentinel-1's radar ability to ‘see' through clouds and rain, and in darkness, makes it particularly useful for monitoring floods. Images acquired before and after flooding offer immediate information on the extent of inundation and support assessments of property and environmental damage.

- The C-band synthetic aperture radar on Sentinel-1 can provide large swath images with a resolution of 20 m and within hours of acquisition to aid emergency response. — With construction starting back in 2013, the dam had been expected to commence commercial operations this year.

- The flood seems to have been caused by a breach in another saddle dam (not the main dam) following heavy rainfall. The effects of this can be seen clearly at larger scale, with the flood following the Vang Ngao river down to the villages. This is shown in the animation here.

Figure 28: Sentinel-1 images show the impact of the dam failure on the Xe-Pian Xe-Namnoy lake area in the southeastern province of Attapeu in Laos (image credit: ESA, the imagery contains modified Copernicus Sentinel data (2018) / processed by CESBIO) 67)

- The catastrophe triggered the International Charter Space and Major Disasters. With 16 members, the Charter takes advantage of observations from several satellites, providing a unified system of space data acquisition and delivery to support disaster management.

- With the ability to mobilize agencies around the world through a single access point that operates 24 hours a day, 7 days a week, the Charter helps civil protection authorities and the international humanitarian community in the face of major emergencies.

- By supplying reliable and accurate information, these entities are better equipped to save lives and limit damage to property, infrastructure and the environment.

- Since its first activation in 2000, the Charter has called on space assets on hundreds of occasions, helping respond to disasters such as floods, hurricanes, tsunamis and earthquakes.

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Figure 29: Dam failure in the Xe-Pian Xe-Namnoy lake area (image credit: ESA, the image contains modified Copernicus Sentinel data (2018) processed by CESBIO)

• July 13, 2018: The Copernicus Sentinel-1 mission has revealed that, on average, Greenland's glaciers are now flowing more slowly into the Arctic Ocean. While glacial flow may have slowed overall, in summer glaciers flow 25% faster than they do in the winter. 68)

- While the general flow has reduced in recent years, during the summer it speeds up, with glaciers flowing up to 25% faster than in the winter.

- A paper published recently in The Cryosphere details the research led by the UK's CPOM (Centre for Polar Observation and Modelling) where the Copernicus Sentinel-1 mission was used to track Greenland's four main glaciers: Jakobshavn Isbrae, Petermann, Nioghalvfjerdsfjorden and Zachariae Isstrom between 2014 and 2017. 69)

- We all know that ice melts pretty quickly under the summer sun, but monitoring exactly how glacial flow changes according to the season is important for understanding glacial dynamics. In turn, this is vital to assess the risk of sea-level rise, which is a major concern around the world.

- Together, these four glaciers contain enough water to raise global sea levels by 1.8 m.

- Adriano Lemos from CPOM noted, "Sentinel-1 has real advantages for studying glaciers. We now get more data and more often so we can see the finer detail in even the most inaccessible and fast-moving areas."

Figure 30: The Copernicus Sentinel-1 mission has revealed that, on average, Greenland's glaciers are flowing more slowly into the Arctic Ocean. While the general flow has reduced in recent years, in the summer glaciers flow up to 25% faster than in the winter. Jakobshavn Isbrae, which is Greenland's fastest flowing glacier, reached a peak of 17 km per year in 2013, the result of an unusually warm summer. But satellite data, in particular from Sentinel-1, show that, on average, it has actually slowed down by 10% since 2012. This is overlaid by a seasonal pattern, with the glacier accelerating by up to 14% over a three-month summer period before slowing down again in winter (image credit: ESA, the image contains modified Copernicus Sentinel data (2014–17), processed by CPOM) 70)

- Part of European Union's fleet of Copernicus missions, Sentinel-1 is a two-satellite constellation that images the entire Earth every six days – important for monitoring rapid change. Each satellite carries an advanced radar instrument that can image Earth's surface through cloud and rain and regardless of whether it is day or night.

- This is essential for monitoring the polar regions, which are shrouded in darkness during the long winter months.

- "We saw this summer speed-up at all four glaciers and it is important that we continue to monitor this speed throughout the year to fully understand how the glaciers are moving" explained Adriano Lemos.

- Anna Hogg also from CPOM added, "Acquiring all this valuable radar data needed international coordination between multiple space agencies such as ESA and the German Aerospace Center DLR. This paper shows how our efforts are being rewarded through improving our understanding of environmental change in Greenland."

• June 2018: The Sentinel-1 mission has set a benchmark for achieving a high-quality end-to-end SAR performance, showing almost identical radiometric and geolocation accuracy for Sentinel-1A &-1B. 71)

- In addition, the 6-day repeat orbit interval along with small orbital baselines enables the implementation of cross-InSAR by combining data acquired by Sentinel-1A&-1B from repeat-pass orbits, reducing significantly the temporal surface decorrelation effect. This supports geophysical applications, such as the monitoring of cryosphere dynamics and the mapping of surface deformation.

- The continuous and systematic Sentinel-1 SAR and InSAR data acquisition, while providing an instantaneous wide area coverage, enables the build-up of long data time series. This has triggered a shift from individual image analysis to time-series processing.

• May 29, 2018: In what the UN describes as the world's fastest growing refugee crisis, almost 700,000 Rohingya Muslims have fled Myanmar for neighboring Bangladesh since August 2017. With the Bangladesh government proposing a vulnerable low-lying island as a relocation site for thousands, Sentinel-1 data have shown how unsuitable this site would be. 72)

- While the Rohingya have faced decades of repression, this recent mass exodus is blamed on large-scale atrocities committed by the Myanmar military. - Not only has the pace of arrivals in Bangladesh made this the fastest growing refugee crisis in the world, but the concentration of displaced people now in Bangladesh's Cox's Bazar is amongst the densest in the world. Even before the crisis, Bangladesh was hosting more than 200,000 Rohingya from Myanmar. For a country already struggling to cope with challenges of its own, this has turned into a huge humanitarian tragedy.

- Desperate to find solutions, the Bangladesh government was prompted, unsurprisingly, to revive a much criticized plan to move thousands to Thengar Char, one of several uninhabited and unstable islands in the Bay of Bengal.

- The area is particularly prone to cyclones, with coastal zones and islands at highest risk. Some nearby islands have a tidal range as high as 6 m, meaning that they are at risk of being completely submerged. - Regardless of cyclones, the region is often inundated by heavy rainfall during the South Asian monsoon, which lasts from June to October.

- Information from satellites is often used during humanitarian crises to map, for example, the extent of camps and other temporary settlements. In this case, however, the Earth Observation-based Services for Dynamic Information Needs in Humanitarian Action project used data from the Copernicus Sentinel-1 radar mission to show exactly how precarious Thengar Char is.

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Figure 31: The Bangladeshi island of Thengar Char in the Bay of Bengal has been identified as a possible relocation site for Rohingya refugees. Information from the Copernicus Sentinel-1 mission has been used to show that the island is particularly susceptible to inundation. At times, flooding has reduced the island from 76 km2 to less than 40 km2 (image credit: EO4HumEn+)

- Andreas Braun from Germany's University of Tübingen said, "As well as using data from Sentinel-1, we also used data from ESA's old ERS and Envisat satellites to work out how the size of the island has changed since 1991 (Figure 32).

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Figure 32: Barely an island: Based on 178 archived satellite radar images from 1991 to 2018, this image shows how often a pixel was identified as land. During this time, the island of Thengar Char mostly varied between 30% and 80% of its mean extent. This shows how vulnerable the island is to flooding (image credit: EO4HumEn+) 73)

- "It turns out that this set of islands has only been there since 2009, and were formed from silt washing down from the Himalayas into the Bay of Bengal. We calculated how big the island has ever been, how small it has ever been and how big it is on average. Importantly, we could report that since Sentinel-1 became operational in 2014, the island, which is currently about 60 km2, has been inundated several times and at the worst, the land area was reduced to 39 km2."

- The notion of placing vulnerable people on an inhospitable island that has no existing infrastructure and is two hours away by boat from the mainland is obviously questionable, but thanks to Sentinel-1, the authorities have hard evidence as to its risk of flooding.

- It remains to be seen whether the government of Bangladesh will move forward with their plan, although construction work has apparently begun.

Mission status 22-28 May, 2018: The Sentinel-1 Yearly Mission Review took place on 24 May 2018, at ESA-ESRIN. The overall mission is in a very good shape, and both satellites demonstrate a good health. The occurrence of satellite anomalies and mission unavailability periods has further decreased over the past months. A major increase of the Sentinel-1 operations capacity has been achieved during the past year with the smooth integration of the EDRS service in operations, and a series of improvements were performed (e.g. systematic production of L2 OCN (Level 2 Ocean) products from IW/EW/SM modes). Substantial improvements on the data quality have been achieved (e.g. provision of de-noising information), and will be pursued. Remaining system issues are being addressed, in particular the Level 2 OCN RVL product qualification. The Copernicus operational services have expressed satisfaction on the routine use of Sentinel-1 data. Data and user access statistics, as well as the numerous exploitation activities based on Sentinel-1 data, confirm the great user uptake in various thematic application and scientific fields. 74) 75)

- The Sentinel-1A and Sentinel-1B routine operations are on-going

- The Sentinel-1 observation scenario supports the systematic coverage of Copernicus Services areas of interest, of European land and coastal waters, of global tectonic/volcanic areas, as well as of other areas worldwide for various applications. The observation plan also includes a regular mapping of all land areas worldwide.

- World maps providing a high level description of the Sentinel-1 constellation observation scenario, in terms of SAR modes, polarization, observation geometry, revisit and coverage frequency are available at: https://sentinels.copernicus.eu/web/sentinel/missions/sentinel-1/observation-scenario

- The detailed observation plan in the form of instrument acquisition segments, for both Sentinel-1A and Sentinel-1B is published at: https://sentinels.copernicus.eu/web/sentinel/missions/sentinel-1/observation-scenario/acquisition-segments

- The operational use of Sentinel-1 data by the Copernicus Marine Environment Monitoring Service (CMEMS) for sea-ice and iceberg monitoring activities is on-going.

- The European Maritime Safety Agency (EMSA) operationally uses Sentinel-1 imagery in quasi-real time in the CleanSeaNet services; operations with EMSA service providers local stations are on-going.

- Specific planning was made to support the activation EMSR286 from the Copernicus Emergency Management Service related to monitoring the risk of failure of the Ituango dam in Colombia.

- Specific actions (fast delivery of already planned acquisitions) were implemented to support the activation EMSR287 from CEMS related to floods in Saxony, Germany.

- Both Sentinel-1A and -1B spacecraft are in a stable state, operating in Nominal Mission Mode (NMM). The Flight Operations Segment (FOS) ensuring the monitoring, control and commanding of the satellites is operating nominally. Orbit control maneuvers are performed once a week.

- The use of the EDRS-A service by Sentinel-1A and -1B is on-going as part of the routine operations.

- X-Band data acquisitions are routinely performed over Matera, Svalbard and Maspalomas X-band core stations. The acquired data are circulated within the Payload Data Ground Segment (PDGS), systematically processed to Level-0 and Level-1 products and archived.

- Wave Mode data are regularly acquired over open oceans, systematically processed to Level-2 OCN products and made available. Sentinel-1 IW and EW Level-2 OCN products over regional ocean areas are available on the Data Hubs. The operational qualification of the Level-2 the OCN Radial Surface Velocity (RVL) component is on-going.

- Operations are performed regularly at the Processing and Archiving Centres (DLR-PAC and UK-PAC). All other PDGS operational services (i.e. Mission Performance, Precise Orbit Determination, Wide Area Network) are operating nominally.

- By 24th May 2018, a total of 153,443 users have self-registered on the Sentinels Scientific Data Hub; 14.6 million Sentinel-1 product downloads have been made by users, corresponding to 19 PB of data. 2.6 million Sentinel-1 products are available on-line for download, representing about 4 PB of data. Statistics of last 24 hours are available in real time at the Open Data Hub home page: https://scihub.copernicus.eu

• March 22, 2018: Two giant sinkholes near Wink, Texas, may just be the tip of the iceberg, according to a new study that found alarming rates of new ground movement extending far beyond the infamous sinkholes. That's the finding of a geophysical team from SMU (Southern Methodist University), Dallas that previously reported the rapid rate at which the sinkholes are expanding and new ones forming. - Now the team has discovered that various locations in large portions of four Texas counties are also sinking and uplifting. 76)

- Radar satellite images show significant movement of the ground across a 4000-square-mile area (10 ,360 km2) - in one place as much as 1 m over the past two-and-a-half years, say the geophysicists.

- The West Texas' Permian Basin, consisting of ancient marine rocks, is underlain by water-soluble rocks and multiple oil-rich formations. In the region that is densely populated with oil producing facilities, many localized geohazards, such as ground subsidence and micro-earthquakes, have gone unnoticed. Here we identify the localized geohazards in West Texas, using the satellite radar interferometry from newly launched radar satellites (Sentinel-1A/1B) that provide radar images freely to public for the first time, and probe the causal mechanisms of ground deformation, encompassing oil/gas production activities and subsurface geological characteristics. Based on our observations and analyses, human activities of fluid (saltwater, CO2) injection for stimulation of hydrocarbon production, salt dissolution in abandoned oil facilities, and hydrocarbon extraction each have negative impacts on the ground surface and infrastructures, including possible induced seismicity. Proactive continuous and detailed monitoring of ground deformation from space over the currently operating and the previously operated oil/gas production facilities, as demonstrated by this research, is essential to securing the safety of humanity, preserving property, and sustaining the growth of the hydrocarbon production industry. 77)

- Geohazards pose a severe threat to humanity, civilian properties, infrastructures, and industries, possibly leading to the loss of life and high economic values. Monitoring areas prone to geohazards is invaluable for locating their precursory signals on the surface, alerting civilians to potential disasters, mitigating the catastrophic outcomes, and facilitating the decision-making processes on the construction and operation of infrastructures and industrial facilities. The United States mid-continent has long been considered geologically stable with no large scale tectonic movements, volcanism, or seismic activities. Therefore, unlike California with its dense GPS networks and frequent survey (aerial, spaceborne, field) campaigns, the mid-continent has garnered less attention from scientific communities and federal/state governments. However, recent studies have revealed that some of the mid-continent, especially the Gulf Coast of the United States including Texas, Louisiana, and Mississippi, is not immune to large-scale and/or localized geohazards.

- The geohazards along the southern United States have been both naturally induced and stimulated by human activities. Besides the occasional, strong tropical storms and flooding in lowlands, natural geohazards include settlement due to sediment loading and glacial isostatic adjustment, which can make the coastline in the Gulf Coast vulnerable to sea-level changes. However, the naturally occurring surface subsidence on the coast displays characteristics of a continuous, slow progression (mm/year) and a large spatial extent (~100 km wide). In contrast, human-induced geohazards are faster growing (up to tens of cm/year) and encompass a varying but generally small area (up to a couple of km wide). The most prominent difference between natural and human-induced geohazards is the correlation between surface instability and anthropogenic activities (e.g., mining, groundwater extraction, hydrocarbon production). Although there can be a time delay of ground deformation after human activities, depending on the geological characteristics (porosity, elasticity, compressibility, pore pressure, permeability) of soils and rocks and types of the operations, human-induced surface subsidence or uplift usually has high proximal and temporal correlation with those activities.

- West Texas is somewhat distant from the Gulf coast, but was inundated by relatively shallow seas during the early part of the Paleozoic Era (approximately 600 to 350 million years ago). The sediments formed during this period contributed to the accumulation of sandstone, shale, and limestone. The seas constituting broad marine environments in West Texas gradually withdrew, and by the Permian Period (approximately 299 to 251 million years ago), thick evaporites (salt, gypsum) accumulated in a hot arid land encompassing shallow basins and wide tidal flats. As a consequence of geological formation in West Texas, the deposited carbonate (reef limestone) and marine evaporite sequences played an important role in the formation of oil reservoirs by helping seal the traps and preserving the hydrocarbons. This resulted in the Permian Basin of West Texas' massive hydrocarbon reservoirs that became so lucrative to the oil and gas industry.

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Figure 33: Locations of ground deformation in West Texas. Six major sites (red stars) in West Texas display the locations influenced by human activities identified based on Sentinel-1A/B multi-temporal interferometry (background image is from Sentinel-2). To estimate 2D (east-west and vertical) deformation, the ascending (path 78; black box) and descending (path 85; white box) track Sentinel-1A/B images were integrated over the overlapped regions. The West Texas' Permian Basin contains two major aquifer systems under the influence of the Pecos River, the Pecos Valley aquifer and the Edwards-Trinity aquifer (SMU, ESA)

- In West Texas, human activities such as groundwater exploitation, fluid injection, and hydrocarbon extraction have resulted in surface instability, leading to geohazards such as surface heave/subsidence, fault reactivation, induced seismicity, and sinkhole formation. The vastness of West Texas challenges our ability to identify and locate the relatively small spatial scale of the deformation corresponding to human activities, particularly for fluctuations over the course of a month or a year. Without concerted focus, the small-sized signal in a short time window can go easily undetected. There have been a few studies documenting the surge of surface uplift/subsidence, sinkhole formations, and induced seismicity in oil fields. However, the role of human activities on the surface and subsurface deformation has yet to be fully established, particularly regarding the identification of small-scale deformation signals over a vast region from big datasets spanning multiple years and analyzing them with supplementary information.

- Challenges to the effective study of the geohazards in West Texas include: identification of their locations in remote and vast regions, measurement of their long-term evolution, and characterization of the causal mechanism with accessible information. Satellite radar interferometry (InSAR) has proven capable of imaging ground surface deformation with a measurement accuracy of centimeters or better at a spatial resolution of meters or better over a large region covering tens of thousands km2. However, satellite radar acquisitions over West Texas have previously been scarce. Here we present the analysis of the ongoing ground deformations induced by various geohazards around Pecos, Monahans, Wink, and Kermit in West Texas (Figure 33), using multi-temporal InSAR observations based on radar imagery from the first free, open-source radar satellites Sentinel-1A/B.

- The objective of our study is to probe the association between the ongoing localized geohazards in West Texas and anthropogenic activities. To achieve the goal, we focus on the localized, small-sized (200 m~2 km wide), and rapidly developing (cm/yr) geohazards in the region, which are categorized based on six possible causes: i) wastewater injection, ii) CO2 injection for enhanced oil recovery (EOR), iii) salt/limestone dissolution, iv) freshwater impoundment in abandoned wells, v) sinkhole formation in salt beds, and vi) hydrocarbon production. In addition, time-series measurements from two different imaging geometries are integrated to decipher the deformation phenomena. Furthermore, through comparative analysis of records of fluid injection, hydrocarbon production, and geological characteristics, we establish the relationship between the possible causes of human activities or natural perturbation and the localized observed geohazards in West Texas.

• February 23, 2018: The Copernicus Sentinel-1 mission takes us over the Bering Strait (Figure 34), which connects the Pacific and Arctic Oceans between Russia (Siberia) and the US state of Alaska. 78)

- Since the Bering Strait lies slightly south of the polar circle, days are short during the winter. Thanks to its radar, Sentinel-1 can ‘see' through clouds and in the dark, making it especially valuable for monitoring parts of the planet that endure relatively dark winter months. Offering this ‘radar vision', images from Sentinel-1 can be used for charting icebergs and for generating maps of sea ice for year-round navigation.

- Additionally, monitoring changes in the extent of sea ice is critical for understanding the effect of climate change on our environment.

- It has been reported that sea ice in the Bering Strait has been particularly low this winter. This is because unusually warm water streamed up from the south, causing some of the sea ice to melt earlier than usual. As a result, areas that would have remained covered with reflective sea ice were open for much longer. The relatively dark surface of the sea was able to absorb a lot of energy from the Sun, which prevented sea ice forming in the autumn. Also, recent storms have helped to break up much of the sea ice that did manage to form.

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Figure 34: The image was created by combining three radar scans of 11 December 2017, 23 December 2017 and 4 January 2018. Each image has been assigned a different color: blue, red and green, respectively. This creates a colorful composite that highlights how the sea ice changed over the four weeks of observation (image credit: ESA, the image contains modified Copernicus Sentinel data (2017–18), processed by ESA, CC BY-SA 3.0 IGO)

• December 15, 2017: The Sentinel-1 radar satellite mission takes us over Orange County and surrounding areas in the US state of California. 79)

- Two prominent geological features are visible in Figure 35: the coastal plains of the Los Angeles Basin in the upper-central left, and the Santa Ana Mountains running from the upper left to the lower right.

- A typical feature of Pacific Coast mountain ranges like Santa Ana is a moister western slope and drier eastern slope – reflected in this radar image by the more prominent colors on the left side of the mountain range. This is due to air masses from the Pacific bringing precipitation to the land, while the mountains force the clouds to rise and produce rain and block them from moving further east, causing a ‘rain shadow' and thus drier areas on the other side.

- To respond to dry conditions in California and all over the world, populations rely on dams and reservoirs to control the water supply. In satellite imagery, these water bodies are easy to identify by the straight-cut line of the dam blocking water flow – two of which are visible in the center-right part of the image.

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Figure 35: Three passes by Sentinel-1's radar from 21 December 2014, 2 January 2015 and 14 January 2015 were combined to create this image. Each image was assigned a color – red, green and blue – and changes on the ground that occurred between passes appear as different colors (image credit: ESA, the image contains modified Copernicus Sentinel data (2014-15), processed by ESA , CC BY-SA 3.0 IGO)

Legend to Figure 35: One obvious example of changes can be seen in the boats in the water on the left side of the image, appearing in the three different colors depending on when they were present. - In other parts of the image we can see colors in agricultural fields showing changes in vegetation between the acquisitions.

• November 24, 2017: The Copernicus Sentinel-1 mission gives us ‘radar vision' over part of Antarctica's third-largest island, Thurston Island. The satellite's radar can ‘see' through clouds and in the dark, making it a valuable tool for monitoring polar regions which are prone to bad weather and long periods of darkness – such as Antarctica. 80)

- The image of Figure 36 combined three passes by Sentinel-1's radar in March, April and May 2017. Each was assigned a color – red, green and blue – and when merged, changes between the acquisitions appear in various colors.

- The ice-covered island appears grey, showing no change over the three-month period. But changes in sea ice in the upper part of the image appear as speckles of green, red and blue. In the lower part of the image we can see part of the Abbot Ice Shelf appearing in light blue.

- Antarctica is surrounded by ice shelves, which are thick bands of ice that extend from the ice sheet and float on the coastal waters. They play an important role in buttressing the ice sheet on land, effectively slowing the sheet's flow as it creeps seaward.

- The ice sheet that covers Antarctica is, by its very nature, dynamic and constantly on the move. Recently, however, there has been a worrying number of reports about its floating shelves thinning and even collapsing, allowing the grounded ice inland to flow faster to the ocean and add to sea-level rise.

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Figure 36: Sentinel-1 ‘radar vision' over part of Antarctica's third-largest island, Thurston Island. The image combines three passes by Sentinel-1's radar in March, April and May 2017 - each was assigned a color – red, green and blue which were merged (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)

• November 7, 2017: In late August, the 60 m-long US Coast Guard Cutter Maple completed its navigation through the Arctic's ice-ridden Northwest Passage (Figure 37). While this was not the first time ships had taken this route, it was the first time that the IIP (International Ice Patrol) had provided iceberg information based exclusively on satellite imagery. — Established in 1914 in response to the sinking of the Titanic, the US Coast Guard IIP monitors iceberg danger in the North Atlantic Ocean for shipping safety. 81)

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Figure 37: The US Coast Guard Cutter Maple being escorted by the Canadian Coast Guard Ship Terry Fox (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by Polar TEP)

- When the Maple departed from Alaska in mid-July en route through the Arctic to Maryland, USA, the IIP was on guard to assist the crew to navigate through the notoriously icy waters.

- The IIP used data from the Copernicus Sentinel-1 satellite mission, among others, to create charts showing the risk of encountering icebergs after exiting from the Northwest Passage and during transit through the Baffin Bay, Davis Strait and Labrador Sea.

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Figure 38: Maple's course. The region through which the ship Maple transited 14–18 August 2017, with approximate ship locations identified in yellow on each day. The map has been overlaid with images from the Sentinel-1 radar satellite mission (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by Polar TEP)

- Sentinel-1 is equipped with radar that can detect icebergs through cloud cover, a capability particularly beneficial in the IIP's operating area. Sentinel-1 can also distinguish between the thinner, more navigable first-year ice and the hazardous, much thicker multiyear ice to help assure safe year-round navigation in ice-covered Arctic and sub-Arctic zones. These radar images are particularly suited to generating high-resolution ice charts, monitoring icebergs and forecasting ice conditions.

- Scientists at the IIP used iceberg detection software available on ESA's online Polar TEP (Thematic Exploitation Platform) to access satellite data to detect icebergs and analyze their densities and trajectories.

- "This experience using the Polar TEP cloud-based technology opens the door for future evaluations of a more robust version of the iceberg detection and iceberg trajectory processors," said Michael Hicks, Chief Scientist of the International Ice Patrol. "Cloud-based technology such as that used by Polar TEP is expected to be an important tool for handling the ever-growing amount of data coming from space."

- Polar TEP is one of six Thematic Exploitation Platforms developed by ESA to serve data user communities. These cloud-based platforms provide an online environment to access information, processing tools and computing resources for collaboration. TEPs allow knowledge to be extracted from large environmental datasets produced through Europe's Copernicus program and other Earth observation satellites.

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Figure 39: Navigating with Polar TEP. Using ESA's online Polar TEP, the International Ice Patrol accessed satellite data to detect icebergs and analyze their densities and trajectories (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by Polar TEP)

• October 31, 2017: In this image from the Copernicus Sentinel-1 satellite mission, we can see the location of the ‘Halloween crack' on Antarctica's Brunt Ice Shelf, highlighted in red. The former and current locations of the British Antarctic Survey's Halley research stations are also marked. 82)

- Discovered on 31 October 2016, the swiftly lengthening Halloween crack prompted the temporary withdrawal of staff from the Halley VI research station for the duration of the 2017 Antarctic winter. Information from the Copernicus Sentinel-1 and Sentinel-2 satellites helped in making this decision.

- The base had already been moved 23 km inland during last Antarctica's summer months because another ice chasm (highlighted in red) had begun to show signs of growth.

- In this image of Figure 40, Sentinel-1's radar was also able to pick up lines in the snow and ice marking the researchers' routes from the former location of the Halley VI station to the coast and to the Halloween crack. To help us identify them, these lines have been colored in black.

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Figure 40: This image was created by combining three Sentinel-1 radar scans in September and October. The colors in the Weddell Sea indicate changes in sea ice between the acquisitions. A ‘polynya' – an area of open water surrounded by ice – is visible in the lower-central part of the image (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)

• October 25, 2017: This year's Atlantic hurricane season has been a harsh reminder of the grief and devastation brought by these vast storms. Imaging the top of hurricanes from space is nothing new, but the Sentinel-1 satellites can see right through these towering spinning weather systems, measuring the sea surface below to help predict the storm's path. 83)

- The 2017 hurricane season isn't even over yet, but 10 Atlantic storms in a row have already reached hurricane strength – the first time this has happened in more than a century.

- Since understanding and predicting these powerful weather systems is essential to saving lives and property, scientists have been looking into how the Copernicus Sentinel-1 radar mission can help.

- Information from this state-of-the art mission is used for numerous applications, from monitoring sea ice and marine oil spills to mapping floods and land-surface deformation caused by earthquakes.

- Observing hurricanes wasn't part of its original remit. Unlike satellites that carry optical instruments, from which we get the familiar images of the top of hurricanes, radar can penetrate clouds to image the sea underneath these powerful and destructive weather systems.

- Taking Sentinel-1 beyond its original scope, scientists at DLR (German Aerospace Center) have developed a technique that allows the radar to probe sea-surface wind and wave heights. - Importantly, this information about the state of the sea can help to assess how destructive a hurricane is and predict its path – and, therefore, where and when it is likely to make landfall. The same information can also be used to warn ships and to issue warnings of coastal flooding.

- This new technique was used for the first time when hurricane Irma struck Cuba and the Florida Keys in early September. Here, waves up to 10 m high were measured.

- Sentinel-1 works in several different operational modes, but it is its ‘wide swath mode', which is 250 km wide with a resolution of 5 x 20 m, is particularly valuable for understanding ocean waves. This is especially important because in situ measurements of wind and sea state cannot be gained from buoys or dropped probes in such extreme weather or over such a wide area.

- ESA's Sentinel-1 project manager, Ramón Torres, said, "We see the Sentinel-1 mission being used for many different applications that benefit society, but this is a particularly good example of how the mission could make a real difference to people's lives. Sentinel-1 is delivering beyond our expectations."

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Figure 41: Wave height during Hurricane Irma. Copernicus Sentinel-1 radar mission images were used to measure waves of up to 10 m high under Hurricane Irma as it struck Cuba and the Florida keys on 9 and 10 September 2017, respectively (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by DLR)

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Figure 42: Sentinel-1 radar image under Hurricane Irma (released on 25 Oct. 2017). Scientists at DLR (German Aerospace Center) are using radar images from the Copernicus Sentinel-1 mission to gain information about the wind and waves at the sea surface under hurricanes. This information is not obvious in this image, but novel processing techniques can reveal important information that can be used to assess how destructive a hurricane is and predict its path. This image was acquired on 9 September 2017 under Hurricane Irma as it passed over Cuba (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by DLR)

• October 20, 2017: The Copernicus Sentinel-1A satellite brings us over part of the Sagaing Division in northwest Myanmar (formerly Burma), and along the border with India. 84)

- Snaking through the image of Figure 43 is the Chindwin River, which breached its banks during a period of severe flooding in 2015. Monsoon rains beginning that July caused multiple rivers in the region to overflow, causing widespread damage and affecting up to a million people.

- The image was created using two passes by Sentinel-1's radar. This information was then released in the form of a map under the International Charter Space and Major Disasters to assist relief efforts.

- Currently led by ESA, the Charter is an international collaboration between 16 owners or operators of Earth observation missions. It provides rapid access to satellite data to help disaster management authorities in the event of a natural or man-made disaster.

- Sentinel-1's radar ability to ‘see' through clouds, rain and in darkness makes it particularly useful for monitoring floods.

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Figure 43: This image was created using two passes by Sentinel-1's radar: one before the flooding on 20 March 2015 and the other during the event on 4 September 2015. Combining them shows changes between the images, such as the inundation of some 111,000 hectares of land on either sides of the river bank appearing in red (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by ESA, CC BY-SA 3.0 IGO)

• September 28, 2017: A NASA-produced map showing areas of eastern Puerto Rico that were likely damaged by Hurricane Maria has been provided to responding agencies, including FEMA (Federal Emergency Management Agency). The hurricane, a Category 4 storm at landfall on Puerto Rico on Sept. 20, caused widespread damage and numerous casualties on the Caribbean island, an unincorporated U.S. territory with a population of about 3.4 million. 85)

- To assist in disaster response efforts, scientists at NASA's Jet Propulsion Laboratory and Caltech, both in Pasadena, California, obtained and used before-and-after interferometric synthetic aperture radar (InSAR) satellite imagery of areas of Eastern Puerto Rico to identify the areas that are likely damaged. The imagery — acquired before the storm on March 25, 2017 and again one day after landfall on Sept. 21, 2017 — is from the radar instruments on the Copernicus Sentinel-1 satellites operated by the European Space Agency.

- The views indicate the extent of likely damage caused by the hurricane, based on changes to the ground surface detected by radar. The color variations from yellow to red indicate increasingly more significant ground and building surface change. The map is used as guidance to identify potentially damaged areas and may be less reliable over vegetated and flooded areas.

- The radar data were processed by the ARIA (Advanced Rapid Imaging and Analysis) team at JPL and Caltech. ARIA is a NASA-funded project that is building an automated system for demonstrating the ability to rapidly and reliably provide GPS and radar satellite data to support local, national and international hazard-monitoring and response communities. InSAR can "see" through clouds and is sensitive to changes in the roughness of the ground or building surfaces.

- Using space-based radar imagery of disasters, ARIA data products can aid responders in making rapid assessments of the geographic region affected by a disaster, as well as detailed imaging of locations where damage occurred.

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Figure 44: NASA/JPL-Caltech-produced map of damage in and around San Juan, Puerto Rico (orange inset box) from Hurricane Maria, based on ground and building surface changes detected by ESA satellites. Color variations from yellow to red indicate increasingly more significant ground and building surface change (image credit: NASA-JPL/Caltech/ESA/Copernicus/Google)

Legend to Figure 44: The map is derived from SAR (Synthetic Aperture Radar) images from the Copernicus Sentinel-1A and Sentinel-1B satellites, operated by the ESA. The images were taken before (March 25, 2017) and after (Sept. 21, 2017) the storm's landfall. The map was delivered to responding agencies, including FEMA (Federal Emergency Management Agency), on Sept. 22, 2017. FEMA combined the map with building infrastructure data to estimate a damage density map, which was sent to its Urban Search and Rescue teams in the field in Puerto Rico. 86)

The map covers an area of 169 x 96 km, shown by the large red polygon in the figure. The inset, denoted by the orange rectangle, shows the extent of damage in and around the capital city of San Juan. Each pixel measures about 30 m across. The color variation from yellow to red indicates increasingly more significant ground surface change. Preliminary validation was done by comparing the map with anecdotal reports of damage. This damage proxy map should be used as guidance to identify damaged areas, and may be less reliable over vegetated and flooded areas. Sentinel-1 data were accessed through the Copernicus Open Access Hub. The image contains modified Copernicus Sentinel data (2017), processed by ESA and analyzed by the NASA-JPL/Caltech ARIA team. This research was carried out at JPL under a contract with NASA.

• September 20, 2017: Witnessed by the Copernicus Sentinel-1 mission on 12 July 2017, a lump of ice more than twice the size of Luxembourg broke off the Larsen C ice shelf, spawning one of the largest icebergs on record and changing the outline of the Antarctic Peninsula forever. Over the following two months, systematic observations from Sentinel-1 showed that the A68 berg remained close, buffeting back and forth against the ice shelf. It was unclear what would happen to the berg because they can remain in one place for years. 87)

- However, the mission has revealed that A68 is now on the move and drifting out to sea. Images from 16 September show that there is a gap of about 18 km as the berg appears to be turning away from the shelf.

Figure 45: Until a few days ago, the huge chunk of ice that broke off Antarctica's ice shelf in July has remained close, buffeting back and forth against the shelf. A68 is now on the move and drifting out to sea (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)

• August 17, 2017: For the first time in India, a state government is using satellites to assess lost crops so that farmers can benefit from speedy insurance payouts. — The southern Indian state of Tamil Nadu is home to around 68 million people, of which almost a million are rice farmers. However, Tamil Nadu is facing the worst drought in 140 years, leading to the land being too dry for paddy fields, lost yield, widespread misery and unrest. 88)

- The Copernicus Sentinel-1 radar mission has been used to alleviate a little of the suffering by providing evidence of damaged land and failed crops so that the Agricultural Insurance Company of India can compensate farmers as quickly as possible. So far, more than 200 000 farmers have received payouts.

- Malay Kumar Poddar, the company's general manager, said, "Assessing damages based on remote-sensing technology is introducing much objectivity into the crop insurance program. "Beyond the area loss assessment, we are also keen to apply the technology to assess actual yields at the end of the season."

- Satellites carrying optical cameras can provide images of Earth's surface only in daylight and in the absence of cloud, but the Sentinel-1 satellites carry radar which works regardless. This makes it an ideal mission to use in tropical and subtropical regions, which are often cloudy.

- Sentinel-1 radar imagery combined with rice-yield modelling is at the heart of the German–Swiss RIICE (Remote-Sensing based Information and Insurance for Crops in Emerging Economies initiative). — Francesco Holecz, from sarmap, set up the service in collaboration with the International Rice Research Institute, RIICE partners, Indian authorities and universities. He said, "The reliable repetitiveness of the Sentinels, their short revisit intervals, the free, quick and easy access to the products and the high quality of the data have contributed a lot to the practicability of satellite-based rice monitoring systems."

- Gagandeep Singh Bedi, agricultural production commissioner and principle secretary to the government in Tamil Nadu added, "RIICE remote-sensing technology allows us to assess crop loss and damages in a more transparent and timely manner. "It was particularly useful during the last cropping season to identify villages that had been hit by drought, and farmers benefited from the technology by getting claims in a record time."

- The research network is also working with partners in other countries to develop the method further. For example, the Tamil Nadu Agricultural University and the International Rice Research Institute in the Philippines are looking to use it to assess yields at the end of the season. Sellaperumal Pazhanivelan, from the university, said, "We believe that this technology can help the state governments to obtain objective and transparent data on actual rice yields so that farmers affected by natural hazards can be identified quickly."

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Figure 46: Assessing rice crops with Sentinel-1: Using radar data from the Copernicus Sentinel-1 mission, areas where rice is grown in the southern Indian state of Tamil Nadu can be assessed. Light blue to magenta colors represent cultivated fields and light to dark green represents forests (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by RIICE/TNAU)

• July 12, 2017: Over the last few months, a chunk of Antarctica's Larsen C ice shelf has been hanging on precariously as a deep crack cut across the ice. Witnessed by the Copernicus Sentinel-1mission, a lump of ice more than twice the size of Luxembourg has now broken off, spawning one of the largest icebergs on record and changing the outline of the Antarctic Peninsula forever. 89)

- The fissure first appeared several years ago, but seemed relatively stable until January 2016, when it began to lengthen.

- In January 2017 alone it travelled 20 km, reaching a total length of about 175 km.

- After a few weeks of calm, the rift propagated a further 16 km at the end of May, and then extended further at the end of June.

- More importantly, as the crack grew, it branched off towards the edge of the shelf, whereas before it had been running parallel to the Weddell Sea. With just a few km between the end of the fissure and the ocean by early July, the fate of the shelf was sealed.

- Scientists from Project MIDAS, an Antarctic research consortium led by Swansea University in the UK, used radar images from the Copernicus Sentinel-1 mission to keep a close eye on the rapidly changing situation.

- Since Antarctica is heading into the dark winter months, radar images are indispensable because, apart from the region being remote, radar continues to deliver images regardless of the dark and bad weather.

- Adrian Luckman, leading MIDAS, said, "The recent development in satellite systems like Sentinel-1 has vastly improved our ability to monitor events such as this."

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Figure 47: Witnessed by the Copernicus Sentinel-1 mission on 12 July 2017, a lump of ice more than twice the size of Luxembourg has broken off the Larsen-C ice shelf, spawning one of the largest icebergs on record and changing the outline of the Antarctic Peninsula forever. The iceberg weighs more than a million million tons and contains almost as much water as Lake Ontario in North America. Since the ice shelf is already floating, this giant iceberg will not affect sea level. However, because ice shelves are connected to the glaciers and ice streams on the mainland and so play an important role in ‘buttressing' the ice as it creeps seaward, effectively slowing the flow. If large portions of an ice shelf are removed by calving, the inflow of glaciers can speed up and contribute to sea-level rise. About 10% of the Larsen C shelf has now gone (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)

- Noel Gourmelen from the University of Edinburgh added. "We have been using information from ESA's CryoSat-2 mission, which carries a radar altimeter to measure the surface height and thickness of the ice, to reveal that the crack was several tens of meters deep."

- As predicted, a section of Larsen C – about 6000 km2 – finally broke away as part of the natural cycle of iceberg calving. The behemoth iceberg weighs more than a million million tons and contains about the same amount of water as Lake Ontario in North America.

- "We have been expecting this for months, but the rapidity of the final rift advance was still a bit of a surprise. We will continue to monitor both the impact of this calving event on the Larsen C ice shelf, and the fate of this huge iceberg," added Prof. Luckman.

- The iceberg's progress is difficult to predict. It may remain in the area for decades, but if it breaks up, parts may drift north into warmer waters. Since the ice shelf is already floating, this giant iceberg does not influence sea level.

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Figure 48: ESA's CryoSat-2 mission measured the depth of the crack in the Larsen C ice shelf, which led to the birth of one of the largest icebergs on record. Carrying a radar altimeter to measure the surface height and thickness of the ice, the mission revealed that the crack was several tens of meters deep (image credit: University of Edinburgh) 90)

- With the calving of the iceberg, about 10% of the area of the ice shelf has been removed.

- The loss of such a large piece is of interest because ice shelves along the peninsula play an important role in ‘buttressing' glaciers that feed ice seaward, effectively slowing their flow.

- Previous events further north on the Larsen A and B shelves, captured by ESA's ERS and Envisat satellites, indicate that when a large portion of an ice shelf is lost, the flow of glaciers behind can accelerate, contributing to sea-level rise.

- Thanks to Europe's Copernicus environmental monitoring program, we have the Sentinel satellites to deliver essential information about what's happening to our planet. This is especially important for monitoring remote inaccessible regions like the poles.

- ESA's Mark Drinkwater said, "Having the Copernicus Sentinels in combination with research missions like CryoSat-2 is essential for monitoring ice volume changes in response to climate warming. In particular, the combination of year-round data from these microwave-based satellite tools provides critical information with which to understand ice-shelf fracture mechanics and changes in dynamic integrity of Antarctic ice shelves."

• June 13, 2017: On 20 May, over a million tons of dirt and rock buried part of California's Highway 1 along the Pacific coastline in the state's Big Sur region. In addition to cutting off the route, the landslide added some 5 hectares of land to the shoreline. — Sentinel-1's radar shows that the ground that slid down the mountain was moving in the two years before the landslide. 91)

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Figure 49: The Sentinel-1 radar data were processed using Small Baseline Subset interferometry (SBAS), a technique that can detect and monitor movements over wide areas with high sensitivity. In this image, red dots represent points where the ground was moving away from the satellite at a rate of more than 70 mm per year. Green dots show stable ground in the surrounding area (image credit: ESA, the image contains modified Copernicus Sentinel data (2015–17), processed by Norut)

• May 12, 2017: Rapid acceleration of an Arctic glacier over the past year has been detected by the Copernicus Sentinel-1 satellites. Sitting on Norway's Spitsbergen island in the Svalbard archipelago, the Negribreen glacier has recently seen a surge in ice surface speed, increasing from 1 m to 13 m a day over the winter. 92)

- When a glacier ‘surges' a large amount of ice flows to the end in an unusually short time. While the causes are not completely understood, they are believed to be linked to changes in the amount of heat or water in the lowest layers of the glaciers.

- The last time Negribreen experienced a surge like this was in the 1930s, as documented in aerial photographs. At that time, it advanced almost 12 km into the fjord in one year along a 15 km-wide section of the front. Since then the front of the glacier had been steadily retreating, with large icebergs breaking off.

- This latest jump in speed began in July 2016 and has been climbing ever since – even over the cold winter months. - Monitoring glaciers in areas prone to bad weather and long periods of darkness – like the Arctic – was difficult before the advent of satellites. Radar satellites can ‘see' through clouds and in the dark, and Sentinel-1 offers frequent and systematic coverage of the Arctic.

- A team of scientists working under ESA's Climate Change Initiative in the Glaciers_cci project are using satellite radar and optical coverage to map glaciers at different times and determine their changes in extent, elevation and speed.

Figure 50: Radar images from the Copernicus Sentinel-1 mission show the sudden advance of the Negribreen glacier in Norway in early 2017 [image credit: ESA, the image contains modified Copernicus Sentinel data (2016–17), processed by T. Strozzi (Gamma)]

- A team of scientists working under ESA's Climate Change Initiative in the Glaciers_cci project are using satellite radar and optical coverage to map glaciers at different times and determine their changes in extent, elevation and speed.

- "Sentinel-1 provides us with a near-realtime overview of glacier flow across the Arctic, remarkably augmenting our capacity to capture the evolution of glacier surges," said Tazio Strozzi from Swiss company Gamma Remote Sensing and scientist on Glaciers_cci.

- "This new information can be used to refine numerical models of glacier surging to help predict the temporal evolution of the contribution of Arctic glaciers to sea-level rise."

Figure 51: Radar images from the Copernicus Sentinel-1 mission were used to create these two ice speed maps of the Negribreen glacier in Norway. In October 2015, only the front of the glacier was moving by more than 300 m a year. By late 2016, the entire glacier was advancing at this accelerated rate.

• May 2, 2017: Over two decades of observations by five radar satellites show the acceleration of ice loss of 30 glaciers in Antarctica's Western Palmer Land in the southwest Antarctic. 93)

- Radar is particularly suited for monitoring polar regions that are prone to bad weather and long periods of darkness because it can collect information regardless of cloud cover, day or night. Mapping 30 glaciers in the region, the research team found that between 1992 and 2016, most of the glaciers sped up by 20 and 30 cm per day. This is equivalent to an average 13% increase in flow speed across the area as a whole (Figure 52).

- The study in Geophysical Research Letters combines over 24 years of radar data from satellites including ESA's Envisat and ERS missions, as well as from the Copernicus Sentinel-1 mission. 94)

- A decrease in the mass and volume of Western Palmer Land has raised the prospect that ice speed has increased in this marine-based sector of Antarctica. To assess this possibility, we measure ice velocity over 25 years using satellite imagery and an optimized modelling approach. More than 30 unnamed outlet glaciers drain the 800 km coastline of Western Palmer Land at speeds ranging from 0.5 to 2.5 m/day, interspersed with near-stagnant ice. Between 1992 and 2015, most of the outlet glaciers sped up by 0.2 to 0.3 m/day, leading to a 13 % increase in ice flow and a 15 km3/yr increase in ice discharge across the sector as a whole. Speedup is greatest where glaciers are grounded more than 300 m below sea level, consistent with a loss of buttressing caused by ice shelf thinning in a region of shoaling warm circumpolar water.

- The two-satellite Sentinel-1 mission for Europe's Copernicus program routinely monitors polar areas at a high resolution, continuing the long-term data record from European satellites.


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Figure 52: Ice speed in the Western Palmer Land measured by the Copernicus Sentinel-1 mission between 2014 and 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2014-16), processed by J. Wuite, ENVEO)

• April 20, 2017: Two Sentinel-1 radar images from 7 and 14 April 2017 were combined to create this interferogram showing the growing crack in Antarctica's Larsen-C ice shelf (Figure 53). Polar scientist Anna Hogg said: "We can measure the iceberg crack propagation much more accurately when using the precise surface deformation information from an interferogram like this, rather than the amplitude – or black and white – image alone where the crack may not always be visible." 95)

- When the ice shelf calves this iceberg it will be one of the largest ever recorded – but exactly how long this will take is difficult to predict. The sensitivity of ice shelves to climate change has already been observed on the neighboring Larsen-A and Larsen-B ice shelves, both of which collapsed in 1995 and 2002, respectively.

- These ice shelves are important because they act as buttresses, holding back the ice that flows towards the sea.

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Figure 53: Larsen-C crack interferogram of Sentinel-1 showing the growing crack of the Larsen-C ice shelf (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by A. Hogg/CPOM/Priestly Centre, CC BY-SA 3.0 IGO)

• April 21, 2017: Earthquake Emergency Management Service in Italy. — A series of strong earthquakes struck Central Italy starting in August 2016, killing over 300 people, injuring some 360 and leaving over 2000 without homes. The Copernicus Emergency Management service was activated by the Italian Civil Protection authorities during this period and produced a total of 120 maps of the damaged areas, supporting their decision-making, rescue and aid delivery activities during these disastrous events. 96)

- Susceptible tectonics: Italy's tectonic and geological characteristics make it a country which is particularly susceptible to the risk of major earthquakes. It straddles the boundary between the Eurasian and African tectonic plates in the south, and a complex series of fault lines run down the entire length of the country along the Apennine mountain chain, collectively known as the Apennine fault. This geological "spine" is clearly visible in the map below, produced by the Italian National Institute for Environmental Protection and Research, ISPRA (Istituto Superiore per la Protezione e la Ricerca Ambientale).

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Figure 54: Map of capable fault lines in Italy. "Capable" faults are defined as having "significant potential for displacement at or near the ground surface"(image credit: ISPRA)

- A series of major earthquakes: During the period between the end of August 2016 and January 2017, a series of significant earthquakes ravaged Central Italy:

1) 24 August 2016: A large earthquake measuring 6.2 Mw (Moment magnitude scale) struck Central Italy in the early hours of the morning.

2) 26 October 2016: Two months later, the Marche region was hit by two major earthquakes on the same day, measuring 5.4 and 5.9 Mw, respectively. Within a week, Umbria suffered a massive 6.5 Mw earthquake.

3) 18 January 2017: A set of large earthquakes struck Lazio and Abruzzo, of which the largest measured 5.7 Mw.

Large earthquakes are usually accompanied by large numbers of smaller shocks of varying intensity, some occurring prior to the main quake. These smaller events can amplify the destruction of the main tremor by further weakening already damaged buildings and infrastructure. The Italian Institute for Geophysics and Volcanology, INGV (Istituto Nazionale di Geofisica e Vulcanologia) maintains a network of sensors across Italy to measure earthquakes. The map (Figure 55) shows the earthquakes recorded by INGV in the regions of Central Italy between August 2016 and February 2017; the total number registered exceeds 45.000, and the sheer quantity and density of the events is overwhelmingly apparent.

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Figure 55: Map of the over 45.000 seismological events recorded by INGV over Central Italy between August 2016 and February 2017. In total, these earthquakes claimed the lives of over 300 people, injured around 360, and caused the temporary displacement of some 2000 citizens from their damaged homes (image credit: INGV)

The earthquake on 24 August 2016 struck at 1:36 (CET) in the morning, with its epicenter closest to the towns of Amatrice, Accumoli and Pescara del Tronto. It sent shock waves rippling over a very large area spanning several of Italy's regions (Lazio, Abruzzo, Umbria, Perugia) and municipalities. Almost 300 people lost their lives, and thousands of buildings were damaged.

The Italian Civil Protection Department, DPC (Dipartimento della Protezione Civile) activated the Copernicus EMS (Emergency Management Service) Rapid Mapping component a few hours later. The quake and its aftershocks had unleashed waves of destruction over a very large rural area, dotted with small towns and remote settlements of varying sizes. These villages are not very well-connected, in many cases accessible only via one or two roads. Several of them lie on the slopes of the Apennine mountains, which further complicates access.

The immediate challenges facing the authorities were to understand the severity of the damages in the various settlements, so as to be able to direct rescue services where they would be most needed, to assess whether people would be able to return safely to their homes, and to locate blocked roads and access routes, to which clearance teams should be urgently dispatched.

In support of this kind of decision-making, the Copernicus EMS provides "grading" maps: rapid assessments of the impact of damages, made by comparing pre- and post-event satellite images. The map below is an example of one of the grading maps produced in the area around the village of Accumoli and delivered to local emergency management authorities rapidly after the quake. This map, along with some 60 others of its type produced during the activation, supported the authorities in making informed decisions about the locations in the most urgent need of intervention (Figure 56). Debris and roadblocks are indicated, as are damaged buildings, marked to show the extent of the damage. The small settlements scattered across the landscape are notable, as are the few roads which connect them.

To be able to inform citizens about whether their homes are safe or not, it was necessary for the authorities to conduct ground surveys to establish that buildings comply with safety standards. The satellite imagery made it possible to prioritize ground survey deployments: if damage to a building is visible from a satellite, then it is not safe for habitation, but ground surveys can then be dispatched to nearby buildings to check whether they are compliant. Visual inspection of potentially damaged buildings must be carried out before they can be declared safe and habitable.

Along with re-homing citizens, the Civil Protection Authorities needed to plan for setting up temporary camps at appropriate locations, which should be large enough to accommodate displaced families in the area. Satellite images can be used for this purpose, and Copernicus Emergency Management Service products include a short report alongside the damage maps with estimates of the affected population, roads and settlements.

A range of tools at the service of the citizen: Satellite imagery is very well-suited for quickly making broad assessments of damage, for calculating requirements for temporary accommodation, and, in general, for taking stock of an unfolding situation over large areas. But there are limitations to what can be seen from a satellite, which usually captures images from directly overhead. Damage to the roofs of buildings is identifiable, as is debris lying next to buildings or in the roads – which is an indicator of structural damages. But damage to the facades of a building, for example, cannot be directly perceived. Factors such as cloudiness and atmospheric haze can also prevent the effective use of satellite imagery, and if the structures being examined are too small, this places a limit on the accuracy of the damage assessment which can be obtained using satellite imagery. For these reasons, a pilot study is currently underway for the Copernicus Emergency Management Service, investigating the potential of deploying manned and unmanned aerial systems (UAS) for acquiring imagery in support of emergency management actors. The use of aerial images can supplement satellite data, providing higher resolution imagery and, since they can fly underneath the cloud line, mitigating the problems associated with bad weather.

In summary, the Copernicus EMS activations over Central Italy generated 120 maps for the Italian Civil Protection Department to guide their decision-making, aid delivery and rescue efforts throughout the course of the unrelenting series of earthquakes which tore through the region starting in August 2016.

In the days and weeks following the quakes, Copernicus Sentinel-1 data was used by researchers at the Italian National Research Council and at the National Observatory of Athens to generate deformation maps of two of the affected regions, showing the extent of the Earth's movement during the earthquakes and providing valuable insights into the cause of their origins.

Table 8: Rapidly mapping the damages: the Copernicus Emergency Management Service (Ref. 96)

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Figure 56: Copernicus EMS Grading Map (Monitoring) of Accumoli, Italy. The village of Accumoli is shown in the zoomed inset, and the map legend has been enlarged for readability. The small, widely spaced settlements are visible (image credit: Copernicus Emergency Management Service)

• April 7, 2017: EMSA (European Maritime Safety Agency), based in Lisbon, Portugal, provides technical assistance and support to the European Commission and Member States, amongst others, in the development and implementation of EU maritime legislation. Its mission is to ensure a high, uniform and effective level of maritime safety, maritime security, prevention of and response to pollution from ships, as well as response to marine pollution caused by oil and gas installations. 97)

- Satellites, with their sophisticated sensors, provide routine, cost-effective, wide-area surveillance over maritime zones. Furthermore, they can be pointed to a targeted location for monitoring specific operations and gather material in response to intelligence information. Earth observation contributes to maritime surveillance to help manage the actions and events that can have an impact on maritime safety and security, including marine pollution, accident and disaster response, search and rescue, as well as fisheries control.

- EMSA also operates CleanSeaNet, a satellite-based oil spill surveillance and vessel detection service. It offers assistance to participating States for the following activities:

1) identifying and tracing oil pollution on the sea surface

2) monitoring accidental pollution during emergencies

3) contributing to the identification of polluters.

- The CleanSeaNet service is based on radar satellite images, covering all European sea areas, which are analyzed in order to detect possible oil spills on the sea surface. When a possible oil spill is detected in national waters, an alert message is delivered to the relevant country. Analyzed images are available to national contact points within 30 minutes of the satellite passing overhead. Approximately 2,000 images are ordered and analyzed per year.

- The service, which is integrated into national and regional pollution response chains, aims to strengthen operational responses to accidental and deliberate discharges from ships, and assist participating States to locate and identify polluters in areas under their jurisdiction.

- Each coastal State has access to the CleanSeaNet service through a dedicated user interface, which enables them to view ordered images. Users can also access a wide range of supplementary information through the interface, such as oil drift modelling (forecasting and backtracking), optical images, and oceanographic and meteorological information.

- SAR satellite images cannot provide information on the nature of a spill (for instance whether it is mineral oil, fish or vegetable oil, or other), but spills from vessels often appear as long, linear dark lines (indicating a substance discharging as the vessel is moving), with a bright spot (the vessel) at the tip. Vessel detection is also available through the CleanSeaNet service. If a vessel is detected in a satellite image, its identity can often be determined by correlating the satellite data with vessel positioning reports from the European monitoring systems operated at EMSA, such as SafeSeaNet.

- The Sentinel-1 mission supports detection of illegal oil spills. 98)

• April 4, 2017: A new processing tool has been developed to bundle information contained in large amounts of satellite data, paving the way for the wealth of Copernicus Sentinel satellite data to be more easily incorporated into online environment-monitoring services. ESA's online U-TEP (Urban Thematic Exploitation Platform) makes information from satellite data available for the non-expert user for urban environment monitoring.

To do this, it processes hundreds of terabytes of data gathered by Earth-observing satellites, and translates them into easy-to-use products for scientists, urban planners and decision-makers.

U-TEP reached a milestone recently with the integration of some 450 000 scenes from the US Landsat-8 mission acquired between 2013 and 2015. The 500 TB was reduced to about 25 TB thanks to the TimeScan processor developed by the DLR (German Aerospace Center). The resulting TimeScan Landsat 2015 product is already available on the U-TEP geobrowser.

This novel tool that distils a single information product from a multitude of satellite scenes is a step towards more efficient access, processing and analysis of the massive amount of high-resolution image data provided by the latest satellites.

The Copernicus Sentinel satellites, for example, are supplying an unprecedented wealth of measurements. By the end of 2017, the operational Sentinel-1, -2 and -3 satellites alone will continuously collect a daily volume of about 20 TB of open and free satellite imagery.

In the past, users had to individually download and process data on their own computers. Now, mass data can be directly archived and processed at the point of reception for maximum speed and efficiency.

Within U-TEP, user algorithms are brought to the data where they run in cloud computing environments. This avoids the transfer of large amounts of input data and makes it unnecessary for the individual user to set up inhouse computing services.

In the near future, the TimeScan approach will be used by the U-TEP team to process both Landsat optical imagery and Sentinel-1 radar data to automatically map human settlements with unprecedented precision: 10 m resolution. This will help entities such as scientists, urban planners, environmental agencies or development banks to better understand urbanization, as well as respond to the challenges posed by growing cities, population increase, climate change and loss of biodiversity.

The data processed by TimeScan will not only benefit urban monitoring, but also land use/land cover mapping, agriculture, forestry, the monitoring of polar and coastal regions, risk management and disaster prevention, or natural resource management.

The TimeScan processor is being used at the DLR, IT4Innovation and Brockmann Consult processing centers to create products based on Sentinel-1, Sentinel-2 and Landsat data.

U-TEP is one of six Thematic Exploitation Platforms developed by ESA to serve data user communities. These cloud-based platforms provide an online environment to access information, processing tools and computing resources for collaboration. TEPs allow knowledge to be extracted from large environmental datasets produced through Europe's Copernicus program and other Earth observation satellites.

Table 9: Urban monitoring boosted by new data processor 99)

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Figure 57: Sentinel-1 TimeScan product: of Germany derived from more than 1500 scans by Sentinel-1 between May 2014 and July 2016 (image credit: DLR, the image contains modified Copernicus Sentinel data (2014-16), processed by DLR) 100)

Legend to Figure 57: In the false-color image, the temporal average, minimal and maximal backscattering values are represented for every pixel in the red, green and blue bands. Urban conglomerations, for example, reflect strongly and appear as prominent, bright areas. Water bodies deflect a large proportion of the oblique synthetic aperture radar beams from the satellite and are therefore dark. Vegetated regions are distinguished by comparatively high minimal backscatter, which causes forests and meadows to appear in green tones. Temporally dynamic land cover types, such as crop acreage, have changed considerably during the acquisition period and appear lilac in the data product.

Figure 58: TimeScan product: Pearl River Delta (image credit: DLR) 101)

Legend to Figure 58: This animation shows the TimeScan Landsat data derived for the Pearl River delta in China for 2002–03 and 2014–15. The illustrated TimeScan RGB images are composed of the temporal maximum built-up index in red, the maximum vegetation index in green and the temporal mean value of the water index in blue. A specific image analysis algorithm developed by DLR in ESA's SAR4Urban project uses the TimeScan data to map the extent of the built-up area (highlighted in black in the animation) in order to finally pinpoint the urban growth that took place in the region over the last 10 years.

• March 31, 2017: This Sentinel-1 radar composite image (Figure 59) takes us to the northeastern tip of Ellesmere Island (lower-left), where the Nares Strait opens up into the Lincoln Sea in the Canadian Arctic. 102)

- The image was created by combining three radar scans from Copernicus Sentinel-1 captured in December, January and February. Each image has been assigned a color – red, green and blue – and create this colorful composite when combined. Colors show changes between acquisitions, such as the movement of ice in the Lincoln Sea, while the static landmass is grey. - The obvious distinction between the red and yellow depicts how the ice cover has changed over the three months.

- The maximum extent of Arctic sea ice hit a record low this winter. Scientists attribute the reduced ice cover to a very warm autumn and winter, exacerbated by a number of extreme winter ‘heat waves' over the Arctic Ocean.

- In the center-left on the land, we can see a straight, dark link with a circle at its left end. This is the runway for Alert – the northernmost known settlement in the world. Inhabited mainly by military and scientific personnel on rotation, Alert is about 800 km from the North Pole.

- A team of researchers on the CryoVex/Karen campaign was recently in Alert validating sea-ice thickness measurements from the CryoSat-2 satellite and testing future satellite mission concepts. 103)

- Taking off from Alert, the team flew two aircraft equipped with instruments that measure sea-ice thickness at the same time the CryoSat-2 satellite flew some 700 km overhead. The measurements from the airborne campaign will be compared to the satellite measurements in order to confirm the satellite's accuracy.

- A team will also make ground measurements of snow and ice along a CryoSat-2 ground track in April. Ground campaigns like this provide a wealth of data that help scientists better understand how the Arctic is changing and, ultimately, how climate is changing.

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Figure 59: Sentinel-1 composite radar image of Ellesmere Island, Canada, acquired in December 2016, and in January and February 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016-17), processed by ESA)

• March 5, 2017: Since the 1920s, excessive pumping of groundwater at thousands of wells has caused land to subside, or sink, by as much as 8.5 meters in sections of California's San Joaquin Valley. This subsidence is exacerbated during droughts, when farmers rely heavily on groundwater to sustain one of the most productive agricultural regions in the United States. 104)

- Subsidence is a serious and challenging concern for California's water managers, putting state and federal aqueducts, levees, bridges and roads at risk of damage. Already, long-term land subsidence has damaged thousands of public and private groundwater wells throughout the San Joaquin Valley. Furthermore, the subsidence can permanently reduce the storage capacity of underground aquifers, threatening future water supplies. It's also expensive. While there is no comprehensive estimate of damage costs associated with subsidence, state and federal water agencies have spent an estimated $100 million on related repairs since the 1960s.

- To determine the extent to which additional groundwater pumping associated with California's recent historic drought has affected land subsidence in the Central Valley, California's Department of Water Resources (DWR) commissioned NASA/JPL ( Jet Propulsion Laboratory) to use its expertise in collecting and analyzing airborne and satellite radar data. An initial report from JPL in August 2015 analyzed radar data from several different sensors collected between 2006 and early 2015. Due to the continuing drought, DWR subsequently commissioned JPL to collect and analyze new radar images from 2015 and 2016 to update DWR.

- Several trouble spots that were identified in 2015 have continued to subside at rates as high as 0.6 m per year. Significant subsidence was measured in subsidence bowls near the towns of Chowchilla, south of Merced; and Corcoran, north of Bakersfield. These bowls cover hundreds of square kilometers and continued to grow wider and deeper between May 2015 and September 2016. Subsidence also intensified near Tranquility in Fresno County, where the land surface has settled up to 51 cm in an area that extends 11 km.

- The map of Figure 60 shows the total subsidence in part of the San Joaquin Valley between May 2015 and September 2016 as observed by the ESA (European Space Agency) Sentinel-1A satellite and analyzed by scientists at JPL. The areas of most extensive subsidence appear in shades of yellow and bright green.

- JPL scientists plotted the history of subsidence of several sites in the mapped areas and found that for some areas in the San Joaquin Valley, subsidence slowed during the winter of 2015-16 when rainfall matched crop water needs. "While we can see the effect that rain has on subsidence, we know that we've run a groundwater deficit for some time, so it will take a long time to refill those reservoirs," said JPL report co-author Tom Farr. 105)

- Cathleen Jones, a co-author and scientist from JPL, said being able to pinpoint where subsidence is happening helps water resource managers determine why it is happening. "If you see a subsidence bowl, then something is going on at the center of the bowl that is causing the land to sink—for example, high levels of groundwater pumping," she said. "We can locate problem spots so the state can focus on those areas, saving money and resources. We find the needle in the haystack, so to speak."

- The researchers compared multiple satellite and airborne interferometric synthetic aperture radar (InSAR) images of Earth's surface to show how subsidence varies over space and time. InSAR is routinely used to produce maps of surface deformation with approximately centimeter-level accuracy. The 2015 and 2017 reports included data from Sentinel-1A, NASA's UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar), Japan's PALSAR on ALOS-2, and Canada's RADARSAT-2.

- "The rates of San Joaquin Valley subsidence documented since 2014 by NASA are troubling and unsustainable," said DWR Director William Croyle. "Subsidence has long plagued certain regions of California. But the current rates jeopardize infrastructure serving millions of people. Groundwater pumping now puts at risk the very system that brings water to the San Joaquin Valley. The situation is untenable."

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Figure 60: NASA Earth Observatory map by Joshua Stevens, using ESA Sentinel-1 SAR data courtesy of Tom Farr and Cathleen Jones, NASA/JPL, caption by Alan Buis of JPL and Ted Thomas of DWR, edited by Mike Carlowicz

• February 24, 2017: California has seen some heavy rains recently after years of drought, filling many of the state's reservoirs. The rising waters are evident in this radar image from the Copernicus Sentinel-1 satellite mission over part of the San Joaquin Valley. 106)

- The three water bodies pictured in Figure 61 are Lake Kawhea (in Tulare County) in the upper right, Bravo Lake to its left and Lake Success (near Porterville on the Tule River) in the lower right. This image was created by combining two scans from Sentinel-1's radar on 15 December and 26 January, and assigning each scan a color. Combined, the colors reveal changes, such as the red coloring in the reservoirs showing the water level increase.

- Officials have begun to release water from Lake Success as heavy rains have nearly filled it to capacity, and the outflow is sometimes exceeding the inflow in these days.

- The problem of too much water is in stark contrast from the situation in previous years, when drought led to water shutoffs and cutoffs, severely hindering yields in the San Joaquin Valley – a major agricultural region. Major crops include grapes, cotton, nuts and fruits, with productivity relying on irrigation from surface water diversions and groundwater pumping from wells.

- Agricultural structures dominate this radar composite image. Like the reservoirs, colors reveal changes between December and January such as vegetation growth or harvests.

- Along the right side of the image, we can see the foothills of the Sierra Nevada mountains.

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Figure 61: A Sentinel-1 radar image of water reservoirs in California as of Dec. 15, 2016 and of Jan. 26, 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data, processed by ESA)

• February 16, 2017: Following the appearance of a large crack in the ice shelf close to the Halley VI research station of BAS (British Antarctic Survey) in Antarctica, information from the Copernicus Sentinel-1 and Sentinel-2 satellites helped to decide to close the base temporarily. 107)

- Nourished by an inflow of ice from grounded glaciers and snow accumulating on its surface, Brunt Ice Shelf is a floating ice sheet in the Weddell Sea Sector of Antarctica. The floating ice moves steadily towards the ocean, where it occasionally calves off as icebergs. Cracks often appear on shelves as the ice deforms. However, rapidly expanding cracks indicate impending calving.

- Since the Halley VI base of BAS was only 17 km from the crack that appeared last October, ENVEO – a company that uses satellite data for cryosphere studies – and the Survey used radar images from Sentinel-1 and optical images from Sentinel-2 to monitor the situation.

- Dubbed Halloween Crack, it was lengthening inland as fast as 600 m a day in November and December 2016. Halley was designed to be relocated if the ice becomes dangerous. In fact, it had already been moved 23 km inland during last Antarctica's summer months because another ice chasm had begun to show signs of growth. 108)

- The station sits on Antarctica's 150 m thick Brunt Ice Shelf. This floating ice shelf flows at a rate of 0.4 km per year west towards the sea where, at irregular intervals, it calves off as icebergs. Halley is crucial to studies into globally important issues such as the impact of an extreme space weather event, climate change, and atmospheric phenomena. It was scientific investigations from this location that led to the discovery of the Antarctic Ozone Hole in 1985.

- Normally, around 70 people live and work at the base during the summer and fewer than 20 during the winter. However, this is the first winter that the base has been completely closed.

- Thomas Nagler, ENVEO CEO, said, "We get Sentinel-1 and Sentinel-2 data shortly after acquisition so we are able extract information on the crack's progression and deliver this information to our Survey colleagues very quickly." Hilmar Gudmundsson, Survey lead scientist, added, "The frequency of Sentinel-2 images and Sentinel-1 radar products allows us to follow in detail and almost in real time the development of the crack as it grows week by week. This also provides us with essential information for ice-deformation models, leading to a deeper understanding of such events."

- Mark Drinkwater, head of ESA's Earth observation mission, added "Routine Antarctic summer observations by the combination of Copernicus Sentinel-2A and Sentinel-1A and -1B are now demonstrating their value for monitoring rapid environmental change and providing information crucial to informed decisions on matters of safety and security in Antarctica.

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Figure 62: The Sentinel-1A and Sentinel-1B interferogram uses images from 14 and 20 January 2017. It shows a discontinuity all along the Halloween crack and a distinct deformation pattern at its tip. The interferogram is laid on a Sentinel-2 optical image from 5 February 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016–17), processed by ENVEO)

• February 3, 2017: Climate change-driven glacial melt is causing landslides in alpine regions. Data from the Sentinel-1 satellite mission are being inserted into a new cloud computing system to monitor such hazards globally. 109)

- The Aletsch Glacier, the largest in the Alps, is experiencing an average retreat of about 50 m a year. The adjacent rocks that were previously constrained by the ice mass are progressively being released, generating slope instabilities. For this reason, the Aletsch region is a unique place where scientists can investigate how changes in glaciers affect the long- and short-term evolution of rock slope stability.

- To monitor the progressive changes occurring throughout a 2 km2 area southeast of the glacier – called the Moosfluh slope – the Chair of Engineering Geology at the Swiss Federal Institute of Technology in Zurich (ETHZ) installed ground-based instruments in 2013.

- Between September and October 2016, Moosfluh experienced an abnormal acceleration. The deformation generated several deep cracks and rock failures, hindering access to hiking paths visited by tourists, and affecting a cable car station located near the crest of the slope.

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Figure 63: Moosfluh slope instability of the Aletsch Glacier (image credit: Geohazards-TEP, the image contains modified Copernicus Sentinel-1 data (2016), processed by Geohazards-TEP)

Legend to Figure 63: Land deformation speed of the Moosfluh area observed by the Sentinel-1 satellite from August to November 2016. The monitoring system installed by the Chair of Engineering Geology at ETHZ includes two Robotized Total Stations (RTS1 and RTS2), which monitor the evolution of surface displacements at point targets located on the unstable area (white and red dots). The results obtained from satellite data helped scientists to define the extension of the most active area and identify locations to place additional monitoring targets (red dots),

• January 30, 2017: A crack in the Larsen-C ice shelf in on the Antarctic Peninsula first appeared several years ago, but recently it has been lengthening faster than before. Carrying radar that can ‘see' through the dark, the Copernicus Sentinel-1 satellites are monitoring the situation. The animation shows that the fissure has opened around 60 km since January last year. And, since the beginning of this January it has split a further 20 km so that the 350 m-thick shelf is held only by a thread. The crack now extends around 175 km. 110)

- When the ice shelf calves this iceberg it will be one of the largest ever recorded – but exactly how long this will take is difficult to predict. The neighboring Larsen-A and Larsen-B ice shelves suffered a similar fate with dramatic calving events in 1995 and 2002, respectively. —These ice shelves are important because they act as buttresses, holding back the ice that flows towards the sea.

Figure 64: Larsen Crack evolution in Antarctica: The Sentinel-1 two-satellite constellation is indispensable for discovering and monitoring events like these because it continues to deliver radar images when Antarctica is shrouded in darkness for several months of the year (image credit: ESA, the image contains modified Copernicus Sentinel data (2016–17), processed by ESA)

• November 25, 2016: The Sentinel-1 satellites have shown that the Millennium Tower skyscraper in the center of San Francisco is sinking by a few centimeters a year. Studying the city is helping scientists to improve the monitoring of urban ground movements, particularly for subsidence hotspots in Europe. 111)

- Completed in 2009, the 58-storey Millennium Tower has recently been showing signs of sinking and tilting. Although the cause has not been pinpointed, it is believed that the movements are connected to the supporting piles not firmly resting on bedrock. - To probe these subtle shifts, scientists combined multiple radar scans from the Copernicus Sentinel-1 twin satellites of the same area to detect subtle surface changes – down to millimeters. The technique works well with buildings because they better reflect the radar beam.

- It is also useful for pinpointing displacement hotspots over large areas, thanks to Sentinel-1's broad coverage and frequent visits. Working with ESA, the team from Norut, PPO.labs and Geological Survey of Norway have also mapped other areas in the wider San Francisco Bay Area that are moving. These include buildings along the earthquake-prone Hayward Fault, as well as subsidence of the newly reclaimed land in the San Rafael Bay.

- An uplift of the land was detected around the city of Pleasanton, possibly from the replenishment of groundwater following a four-year drought that ended in 2015.

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Figure 65: Data from the Sentinel-1 satellites acquired between 22 February 2015 and 20 September 2016 show that Millennium Tower in San Francisco is sinking by about 40 mm a year in the ‘line of sight' – the direction that the satellite is ‘looking' at the building. This translates into a vertical subsidence of almost 50 mm a year, assuming no tilting. The colored dots represent targets observed by the radar. The color scale ranges from 40 mm a year away from radar (red) to 40 mm a year towards radar (blue). Green represents stable targets (image credit: ESA, the image contains modified Copernicus Sentinel data (2015–16) / ESA SEOM INSARAP study / PPO.labs / Norut / NGU) 112)

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Figure 66: Sentinel-1 radar data show ground displacement of downtown San Francisco. While green indicates no detected movement, points in yellow, orange and red indicate where structures are subsiding, or sinking (image credit: ESA, the image contains modified Copernicus Sentinel data (2015–16) / ESA SEOM INSARAP study / PPO.labs / Norut / NGU) 113)

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Figure 67: Sentinel-1 radar data show ground displacement of the San Francisco Bay Area. Hot spots are clearly observed, including the Hayward fault running north–south of the central-right side of the image. Subsidence of the newly reclaimed land in the San Rafael Bay on the left is also visible, while an uplift of land is visible in the lower right, possibly a result of a recovering groundwater level after a four-year long drought that ended in autumn 2015 (image credit: ESA, the image contains modified Copernicus Sentinel data (2015–16) / ESA SEOM INSARAP study / PPO.labs / Norut / NGU) 114)

- European cities experience similar subsidence, and the San Francisco study is helping because it contains a multitude of features (Ref. 111).

- For example, the area around Oslo's train station in Norway is reclaimed land. Newer buildings, such as the nearby opera house, have proper foundation into bedrock, but the older parts of the station experience severe subsidence.

- "Experience and knowledge gained within the ESA's Scientific Exploitation of Operational Missions program give us strong confidence that Sentinel-1 will be a highly versatile and reliable platform for operational deformation monitoring in Norway, and worldwide," noted John Dehls from the Geological Survey of Norway.

- The studies of San Francisco and Oslo are paving the way for moving from targeted case studies to a nationwide or even continental-scale land deformation service.

- "The Copernicus Sentinel-1 mission is, for the first time, making it possible to launch operational national deformation mapping services," said Dag Anders Moldestad from the Norwegian Space Center. The open data policy and regular coverage plan of Copernicus promise cost-efficient and reliable services. "In Norway, we have already initiated a framework project to provide nationwide basic deformation products to the public, with a free and open data policy. Many other countries in Europe are also working towards setting up similar services," noted Dr. Moldestad.

- The Sentinel-1 twins provide ‘radar vision' for Europe's Copernicus environment monitoring program. In addition to watching land movements, they feed numerous other services for monitoring Arctic sea ice, routine sea-ice mapping, surveillance of the marine environment, mapping for forest, water and soil management, and mapping to support humanitarian aid and crisis situations.

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Figure 68: Data from the Sentinel-1 satellites acquired between 26 December 2014 and 28 October 2016 show that parts of the Oslo train station are sinking by 10–15 mm a year in the ‘line of sight' – the direction that the satellite is ‘looking' at the building. This translates into a vertical subsidence of 12–18 mm a year. It can also be observed that the new opera house – the white structure located by the fjord south of the subsiding area – has not moved (image credit: ESA, the image contains modified Copernicus Sentinel data (2015–16) / ESA SEOM INSARAP study / PPO.labs / Norut / NGU) 115)

• November 11, 2016. The Sentinel-1 image of Figure 69 shows the Virunga Mountains in East Africa and their volcanoes. While most are dormant, two of the eight volcanoes are active, with the most recent eruptions in 2006 and 2010. 116)

- The mountains are on the Albertine Rift, where the Somali Plate is splitting away from the rest of the African continent. The area is one of Africa's most biologically diverse regions, but high human population density, poverty and conflict pose a challenge to conservation. Across the mountain range, however, a series of national parks has been established to protect the fauna and flora.

- In this image, we can easily identify the delineation between the protected and non-protected lands – the green, orange and yellow dots indicate changes in the surface of non-protected lands between the radar scans that make up this composite image. These changes are primarily in vegetation as the land surrounding the mountains is blanketed with agricultural plots. In particular, we can see the grid-like pattern of agriculture is visible in the green and yellow square at the center of the image.

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Figure 69: This Sentinel-1 radar composite image features the Virunga Mountains in East Africa: a chain of volcanoes stretching across Rwanda's northern border with Uganda and east into the Democratic Republic of the Congo (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)

• November 3, 2016: In the early hours of 30 October 2016, a 6.5 magnitude earthquake struck central Italy. The team od scientists combined several pairs of Sentinel-1 radar images acquired between 25 October and 1 November 2016 to analyze the ground displacements caused by the quake. 117)

- New information on the effects of the 30 October earthquake that struck central Italy continues to emerge as scientists analyze radar scans from satellites. Using radar imagery from the Copernicus Sentinel-1 satellites, Italian experts have identified significant east–west displacements of the ground in the area struck by the earthquake. An eastwards shift of about 40 cm was mapped in the vicinity of Montegallo, while a westwards shift of about 30 cm is centered in the area of Norcia (Figure 70).

- The team of scientists from the Institute for Electromagnetic Sensing of the Environment of the National Research Council and the National Institute of Geophysics and Volcanology combined radar scans taken before and after the event to map centimeter-scale changes. Vertical displacement is also evident, with the ground sinking 60 cm around Castelluccio but rising by about 12 cm around Norcia (Figure 71).

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Figure 70: East-West displacements: The results of the analysis show an eastwards shift of about 40 cm in the vicinity of Montegallo, while a westwards shift of about 30 cm is centered in the area of Norcia (image credit: ESA, the image contains modified Copernicus Sentinel data (2016)/ESA/CNR-IREA)

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Figure 71: Vertical displacements: The results show ground subsiding or sinking down to 60 cm around Castelluccio. Around Norcia, there is an uplift of about 12 cm (image credit: ESA, the image contains modified Copernicus Sentinel data (2016)/ESA/CNR-IREA)

• October 28, 2016: The Geohazards Exploitation Platform gives users direct access to large Earth-observation datasets for areas at risk of geohazards such as earthquakes and volcanic activity. Radar ‘interferometry' involves taking successive radar images of the same location and combining them to produce rainbow-hued ‘interferograms'. Like playing spot the difference, the slightest shift between images gives rise to distinct interference fringes, resembling contour lines on a map. 118)

- Pairs of Sentinel-1A radar images from consecutive passes over the same spot on Earth's service are processed continuously and automatically to provide medium-resolution (200 m) images. This, and related interferograms, allows users to identify ground movement and other changes that may have occurred between satellite acquisitions. The service currently covers tectonic areas in Europe. Covering three million km2, this represents 360 interferometric pairs every 12 days.

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Figure 72: An overview of seismic zones in Europe provided by the Sentinel-1 twin radar satellites (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by DLR/ESA/Terradue)

- The image of Figure 73 was generated automatically on the Geohazards Exploitation Platform and combines images captured by Sentinel-1A before and after the quakes. The Geohazards Exploitation Platform gives users direct access to large Earth-observation datasets for areas at risk of earthquakes or volcanic activity, for example. 119)

Pairs of Sentinel-1A radar images from consecutive passes over the same spot on Earth's service are processed continuously and automatically to provide medium-resolution (200 m) images. These interferograms allow users to identify ground movement and other changes that may have occurred between satellite acquisitions. Although the service only covers Europe, this illustrates how information on major events can be made available to users. Over the next months, the browse service will be ramped up gradually to cover the global tectonic ‘mask'. This mask corresponds to regions where the shape of the ground is deforming because of tectonic activity and prioritised by the geohazards user community.

"The quick-browse service has been under way across European tectonic regions since January, harnessing automated processing developed by the DLR German Aerospace Center," explains Fabrizio Pacini of Terradue, overseeing the Platform. "Our plan next year is to gradually scale up to cover the entire world's tectonic regions, which adds up to a quarter of Earth's land surface. Such wide-area coverage is really unprecedented. It is a crucial step towards empowering society at large to reduce the risk from earthquakes and volcanoes."

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Figure 73: This interferogram of Sentinel-1 data shows how the ground moved as a result of the earthquakes that struck Amatrice in Italy on 24 August 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by DLR/ESA/Terradue)

- Today, it is a well-established technique used to give authoritative snapshots of ground movements following events such as the recent earthquakes in central Italy. — Earth scientists were surprised in the 1980s when centimeter-accuracy GPS networks revealed previously unsuspected motion along tectonic plates, occurring between larger-scale seismic events. 120)

Combined radar scans are sensitive down to a level of millimeters and over wide areas, compared to point-by-point GPS measurements, but the process demands heavy computing power. "The real step change here is that they are being produced across extended areas on an entirely automated basis," adds Fabrizio.

- The service is processing an average 50 image pairs per day across Europe from the Sentinel-1A and Sentinel-1B satellites, with six days between coverage.

- Next year, this will increase to 130 pairs per day, with a maximum of 24 days and potentially 12 days between acquisitions outside Europe, involving the daily processing of 1 terabyte of data, with additional higher resolution produced on request.

Processing on such a grand scale is enabled by the online, cloud-based Geohazards Exploitation Platform, specifically tailored for working with vast amounts of satellite data.

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Figure 74: Scientists from Italy's Institute for Electromagnetic Sensing of the Environment combined Sentinel-1 radar acquisitions over central Italy from before and after the 24 August 2016 earthquake: 15 August, 21 August and 27 August 2016. The result shows vertical ground subsidence, reaching about 20 cm in correspondence to the Accumoli area, and lateral movement of up to 16 cm. The blue line indicates the location of the fault trace (image credit: ESA, the image contains modified Copernicus Sentinel data (2016)/ESA/CNR-IREA)

• Sept. 16, 2016: Sentinel-1B was declared operational. On 14 September, project manager Ramón Torres who led the development team, handed over the satellite to the mission manager, Pierre Potin in the presence of Volker Liebig, Senior Advisor to ESA's Director General. — Following liftoff on 25 April 2016, the Copernicus Sentinel-1B satellite has been commissioned and handed over for mission operations. It joins its identical twin, Sentinel-1A, which has been systematically scanning Earth with its radar since October 2014. Orbiting 180° apart, the two satellites optimize coverage and data delivery for the Copernicus services that are making a step change in the way our environment is managed. More than 45,000 users have registered to access Sentinel data, under the free and open data policy data framework of Europe's Copernicus environmental monitoring program. 121)

- Both satellites carry a radar that images Earth's surface through cloud and rain and regardless of whether it is day or night. These images are used for many applications, such as monitoring ice in the polar seas, tracking land subsidence, and for responding to disasters such as floods.

• Sept. 16, 2016: Southern China's Poyang Lake is the largest freshwater lake in the country. Located in Jiangxi province, this lake is an important habitat for migrating Siberian cranes, many of which spend the winter there. The lake is also home to the endangered finless porpoise, a freshwater mammal known for its high level of intelligence. Amid fears that it would soon become extinct, the porpoise made headlines last year when the Chinese government moved eight of them from Poyang Lake to two secure habitats in an effort to increase the population over the coming years. 122)

- One study found that, without action, the current rate of population decrease would likely mean extinction by 2025.

- For the human population, Poyang is one of China's most important rice-producing regions, although local inhabitants must contend with massive seasonal changes in water level.

- Local scientists collaborating with ESA through the Dragon program have identified an overall drop in water level in the lake over the last decade, but the El Niño weather phenomenon earlier this year caused precipitation levels to increase and water levels of the lake to rise.

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Figure 75: Radar images from the Copernicus Sentinel-1 mission have been used to monitor the evolution of the lake, including this image which combines two radar scans from 7 and 19 March, 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)

• August 31, 2016: ESA engineers have discovered that a solar panel on the Copernicus Sentinel-1A satellite was hit by a millimeter-size particle in orbit on 23 August. Thanks to onboard cameras, ground controllers were able to identify the affected area. So far, there has been no effect on the satellite's routine operations. 123)

- A sudden small power reduction was observed in a solar array of Sentinel-1A, orbiting at 700 km altitude, at 17:07 GMT on 23 August. Slight changes in the orientation and the orbit of the satellite were also measured at the same time. Following a preliminary investigation, the operations team at ESA's control center in Darmstadt, Germany suspected a possible impact by space debris or micrometeoroid on the solar wing.

- Detailed analyses of the satellite's status were performed to understand the cause of this power loss. In addition, the engineers decided to activate the board cameras to acquire pictures of the array. These cameras were originally carried to monitor the deployment of the solar wings, which occurred just a few hours after launch in April 2014, and were not intended to be used afterwards.

- Following their switch-on, one camera provided a picture that clearly shows the strike on the solar panel. The power reduction is relatively small compared to the overall power generated by the solar wing, which remains much higher than what the satellite requires for routine operations.

- "Such hits, caused by particles of millimeter size, are not unexpected," notes Holger Krag, Head of the Space Debris Office at ESA's establishment in Darmstadt, Germany. "These very small objects are not trackable from the ground, because only objects greater than about 5 cm can usually be tracked and, thus, avoided by maneuvering the satellites. In this case, assuming the change in attitude and the orbit of the satellite at impact, the typical speed of such a fragment, plus additional parameters, our first estimates indicate that the size of the particle was of a few millimeters.

- "Analysis continues to obtain indications on whether the origin of the object was natural or man-made. The pictures of the affected area show a diameter of roughly 40 cm created on the solar array structure, confirming an impact from the back side, as suggested by the satellite's attitude rate readings." This event has no effect on the satellite's routine operations, which continue normally.

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Figure 76: Solar panel image of the Sentinel-1A spacecraft hit by a space particle (image credit: ESA)

• June 22, 2016: The twin Sentinel-1 satellites have – for the first time – combined to show their capability for revealing even small deformations in Earth's surface. Following its orbital maneuvers, the recently launched Sentinel-1B satellite reached its designated orbit position on 15 June. The satellite is now orbiting Earth 180° apart from its twin, Sentinel-1A, at an altitude of almost 700 km. With both satellites finally in the same orbit, together they can cover the whole globe every six days. — It has now been demonstrated that future images acquired by the pair can be merged to detect slight changes occurring between scans. 124)

- The rainbow-colored patterns (Figure 77) are related to topography, and they demonstrate that the two satellites' identical radars are accurately synchronized, pointing in the same direction and that the satellites are in their correct orbits.

- Once commissioning is completed in mid-September, the pair will be ready to deliver data for the systematic and routine monitoring of Earth surface deformation and ice dynamics.

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Figure 77: This ‘interferogram' combines a Sentinel-1A radar scan from 10 June 2016 over northwestern Romania with a Sentinel-1B acquisition from 16 June over the same area – shortly before Sentinel-1B reached its designated orbit. The city of Cluj-Napoca is at the center of the image. The color pattern is related to local terrain topography (image credit: the image contains modified Copernicus Sentinel data (2016)/ESA/DLR)

Sentinel-1 is based on a constellation of two SAR satellites that ensures continuity of C-band SAR observations. Sentinel-1A was launched on 3 April 2014, the second Sentinel-1 satellite, Sentinel-1B, was launched on 25th April 2016.

The operational nature of the Sentinel-1 mission represents a game changer in a number of application domains, thanks to the large-scale mapping capability and revisiting frequency of the two identical satellites, together with a high capacity ground segment that systematically processes, archives and makes available all the generated data products to users online, in a routine operational way.

Sentinel-1 Operations Strategy: The main objective of the Sentinel operations strategy is to ensure a reliable provision of data to Copernicus users, with systematic and routine operational activities. The Sentinels are operated via a pre-defined observation plan. All Sentinels acquired data are systematically downlinked and processed to generate a predefined list of core products within specific timeliness. For Sentinel-1, the goal is to minimize the number of potential conflicts during operations, therefore solve anticipated conflicts a priori, in particular in the elaboration of optimized mission observation scenarios. This concept allows on the service and user side to guarantee the observations required for stable and sustained value-added activities.

Organization of Operations Activities: The Sentinel-1 operations are based on a range of activities tightly coordinated, involving the satellite and the ground segment. The satellite is routinely monitored and controlled by the FOS (Flight Operations Segment) managed by ESA/ESOC. The FOS ensures overall satellite safety, routine tasks include the execution of all platform activities and the commanding of the payload schedules. The mission operations, flight dynamic operations and collision avoidance monitoring operations are performed routinely, involving the various facilities and teams of the FOCC (Flight Operations Control Centre) at ESOC, including: Mission Control, Mission Scheduling, the use of the specific Sentinel-1 Spacecraft Operational Simulator, Flight Dynamics operations and the activities of the SDO (Space Debris Office).

The so-called PLS (Post-Launch Support) activities, managed by ESA/ESTEC, are related to the satellite and started at the end of the satellite commissioning phase, with the support of expertise from the satellite industrial team gained during the development and integration phase of the satellite. The main activities include satellite preventive maintenance, support to satellite operations, anomaly investigations & analysis, on-board software maintenance, and maintenance of relevant test facilities.

As part of the PDGS (Payload Data Ground Segment) managed by ESA/ESRIN, satellite tasking and downlink activities are daily defined at the Payload Data Management Center in ESRIN and provided to the FOS for satellite uplink. X-band data acquisitions are routinely performed over Matera, Svalbard and Maspalomas X-band core stations. The acquired data are circulated within the PDGS, systematically processed to the various products levels, archived and disseminated. Operations are regularly performed at the PACs (Processing and Archiving Centers), DLR-PAC and UK-PAC. The other PDGS operational services include the Mission Performance monitoring, the Precise Orbit Determination and the Wide Area Network operations. Through its high performance network configuration, the Sentinel-1 PDGS is a unique virtual center interfacing a cluster of physically separated sites and providing an overall operations performance, centrally monitored.

Sentinel-1 Observation Scenario: The Sentinel-1 observation plans are defined based on a process that includes the collection of observation requirements from the various user groups (Copernicus and National services from ESA and EU Member States, scientific communities, international partners or initiatives, etc.). Extensive simulations are then performed to elaborate and optimize the Sentinel-1 observation scenarios, from which the detailed instrument planning and data downlink plans are derived. Regular revisions and adaptations of the observation scenario are necessary during operations and will continue for the full operations phase, based on the evolution of the requirements, the system capacity increase, in particular with the second satellite and the use of the EDRS (European Data Relay System).

The implementation of the ramp-up observation scenario included among others the coverage of a first set of Copernicus Services areas of interest, of European land and coastal waters, of a large set of global tectonic/volcanic areas, as well as of other specific targets worldwide for various applications. During ramp-up these observations were gradually complemented with observations outside the above areas to achieve a full mapping of all land areas worldwide at the time of the ramp-up phase completion. Observations were then further increased during the routine operations. Today, beyond the global areas very frequently observed, global landmasses has been mapped several times. Specific observation campaigns have been performed for the Greenland and Antarctica icesheets.

The resources allocated to the CMENS Copernicus Marine Environment Monitoring Service) for sea-ice and iceberg monitoring are quite substantial, this service having a high priority for accessing Sentinel-1 resources. Many applications have been developed in Europe based on the available time series, considering that a full mapping of EEA-38 (European Environment Agency) countries is performed systematically every repeat cycle of 12 days, in both ascending and descending passes, dual-polarization VV+VH. The coverage will be increased by a factor 2 once Sentinel-1B will enter in operations.

Processing & Dissemination Concept: The processing scenario is based on the systematic generation, archiving and dissemination of Level-0, Level-1 and Level-2 products, in NRT (Near Real Time) or within 24h from sensing, with no user ordering required. The set of products to be systematically generated responds to the requirements of the Copernicus services and allows generating several products with different characteristics for the same data take.

The scenario foresees the systematic availability of Level-0 products and Level-1 GRD (Ground Range Detected) products for all data acquired in SM, IW and EW instrument modes within 24h from sensing and within NRT 3h from sensing for a subset of data acquired over specific regional areas.

It also foresees the systematic availability of Level-2 OCN (Ocean) products for all data acquired in WV mode, as well as from data acquired in IW and EW modes over regional ocean areas.

Although the original Sentinel-1 operations concept foresaw the generation of SLC (Single Look Complex) over a limited set of areas over land, since 21 July 2015, 100% of the IW and SM data acquired over land are systematically produced to level 1 SLC, to support interferometric applications.

This has represented a major evolution of the initial processing and dissemination concept, with a huge increase in the overall ground segment operations load and user data access volumes. This global SLC production scenario enables to foster the exploitation of Sentinel-1 data for an increasing number of InSAR based applications worldwide.

Operational performance: The overall operations capacity has been regularly increasing since October 2014 in line with the increase of the observation scenario and the increase of the systematic SLC production over land masses.

Figure 78 shows the evolution of the volume of Sentinel-1 products generated on a daily basis since the end of the satellite commissioning phase in September 2014. To date more than 3.5 TB of Sentinel-1 products are daily generated and available for user download.

Operational User Products qualification: Sentinel-1 operational user products have been progressively qualified since the Sentinel-1A launch. By the end of the satellite commissioning phase, the Level-0 operational qualification and the Level-1 preliminary qualification were completed as planned, enabling the start of the Level-0 and Level-1 products dissemination to users.

Level-1 product quality has been continuously improved since October 2014 and available products are operationally qualified since end 2015, achieving the target geometric and radiometric quality.

Level-2 OCN products preliminary qualification was completed in July 2015, enabling the operational user data access to Sentinel-1 Level-2 products. Level-2 OCN products are currently operationally qualified except for the radial velocity component

Precise Orbit performance: The Sentinel-1 precise orbit determination operations provide restituted orbit information within 3 hours from sensing which is nominally used for the systematic processing of Fast24 products. The quality of the restituted orbits has proven to be in 95% of the cases twice better than expected, resulting in the very good absolute geolocation accuracy of Sentinel-1 products. The precise orbit information is available 21 days after sensing and used operationally only in case of data reprocessing.

Data Access: Under the free and open Sentinel data policy framework of the Copernicus program, the opening of the Sentinel-1A data flow to all users took place on 3rd October 2014 on the so-called scientific data hub: https://scihub.copernicus.eu/

Other data hubs have been set up to allow customized access by specific user categories and include: Copernicus Services data hub, Collaborative data hub (for collaborative ground segment partners having signed an agreement with ESA), International data hub (for International partners having signed an agreement with ESA).

All Sentinel-1 core products (Level-0, Level-1 and Level 2) are routinely made available for download upon simple self-registration. By end April 2016, more than 32,000 users have self-registered, and since the opening of the regular data flow on 3 October 2014, more than 4 million product download have been made by users (see Figure 79), representing about 5 PB (Petabyte) of data. More than 500,000 products are today available online for download (see Figure80). The scientific data access service relies on a high capacity dissemination network of 10 Gbit/s. The user download activity is closely monitored and the highest observed peak download by users has never reached the maximum available capacity, meaning that it is currently not a limiting factor to the user data access. The user download capacity may be however constrained by the user available Internet capacity.

Examples of mission results: During its first 2 years in orbit, Sentinel-1A has contributed to a number of Copernicus services, to the support of emergency management of natural disasters, as well as to a number of scientific results. Only very few of them are presented below. The great potential of the mission for various operational and scientific applications domains has been demonstrated by many concrete results.

The operational use of Sentinel-1 data by CMEMS (Copernicus Marine Environment Monitoring Service) for sea-ice and iceberg monitoring started on 30 September 2014, with the provision of data in near-real time for an agreed set of priority areas. Sentinel-1 provides unprecedented radar coverage of the polar regions (an example is in Figure 81) and constitutes a major source of data for the CMEMS operational monitoring activities.

Sentinel-1A responded to 17 activations from CEMS (Copernicus Emergency Management Service) and to 16 calls from the International Charter on Space and Major Disasters. These activations were mainly related to large floods and major earthquakes. In some cases no dedicated satellite tasking was necessary, thanks to the pre-defined observation plan that ensures large scale systematic mapping (e.g. Europe and global tectonic areas), with the 250 km swath of the Interferometric Wide swath mode.

Perspectives: With Sentinel-1A in orbit since 2 years, the huge demand of Sentinel-1 data demonstrates the success of the mission, characterized by a large-scale regular mapping and a very high and systematic throughput in terms of product generation and delivery. Today Sentinel-1A operations generate about 3.5 TB of data per day. With the inclusion of Sentinel-1B, and in particular the use of the EDRS (European Data Relay System), it is expected, once the Full Operations Capacity will be reached, that more than 10 TB of data will be available daily. The Sentinel-1 mission is seen as a game changer in operational SAR missions for the decades to come.

Table 10: Overview of the overall Sentinel-1 mission status in June 2016 with focus on the Sentinel-1A routine operations activities that started in June 2015 following the operational qualification phase, in terms of mission achievements, mission observation scenario, ground segment operations, throughput and data access. 125)

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Figure 78: Sentinel-1A production volume evolution (image credit: ESA)

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Figure 79: Evolution of number of Sentinel-1A products downloaded by users since opening in Oct 2014 (image credit: ESA)

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Figure 80: Evolution of number of Sentinel-1A products available for download since opening in Oct 2014 (image credit: ESA)

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Figure 81: Mosaic of Sentinel-1A data acquired on October 27-29, 2015. Daily ice drift is derived from consecutive overlapping scenes (image credit: ESA, the image contains modified Copernicus Sentinel data (2015)/ ESA/DTU/CMEMS)

• June 2016: The Sentinel-1B spacecraft has been launched on 25 April 2016, two years after Sentinel-1A to complete the Copernicus Sentinel-1 constellation. After its launch, the LEOP Phase was successfully completed in less than three days when all subsystems were checked. The SAR instrument was switched on, checked up and acquired the first images that were downloaded and processed by the operational Ground Segment. At present, the four-month Commissioning Phase is on-going; it includes the in-orbit Calibration and Characterization and the verification of the satellite, in order to deliver a full functional and well performing satellite to the mission operations mid September 2016. 126)

- The on-going IOCP (In-Orbit Commissioning Phase) comprises the commissioning of all spacecraft (i.e. platform subsystems, SAR payload, and the Optical Communication Payload interface) and Ground Segment components. It will conclude with the IOCR (In-Orbit Commissioning Review) in September.

- For the SAR instrument switch-on and check-out, some SAR acquisitions in IW (Interferometric Wideswath) mode were performed. These first images were taken just 56 hours after lift-off, two hours after SAR instrument switch-on (see Figure 85) and revealed already an excellent instrument performance. They were processed by the Sentinel-1 operational processor and adjusted to the non-nominal orbital parameters by the Ground Segment Team.

- Commissioning phase: Being the Ground System already commissioned during the Sentinel-1A commissioning phase and subsequent ground segment rump-up phase, the Sentinel-1B System Commissioning comprises only the commissioning of all Spacecraft components. This includes the following activities:

a) Spacecraft in-orbit verification (i.e. platform and payload)

b) SAR calibration and system performance verification

c) SAR cross-calibration with Sentinel-1A

d) Functional verification of the Sentinel-1B basic SAR products (i.e. L0 and L1b products w.r.t. SAR instrument performance and parameter settings

e) Functional verification of the OCP (Optical Communication Payload) interface. OCP is a laser communication terminal that is designed to send and receive data from a similar terminal located on another satellite, such as the geostationary EDRS.

- IOC main activities: The Sentinel-1B commissioning is planned for a period of 6 repeat orbit cycles (12 days each) once the reference orbit is reached. The commissioning phase will, therefore, have two sub-phases corresponding to the period determined to acquire such final reference orbit (Orbit Acquisition Phase) and once the reference orbit is acquired (Reference Orbit Phase).

• June 2016: Performance results of Sentinel-1A & Sentinel-1B repeat-pass SAR interferometry (InSAR) verification, using data acquired with the novel IW (Interferometric Wide-swath) mode. The IW mode, operational for the first time, utilizes ScanSAR-type burst imaging with an additional antenna beam steering in azimuth referred to as TOPS (Terrain Observation with Progressive Scans). 127)

- The Sentinel-1 SAR instrument with its active phased array antenna supports four exclusive imaging modes providing different resolution and coverage: Interferometric Wide Swath (IW), Extra Wide Swath (EW), Stripmap (SM), and Wave (WV). All modes, except the WV mode can be operated in dual polarization.

- Both the IW and EW mode use the TOPS technique to provide large swath width of 250 km at ground resolution of 5 m x 20 m and 400 km at ground resolution of 20 m x 40, respectively with enhanced image performance as compared to the conventional ScanSAR mode.

- The characteristic of the TOPS SAR imaging mode is that, besides the scanning in elevation, the antenna azimuth beam is steered from aft to the fore at a constant rate. As a result and in contrary to ScanSAR, all targets on ground are observed by the entire azimuth antenna pattern. This eliminates almost entirely the scalloping effect and also leads to constant azimuth ambiguities and SNR (Signal-to-Noise Ratio) along azimuth. - However, the fast azimuth beam steering reduces the target dwell time causing a lower spatial azimuth resolution than is achievable in Stripmap mode.

- The Sentinel-1 A& Sentinel-1B SAR constellation mission enables the build-up of long and equidistant InSAR IW mode data time series with a 6-day repeat-pass interval for geophysical applications, such as surface change detection monitoring.

• May 26, 2016: Cyclone Roanu has claimed over 100 lives in Sri Lanka and Bangladesh, and has left tens of thousands in need of aid. Officials are looking to the sky for information on flooded areas to analyze the cyclone's aftermath and support emergency response activities. On May 23, the Sentinel-1A satellite captured about 80% of the country of Bangladesh during a single pass. The images were quickly delivered to the Copernicus EMS (Emergency Management Service) to create flood maps, revealing over 170,000 hectares of land to be inundated. 128)

- The response to the request for data was quick, as was the generation of flood information by EMS: less than 30 hours from activation to the delivery of the first flood map. A ‘rush mode' to process and make Sentinel-1 data available for EMS has been set up in order to reduce the response time as much as possible.

- The Sentinel-1 mission for Europe's Copernicus program is revolutionizing the use of satellites in managing risk assessment and emergency response with the provision of large-scale radar data in a systematic fashion. Sentinel-1A can map a 250 km-wide strip while achieving a ground resolution of 20 m per pixel. The radar on Sentinel-1 is able to ‘see' through clouds, rain and in darkness, making it particularly useful for monitoring floods, usually connected to bad weather conditions. Images acquired before and after a flood offer immediate information on the extent of inundation and help to assess property and environmental damage.

- The International Charter for Space and Major Disasters also requested data for flood maps in western Sri Lanka – hit by the precursor of the cyclone on 16 May. The Charter was triggered by the Disaster Management Center of Sri Lanka on 17 May, channelled through the Asian Disaster Reduction Center.

- In response to Cyclone Roanu, additional Sentinel-1A radar scans are planned for the coming days to help the relief activities further. Once the twin satellite – Sentinel-1B – is operational, the mission's potential revisit time will be cut in half, further improving the response time to disasters.

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Figure 82: Sentinel-1A flood map of Barguna, Bangladesh, acquired on May 23, 2016; showing over 85,000 hectares of flooded areas in light blue (image credit: Copernicus Service information (2016) / Copernicus EMS / e-GEOS)

• May 11, 2016: The Antarctic Peninsula is a narrow mountainous finger or spine of land extending northwards away from the Central Antarctic ice sheet and comprises the northernmost arm of the Antarctic ice sheet (Figure 83). 129)

- The color scale indicates the speed of ice movement in meters per day, ranging from 1 cm/day or less in dark blue to up to 1 m/day in red. The vivid colors trace a complex network of channels along which streams of ice flow from the high mountains down towards the coast where the ice flow speeds up and spreads out into floating ice shelves. The white area on the western flank of the peninsula is where snowfall is likely to have concealed features and so prevented tracking between the image pairs.

- As one of the most dynamic glacial environments on Earth, this region has been experiencing rapid climate warming over recent decades. Since 1991, satellites such as ESA's ERS and Envisat have observed the disintegration of various ice shelves, including the northern portion of the Larsen ice shelf and the Wilkins ice shelf.

- This example shows the spectacular potential of the Sentinel-1 mission for routine mapping and monitoring the surface velocity of glaciers and ice sheets. The combination of Sentinel-1A and -1B will support comprehensive and long-term monitoring of changes in ice sheet velocity and how they respond to climate change.

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Figure 83: Successive radar images captured by the Copernicus Sentinel-1A satellite during December 2014 – March 2016 were used to create this spectacular map showing how fast the ice flows on the Antarctic Peninsula. The map was constructed by tracking the movement of ice features in pairs of radar images taken 12 days apart (image credit: ESA, contains modified Copernicus Sentinel data (2015), processed by Enveo)

• May 6, 2016: Figure 84 of the Sentinel-1A SAR instrument shows the Zachariae glacier on the northeast cost of Greenland. The shades of grey on the left side of the image depict the static landmass, while the colors on the right show changes in sea-ice type and cover between the three radar scans. Near the center-left we can see the Zachariae Isstrom (Isstrφm is Danish for ice stream) glacier, which began its "accelerated retreat" in 2012 and is currently losing about five billion tons of ice a year to the ocean. 130)

- Zachariae's dynamics have been changing over the last few years, calving high volumes of icebergs, which will inevitably affect sea levels. It is estimated that the entire Zachariae Isstrom glacier in northeast Greenland holds enough water to raise global sea levels by more than 46 cm.

- Scientists have determined that the bottom of Zachariae Isstrom is being rapidly eroded by warmer ocean water mixed with growing amounts of meltwater from the ice sheet surface. 131)

- Zachariae and the nearby Nioghalvfjerdsfjorden to its north are two of six glaciers being monitored in near-real time by Sentinel-1 through a new web portal by the UK's CPOM (Center for Polar Observation and Modelling). The portal provides frequent maps of ice velocity of key glaciers in both Greenland and Antarctica.

- The polar regions are some of the first to experience and visibly demonstrate the effects of climate change, serving as barometers for change in the rest of the world. It is therefore critical that polar ice is monitored comprehensively and in a sustained manner.

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Figure 84: SAR image taken over part of northeast Greenland's coast combines three images from Sentinel-1A's radar observed on 15 February, 10 March and 3 April 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)

• April 28, 2016: Sentinel-1B has produced its first images only two hours after the radar was switched on – a record time for a space radar. The first observations were taken a little more than two days after launch, after Sentinel-1B had followed a complicated routine to deploy its 12 m-long radar and two 10-m long solar wings, as well as passing a series of initial checks. The first image (Figure 85), 250 km wide and 600 km long, captured Svalbard, the Norwegian archipelago in the Arctic Ocean, with the Austfonna glacier clearly visible. 132)

- At ESA's operations center in Darmstadt, Germany, mission controllers thoroughly checked the satellite's control, navigation and power systems, among others, during the intense first few orbits. The team also conducted the complex unfolding of the radar wings and solar arrays.

- When Sentinel-1B reaches its final orbit, on the other side of Earth from Sentinel-1A, the radar vision constellation will be complete, meeting the coverage and revisit needs of Copernicus. In the coming months, the satellite will be tested and calibrated before it is declared to be operational.

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Figure 85: Sentinel-1B's first data strip stretches 600 km from 80ºN through the Barents Sea. The image, which shows the Norwegian Svalbard archipelago on the left, was captured on 28 April 2016 at 05:37 GMT - just two hours after the satellite's radar was switched on (image credit: ESA, contains modified Copernicus Sentinel data [2016], processed by ESA)

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Figure 86: This full resolution subset of the first Sentinel-1B image shows Norway's Nordaustlandet island in the Svalbard archipelago, covered by the Austfonna ice cap ((image credit: ESA, contains modified Copernicus Sentinel data [2016], processed by ESA)

• April 27, 2016: Following liftoff on 25 April from Europe's Spaceport in French Guiana, Sentinel-1B has opened its large solar wings and radar antenna. 133)

- After its launch, Sentinel-1B has followed a carefully planned sequence over 10 hours to open its large radar antenna and solar wings. During ascent, the satellite's 12 m-long radar antenna and two 10 m-long solar wings were folded up to fit into the Soyuz rocket's protective fairing. They opened together in a specific sequence, which also allowed power from the solar panels to be available as soon as possible, so that the satellite no longer depends on batteries.

- ESA's Sentinel-1 project manager, Ramón Torres, said, "The launch last night meant that we were able to forget the disappointment of the delays of the last few days in the blink of an eye. "We had a long night, staying awake to make sure the radar and solar panels deployed properly after the satellite had separated from the rocket. All of this was commanded by the team at ESA 's mission control in Germany. "The deployment is particularly complicated because of the sizes involved but all went well and the teams and I are extremely happy that we now have two Sentinel-1 satellites safely in orbit."

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Figure 87: Artist's rendition of the Sentinel-1B satellite delivery into orbit (image credit: ESA)

• April 26, 2016: The launch of Sentinel-1B went according to plan; the spacecraft was placed into its orbit (altitude = 693 km) 23 minutes and 35 seconds after launch (launch mass of 2164 kg). Sentinel-1B is the fourth in a series of Sentinel satellites for the European Copernicus program, a joint project of the EC (European Commission) and ESA (European Space Agency).

Deployment sequence of the secondary payloads: 134) 135)

- The trio of "Fly Your Satellite!" student-built CubeSats were released into space at 23:50 GMT (2 hours 48 minutes after liftoff). Transmissions from the Fregat upper stage show that the door on the CubeSat deployer opened regularly, around 2 hours and 48 minutes after launch. Now the CubeSats are travelling in their final orbits, and their university teams are waiting for them to establish contact. - In the first hour of flight, the CubeSats will be working autonomously in order to stabilize their motion, perform an internal health check, and deploy their antennae. Then they will establish communication with Earth.

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Figure 88: Artist's rendition of the CubeSats orbiting Earth (image credit: ESA, Medialab)

- The CubeSats were deployed into an elliptical orbit of 665 km x 453 km. From this orbit they will re-enter Earth's atmosphere in approximately 8 years, preventing they become space junk after their missions are over.

- The MicroSCOPE minisatellite of CNES was the last deployment in the launch sequence at 01:02 GMT (4 hours into the flight) on April 26.

• April 22, 2016: The swirling landscape of Iran's salt desert, Dasht-e Kavir, is reminiscent of an abstract painting in this Sentinel-1 image (Figure 89). With temperatures reaching about 50ºC in the summer, this area sees little precipitation, but runoff from the surrounding mountains creates seasonal lakes and marshes. The high temperatures cause the water to evaporate, leaving behind clays and sand soils with a high concentration of minerals. The ‘brushstroke' patterns are geological layers eroded primarily by wind. 136)

- Iran is one of the world's most important mineral producers. Earth-observing satellites are useful for finding and monitoring natural resources like minerals.

- Along the left side of the image we can see part of an area known as the ‘devil's dunes' because it was believed to be haunted by evil spirits. This belief likely originated from its hostile conditions, and the early travellers who did attempt to cross it probably never returned due to starvation or dehydration.

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Figure 89: This image combines three scans from Sentinel-1A's radar, acquired on 21 January, 14 February and 9 March 2016. Changes between the acquisitions appear in vibrant bright colors – such as the blues, reds and greens we see primarily on the left half of the image. These areas are salt lakes and the colors show fluctuations in the amount of water present over time (image credit: ESA, contains modified Copernicus Sentinel data [2016], processed by ESA)

• April 21, 2016: Images from the Sentinel-1A satellite are being used to monitor aquaculture in the Mediterranean, in another example of the mission's contribution to food security, as fisheries become the main source of seafood. The satellite counted nearly 4500 fish cages over six months, mainly of mussel racks or finfish, along the western Mediterranean's coastline (Figures 90 and 91). The number of fish hatching cages in the Mediterranean was not known before this survey. Farming finfish, shellfish and aquatic plants is one of the world's fastest growing food sectors, which already provides the planet with about half of the fish we eat. 137)

- Aquaculture surpassed wild fisheries as the main source of seafood in 2014, according to the UN FAO (Food & Agriculture Organization). This reflects the earlier transformation of land from hunting to farming. The EU's aquaculture furnishes a fresh, local supply of healthy seafood, following strict rules that protect the consumer, the fish and the environment.

- ESA is promoting the innovative use of satellite data for aquaculture through its SMART (Sustainable Management of Aquaculture through Remote sensing Technology) project. Remote sensing of oceans is a window into the marine ecosystem, providing essential information for their governance. Satellites can cover site locations, map aquaculture facilities, monitor meteorological events, provide early flood warnings and track water pollution.

- Giuseppe Prioli, President of the European Mollusc Producers' Association, says: "The services being tested in SMART could be very useful for supporting shellfish industry in Italy. In particular, near-realtime data on water quality parameters at each farm, such as sea-surface temperature, chlorophyll content and turbidity, are important for farmers because they affect shellfish growth. "Short-term forecasting of shellfish biomass will also help in planning the harvest. The assessment of the potential biomass yield in a given area, based on Earth observation data, could also be useful for reallocating farms or starting the farming of new species, such as oysters, along the Emilia-Romagna coast."

- The mission benefits numerous services, which relate to the monitoring of Arctic sea-ice extent, routine sea-ice mapping and surveillance of the marine environment. This includes oil-spill monitoring and ship detection for maritime security, monitoring land-surface for motion risks, mapping for forest, water and soil management, and mapping to support humanitarian aid and crisis situations.

- Its twin Sentinel-1B will soon create a constellation of two satellites orbiting 180° apart. The mission will be able to revisit a point on Earth in less than six days, providing more frequent coverage for aquaculture.

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Figure 90: The ESA SMART (Sustainable Management of Aquaculture through Remote sensing Technology) poster features the nearly 4500 fish cages detected in the western Mediterranean Sea by Sentinel-1 and other satellites (image credit: ESA, contains modified Copernicus Sentinel data [2016] / ESA / ACRI / Bluefarm / Ifremer)

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Figure 91: Sentinel-1 detected fish cages in the Western Mediterranean Sea (image credit: ESA, contains modified Copernicus Sentinel data [2016] /ESA/ACRI) 138)

Minimize Mission Status continued

Sensor complement: (C-SAR)

C-SAR (C-band SAR instrument):

The C-SAR instrument is designed and developed by EADS Astrium GmbH of Germany. The instrument provides an all-weather, day and night imaging capability to capture measurement data at high and medium resolutions for land, coastal zones and ice observations.

The C-SAR instrument is an active phased array antenna providing fast scanning in elevation (to cover the large range of incidence angle and to support ScanSAR operation) and in azimuth (to allow use of TOPS technique to meet the required image performance). To meet the polarization requirements, it has dual channel transmit and receive modules and H/V-polarised pairs of slotted waveguides.

It has an internal calibration scheme, where transmit signals are routed into the receiver to allow monitoring of amplitude/phase to facilitate high radiometric stability.

Sentinel-1's metalized carbon-fiber-reinforced-plastic radiating waveguides ensure good radiometric stability even though these elements are not covered by the internal calibration scheme. The digital chirp generator and selectable receive filter bandwidths allow efficient use of on-board storage considering the ground range resolution dependence on incidence angle.

The goal of the all-weather imaging capability of the C-SAR instrument is to provide measurement data at high and medium resolutions for land, coastal zones and ice observations in cloudy regions and during night, coupled with radar interferometry capability for detection of small (mm or sub-mm level) ground movements, with the appropriate frequencies and operating modes required to support the Copernicus services. 207) 208) 209) 210) 211) 212) 213) 214) 215) 216) 217) 218) 219) 220)

The Sentinel-1 requirements call for the support of four observation/acquisition modes:

SM (Stripmap mode): 80 km swath with a spatial resolution of 5 m x 5 m

IW (Interferometric Wide swath) mode: 250 km swath, 5 m x 20 m spatial resolution and burst synchronization for interferometry. IW is considered to be the standard mode over land masses.

- satisfies most currently known service requirements

- avoids conflicts and preserves revisit performance

- provides robustness and reliability of service

- simplifies mission planning & decreases operational costs

- satisfies also tomorrow's requests by building up a consistent long-term archive.

The IW mode images three subswaths using TOPSAR (Terrain Observation with Progressive Scans SAR). With the TOPSAR technique, in addition to steering the beam in range as in ScanSAR, the beam is also electronically steered from backward to forward in the azimuth direction for each burst, avoiding scalloping and resulting in a higher quality image. Interferometry is ensured by sufficient overlap of the Doppler spectrum (in the azimuth domain) and the wave number spectrum (in the elevation domain). The TOPSAR technique ensures homogeneous image quality throughout the swath.

EW (Extra Wide Swath) mode: 400 km swath and 25 m x 100 m spatial resolution (3-looks). - Six overlapping swathes have to be foreseen to cover the required access range of 375 km.

WV (Wave mode): low data rate and 5 m x 20 m spatial resolution. Sampled images of 20 km x 20 km at 100 km intervals along the orbit. The Wave mode at VV polarization is the default mode for acquiring data over open ocean. WV mode is acquired at the same bit rate as SM however, due to the small vignettes, single polarization and sensing at 100 km intervals, the data volume is much lower. The table below shows the main characteristics of the Wave mode.

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Figure 147: Alternating WV mode acquisitions (image credit: ESA)

Except for the wave mode, which is a single polarization mode (HH or VV), the SAR instrument has to support operations in dual polarization (HH-HV, VV-VH), requiring the implementation of one transmit chain (switchable to H or V) and two parallel receive chains for H and V polarization. The specific needs of the four different measurement modes with respect to antenna agility require the implementation of an active phased array antenna. For each swath the antenna has to be configured to generate a beam with fixed azimuth and elevation pointing. Appropriate elevation beamforming has to be applied for range ambiguity suppression.

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Figure 148: Overview of the Sentinel-1 C-SAR instrument observation scheme and operational support modes (image credit: ESA)

Center frequency of C-band

5.405 GHz (corresponding to a wavelength of 5.55 cm)

Bandwidth

0-100 MHz (programmable)

Polarization

HH+HV, VV+VH, HH

Incidence angle range

20º-46º

Look direction

right

Antenna type

Slotted waveguide radiators

Antenna size

12.3 m x 0.821 m

Antenna mass

880 kg (representing 40% of the total launch mass)

Azimuth beam width

0.23º

Azimuth beam steering width

-0.9º to +0.9º

Elevation beam width

3.43º

Elevation beam steering range

-13.0º to +12.3º

RF Peak Power (sum of all TRM, at TRM o/p) DC power consumption

- 4.368 kW - 4.075 kW [IW (Interferometric Wide Swath Mode), two polarizations]

Pulse width

5-100 µs (programmable)

Transmit duty cycle

Max 12%, SM 8.5%, IW 9%, EW 5%, WV 0.8%

Receiver noise figure at module input

3 dB

Maximum range bandwidth

100 MHz

PRF (Pulse Repetition Frequency)

1000-3000 Hz (programmable)

Data compression (selectable)

FDBAQ (Flexible Dynamic Block Adaptive Quantization)

ADC sampling frequency

300 MHz (real sampling)

Data quantization

10 bit

Total instrument mass (including antenna)

945 kg

Attitude steering

Zero-Doppler steering and roll steering

Table 15: Key parameters of the C-SAR instrument

The Sentinel 1 mission operational concept foresees the following capabilities and/or services:

• A continuous and systematic acquisition of data to maximize mission return and system exploitation efficiency.

• A complete Earth coverage after each single orbit repeat cycle (175 orbits in 12 days). This dramatically improves the past and current EO systems' capabilities; the system supports up to 25 minutes per orbit for STRIPMAP/TOPSAR operations and up to 75 minutes for WAVE operations per orbit

• The minimum revisit time possible on few selected regions, mainly Maritime Transport over European and North Atlantic zones, European coastal zones. A constellation of two satellites, Sentinel-1A and Sentinel-1B, is deployed on the same orbit with a proper phasing.

• The minimum data/product latency after SAR acquisitions: requirements ask for an on-board data latency from a maximum of two orbits (about 3 hours) down to one orbit for the so-called near-real time data down to simultaneous SAR acquisition and data download to ground for real-time data. Basic products will be available, after data downlink, after a maximum of 24 hours for all data, down to 1 hour for near-real time data, down to 10 minutes for L0 products for real time data.

• The capability to include in the pre-defined mission timeline sporadic and asynchronous user orders submitted to the system following emergency occurrences.

• Repeat-pass TOPSAR interferometric capability: accurate burst synchronization and fine orbit control are specific drivers for this system feature.

Table 16: Overview of the Sentinel-1 operational concept (Ref. 15)

 

Introduction of a new SAR imaging mode (new observation technology):

The IW (Interferometric Wide swath) mode is being implemented with a new type of ScanSAR mode called TOPS (Terrain Observation with Progressive Scan) SAR operations support mode (note: the terms TOPS and SAR is simply contracted to TOPSAR). TOPSAR is an ESA-proposed acquisition mode (Francesco De Zan and Andrea Monti Guarnieri) for wide swath imaging which aims at reducing the drawbacks of the ScanSAR mode. The basic principle of TOPSAR is the shrinking of the azimuth antenna pattern (along-track direction) as seen by a spot target on ground. This is obtained by steering the antenna in the opposite direction as for Spotlight support. The TOPSAR signal includes particularities of both ScanSAR and Spotlights modes, but existing processing algorithms do not provide an efficient processing of TOPSAR data. - The EW (Extra Wide swath) mode is also implemented with the TOPS capability (Table 17).

The TOPSAR mode is intended to replace the conventional ScanSAR mode. The technique aims at achieving the same coverage and resolution as ScanSAR, but with a nearly uniform SNR (Signal-to-Noise Ratio) and DTAR (Distributed Target Ambiguity Ratio). 221) 222) 223)

The TOPSAR mode will be implemented on the Sentinel-1 mission due to the performance advantages compared to ScanSAR. The TOPSAR technique has already been demonstrated on the TerraSAR-X spacecraft during its commissioning phase (fall 2007) and showed very promising results. The measured values of the intensity variation of the analyzed images corresponded very well with the expected theoretical values. Scalloping in the TOPSAR image is 0.3 dB against 1.2 dB in the ScanSAR image. Additionally, fewer bursts are required in TOPSAR, which also positively affects the image quality. 224) 225) 226) 227) 228) 229)

TOPS is employing a rotation of the antenna in the azimuth direction as is shown in Figure 149. Like in ScanSAR, several subswaths are acquired quasi simultaneously by subswath switching from burst to burst. The increased swath coverage is as in ScanSAR achieved by a reduced azimuth resolution. However, in TOPS the resolution reduction is obtained by shrinking virtually the effective antenna footprint to an on-ground target, rather than slicing the antenna pattern, as it happens for ScanSAR. 230)

Concerning the implementation of TOPS InSAR, the Sentinel-1 C-SAR system is designed to enable TOPS burst synchronization of repeat-pass datatakes supporting the generation of TOPS interferograms and coherence maps. Specifically, for the IW and EW modes the TOPS burst duration is 0.82 s and 0.54 s (worst case), respectively, with a requirement for achieving a synchronization of less than 5 ms between corresponding bursts (Ref. 238).

Furthermore, a critical issue for TOPS InSAR performance is the accuracy that is required for TOPS image co-registration. A small co-registration error in azimuth can introduce an azimuth phase ramp due to the SAR antenna azimuth beam sweeping causing Doppler centroid frequency variations of 5.5 kHz.

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Figure 149: Sketch of the TOPSAR acquisition geometry. TB is the burst duration and ω r is the steering angle rate (image credit: DLR)

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Figure 150: Alternate view of the TOPSAR subswath acquisition (image credit: ESA)

The TOPS demonstration, conducted for ESA in 2007 with TerraSAR-X data, was conducted with the ETT (Experimental TerraSAR-X TOPS) processor; the test was based on sub-aperture processing, the Extended Chirp scaling algorithm and BAS (Baseband Azimuth Scaling). - The SPT (Sentinel-1 Prototype TOPS) processor is based on a pre-processing stage to unfold the azimuth spectrum, a standard ω-k focusing block and an azimuth one-dimensional ‘unfolding' processing block. It is an extension of the standard ω-k based ScanSAR processor developed for the Envisat ASAR instrument (Ref. 230).

Comparison of both processors: The comparison of the SPT (Sentinel-1 Prototype TOPS) processor with the ETT (Experimental TerraSAR-X TOPS) processor turned out to be a complex task. The results are confirming both processing approaches mutually.

 

TOPS implementation on RADARSAT-2: The objective of simulating Sentinel-1 TOPS mode image data products using RADARSAT-2 is to support the implementation of the TOPS mode, specifically the Interferometric Wide swath (IW) mode, on ESA's Sentinel-1 mission. The use of real C-band RADARSAT-2 TOPS image data enables the preparation for the Sentinel-1 exploitation phase (i.e. GMES Initial Operations (GIO)). In particular, the provision of Sentinel-1 like TOPS image products to operational Copernicus/GMES services and other users will help the user community to prepare and verify their SAR data post-processing chains including ingestion tools etc., prior to the launch of Sentinel-1A. 231) 232)

The Canadian RADARSAT-2 mission operates at the same C-band frequency (5.405 GHz) as the Sentinel-1 mission. The RADARSAT-2 SAR instrument with its phased array antenna has multiple SAR imaging modes, including ScanSAR modes, as well as it has quad-polarization and repeat-pass SAR Interferometry (InSAR) capabilities. The RADARSAT-2 mission has been implemented as a public-private partnership between the Government of Canada and MDA (MacDonald, Dettwiler and Associates Ltd.), whereby MDA has the commercial data rights.

The design and implementation of the experimental TOPS mode on RADARSAT-2 resembles as closely as possible the performance characteristics of the Sentinel-1 IW mode, within the constraints imposed by the design and implementation of RADARSAT-2. The RADARSAT-2 TOPS image data sets have been processed to Level 1 SLC (Single Look Complex) data with the Sentinel-1 Image Processing Facility (IPF) and are provided in the official Sentinel-1 Level (SLC) product format.

The experimental RADARSAT-2 TOPS mode is referred to as PSNB (Progressive ScanSAR Narrow B). It is based on the existing RADARSAT-2 SCNB (ScanSAR Narrow B) mode. This mode uses 3 sub-swaths, like the Sentinel-1 IW mode, and covers a comparable range of incidence angles.

 

Instrument description:

The Sentinel-1 satellites carry a single payload consisting of a C-band Synthetic Aperture Radar (SAR) instrument. The instrument is composed of two major subsystems:

SES (SAR Electronics Subsystem)

SAS (SAR Antenna Subsystem).

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Figure 151: The block diagram of C-SAR (image credit: EADS Astrium, ESA)

The radar signal is generated at baseband by the chirp generator and up-converted to C-band within the SES. This signal is distributed to the HPA (High Power Amplifiers) inside the EFE (Electronic Front End) Transmit/Receive Modules (TRMs) via the beam forming network of the SAS. Signal radiation and echo reception are performed with the same antenna using slotted waveguide radiators. When receiving, the echo signal is amplified by the low noise amplifiers inside the TRM and summed up using the same network as for transmit signal distribution. After filtering and down conversion to baseband inside the SES (SAR Electronics Subsystem), the echo signal is digitized and formatted for recording. 233) 234) 235)

The key design aspects of the C-SAR instrumentation can be summarized as follows:

• Active phased array antenna providing fast scanning in elevation (to cover the large range of incidence angle and to support ScanSAR operation) and in azimuth (to allow use of the TOPS technique to meet the required image performance)

• Dual channel TRM (Transmit & Receive Modules) and H/V-polarized pairs of slotted waveguides (to meet the polarization requirements)

• Internal Calibration scheme, where transmit signals are routed into the receiver to allow monitoring of amplitude/phase to facilitate high radiometric stability

• Metalized CFRP (Carbon Fiber Reinforced Plastic) radiating waveguides to ensure good radiometric stability even though these elements are not covered by the internal calibration scheme

• Digital chirp generator and selectable receive filter bandwidths to allow efficient use of on board storage considering the ground range resolution dependence on incidence angle

• FDBAQ (Flexible Dynamic Block Adaptive Quantization) to allow efficient use of on-board storage and minimize downlink times with negligible impact on image noise.

 

SES (SAR Electronics Subsystem)

The SES forms the core of the radar instrument connecting the SAS for transmission of Tx pulses and receiving of backscattered pulses from ground targets. The SES provides all radar control, IF/RF signal generation and receive data handling functions comprising: 236)

- radar command and control, timing control, and redundancy control

- transmit chirp generation, frequency generation, up-conversion/down-conversion, modulation/demodulation and filtering

- digitization, data compression and formatting.

A digital chirp generator and selectable receive filter bandwidths allow an efficient use of on board storage capacity considering the ground range resolution dependence on the incidence angle. The radar signal is generated at base band by the chirp generator and up-converted to C-band within the SES. This signal is distributed to the high-power amplifiers inside the EFE TRMs via the beam-forming network of the SAS. Signal radiation and echo reception are performed with the same antenna using slotted waveguide radiators. When receiving, the echo signal is amplified by the low noise amplifiers inside the EFE TRMs and summed up using the same network as for transmit signal distribution. After filtering and down-conversion to base band inside the SES, the echo signal is digitized and formatted for recording. Flexible dynamic block adaptive quantization allows the efficient use of on-board storage and to minimize downlink times with negligible impacts on image noise.

The SES hardware comprises the following units:

• ICE (Integrated Central Electronics) unit

• MDFE (Mission Dependent Filter Equipment)

• TGU (Transmit Gain Unit)

The ICE unit is the principal module of the SES providing the radar with its core functionality, control and monitoring. The subsystem uses a fully digital design approach for both the derivation of the C-band chirped radar signal and the digital receiver which samples the echo signal at an IF close to base band. The ICE maintains and manages a database of operational parameters such as transmit pulse and beam characteristics for each swath of each mode, and timing characteristics like pulse repetition frequencies and window timings. The MDFE is passive, providing a set of RF filters for the Tx path (to control out-of-band transmissions) and for the Rx path (to limit out-of-band interference). The TGU provides the final RF amplification of the Tx pulse signal before sending it to the SAS. The TGU receives its own dedicated primary power supply from the platform. Switching the TGU on and off is performed by the ICE.

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Figure 152: Photo of the SES device (image credit: EADS Astrium Ltd.)

To augment this design and provide mission variable compatibility, the SES also includes mission dependent units that comprise amplification and filtering to provide an ideal signal level and match to the antenna subsystem to be supported.

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Figure 153: SES context diagram (image credit: EADS Astrium Ltd)

The SES configuration is implemented as a fully cold redundant pair of chains. The TGU being common to both chains only in as much as the two amplifier chains are mounted in a single physical equipment unit before the paths do combine within a passive hybrid device which in turn permits dual outputs to the antenna supplying both fore and aft antenna segments.

The ICE (Integrated Central Electronics) unit is the principal module of SES consisting in turn of highly-integrated modules (Figure 155). ICE is being produced at Astrium UK (Portsmouth). This equipment provides the radar with its core functionality, control and monitoring. The subsystem uses a fully digital design approach for both the derivation of the (up to 100 MHz) C-band chirped radar signal and the digital receiver which samples the echo signal at an IF close to baseband. With single up-conversion and down-conversion stages and data processing using efficient digital filtering and data compression algorithms it is anticipated that this equipment will provide a highly stable core electronics base for this new exciting Copernicus utility. 237)

The Astrium UK ICE design is aimed at providing not only a solution for the Sentinel-1 system but also aims to provide a modern solution for the complex electronics at the heart of radars and particularly that of a SAR. The architecture is designed for adaptability using the inherent flexibility of the digital approach. It is therefore able to adapt easily to the needs of different missions.

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Figure 154: Configuration of SES (image credit: EADS Astrium Ltd.)

The ICE modular design makes use of the integrated RF and digital design technologies now commonly available. High speed ADC (Analog Digital Converter)) and DAC (Digital Analog Converter) components along with flexible design of digital processing through the use of large scale FPGAs and dedicated ASICs, as well as the use of MMIC (Modular Microwave Integrated Circuitry) has allowed the design to respond to the demands of the Sentinel-1 mission.

The design of ICE is comprised of the following elements:

• ICM (Instrument control Module): A Leon ll processor based module, developed by Syderal of Switzerland with:

- PROM for boot software and EEPROM for the application software and the radar characterization database

- Multiple interface formats allowing 1553B communication with the platform, SpaceWire for the internal modules (using the Atmel AT7910/SpW_10X SpaceWire Router ASIC) and CAN for external equipments TGU and SAS.

• Ty module: This RUAG designed and built module uses a direct digital synthesis chirp generation method at an IF of 150 MHz, with up-conversion in a single stage to the nominal 5.405 GHz center frequency to deliver the radars a fully programmable chirp transmission chain. This requires only a further amplification stage provided by the externally provided DAD designed TGU (Transmit Gain Unit) to drive the SAS (SAR Antenna Subsystem).

• Rx modules: The dual polarization approach required by the C-SAR instrument necessitates a pair of matched receive modules to be implemented within the ICE. The receive path is band filtered externally to the ICE by a MDFE (Mission Dependent Filter Equipment) provided by DAD of Finland prior to its input to the ICE Rx modules Here the signal is down-converted directly to an IF of 75 MHz before being digitized in the ADC which sample's at approx 300 Msamples. This in turn feeds the digital processing chain of a decimation filter followed by, compression and packetization stages before the output is piped to the on board mass memory via a Wizard link interface in a standard CCSDS format at 640 Mbit/s.

• TCM (Timing Control Module): TCM represents the timeline control element for the system. Implementing ECC program driven FPGA logic to provide the necessary timing waveforms required to define and control the within pulse precise timing relationships of all the required timing signals used by the instrument. These timing pulses and the PRI rate communication bus to the antenna are the means whereby the radar establishes the autonomous complex timeline of each mode acquisition with the absolute repeatability required to provide the synthetic aperture quality and the Interferometric property of the system data output.

• PCM (Power Control Modules): These modules are implemented so as to reduce the individual module voltage conversion effort and to reduce the power losses. These modules use modular common DC/DC converters designed by BLU Electronics to provide 3 voltage rails to all internal ICMs. However, It is to be noted that point of load regulation at module level is still expected for more user specific voltages.

• FDM (Frequency Distribution Module) and USO (Ultra Stable Clock): Using FOAMO (Foam Insulated Master Oscillator) of Astrium as the master clock, the FDM generates the timing reference frequencies used by all other signal modules in ICE. To maintain the highest level of phase stability, this unit also takes in the Tx LO (Local Oscillator) and creates from this the offset Rx down convertor LO for both Rx module channels.

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Figure 155: Block diagram of SES (only one of two redundancy chains is shown), image credit: EADS Astrium

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Figure 156: Illustration of the modular configuration of ICE (image credit: EADS Astrium Ltd.)

The ICE equipment has a mass of 20.6 kg. The modules have been selected to be integrated into an equipment enclosure with a backplane wiring loom rather than a fixed motherboard interface plate. This approach allows greater flexibility for test and diagnosis as well as a mechanical flexibility that offers a simpler solution to the thermal challenges of the mission.

The low internal interface count which also allows this open loom approach is in part due to the use of the SpaceWire interconnect for control which has been implemented on the front face of the unit. This being so implemented to facilitate an ESA objective for the ICM module development aimed at further mission systems (Ref. 237).

 

Roll steering mode (Ref: 212): The roll steering mode of the spacecraft provides a continuous roll maneuver around orbit (similar to yaw steering in azimuth) compensating for the altitude variation such that it allows usage of a continuous PRF (Pulse Repetition Frequency) and a minimal number of different sample window lengths (SWLs) around the orbit. In addition, the update rate of the sampling window position around orbit is minimized (< 1 /2.5 min), which simplifies instrument operations significantly. Since the instrument can work with a single fixed beam for each swath/sub-swath over the complete orbit, also the number of elevation beams is minimized. The roll steering rate has been fixed to 1.6º/27 km altitude variation. The roll applied to the sensor attitude depends linearly on altitude and varies within the interval -0.8º (minimum sensor altitude) to 0.8º (maximum sensor altitude).

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Figure 157: Variation of the roll angle along the orbit (image credit: ESA, TAS)

The attitude steering mode introduces an additional roll angle as a function of latitude to compensate changes in the satellite's altitude around the orbit, hence maintaining a specific, quasi "constant", slant range for each SAR imaging mode. This enables the use of a single PRF per swath or subswath around the orbit, except for SM-5 (i.e. different PRF for SM-5N and SM-5S), and a fixed set of constant elevation antenna beam patterns. 238) 239)

Figure 158 illustrates that for the minimum orbital height (693 km) the mechanical SAR antenna off-nadir angle is more shallow (30.25º) than it is for the maximum orbital height (726 km). In the latter case, the mechanical SAR antenna off-nadir angle is 28.65º.

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Figure 158: Schematic view of the Sentinel-1 roll-steering mode (image credit: ESA)

 

SAS (SAR Antenna Subsystem):

SAS represents the sensor part of the C-SAR instrument and is an active phased array system with Tx and Rx gain and phase control distributed over the antenna area. These functions are provided by so called Transmit Receive Modules (TRMs) as part of the EFE (Electronic Frontend End) assemblies. The SAS is capable of performing rapid electronic beam steering, beam shaping, and also polarization selection. The dual polarized antenna allows at one time either transmission in one single, but selectable polarization (H or V) or simultaneous reception of both H and V polarization. 240) 241)

The SAS consists of 14 identical tiles (12.3 m x 0.84 m) in 5 deployable panels as shown in Figure 159. The electrical functions of the SAS comprise:

- signal radiation and reception

- distributed transmit signal high power amplification

- distributed receive signal low noise amplification with LNA protection

- signal and power distribution (corporate feed, power converter)

- phase and amplitude control including temperature compensation

- internal calibration loop

- deployment mechanisms, including hold down and release

- antenna mechanical structure.

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Figure 159: C-SAR antenna in deployed and stowed configuration on the PRIMA bus (image credit: Astrium GmbH)

The instrument is based on a deployable planar phased array antenna carrying TRMs allowing for horizontal and vertical polarizations. The dual polarized antenna allows either transmission in one single but selectable polarization (H or V) or, simultaneous reception of both H and V polarization, at any time. The C-SAR antenna comprises two wings, stowed on the platform's lateral panels during launch, which are deployed once in orbit. Each antenna wing consists of two antenna panels. An antenna panel consists in principle, of a panel frame and a number of antenna tiles. The SAS central panel comprises two antenna tiles, whereas the wing panels comprise three antenna tiles each. The complete antenna is symmetrical around the middle of the central panel.

The active phased array antenna is capable of performing rapid electronic beam steering, beam shaping and polarization selection, providing fast scanning in elevation and azimuth to cover the large range of incidence angles and to meet the image quality requirements for the TOPSAR mode. TRMs are arranged across the antenna such that, by adjusting the gain and phase of individual modules, the transmit and receive beams may be steered and shaped.

The SAS consists of 14 tiles with 20 dual-polarized sub-arrays on each tile. Each subarray is a dual-polarized unit with two parallel slotted resonant waveguides. The vertical polarization is excited by offset longitudinal slots in a ridge waveguide, while the horizontal polarization is generated by transverse narrow wall slots excited by inserted tilted wires.

A SAS tile is composed of 10 'Waveguide 4' assemblies (two vertically and two horizontally polarized waveguides), which form the smallest building block in the tile manufacturing. Each 'Waveguide 4'-assembly is exposed to a kind of RF-incoming / diagnostic inspection consisting of a passive return loss measurement followed by a measurement of the far-field azimuth pattern in a special anechoic test environment at Astrium GmbH.

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Figure 160: Photo of the SAS tile (20 HP+20 VP subarrays), image credit: EADS Astrium GmbH

Legend to Figure 160: The instrument comprises three RF networks: Tx network, RxH (H polarization) network and RxV (V polarization) network. During radar operation the Tx network carries the transmit RF signal and the RxH/RxV networks carry the echo signals. The dual polarized antenna allows transmission in one single but selectable polarization (H or V) and simultaneous reception of both H and V polarization.

The tile (size: ~ 0.87 m x 0.84 m) forms the smallest functional entity of the SAS, encompassing all functions necessary to ensure beam shaping / beam steering of the active phased array antenna. The SAS Tile is composed of 10 'Waveguide 4' assemblies and the associated electronics, namely:

- The RF Distribution Network

- 40 Transmit/Receive Modules (20 TRMs for HP & 20 TRMs for VP / supplier: Thales Alenia Space, Italy)

- 2 Tile Controller Units (TCUs)

- 2 Tile Power Supply Units (TPSUs)

allowing signal radiation and reception, distributed transmit signal high power amplification, distributed receive signal low noise amplification with LNA protection, signal and power distribution, phase and amplitude control including temperature compensation and internal calibration.

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Figure 161: The SAS tile configuration scheme of the SAR antenna (image credit: EADS Astrium)

The CFRP (Carbon Fiber Reinforced Plastic) waveguide radiator is along with the cross stiffeners the major structural element of a tile. All electronic boxes are either placed onto the rear side of the radiators (e.g. the EFEs) or attached to the inner side of the cross stiffeners (e.g. TCU and TPSU). The low loss CFRP slotted waveguides radiators together with the high performance EFE TRMs ensure to meet the stringent sensitivity requirement of -22 dB. The optimized sizing of the overall SAR antenna and its waveguide radiators ensure further that also the ambitious 2D distributed target ambiguity requirement (DTAR) of -22 dB can be met.

EFE is the main transmitting/receiving section of the Sentinel-1 antenna while 195 EFE are necessary to assure the full functionality of the SAR instrument. Each EFE has been optimized for the best trade-off between integration level and RF performances and is composed of four main sections: Power Supply card, Digital card, RF distribution section and the TRM section.

The EFE is composed of four main sections: Digital card, Power Supply card, RF distribution and the TRM (T/R Module) section. A functional scheme of the EFE architecture is shown in Figures 162 and 163.

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Figure 162: Illustration of the EFE architecture (image credit: TAS-I)

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Figure 163: Illustration of the EFE prototype (image credit: TAS-I)

The RF networks provide the EFEs with the Tx pulses, and collect the H and the V polarized echoes. On the tile, these networks form the EPDN (Elevation Plane Distribution Network) which is placed on top of the EFEs (Figure 161). Each network (Tx, RxH, RxV) of the EPDN consists of a 1:10 divider to supply the 10 EFEs. Short cables connect the outputs of the 1:10 dividers to the EFEs.

Operational mode

Polarization

Swath width

Single Look Resolution (range x azimuth)

Access Angles

Stripmap (SM)

HH-HV or VV-VH

> 80 km

5 m x 5 m

20º-45º

Interferometric Wide Swath (IWS)

HH-HV or VV-VH

> 250 km

5 m x 20 m

> 25º

Extra Wide Swath (EWS)

HH-HV or VV-VH

> 400 km

25 m x 40 m

> 20º

Wave mode (WM)

HH (23º) or VV (36.5º)

20 km x 20 km (vignettes at 100 km intervals)

5 m x 5 m

23º and 36.5º

For all modes

Radiometric accuracy (3σ)

1 dB

NESZ (Noise Equivalent Sigma Zero)

-22 dB

Point Target Ambiguity Ratio

-25 dB

DTAR (Distributed Target Ambiguity Ratio)

-22 dB

Table 17: Performance parameters of the C-SAR instrument in the various operational modes 242)

The EFE comprises several TRMs (Transmit/Receive Modules) and associated electronics. It represents the active part of the RF equipment of the antenna. The basic function of each EFE is:

• to transmit Tx pulses in one of two polarizations (either H or V) to the corresponding two radiator elements

• to receive the echoes from the two H and the two V radiator elements independently and simultaneously.

The EFE provides the capability to perform antenna beam steering and forming by electronic means:

• control phase setting in transmit

• control phase and gain settings in receive.

 

C-SAR instrument calibration:

In contrast to SAR systems already existing in C-band like ASAR/ENVISAT or RADARSAT-2, high demands on the radiometric accuracy are made for C-SAR on Sentinel-1. Thus, product quality is of paramount importance and the success or failure of the mission depends essentially on the method of calibrating the entire Sentinel-1 system in an efficient way. 243) 244) 245) 246) 247) 248)

The most important point with respect to the calibration of this flexible SAR system is the tight performance with an absolute radiometric accuracy of only 1 dB (3σ) in all operation modes. Never before has such a strong requirement (a few tenths of dB) been defined for a SAR system. - With respect to the duration of the Sentinel-1 commissioning phase of three months only, the number of passes and the selection of test sites have to be optimized versus cost and time effort. e.g. calibrating several beams and polarization modes with the same test site. The calibration strategy of Sentinel-1 is based on the experience derived from TerraSAR-X.

Calibration is the process of quantitatively defining the system response to known controlled signal inputs. Calibration tasks are executed throughout the mission to ensure the normalized radar cross-section and the phase of the individual pixels are provided with stability and accuracy. Calibration of the entire SENTINEL-1 system is critical to guaranteeing product quality for operational demands. The SAR system must perform within an absolute radiometric accuracy of only 1 dB in all operation modes. This is a higher radiometric accuracy than any other SAR mission before it.

Calibration can be divided into two forms:

Internal calibration: Internal calibration provides an assessment of radar performance using internally generated calibrated signal sources, in particular from pre-flight testing.

External calibration: External calibration makes use of ground targets of known backscatter coefficients to render an end-to-end calibration of the SAR system.

In addition to the commissioning of Sentinel-1B executed by ESA, an independent SAR system calibration will be performed by DLR. For this purpose, the complete calibration chain was developed and established by DLR, starting with an efficient calibration strategy, a detailed in-orbit calibration plan, the SW-tools for analyzing and evaluating all the measurements up to the calibration targets serving as accurate reference. 249)

 

Internal Calibration

Internal calibration uses calibration signals which are routed as closely as possible along the nominal signal path. The calibration signals experience the same gain and phase variations as the nominal measurement signals. The ground processing then evaluates the calibration signals to identify gain and phase changes and correct the acquired images accordingly.

Transmit power, receiver gain and antenna gain are subject to instrument noise due to temperature changes or other effects over time. Internal calibration provides corrections for changes in the transmit power and the electronics gain as well as validating the antenna model. The resulting calibration data are used in ground processing to correct image data.

Internal calibration also covers the signal phase. The overall phase of the echo signal depends on two major elements: measurement geometry and instrument internal phase stability. As the hardware cannot generally provide the required phase stability, it is a task of the internal calibration scheme to cover the internal phase variations by adequate measurements. All internal calibration measurements, either for gain or for phase, are used in ground processing to correct data products and achieve the required stability.

Internal calibration uses a PCC (Pulse-Coded Calibration) technique to embed a unique pulse code on a signal such that it can be identified and measured when embedded in other signals. This allows the amplitude and phase of individual signal paths to be measured while operating the complete antenna. The PCC technique is implemented by sending a series of coherent calibration pulses in parallel through the desired signal paths. The individual successive signals are multiplied by factors of +1 or -1. Factor -1 is implemented by adding a phase shift of 180°, while factor +1 means no additional phase. Each path is identified by a unique sequence.

The PCC technique can be applied if:

- the receiver detects the signals coherently

- the whole sequence is executed in a sufficiently short time such that the parameters to be measured are stationary

- the system is linear with respect to the individual signals.

The PCC technique can measure the signal paths via individual Transmit (TX) /Receive (RX) Modules (TRMs) or via groups of TRMs (either TX or RX paths, either polarization).

The average properties of rows or columns of TRMs can be measured by a short PCC sequence. The length of a PCC sequence is always a power of two. There are 20 rows of waveguides, therefore the PCC sequence has a minimum of 32 pulses. Although the 14 columns (14 tiles) could be measured by a PCC sequence of 16 pulses, it is assumed that a sequence length of 32 pulses is also used. All 20 rows are operated together, meaning the antenna is in a full operational state. The overall signal from all rows is received, digitized and packed into calibration packets. These packets are evaluated (on the ground) to determine the properties of the individual rows. The approach for measuring the average azimuth excitation coefficient is similar to the elevation pattern, using columns of TRMs instead of rows.

The PCC-32 measurements described above need approximately 129 pulses. Additional warm-up pulses may also be needed. Such a large number of calibration pulses represent a significant interruption in image generation when operated within the image acquisition of the stripmap mode. For intermediate calibration pulses in stripmap mode, and also for calibration pulses related to each sub-swath measurement in the ScanSAR modes, a shorter sequence is needed. The shortest possible PCC sequence is based on two measurements, however this procedure introduces PCC-inherent error contributions. These latter errors are to be expected, although they are significantly smaller than those due to leakage signals.

For the antenna model, the reference patterns of all beams are derived for radiometric correction of the SAR data. The active antenna of the SAR instrument allows a multitude of different antenna beams with their associated gain patterns. All these patterns are described by the mathematical antenna model which provides the antenna patterns as functions of the commanded amplitudes and phases within the front end EFEs and within the tile amplifiers. The quality of the patterns is ensured by the on-board temperature compensation controlled by the tile control units. The internal calibration signals measure the actual phases and amplitudes and allow verifying the correct function and performance of all included elements. The antenna model is established on-ground, based on pattern tests at various integration levels up to the complete antenna.

RF Characterization Mode:

The RF characterization mode is a self-standing mode and is not associated with the individual imaging data-takes. It is operated at least once per day during a convenient point within the long duration of wave mode.

The RF characterization mode verifies in-flight the correct function and characteristics of the individual TRMs. Operating it two or more times at different temperatures during the cool-down phases between the high dissipating imaging modes can provide in-orbit characterization versus temperature where necessary. The RF characterization mode performs measurements with internal signals and is designed to achieve a number of goals. The RF calibration mode will:

- cover all those measurements needed in-orbit but which are not required for each individual data-take

- provide data sets to assess the instrument health and performance as far as possible

- verify the correct function of the individual TRMs, both within the front-end and the tile amplifiers

- verify the excitation coefficients for the TX and RX patterns to ensure the validity of the antenna model.

This mode is based on the same measurement types as the internal calibration. The mode has to address the individual TRMs while operating the full antenna in representative thermal conditions and with nominal power consumption. This can be achieved using the PCC technique. As a standalone mode, it is not forced to use the signal parameters of a dedicated imaging mode, but instead an optimized set of parameters can be used. The calibration mode is to be operated for both TX polarizations. The receiver will measure both polarizations in any case.

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Figure 164: In-orbit calibration plan for Sentinel-1 versus 12 days repeat cycles (image credit: (image credit: DLR, Ref. 244)

 

External Calibration

External calibration derives the calibration constant by measurement of corner reflector targets and homogeneous areas such as rainforest with exactly known backscatter coefficients. This is necessary as it will not generally be possible to know all parameters with sufficient accuracy prior to the in-flight measurements.

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Figure 165: In-orbit external calibration (image credit: ESA)

External calibration comprises five steps as shown below.

1) Radiometric Calibration: Radiometric calibration is applied to correct for the bias of SAR data products. The required absolute calibration factor is derived by measuring the SAR system against reference point targets with well-known radar cross section. Due to the high demand on the radiometric accuracy of 1 dB (3&#963;) in all four operational modes, it is recommended to measure at least one beam of each mode against the SENTINEL-1 transponders deployed at different locations. Each selected beam will be measured during two passes (ascending and descending). Furthermore, two receive polarization combinations per operation mode are to be measured simultaneously. By measuring SENTINEL-1 against the three transponders for selected beams, the radiometric calibration can be performed within a limited number of repeat cycles. The absolute calibration factor of all other beams is then derived by applying the antenna model.

2) Antenna Model Verification: Antenna model verification ensures the provision of precise reference patterns of all operation modes and the gain offset between different beams. Verification of the antenna model is performed for selected beams, at least one with low, one with mid- and one with high incidence angle, all with the same polarization condition. In addition, some of the beams are selected for measuring the second polarization condition. Assuming acquisitions for each of the selected beams, using the receiver mode of the transponders and by using acquisitions over rainforest, antenna model verification can be performed within a few cycles.

3) Geometric Calibration: Geometric calibration is applied to assign the SAR data to the geographic location on the Earth's surface. Using well surveyed reference targets, the internal delay of the instrument and systematic azimuth shifts can be derived. For this purpose the acquired scenes are measured simultaneously against point targets deployed and precisely surveyed.

4) Antenna Pointing Determination: Antenna pointing determination is performed to achieve correct beam pointing of the antenna. The determination of the antenna pointing by the receiver mode of the transponders is performed using notch patterns in azimuth with different incidence angles (near, mid- and far). Using three transponders with a receiver function within one cycle (two passes) sufficient measurements can be acquired to derive the required accuracy. The appropriate antenna pattern is measured across the rainforest and using ground receivers.

5) Inter-Channel Phase Calibration: As the signal travels through different receive channels for H and V polarization, it may experience different gains, phase offsets and even different time delays. Inter-channel phase accuracy is calibrated using the SENTINEL-1 transponders that return the signal with H and V polarization components, and which therefore allow a direct phase comparison between H and V channels. The antenna model to be derived on the ground describes the antenna patterns with high accuracy. This antenna model is verified for a limited set of elevation beams via measurements over a homogeneous target, i.e. over rainforest. The azimuth beams will be measured using the receiver function of the SENTINEL-1 transponder.

 

Independent calibration verification:

In addition to the commissioning of Sentinel-1A executed by ESA, an independent verification of the system calibration will be executed for the first time by an external institution. For this purpose, the complete calibration chain was developed and established by DLR, starting with an efficient calibration concept, a detailed in-orbit calibration plan, the SW-tools for analyzing and evaluating all the measurements up to the calibration targets serving as accurate reference. 250)

DLR calibration facility: The Sentinel-1 calibration strategy requires a facility that is well-equipped with ground calibration hardware as well as software tools for analyzing and evaluating all the measurements. For this purpose, DLR/MRI (Microwave and Radar Institute) has been developed and established the following reliable and accurate ground equipment:

• Accurate and remote controlled ground targets like the DLR's novel corner reflectors as depicted in Figure 166 and the novel transponders as depicted in Figure 167, precisely surveyed for geometric and radiometric calibration. Using the receiver unit of the transponder, the pointing and the pattern of the antenna in azimuth direction can be measured during an overflight.

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Figure 166: DLR's novel corner reflector which is remote controlled (image credit: DLR)

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Figure 167: DLR's novel transponder, designed and developed for Sentinel-1A (image credit: DLR)

• Different analysis and evaluation tools have been modified w.r.t. the Sentinel-1A characteristics, like:

- Internal Calibration Module for analyzing the stability of the instrument and deriving several instrument offsets like the channel imbalance.

- Antenna Characterization Module for deriving the actual pointing of Sentinel-1A and verifying the antenna model in-flight

- CALIX, a software tool for point target analysis and deriving the absolute calibration factor. Furthermore by geometric analysis of accurately surveyed targets the internal delay of the instrument and the dating of the SAR data can be determined.

- TAXI, the Institute's experimental TanDEM-X interferometric processor, which will be used for interferometric analysis and for phase analysis of the TOPS mode of Sentinel-1A.

Test site selection: The next important point is concerned with the coverage of Sentinel-1A, because the coverage defines the number of visible measurements across a test site and drives consequently the schedule. Considering all aspects described before, the coverage of Sentinel-1A across the DLR calibration field in South Germany has been investigated for all beams being selected for in-flight measurements, as depicted in Figure 168 by the blue hatched swathes. The red framed area indicates a region covering all beams. Hence, deploying the transponders within this area, reference targets are available providing simultaneously a point target for both polarization channels of Sentinel-1A. The position of the corner reflectors is mainly driven by the edges of the swaths and the small vignettes of the wave mode (indicated by the black framed boxes).

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Figure 168: Coverage of Sentinel-1A for all beams being selected for in-flight measurements (SM1, SM2, IW1, EW3, IW3, SM5, WV1) across the DLR calibration field deployed in South Germany (image credit: DLR)

Hence, the test site shown in Figure 168, composed of three transponders and three corner reflectors, enclosing an area of about 85 km x 20 km, is sufficient to cope with the tight requirements of commissioning Sentinel-1A, i.e all measurements required for calibrating the whole Sentinel-1A system can be performed within the commissioning phase of three months.

 


 

Copernicus Program Ground Segment

The ground segment is composed of the CGS (Core Ground Segment), the" Collaborative Ground Segment" and the Copernicus contributing missions' ground segments.

The Core ground segment monitors and controls the Sentinels spacecraft, ensures the measurement data acquisition, processing, archiving and dissemination to the final users. In addition, it is responsible for performing conflict-free mission planning according to a predefined operational scenario, and it ensures the quality of the data products and the performance of the space borne sensors by continuous monitoring, calibration and validation activities, guaranteeing the overall performance of the mission. 251)

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Figure 169: Copernicus Ground Segment Architecture (image credit: ESA)

The Copernicus Ground Segment is complemented by the Sentinel Collaborative Ground Segment, which was introduced with the aim of exploiting the Sentinel missions even further. This entails additional elements for specialized solutions in different technological areas such as data acquisition, complementary production and dissemination, innovative tools and applications, and complementary support to calibration & validation activities.

For Copernicus operations, ESA has defined the concept and architecture for the Copernicus Core ground segment, consisting of a FOS (Flight Operations System) and a PDGS (Payload Data Ground Segment). Whereas the flight operations and the mission control of Sentinel-1 and -2 is performed by ESOC (ESA's European Space Operations Center in Darmstadt, Germany), the operations of Sentinel-3 and the Sentinel-4/-5 attached payloads to meteorological satellites is performed by EUMETSAT.

The EC (European Commission), supported by its agencies, is in charge to implement the Copernicus Services. The Commission is defined to be the owner and financing organization of Copernicus. The technical implementation is granted to other European organizations, namely ESA, EUMETSAT, EEA (European Environment Agency), ECMWF (European Centre for Medium-Range Weather Forecasts) and others. - Complemented by ESA programs and national contributions, ESA has the responsibility to build and operate a dedicated space segment (Sentinels) and the ground segment of Copernicus. 252)

The EC has also defined an overall Copernicus data policy, declaring the Sentinel mission data free and open. 253) This decision is reflecting the experience made with similar missions in the US (e.g. Landsat) and the new possibilities of the Internet. It will stimulate the use of Earth observation data, but also may challenge commercial suppliers, selling data similar to those of the Sentinels. The Copernicus data policy is also based on the European INSPIRE (Infrastructure for Spatial Information in the European Community) directive, which harmonizes the policy and electronic access to geographic information within Europe.

The majority of the Earth observation data for these services will come from a fleet of dedicated Copernicus satellites: the Sentinels. The features of the Copernicus Sentinel missions are depicted in Table 18. The series of satellites guarantees continuity of the ERS/ENVISAT missions and adds further features and parameters. Moreover, always two Sentinels of each series should be in orbit at any time, increasing the coverage for many applications. Applications and services will also benefit from a supply from other European national and commercial GMES Contributing Missions (GCM), managed in Copernicus by the ESA GSCDA (GMES Space Component Data Access) system.

Copernicus Mission

Launch

Sensor complement

Objective

Sentinel-1

2014

C-SAR (C-band SAR)

ERS/ENVISAT SAR data continuity for Land and Ocean surveillance; interferometry

Sentinel-2

2014

MSI (Multispectral Instrument)

Deliver high resolution optical information of all land-masses of the Earth, complementing e.g. Landsat & SPOT series.

Sentinel-3

2016

OLCI (Ocean and Land Color Instrument) SLSTR (Sea and Land Surface Temp. Radiometer) SRAL (Ku/C-band Radar Altimeter) MWR (Micro-Wave Radiometer)

Global daily land and sea parameter observation POD (Precise Orbit Determination)

Sentinel-4 (on MTG in GEO)

2019

UVN (UV-VIS-NIR) instrument

Monitoring of air quality, stratospheric ozone, solar radiation, and climate monitoring.

Sentinel-5 (on MetOp SG in LEO)

2020

UVNS (UV-VIS-NIR-SWIR) instrument

Atmospheric composition, cloud and aerosol for air quality and climate applications

Sentinel-5P (Precursor)

2016

TROPOMI (Tropospheric Monitoring Instrument)

Atmospheric composition, cloud and aerosol for air quality and climate applications

Table 18: Copernicus Sentinel missions characteristics

The management of the payload data from the Sentinel missions is performed by the CGS (Core Ground Segment) defined by ESA. The CGS consists of a series of X-band data acquisition stations, which will capture all global Sentinel-1/-2/-3 mission data (Sentinel-4/-5 will use dedicated EUMETSAT data acquisition facilities for its next generation geostationary and polar orbiting satellites). These stations are designed for dumping all data recorded on the satellites on-board data recorders, as well as generating near real time products (1-3h after sensing) directly at the stations. The PDGS will also make use of the EDRS (European Data Relay Satellite). This PPP (Public Private Partnership) between ESA and ASTRIUM GmbH, operates a communication payload on two geostationary satellites. The primary link between the Sentinels and the geostationary satellites is a LCT (Laser Communication Terminal), built by Tesat Space, Backnang, Germany and provided as contribution-in-kind by Germany to the Sentinel-1 and -2 satellite series. The downlink from the geostationary satellites is performed via Ka-band to dedicated stations and to user terminals (Ref. 252). 254)

The acquired mission data is then transferred to Sentinel PACs (Processing and Archiving Centers). The PACs are designed to take specifically care for a certain Sentinel/instrument project. For security and redundancy reasons, each Sentinel data set is hosted by two PACs (EUMETSAT is assigned to act as the second PAC for the Sentinel-3 mission data). The PACs generate systematically base level products from all acquired data, archive them in a mission archive and electronically distribute them to the Copernicus users.

The products and performance of each Sentinel is monitored by MPCs (Mission Performance Centers). The entire data flow is managed by a PDMC (Payload Data Management Center), hosted by ESA at ESRIN, Frascati, Italy. The transport and circulation of the data is performed via terrestrial networks. The GMES WAN therefore connects all PDGS elements with links, having appropriate bandwidth.

In 2011, ESA started a series of procurement actions to select European providers to offer their facilities for the set-up and operations of the PDGS elements. Figure 170 displays the structure of the PDGS and the outcome of the selection of the providers.

Sentinel1_AutoD

Figure 170: Overall structure of Copernicus Payload Data Ground Segment for Sentinels-1 to -3 (Status May 2013), image credit: ESA (Ref. 252)

Within this competitive selection process, ESA has awarded the DLR/DFD ( German Remote Sensing Data Center) with the set-up and operations of the PACs for Sentinel-1 and Sentinel-3 (OLCI part). T-Systems, Germany, is assisting DLR in the network parts of the PACs. In addition and under separate procurement, DFD designs, builds and operates the payload data ground segment) for the Sentinel-5 Precursor mission.

High-level tasks of the DLR Sentinel PAC are:

- receive Sentinel data from CGSs via the GMES WAN

- ingest these data into the STA (Short-Term Archive) and MTA (Mid-Term Archive) of the Sentinel PGDS

- ingest these data in a LTA (Long-Term Archive) for a period of more than 7 years

- perform consolidation and re-assembly of level-0 data received from CGS facilities

- perform systematic and request-driven processing of Sentinel data to higher-level products

- host Sentinel data products within a layered architecture of on-line dissemination elements that will facilitate the direct access of end-users via public networks

- share and exchange any locally processed data with a 2nd partner PAC for the purpose of redundancy.

According to the GSC (GMES Space Component) operations concept, the Sentinel PDGS will become operationally embedded in the GSCDA (GMES Space Component Data Access) System that ESA implements in support of data access to GMES/Copernicus Service Projects and their users.

Sentinel1_AutoC

Figure 171: Overall structure of the Sentinel-1 (S1) and Sentinel-3-OLCI PACs at DFD in Oberpfaffenhofen (image credit: DLR)

Sentinel-5P: The Sentinel-5 Precursor satellite will deliver a key set of atmospheric composition, cloud and aerosol data products for air quality and climate applications. The sensing instrument TROPOMI together with the operational level 1 and level 2 processors will bring a significant improvement in the precision as well as temporal and spatial resolution of derived atmospheric constituents. Sentinel-5 Precursor is planned for launch in 2016.

For the Sentinel-5P mission, DLR/DFD was selected by ESA for the development and operation of the entire PDGS (Payload Data Ground Segment), which covers the whole chain of payload data handling on ground: data reception, processing, archiving, near-real-time and offline delivery to end users. In addition, DLR/IMF (Institut für Methodik der Fernerkundung - Remote Sensing Technology Institute) was selected for the development of retrieval algorithms and operational processors for a number of key atmospheric trace gases and cloud products.

Sentinel-5P will continue the strong DFD heritage on development/operations of processors and ground segments for atmospheric missions started with GOME-1/ERS-2, SCIAMACHY/ENVISAT, and GOME-2 on the MetOp series. The Sentinel-5P PDGS - as well as the LTA for Sentinel-1 and Sentinel 3 OCLI - will be based on the DFD development of DIMS (Data and Information Management System). DIMS will be configured for the Sentinel 5P workflows and mission specific extensions for the demanding throughput and storage requirements (Ref. 252).

In summary, DLR/DFD is involved in the Core and collaborative ground segment of the Copernicus program. It has been developing PDGS (Payload Data Ground Segment) elements and will operate PACs (Processing and Archiving Centers) for Sentinels and national data acquisition stations, both in X-band and using EDRS acquisition services.

 

Sentinel-1 FOS (Flight Operations Segment)

The main responsibilities of the FOS at ESA encompass satellite monitoring and control, including execution of all platform activities and the commanding of the payload schedules. The principal components of the FOS are (Ref. 254): 255)

1) The Ground Station and Communications Network, which performs TT&C (Telemetry, Tracking and Commanding) operations within the S-band frequency. A single S-band ground station will be used throughout all mission phases, complemented by additional TT&C stations as launch and early operations (LEOP) and backup stations.

2) The FOCC (Flight Operations Control Center), which includes:

• the Sentinel Mission Control System, which supports telecommand coding and transfer and housekeeping telemetry (HKTM) data archiving and processing

• the Sentinel Mission Planning System which supports command request handling, the planning and scheduling of satellite operations and the scheduling of payload operations as prepared by the PDGS Mission Planning System

• the specific Sentinel Satellite Simulators, which support procedure validation, operator training and the simulation campaign before each major phase of the mission

• the Sentinel Flight Dynamics System, which supports all activities related to attitude and orbit determination and prediction, the preparation of slew and orbit maneuvers, satellite dynamics evaluation and navigation

• The Sentinel Key Management Facilities, which support the management of the telecommand security functions.

3) A General Purpose Communication Network, which provides the services for exchanging data with any other external system during all mission phases.

Sentinel1_AutoB

Figure 172: Simplified view of the Sentinel-1 Ground Segment (image credit: Astrium SAS)

Sentinel1_AutoA

Figure 173: Overall Layout of the Sentinel-1 Core PDGS (image credit: Astrium SAS)

The selected geographical locations and operators for the Sentinel-1 PDGS centers are (Ref. 254):

• KSAT for X-band reception (CGS) in Svalbard (Norway) and Alaska

• INTA for X-band reception in Maspalomas (Spain)

• E-Geos for X-band reception in Matera (Italy)

• Astrium Services for the PAC (Processing and Archiving Center) in Farnborough (UK)

• DLR for the PAC in Oberpfaffenhofen (Germany)

• CLS for the MPC (Mission Performance Center) operations in Brest (France).

• PDMC (Payload Data Management Center) will be located at ESRIN and be operated by the European Space Agency.

• The POD (Precise Orbit Determination) service will be provided by GMV (Spain).

Sentinel1_Auto9

Figure 174: Illustration of Sentinel-1 ground segment configuration (image credit: ESA, Ref. 168)

 

CPOD (Copernicus Precise Orbit Determination) Service

The CPOD service is part of the PDGS (Payload Data Ground Segment) of the Sentinel missions. A GMV-led consortium of Spain is operating the CPOD being in charge of generating precise orbital products and auxiliary data files for their use as part of the processing chains of the respective Sentinel PDGS. 256)

Figure 175 shows the different elements that interact with the CPOD service. On top we have the Sentinels satellites, all of them with two GPS Receivers on-board (Sentinel-3 also has a LRR and DORIS). The raw L0 data is downloaded at least once per orbit to one of the Ground Stations used (particularly Svalbard, but also Maspalomas and Matera are used). The raw L0 data that contains the GPS and attitude data is circulated to the Sentinels PDGS and from there it is made available to the CPOD Service Center, which will generate orbital products with different timelines.

Sentinel1_Auto8

Figure 175: Overview of the CPOD service elements (image credit: GMV, ESA)

The first three Sentinel missions require orbital products in NRT (Near Real Time), with latencies as low as 30 minutes, in STC (Short Time Critical), with latencies of 1.5 days and in NTC (Non-time Critical) with latencies of 20-30 days. The accuracy requirements are very challenging, targeting 5 cm in 3D for Sentinel-1 and 2-3 cm in radial direction for Sentinel-3.

Mission

Orbit Product

Product Category

Latency Requirement

Position Accuracy (RMS orbit)

S-1

NRT

Restituted

Within 3 hours (from the reception of GNSS data)

< 10 cm (2D)

S-2

NRT

Restituted

90 minutes before Sentinel-2 A/B ANX is crossed

< 10 m (2D) 3-sigma

S-2

NRT

Restituted

Within 30 minutes (from the reception of GNSS data)

< 3 m (3D) 3-sigma

S-3

NRT

Restituted

Within 30 minutes (from the reception of GNSS data)

10 cm threshold with a target of 8 cm (radial)

S-3

STC

Preliminary

Within 1,5 days (36 hr)

4 cm threshold with a target of 3 cm (radial)

S-1

NTC

Precise

Within 20 days

5 cm (3D)

S-3

NTC

Precise

Within 28 days (i.e. 2 days before NTC science product delivery)

3 cm threshold with a target of 2 cm (radial)

Table 19: Summary of timeliness and accuracy requirements 257)

The CPOD Service has been developed and it is being operated by a GMV-led consortium with a system running at GMV premises to provide orbital products for the Sentinel missions with different timeliness: NRT, STC , NTC and reprocessing REP. Additionally the Sentinel-3 POD IPF (Instrument Processing Facility), a software package developed as part of the CPOD Service, will run at the Sentinel-3 PDGS (on both, the Marine Center and Core Ground Station) generating NRT orbital products for the Sentinel-3 mission.

The accuracy of the orbital products is being assessed by a number of external validation institutions, all of them being part of the Copernicus POD QWG (Quality Working Group). The main purpose of the Copernicus POD QWG is to monitor the performance of the operational POD products (both the orbit products as well as the input tracking data) and to define potential and future enhancements to the orbit solutions.

The different Sentinel FOSs (Flight Operation Segments) provide orbital products (restituted and predicted) plus maneuver and mass history information. CNES provides also orbital products and DORIS data for Sentinel-3, and it receives GPS RINEX (Receiver Independent Exchange Format) files from the CPOD Service Center.

Veripos Ltd is the source of accurate GPS orbits and clocks for NRT and STC latencies and IGS for NTC and REP latencies. The CPOD also has an in-house back-up of Veripos based on magicGNSS, which provides NRT GPS orbits and clocks. For Sentinel-3, ILRS (International Laser Ranging Service) and DORIS data will also be used. Finally, the CPOD Service interacts with the CPOD QWG and a number of external validation centers.

The Copernicus POD Service has been developed and it is operated by GMV, but it interacts with different entities, both public and private, that act as clients, users and subcontractors. Following are the current main members of the Copernicus POD Service:

- ESA/ESRIN (European Space Research Institute) Frascati, Italy. This center leads the development of the different PGDSs, and in particular, the Sentinel-1 and -2 PDGS are located here.

- ESA/ESOC (European Space Operation Center), Darmstadt, Germany. This center hosts the FOS (Flight Operations Segment) of Sentinel-1, -2, and -3 missions during the commissioning phase and also during the Routine Operation phase except for Sentinel-3 mission, which is handed over to EUMETSAT.

- EUMETSAT (European Organization for the Exploitation of Meteorological Satellites), Darmstadt, Germany. This center hosts the FOS ( Flight Operations Segment) of Sentinel-3 mission during the Routine Operation Phase, and also the so-called Marine Center PDGS of Sentinel-3.

- CNES (Centre National d'Études Spatiales), Toulouse, France provides accurate orbits and platform data files for the Sentinel-3 mission. CNES has also contributed with the DORIS instrument, and as so, it also provides RINEX DORIS files to the Copernicus POD Service.

- GMV Innovating Solutions is the prime of the Copernicus POD Service. It has developed and it is operating the Service from its headquarters in Tres Cantos, near Madrid (Spain). It is responsible also of the overall management and the evolutions of the system.

- POSITIM UG provides expertise in the LEO POD field, prototypes improvements in algorithms and manages, on behalf of ESA/GMV, the Quality Working Group.

- DLR (Deutsches Zentrum für Luft- und Raumfahrt) Oberpfaffenhofen, Germany provides expertise in the LEO POD and GNSS fields. Additionally, it contributes with orbital products for external validation of products.

- TUM (Technische Universität München) provides expertise in the LEO POD field. Additionally, it contributes with orbital products for external validation of products.

- AIUB (Astronomisches Institut, Universität Bern), Bern, Switzerland contributes with orbital products for external validation of products.

- TU Delft (Technische Universiteit Delft), Delft, The Netherlands contributes with orbital products for external validation of products.

- VERIPOS Ltd, Aberdeen, UK is the provider of accurate GPS orbits and clocks in NRT and STC timeliness for it use in the GNSS POD processing.

There are two places where the operational orbits are computed. The so-called CPOD Service Center, located in GMV's premises, is in charge of computing all orbital products of Sentinel-1 and -2 and all STC and NTC products of Sentinel-3. The Sentinel-3 POD IPF (Instrument Processing Facility) is in charge of computing the Sentinel-3 NRT orbital products and it will be running at two locations, the Marine center (located in EUMETSAT, Darmstadt) and the Core Ground Station (located in Svalbard).

Orbital accuracy results:

• Sentinel-1A was launched on April 3, 2014. After 6 months of commissioning, the CPOD Service started the ROP (Routine Operation Phase) in October 2014. Since then, every four months the quality of the service is assessed, including the accuracy of the orbital products. For this, a specific period of time is selected for re-processing by the external validation institutions (i.e. AIUB, DLR, ESOC, TU Delft and TUM). This exercise has been performed twice since the beginning of the ROP phase.

• Sentinel-2A was launched on June, 23, 2015. The commissioning phase is expected to finish by mid/end October 2015, so the ROP (Routine Operation Phase) is expected to begin in November 2015. During the commissioning phase the orbit accuracy has been assessed by the same means used with Sentinel-1A, selecting a period of time to be re-processed by the external validation institutions (Ref. 256).

In the case of Sentinel-1A, the institutions compute offline accurate orbits and provide them to GMV for cross-comparison. It has been shown that systematically the accuracy requirements are fulfilled without major problems. Figure 176 shows the results of the last comparison campaign of January 2016; it shows the 3D RMS per day, during 10 days in January 2016, between the operational Sentinel-1 NTC solution (CPOD) and the daily solutions provided by each institution. Additionally, there is a combined solution (COMB) computed as a weighted average of all individual solutions. It can be seen that the differences are systematically below the required 5 cm (Ref. 257).

Sentinel1_Auto7

Figure 176: Sentinel-1A orbit comparisons (3D RMS; cm) between CPOD and external solutions; red line is threshold (image credit: GMV)

In addition, all NRT and NTC products are compared routinely against an offline ESOC solution (which used the same POD SW, NAPEOS, but of a different version and using different configuration and inputs). The following plots (Figures 177 and 178) show the differences with respect to ESOC from October 2015 to January 2016, where it can be seen that systematically the differences are well below the threshold. The cases above the threshold are typically due to maneuvers and data gaps.

Sentinel1_Auto6

Figure 177: Sentinel-1A Restituted Orbital Product vs. ESOC (2D RMS) from 1st October 2015 until 31st January 2016 (image credit: GMV)

Sentinel1_Auto5

Figure 178: Sentinel-1A Precise Orbital Product vs. ESOC (3D RMS) from 1st October 2015 to 31st January 2016 (image credit: GMV)

In the case of Sentinel-2A, the accuracy results are similar to those of Sentinel-1A. Figure 179 shows the results of the last comparison campaign of January 2016; it shows the 3D RMS per day, during 10 days in January 2016, between the operational Sentinel-2 NTC solution (CPOD) and the daily solutions provided by each institution. Additionally there is a combined solution (COMB) computed as a weighted average of all individual solution. It can be seen that the differences are systematically below 5 cm, like in the case of Sentinel-1A.

Sentinel1_Auto4

Figure 179: Sentinel-2A orbit comparisons (3D RMS; cm) between CPOD and external solutions (image credit: GMV, Ref. 257)

 


 

Copernicus / Sentinels EDRS system operations:

EDRS (European Data Relay Satellite) will provide a data relay service to Sentinel-1 and -2 and initially is required to support 4 Sentinels simultaneously. Each Sentinel will communicate with a geostationary EDRS satellite via an optical laser link. The EDRS GEO satellite will relay the data to the ground via a Ka-band link. Optionally, the Ka-band downlink is planned to be encrypted, e.g. in support to security relevant applications. Two EDRS geo-stationary satellites are currently planned, providing in-orbit redundancy to the Sentinels. 258)

EDRS will provide the same data at the ground station interface as is available at the input to the OCP (Optical Communications Payload) on-board the satellites, using the same interface as the X-band downlink. The EDRS transparently adapts the Sentinels data rate and format to the internal EDRS rate and formats, e.g. EDRS operates at bit rates of 600 Mbit/s and higher.

With EDRS, instrument data is directly down-linked via data relay to processing and archiving centers, while other data continues to be received at X-band ground stations. The allocation of the data to downlink via X-band or EDRS is handled as part of the Sentinel mission planning system and will take into account the visibility zones of the X-band station network and requirements such as timeliness of data.

Sentinel1_Auto3

Figure 180: Sentinel missions - EDRS interfaces (image credit: ESA)

 

Copernicus / Sentinel data policy:

The principles of the Sentinel data policy, jointly established by EC and ESA, are based on a full and open access to the data:

• anybody can access acquired Sentinel data; in particular, no difference is made between public, commercial and scientific use and in between European or non-European users (on a best effort basis, taking into consideration technical and financial constraints);

• the licenses for the Sentinel data itself are free of charge;

• the Sentinel data will be made available to the users via a "generic" online access mode, free of charge. "Generic" online access is subject to a user registration process and to the acceptation of generic terms and conditions;

Following registration, the user will have the possibility to immediately download a test data set that simulates the data products that will be generated by Sentinel-1. Following launch, registered users will be granted early access to Sentinel-1 data samples, even before the full operational qualification of the products is completed.

Registration is open to all users via simple on-line self-registration accessible via the Sentinel Data Hub. 259)

• additional access modes and the delivery of additional products will be tailored to specific user needs, and therefore subject to tailored conditions;

• in the event security restrictions apply to specific Sentinel data affecting data availability or timeliness, specific operational procedures will be activated.

ESA Member States approved these principles in September 2009. 260) 261) 262) 263) 264)

 

Sentinel-1 operational products:

• Level-0 products: Compressed, unprocessed instrument source packets, with additional annotations and auxiliary information to support the processing. 265)

• Level-1 products:

- Level-1 Slant-Range Single-Look Complex Products (SLC): Focused data in slant-range geometry, single look, containing phase and amplitude information.

- Level-1 Ground Range Detected Geo-referenced Products (GRD): Focused data projected to ground range, detected and multi-looked. Data is projected to ground range using an Earth ellipsoid model, maintaining the original satellite path direction and including complete geo-reference information.

• Level-2 Ocean products: Ocean wind field, swell wave spectra and surface currents information as derived from SAR data.

Product generation policy

Product type

Access mode

Timeliness

Systematic Global (for all acquired data)

L0 L1 GRD L2 Ocean

Subscription

3 hours from observation (NRT data) 24 hours from observation (standard)

Free online access from archive

> 24 hours from observation

Systematic Regional (for a subset of acquired data)

L1 SLC (Single-Look Complex)

Subscription

3 hours from observation (NRT data) 24 hours from observation (standard)

Free online access from archive

> 24 hours from observation

Systematic Local (for a subset of data acquired over ocean in the visibility of a Core Ground Station)

L0

Subscription

< 1 hour from observation

Table 20: Sentinel-1 Operational products access policy

Acquisition mode

Product type

Resolution class

Resolution (range x azi) (m)

Pixel spacing (range x azi) (m)

No of looks (range x azi)

ENL

SM (Stripmap Mode)

SLC

-

1.7 x 4.3 to 3.6 x 4.9

1.5 x 3.6 to 3.1 x 4.1

1 x 1

1

GRD

FR

9 x 9

4 x 4

2 x 2

3.9

HR

23 x 23

10 x 10

6 x 6

34.4

MR

84 x 84

40 x 40

22 x 22

464.7

IW

(Interferometric Wide Swath)

SLC

-

2.7 x 22 to 3.5 x 22

2.3 x 17.4 to 3 x 17.4

1

1

GRD

HR

20 x 22

10 x 10

5 x 1

4.9

MR

88 x 89

40 x 40

22 x 5

105.7

EW (Extra Wide Swath)

SLC

-

7.9 x 42 to 14.4 x 43

5.9 x 34.7 to 12.5 x 34.7

1 x 1

1

GRD

HR

50 x 50

25 x 25

3 x 1

3

MR

93 x 87

40 x 40

6 x 2

12

WV (Water Vapor)

SLC

-

2.0 x 4.8 and 3.1 x 4.8

1.7 x 4.1 and 2.7 x 4.1

1 x 1

1

GRD

MR

52 x 51

25 x 25

13 x 13

139.7

Table 21: Planned operational ESA Sentinel-1 products - L1 characteristics 266)

• For GRD (Ground Range Detected) products, the resolution corresponds to the mid range value at mid orbit altitude, averaged over all swaths.

• For SLC (Slant-Range Single-Look Complex) products SM/IW/EW products, the resolution and pixel spacing are provided from lowest to highest incidence angle. For SLC WV products, the resolution and pixel spacing are provided for beams WV1and WV2.

• For SLC SM/IW/EW products, the resolution and pixel spacing are provided from lowest to highest incidence angle. For SLC WV products, the resolution and pixel spacing are provided for beams WV1and WV2.

 


 

Preparatory campaigns:

In the context of the Copernicus program, ESA is conducting a number of coordinated preparatory activities (studies, campaigns, etc.) to demonstrate/validate the observation concepts (as well as many other system aspects) that are being planned for the various Sentinel missions. The following campaigns are in particular dedicated in support of Sentinel-1 (and -2, AgriSAR) applications.

AgriSAR 2009:

The AgriSAR 2009 campaign of ESA took place in April 2009. The objective is to evaluate how frequent multi-polarization acquisitions provided by Sentinel-1 will improve applications such as land-cover mapping and crop monitoring. To accomplish this ambitious task, ESA has asked MDA Geospatial Services to acquire multi-temporal, quad-polarization RADARSAT-2 imagery throughout the 2009 growing season over three test sites. The chosen sites are located in Flevoland in the Netherlands, Barrax in Spain and Indian Head in mid-west Canada.

In addition to the contribution from MDA Geospatial Services, the campaign included also a number of European and Canadian scientists to help with ground activities. These activities included the collection and analysis of information about land cover, crop type, crop condition and other parameters such as soil moisture. Of particular interest were the new algorithms and methods required to extract land-cover information from a dense temporal series of SAR images and follow how the crops develop. 267)

Sentinel1_Auto2

Figure 181: The color composite of a RADARSAT-2 polarimetric radar image acquired over the Flevoland test site in the Netherlands on April 4, 2009 (image credit: ESA)

Sentinel1_Auto1

Figure 182: Polarimetric RADARSAT-2 SAR image of the Barrax test site in Spain on April 9, 2009 (image credit: ESA)

IceSAR 2007:

The IceSAR airborne campaign (3 weeks in March 2007), which took place near Longyearbyen in Svalbard (Norway), was conducted by AWI (Alfred Wegner Institut), Bremerhaven, DLR/HR (Microwave and Radar Institute), and ESA. The radar configuration consisted of a C-band instrument with VV and VH polarizations, very similar to the future Sentinel-1 sensor. The C-band SAR was flown on the DO-228 aircraft of DLR (E-SAR instrument with C- and X-band capability). In addition, the Polar-2 aircraft of AWI was flown carrying the AWI infrared line scanner during the IceSAR campaign in coordination with the radar aircraft. 268) 269)

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Figure 183: An airborne SAR sea-ice image taken over Storfjorden, Svalbard on March, 16, 2007 (image credit: ESA)

AgriSAR 2006:

The AgriSAR campaign of ESA took place in the summer of 2006 (Apr. 18 - Aug. 2, 2006) - representing an ambitious large-scale attempt to assess the performance of the Sentinel-1 (C-band SAR) and Sentinel-2 (Optical Multispectral) for land applications. The campaign was unique in scope and scale representing frequent airborne SAR coverage during the entire crop-growing season, from sowing to harvest. 270) 271) 272)

The main test site was Demmin (Durable Environmental Multidisciplinary Monitoring Information Network), an agricultural site located in Mecklenburg-Vorpommern in North-East Germany, approximately 150 km north of Berlin. Main crop types in the area are winter wheat, barley, maize, rape and sugar beet. The DLR (German Aerospace Center) E-SAR system was flown over the Demmin test site more than 14 times between the months of April and July. Weekly in-situ measurements were taken on the ground in selected fields throughout the same period.

In addition to SAR coverage, optical data using the Canadian CASI instrument from ITRES Research and the Spanish AHS from the National Institute for Aerospace Technology (INTA), were acquired during critical phases of the growing season in June and July. The June acquisitions were extended to include a forest and grassland site in the central Netherlands, used by the EU EAGLE project.

In total, over 15 research institutes from Germany, Spain, Italy, Belgium, The Netherlands, Britain, Canada and Denmark participated in the campaign.

Minimize Sensor Complement

Sensor complement: (C-SAR)

C-SAR (C-band SAR instrument):

The C-SAR instrument is designed and developed by EADS Astrium GmbH of Germany. The instrument provides an all-weather, day and night imaging capability to capture measurement data at high and medium resolutions for land, coastal zones and ice observations.

The C-SAR instrument is an active phased array antenna providing fast scanning in elevation (to cover the large range of incidence angle and to support ScanSAR operation) and in azimuth (to allow use of TOPS technique to meet the required image performance). To meet the polarization requirements, it has dual channel transmit and receive modules and H/V-polarised pairs of slotted waveguides.

It has an internal calibration scheme, where transmit signals are routed into the receiver to allow monitoring of amplitude/phase to facilitate high radiometric stability.

Sentinel-1's metalized carbon-fiber-reinforced-plastic radiating waveguides ensure good radiometric stability even though these elements are not covered by the internal calibration scheme. The digital chirp generator and selectable receive filter bandwidths allow efficient use of on-board storage considering the ground range resolution dependence on incidence angle.

The goal of the all-weather imaging capability of the C-SAR instrument is to provide measurement data at high and medium resolutions for land, coastal zones and ice observations in cloudy regions and during night, coupled with radar interferometry capability for detection of small (mm or sub-mm level) ground movements, with the appropriate frequencies and operating modes required to support the Copernicus services. 206) 207) 208) 209) 210) 211) 212) 213) 214) 215) 216) 217) 218) 219)

The Sentinel-1 requirements call for the support of four observation/acquisition modes:

SM (Stripmap mode): 80 km swath with a spatial resolution of 5 m x 5 m

IW (Interferometric Wide swath) mode: 250 km swath, 5 m x 20 m spatial resolution and burst synchronization for interferometry. IW is considered to be the standard mode over land masses.

- satisfies most currently known service requirements

- avoids conflicts and preserves revisit performance

- provides robustness and reliability of service

- simplifies mission planning & decreases operational costs

- satisfies also tomorrow's requests by building up a consistent long-term archive.

The IW mode images three subswaths using TOPSAR (Terrain Observation with Progressive Scans SAR). With the TOPSAR technique, in addition to steering the beam in range as in ScanSAR, the beam is also electronically steered from backward to forward in the azimuth direction for each burst, avoiding scalloping and resulting in a higher quality image. Interferometry is ensured by sufficient overlap of the Doppler spectrum (in the azimuth domain) and the wave number spectrum (in the elevation domain). The TOPSAR technique ensures homogeneous image quality throughout the swath.

EW (Extra Wide Swath) mode: 400 km swath and 25 m x 100 m spatial resolution (3-looks). - Six overlapping swathes have to be foreseen to cover the required access range of 375 km.

WV (Wave mode): low data rate and 5 m x 20 m spatial resolution. Sampled images of 20 km x 20 km at 100 km intervals along the orbit. The Wave mode at VV polarization is the default mode for acquiring data over open ocean. WV mode is acquired at the same bit rate as SM however, due to the small vignettes, single polarization and sensing at 100 km intervals, the data volume is much lower. The table below shows the main characteristics of the Wave mode.

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Figure 146: Alternating WV mode acquisitions (image credit: ESA)

Except for the wave mode, which is a single polarization mode (HH or VV), the SAR instrument has to support operations in dual polarization (HH-HV, VV-VH), requiring the implementation of one transmit chain (switchable to H or V) and two parallel receive chains for H and V polarization. The specific needs of the four different measurement modes with respect to antenna agility require the implementation of an active phased array antenna. For each swath the antenna has to be configured to generate a beam with fixed azimuth and elevation pointing. Appropriate elevation beamforming has to be applied for range ambiguity suppression.

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Figure 147: Overview of the Sentinel-1 C-SAR instrument observation scheme and operational support modes (image credit: ESA)

Center frequency of C-band

5.405 GHz (corresponding to a wavelength of 5.55 cm)

Bandwidth

0-100 MHz (programmable)

Polarization

HH+HV, VV+VH, HH

Incidence angle range

20º-46º

Look direction

right

Antenna type

Slotted waveguide radiators

Antenna size

12.3 m x 0.821 m

Antenna mass

880 kg (representing 40% of the total launch mass)

Azimuth beam width

0.23º

Azimuth beam steering width

-0.9º to +0.9º

Elevation beam width

3.43º

Elevation beam steering range

-13.0º to +12.3º

RF Peak Power (sum of all TRM, at TRM o/p) DC power consumption

- 4.368 kW - 4.075 kW [IW (Interferometric Wide Swath Mode), two polarizations]

Pulse width

5-100 µs (programmable)

Transmit duty cycle

Max 12%, SM 8.5%, IW 9%, EW 5%, WV 0.8%

Receiver noise figure at module input

3 dB

Maximum range bandwidth

100 MHz

PRF (Pulse Repetition Frequency)

1000-3000 Hz (programmable)

Data compression (selectable)

FDBAQ (Flexible Dynamic Block Adaptive Quantization)

ADC sampling frequency

300 MHz (real sampling)

Data quantization

10 bit

Total instrument mass (including antenna)

945 kg

Attitude steering

Zero-Doppler steering and roll steering

Table 15: Key parameters of the C-SAR instrument

The Sentinel 1 mission operational concept foresees the following capabilities and/or services:

• A continuous and systematic acquisition of data to maximize mission return and system exploitation efficiency.

• A complete Earth coverage after each single orbit repeat cycle (175 orbits in 12 days). This dramatically improves the past and current EO systems' capabilities; the system supports up to 25 minutes per orbit for STRIPMAP/TOPSAR operations and up to 75 minutes for WAVE operations per orbit

• The minimum revisit time possible on few selected regions, mainly Maritime Transport over European and North Atlantic zones, European coastal zones. A constellation of two satellites, Sentinel-1A and Sentinel-1B, is deployed on the same orbit with a proper phasing.

• The minimum data/product latency after SAR acquisitions: requirements ask for an on-board data latency from a maximum of two orbits (about 3 hours) down to one orbit for the so-called near-real time data down to simultaneous SAR acquisition and data download to ground for real-time data. Basic products will be available, after data downlink, after a maximum of 24 hours for all data, down to 1 hour for near-real time data, down to 10 minutes for L0 products for real time data.

• The capability to include in the pre-defined mission timeline sporadic and asynchronous user orders submitted to the system following emergency occurrences.

• Repeat-pass TOPSAR interferometric capability: accurate burst synchronization and fine orbit control are specific drivers for this system feature.

Table 16: Overview of the Sentinel-1 operational concept (Ref. 15)

 

Introduction of a new SAR imaging mode (new observation technology):

The IW (Interferometric Wide swath) mode is being implemented with a new type of ScanSAR mode called TOPS (Terrain Observation with Progressive Scan) SAR operations support mode (note: the terms TOPS and SAR is simply contracted to TOPSAR). TOPSAR is an ESA-proposed acquisition mode (Francesco De Zan and Andrea Monti Guarnieri) for wide swath imaging which aims at reducing the drawbacks of the ScanSAR mode. The basic principle of TOPSAR is the shrinking of the azimuth antenna pattern (along-track direction) as seen by a spot target on ground. This is obtained by steering the antenna in the opposite direction as for Spotlight support. The TOPSAR signal includes particularities of both ScanSAR and Spotlights modes, but existing processing algorithms do not provide an efficient processing of TOPSAR data. - The EW (Extra Wide swath) mode is also implemented with the TOPS capability (Table 17).

The TOPSAR mode is intended to replace the conventional ScanSAR mode. The technique aims at achieving the same coverage and resolution as ScanSAR, but with a nearly uniform SNR (Signal-to-Noise Ratio) and DTAR (Distributed Target Ambiguity Ratio). 220) 221) 222)

The TOPSAR mode will be implemented on the Sentinel-1 mission due to the performance advantages compared to ScanSAR. The TOPSAR technique has already been demonstrated on the TerraSAR-X spacecraft during its commissioning phase (fall 2007) and showed very promising results. The measured values of the intensity variation of the analyzed images corresponded very well with the expected theoretical values. Scalloping in the TOPSAR image is 0.3 dB against 1.2 dB in the ScanSAR image. Additionally, fewer bursts are required in TOPSAR, which also positively affects the image quality. 223) 224) 225) 226) 227) 228)

TOPS is employing a rotation of the antenna in the azimuth direction as is shown in Figure 148. Like in ScanSAR, several subswaths are acquired quasi simultaneously by subswath switching from burst to burst. The increased swath coverage is as in ScanSAR achieved by a reduced azimuth resolution. However, in TOPS the resolution reduction is obtained by shrinking virtually the effective antenna footprint to an on-ground target, rather than slicing the antenna pattern, as it happens for ScanSAR. 229)

Concerning the implementation of TOPS InSAR, the Sentinel-1 C-SAR system is designed to enable TOPS burst synchronization of repeat-pass datatakes supporting the generation of TOPS interferograms and coherence maps. Specifically, for the IW and EW modes the TOPS burst duration is 0.82 s and 0.54 s (worst case), respectively, with a requirement for achieving a synchronization of less than 5 ms between corresponding bursts (Ref. 237).

Furthermore, a critical issue for TOPS InSAR performance is the accuracy that is required for TOPS image co-registration. A small co-registration error in azimuth can introduce an azimuth phase ramp due to the SAR antenna azimuth beam sweeping causing Doppler centroid frequency variations of 5.5 kHz.

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Figure 148: Sketch of the TOPSAR acquisition geometry. TB is the burst duration and ω r is the steering angle rate (image credit: DLR)

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Figure 149: Alternate view of the TOPSAR subswath acquisition (image credit: ESA)

The TOPS demonstration, conducted for ESA in 2007 with TerraSAR-X data, was conducted with the ETT (Experimental TerraSAR-X TOPS) processor; the test was based on sub-aperture processing, the Extended Chirp scaling algorithm and BAS (Baseband Azimuth Scaling). - The SPT (Sentinel-1 Prototype TOPS) processor is based on a pre-processing stage to unfold the azimuth spectrum, a standard ω-k focusing block and an azimuth one-dimensional ‘unfolding' processing block. It is an extension of the standard ω-k based ScanSAR processor developed for the Envisat ASAR instrument (Ref. 229).

Comparison of both processors: The comparison of the SPT (Sentinel-1 Prototype TOPS) processor with the ETT (Experimental TerraSAR-X TOPS) processor turned out to be a complex task. The results are confirming both processing approaches mutually.

 

TOPS implementation on RADARSAT-2: The objective of simulating Sentinel-1 TOPS mode image data products using RADARSAT-2 is to support the implementation of the TOPS mode, specifically the Interferometric Wide swath (IW) mode, on ESA's Sentinel-1 mission. The use of real C-band RADARSAT-2 TOPS image data enables the preparation for the Sentinel-1 exploitation phase (i.e. GMES Initial Operations (GIO)). In particular, the provision of Sentinel-1 like TOPS image products to operational Copernicus/GMES services and other users will help the user community to prepare and verify their SAR data post-processing chains including ingestion tools etc., prior to the launch of Sentinel-1A. 230) 231)

The Canadian RADARSAT-2 mission operates at the same C-band frequency (5.405 GHz) as the Sentinel-1 mission. The RADARSAT-2 SAR instrument with its phased array antenna has multiple SAR imaging modes, including ScanSAR modes, as well as it has quad-polarization and repeat-pass SAR Interferometry (InSAR) capabilities. The RADARSAT-2 mission has been implemented as a public-private partnership between the Government of Canada and MDA (MacDonald, Dettwiler and Associates Ltd.), whereby MDA has the commercial data rights.

The design and implementation of the experimental TOPS mode on RADARSAT-2 resembles as closely as possible the performance characteristics of the Sentinel-1 IW mode, within the constraints imposed by the design and implementation of RADARSAT-2. The RADARSAT-2 TOPS image data sets have been processed to Level 1 SLC (Single Look Complex) data with the Sentinel-1 Image Processing Facility (IPF) and are provided in the official Sentinel-1 Level (SLC) product format.

The experimental RADARSAT-2 TOPS mode is referred to as PSNB (Progressive ScanSAR Narrow B). It is based on the existing RADARSAT-2 SCNB (ScanSAR Narrow B) mode. This mode uses 3 sub-swaths, like the Sentinel-1 IW mode, and covers a comparable range of incidence angles.

 

Instrument description:

The Sentinel-1 satellites carry a single payload consisting of a C-band Synthetic Aperture Radar (SAR) instrument. The instrument is composed of two major subsystems:

SES (SAR Electronics Subsystem)

SAS (SAR Antenna Subsystem).

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Figure 150: The block diagram of C-SAR (image credit: EADS Astrium, ESA)

The radar signal is generated at baseband by the chirp generator and up-converted to C-band within the SES. This signal is distributed to the HPA (High Power Amplifiers) inside the EFE (Electronic Front End) Transmit/Receive Modules (TRMs) via the beam forming network of the SAS. Signal radiation and echo reception are performed with the same antenna using slotted waveguide radiators. When receiving, the echo signal is amplified by the low noise amplifiers inside the TRM and summed up using the same network as for transmit signal distribution. After filtering and down conversion to baseband inside the SES (SAR Electronics Subsystem), the echo signal is digitized and formatted for recording. 232) 233) 234)

The key design aspects of the C-SAR instrumentation can be summarized as follows:

• Active phased array antenna providing fast scanning in elevation (to cover the large range of incidence angle and to support ScanSAR operation) and in azimuth (to allow use of the TOPS technique to meet the required image performance)

• Dual channel TRM (Transmit & Receive Modules) and H/V-polarized pairs of slotted waveguides (to meet the polarization requirements)

• Internal Calibration scheme, where transmit signals are routed into the receiver to allow monitoring of amplitude/phase to facilitate high radiometric stability

• Metalized CFRP (Carbon Fiber Reinforced Plastic) radiating waveguides to ensure good radiometric stability even though these elements are not covered by the internal calibration scheme

• Digital chirp generator and selectable receive filter bandwidths to allow efficient use of on board storage considering the ground range resolution dependence on incidence angle

• FDBAQ (Flexible Dynamic Block Adaptive Quantization) to allow efficient use of on-board storage and minimize downlink times with negligible impact on image noise.

 

SES (SAR Electronics Subsystem)

The SES forms the core of the radar instrument connecting the SAS for transmission of Tx pulses and receiving of backscattered pulses from ground targets. The SES provides all radar control, IF/RF signal generation and receive data handling functions comprising: 235)

- radar command and control, timing control, and redundancy control

- transmit chirp generation, frequency generation, up-conversion/down-conversion, modulation/demodulation and filtering

- digitization, data compression and formatting.

A digital chirp generator and selectable receive filter bandwidths allow an efficient use of on board storage capacity considering the ground range resolution dependence on the incidence angle. The radar signal is generated at base band by the chirp generator and up-converted to C-band within the SES. This signal is distributed to the high-power amplifiers inside the EFE TRMs via the beam-forming network of the SAS. Signal radiation and echo reception are performed with the same antenna using slotted waveguide radiators. When receiving, the echo signal is amplified by the low noise amplifiers inside the EFE TRMs and summed up using the same network as for transmit signal distribution. After filtering and down-conversion to base band inside the SES, the echo signal is digitized and formatted for recording. Flexible dynamic block adaptive quantization allows the efficient use of on-board storage and to minimize downlink times with negligible impacts on image noise.

The SES hardware comprises the following units:

• ICE (Integrated Central Electronics) unit

• MDFE (Mission Dependent Filter Equipment)

• TGU (Transmit Gain Unit)

The ICE unit is the principal module of the SES providing the radar with its core functionality, control and monitoring. The subsystem uses a fully digital design approach for both the derivation of the C-band chirped radar signal and the digital receiver which samples the echo signal at an IF close to base band. The ICE maintains and manages a database of operational parameters such as transmit pulse and beam characteristics for each swath of each mode, and timing characteristics like pulse repetition frequencies and window timings. The MDFE is passive, providing a set of RF filters for the Tx path (to control out-of-band transmissions) and for the Rx path (to limit out-of-band interference). The TGU provides the final RF amplification of the Tx pulse signal before sending it to the SAS. The TGU receives its own dedicated primary power supply from the platform. Switching the TGU on and off is performed by the ICE.

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Figure 151: Photo of the SES device (image credit: EADS Astrium Ltd.)

To augment this design and provide mission variable compatibility, the SES also includes mission dependent units that comprise amplification and filtering to provide an ideal signal level and match to the antenna subsystem to be supported.

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Figure 152: SES context diagram (image credit: EADS Astrium Ltd)

The SES configuration is implemented as a fully cold redundant pair of chains. The TGU being common to both chains only in as much as the two amplifier chains are mounted in a single physical equipment unit before the paths do combine within a passive hybrid device which in turn permits dual outputs to the antenna supplying both fore and aft antenna segments.

The ICE (Integrated Central Electronics) unit is the principal module of SES consisting in turn of highly-integrated modules (Figure 154). ICE is being produced at Astrium UK (Portsmouth). This equipment provides the radar with its core functionality, control and monitoring. The subsystem uses a fully digital design approach for both the derivation of the (up to 100 MHz) C-band chirped radar signal and the digital receiver which samples the echo signal at an IF close to baseband. With single up-conversion and down-conversion stages and data processing using efficient digital filtering and data compression algorithms it is anticipated that this equipment will provide a highly stable core electronics base for this new exciting Copernicus utility. 236)

The Astrium UK ICE design is aimed at providing not only a solution for the Sentinel-1 system but also aims to provide a modern solution for the complex electronics at the heart of radars and particularly that of a SAR. The architecture is designed for adaptability using the inherent flexibility of the digital approach. It is therefore able to adapt easily to the needs of different missions.

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Figure 153: Configuration of SES (image credit: EADS Astrium Ltd.)

The ICE modular design makes use of the integrated RF and digital design technologies now commonly available. High speed ADC (Analog Digital Converter)) and DAC (Digital Analog Converter) components along with flexible design of digital processing through the use of large scale FPGAs and dedicated ASICs, as well as the use of MMIC (Modular Microwave Integrated Circuitry) has allowed the design to respond to the demands of the Sentinel-1 mission.

The design of ICE is comprised of the following elements:

• ICM (Instrument control Module): A Leon ll processor based module, developed by Syderal of Switzerland with:

- PROM for boot software and EEPROM for the application software and the radar characterization database

- Multiple interface formats allowing 1553B communication with the platform, SpaceWire for the internal modules (using the Atmel AT7910/SpW_10X SpaceWire Router ASIC) and CAN for external equipments TGU and SAS.

• Ty module: This RUAG designed and built module uses a direct digital synthesis chirp generation method at an IF of 150 MHz, with up-conversion in a single stage to the nominal 5.405 GHz center frequency to deliver the radars a fully programmable chirp transmission chain. This requires only a further amplification stage provided by the externally provided DAD designed TGU (Transmit Gain Unit) to drive the SAS (SAR Antenna Subsystem).

• Rx modules: The dual polarization approach required by the C-SAR instrument necessitates a pair of matched receive modules to be implemented within the ICE. The receive path is band filtered externally to the ICE by a MDFE (Mission Dependent Filter Equipment) provided by DAD of Finland prior to its input to the ICE Rx modules Here the signal is down-converted directly to an IF of 75 MHz before being digitized in the ADC which sample's at approx 300 Msamples. This in turn feeds the digital processing chain of a decimation filter followed by, compression and packetization stages before the output is piped to the on board mass memory via a Wizard link interface in a standard CCSDS format at 640 Mbit/s.

• TCM (Timing Control Module): TCM represents the timeline control element for the system. Implementing ECC program driven FPGA logic to provide the necessary timing waveforms required to define and control the within pulse precise timing relationships of all the required timing signals used by the instrument. These timing pulses and the PRI rate communication bus to the antenna are the means whereby the radar establishes the autonomous complex timeline of each mode acquisition with the absolute repeatability required to provide the synthetic aperture quality and the Interferometric property of the system data output.

• PCM (Power Control Modules): These modules are implemented so as to reduce the individual module voltage conversion effort and to reduce the power losses. These modules use modular common DC/DC converters designed by BLU Electronics to provide 3 voltage rails to all internal ICMs. However, It is to be noted that point of load regulation at module level is still expected for more user specific voltages.

• FDM (Frequency Distribution Module) and USO (Ultra Stable Clock): Using FOAMO (Foam Insulated Master Oscillator) of Astrium as the master clock, the FDM generates the timing reference frequencies used by all other signal modules in ICE. To maintain the highest level of phase stability, this unit also takes in the Tx LO (Local Oscillator) and creates from this the offset Rx down convertor LO for both Rx module channels.

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Figure 154: Block diagram of SES (only one of two redundancy chains is shown), image credit: EADS Astrium

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Figure 155: Illustration of the modular configuration of ICE (image credit: EADS Astrium Ltd.)

The ICE equipment has a mass of 20.6 kg. The modules have been selected to be integrated into an equipment enclosure with a backplane wiring loom rather than a fixed motherboard interface plate. This approach allows greater flexibility for test and diagnosis as well as a mechanical flexibility that offers a simpler solution to the thermal challenges of the mission.

The low internal interface count which also allows this open loom approach is in part due to the use of the SpaceWire interconnect for control which has been implemented on the front face of the unit. This being so implemented to facilitate an ESA objective for the ICM module development aimed at further mission systems (Ref. 236).

 

Roll steering mode (Ref: 211): The roll steering mode of the spacecraft provides a continuous roll maneuver around orbit (similar to yaw steering in azimuth) compensating for the altitude variation such that it allows usage of a continuous PRF (Pulse Repetition Frequency) and a minimal number of different sample window lengths (SWLs) around the orbit. In addition, the update rate of the sampling window position around orbit is minimized (< 1 /2.5 min), which simplifies instrument operations significantly. Since the instrument can work with a single fixed beam for each swath/sub-swath over the complete orbit, also the number of elevation beams is minimized. The roll steering rate has been fixed to 1.6º/27 km altitude variation. The roll applied to the sensor attitude depends linearly on altitude and varies within the interval -0.8º (minimum sensor altitude) to 0.8º (maximum sensor altitude).

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Figure 156: Variation of the roll angle along the orbit (image credit: ESA, TAS)

The attitude steering mode introduces an additional roll angle as a function of latitude to compensate changes in the satellite's altitude around the orbit, hence maintaining a specific, quasi "constant", slant range for each SAR imaging mode. This enables the use of a single PRF per swath or subswath around the orbit, except for SM-5 (i.e. different PRF for SM-5N and SM-5S), and a fixed set of constant elevation antenna beam patterns. 237) 238)

Figure 157 illustrates that for the minimum orbital height (693 km) the mechanical SAR antenna off-nadir angle is more shallow (30.25º) than it is for the maximum orbital height (726 km). In the latter case, the mechanical SAR antenna off-nadir angle is 28.65º.

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Figure 157: Schematic view of the Sentinel-1 roll-steering mode (image credit: ESA)

 

SAS (SAR Antenna Subsystem):

SAS represents the sensor part of the C-SAR instrument and is an active phased array system with Tx and Rx gain and phase control distributed over the antenna area. These functions are provided by so called Transmit Receive Modules (TRMs) as part of the EFE (Electronic Frontend End) assemblies. The SAS is capable of performing rapid electronic beam steering, beam shaping, and also polarization selection. The dual polarized antenna allows at one time either transmission in one single, but selectable polarization (H or V) or simultaneous reception of both H and V polarization. 239) 240)

The SAS consists of 14 identical tiles (12.3 m x 0.84 m) in 5 deployable panels as shown in Figure 158. The electrical functions of the SAS comprise:

- signal radiation and reception

- distributed transmit signal high power amplification

- distributed receive signal low noise amplification with LNA protection

- signal and power distribution (corporate feed, power converter)

- phase and amplitude control including temperature compensation

- internal calibration loop

- deployment mechanisms, including hold down and release

- antenna mechanical structure.

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Figure 158: C-SAR antenna in deployed and stowed configuration on the PRIMA bus (image credit: Astrium GmbH)

The instrument is based on a deployable planar phased array antenna carrying TRMs allowing for horizontal and vertical polarizations. The dual polarized antenna allows either transmission in one single but selectable polarization (H or V) or, simultaneous reception of both H and V polarization, at any time. The C-SAR antenna comprises two wings, stowed on the platform's lateral panels during launch, which are deployed once in orbit. Each antenna wing consists of two antenna panels. An antenna panel consists in principle, of a panel frame and a number of antenna tiles. The SAS central panel comprises two antenna tiles, whereas the wing panels comprise three antenna tiles each. The complete antenna is symmetrical around the middle of the central panel.

The active phased array antenna is capable of performing rapid electronic beam steering, beam shaping and polarization selection, providing fast scanning in elevation and azimuth to cover the large range of incidence angles and to meet the image quality requirements for the TOPSAR mode. TRMs are arranged across the antenna such that, by adjusting the gain and phase of individual modules, the transmit and receive beams may be steered and shaped.

The SAS consists of 14 tiles with 20 dual-polarized sub-arrays on each tile. Each subarray is a dual-polarized unit with two parallel slotted resonant waveguides. The vertical polarization is excited by offset longitudinal slots in a ridge waveguide, while the horizontal polarization is generated by transverse narrow wall slots excited by inserted tilted wires.

A SAS tile is composed of 10 'Waveguide 4' assemblies (two vertically and two horizontally polarized waveguides), which form the smallest building block in the tile manufacturing. Each 'Waveguide 4'-assembly is exposed to a kind of RF-incoming / diagnostic inspection consisting of a passive return loss measurement followed by a measurement of the far-field azimuth pattern in a special anechoic test environment at Astrium GmbH.

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Figure 159: Photo of the SAS tile (20 HP+20 VP subarrays), image credit: EADS Astrium GmbH

Legend to Figure 159: The instrument comprises three RF networks: Tx network, RxH (H polarization) network and RxV (V polarization) network. During radar operation the Tx network carries the transmit RF signal and the RxH/RxV networks carry the echo signals. The dual polarized antenna allows transmission in one single but selectable polarization (H or V) and simultaneous reception of both H and V polarization.

The tile (size: ~ 0.87 m x 0.84 m) forms the smallest functional entity of the SAS, encompassing all functions necessary to ensure beam shaping / beam steering of the active phased array antenna. The SAS Tile is composed of 10 'Waveguide 4' assemblies and the associated electronics, namely:

- The RF Distribution Network

- 40 Transmit/Receive Modules (20 TRMs for HP & 20 TRMs for VP / supplier: Thales Alenia Space, Italy)

- 2 Tile Controller Units (TCUs)

- 2 Tile Power Supply Units (TPSUs)

allowing signal radiation and reception, distributed transmit signal high power amplification, distributed receive signal low noise amplification with LNA protection, signal and power distribution, phase and amplitude control including temperature compensation and internal calibration.

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Figure 160: The SAS tile configuration scheme of the SAR antenna (image credit: EADS Astrium)

The CFRP (Carbon Fiber Reinforced Plastic) waveguide radiator is along with the cross stiffeners the major structural element of a tile. All electronic boxes are either placed onto the rear side of the radiators (e.g. the EFEs) or attached to the inner side of the cross stiffeners (e.g. TCU and TPSU). The low loss CFRP slotted waveguides radiators together with the high performance EFE TRMs ensure to meet the stringent sensitivity requirement of -22 dB. The optimized sizing of the overall SAR antenna and its waveguide radiators ensure further that also the ambitious 2D distributed target ambiguity requirement (DTAR) of -22 dB can be met.

EFE is the main transmitting/receiving section of the Sentinel-1 antenna while 195 EFE are necessary to assure the full functionality of the SAR instrument. Each EFE has been optimized for the best trade-off between integration level and RF performances and is composed of four main sections: Power Supply card, Digital card, RF distribution section and the TRM section.

The EFE is composed of four main sections: Digital card, Power Supply card, RF distribution and the TRM (T/R Module) section. A functional scheme of the EFE architecture is shown in Figures 161 and 162.

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Figure 161: Illustration of the EFE architecture (image credit: TAS-I)

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Figure 162: Illustration of the EFE prototype (image credit: TAS-I)

The RF networks provide the EFEs with the Tx pulses, and collect the H and the V polarized echoes. On the tile, these networks form the EPDN (Elevation Plane Distribution Network) which is placed on top of the EFEs (Figure 160). Each network (Tx, RxH, RxV) of the EPDN consists of a 1:10 divider to supply the 10 EFEs. Short cables connect the outputs of the 1:10 dividers to the EFEs.

Operational mode

Polarization

Swath width

Single Look Resolution (range x azimuth)

Access Angles

Stripmap (SM)

HH-HV or VV-VH

> 80 km

5 m x 5 m

20º-45º

Interferometric Wide Swath (IWS)

HH-HV or VV-VH

> 250 km

5 m x 20 m

> 25º

Extra Wide Swath (EWS)

HH-HV or VV-VH

> 400 km

25 m x 40 m

> 20º

Wave mode (WM)

HH (23º) or VV (36.5º)

20 km x 20 km (vignettes at 100 km intervals)

5 m x 5 m

23º and 36.5º

For all modes

Radiometric accuracy (3σ)

1 dB

NESZ (Noise Equivalent Sigma Zero)

-22 dB

Point Target Ambiguity Ratio

-25 dB

DTAR (Distributed Target Ambiguity Ratio)

-22 dB

Table 17: Performance parameters of the C-SAR instrument in the various operational modes 241)

The EFE comprises several TRMs (Transmit/Receive Modules) and associated electronics. It represents the active part of the RF equipment of the antenna. The basic function of each EFE is:

• to transmit Tx pulses in one of two polarizations (either H or V) to the corresponding two radiator elements

• to receive the echoes from the two H and the two V radiator elements independently and simultaneously.

The EFE provides the capability to perform antenna beam steering and forming by electronic means:

• control phase setting in transmit

• control phase and gain settings in receive.

 

C-SAR instrument calibration:

In contrast to SAR systems already existing in C-band like ASAR/ENVISAT or RADARSAT-2, high demands on the radiometric accuracy are made for C-SAR on Sentinel-1. Thus, product quality is of paramount importance and the success or failure of the mission depends essentially on the method of calibrating the entire Sentinel-1 system in an efficient way. 242) 243) 244) 245) 246) 247)

The most important point with respect to the calibration of this flexible SAR system is the tight performance with an absolute radiometric accuracy of only 1 dB (3σ) in all operation modes. Never before has such a strong requirement (a few tenths of dB) been defined for a SAR system. - With respect to the duration of the Sentinel-1 commissioning phase of three months only, the number of passes and the selection of test sites have to be optimized versus cost and time effort. e.g. calibrating several beams and polarization modes with the same test site. The calibration strategy of Sentinel-1 is based on the experience derived from TerraSAR-X.

Calibration is the process of quantitatively defining the system response to known controlled signal inputs. Calibration tasks are executed throughout the mission to ensure the normalized radar cross-section and the phase of the individual pixels are provided with stability and accuracy. Calibration of the entire SENTINEL-1 system is critical to guaranteeing product quality for operational demands. The SAR system must perform within an absolute radiometric accuracy of only 1 dB in all operation modes. This is a higher radiometric accuracy than any other SAR mission before it.

Calibration can be divided into two forms:

Internal calibration: Internal calibration provides an assessment of radar performance using internally generated calibrated signal sources, in particular from pre-flight testing.

External calibration: External calibration makes use of ground targets of known backscatter coefficients to render an end-to-end calibration of the SAR system.

In addition to the commissioning of Sentinel-1B executed by ESA, an independent SAR system calibration will be performed by DLR. For this purpose, the complete calibration chain was developed and established by DLR, starting with an efficient calibration strategy, a detailed in-orbit calibration plan, the SW-tools for analyzing and evaluating all the measurements up to the calibration targets serving as accurate reference. 248)

 

Internal Calibration

Internal calibration uses calibration signals which are routed as closely as possible along the nominal signal path. The calibration signals experience the same gain and phase variations as the nominal measurement signals. The ground processing then evaluates the calibration signals to identify gain and phase changes and correct the acquired images accordingly.

Transmit power, receiver gain and antenna gain are subject to instrument noise due to temperature changes or other effects over time. Internal calibration provides corrections for changes in the transmit power and the electronics gain as well as validating the antenna model. The resulting calibration data are used in ground processing to correct image data.

Internal calibration also covers the signal phase. The overall phase of the echo signal depends on two major elements: measurement geometry and instrument internal phase stability. As the hardware cannot generally provide the required phase stability, it is a task of the internal calibration scheme to cover the internal phase variations by adequate measurements. All internal calibration measurements, either for gain or for phase, are used in ground processing to correct data products and achieve the required stability.

Internal calibration uses a PCC (Pulse-Coded Calibration) technique to embed a unique pulse code on a signal such that it can be identified and measured when embedded in other signals. This allows the amplitude and phase of individual signal paths to be measured while operating the complete antenna. The PCC technique is implemented by sending a series of coherent calibration pulses in parallel through the desired signal paths. The individual successive signals are multiplied by factors of +1 or -1. Factor -1 is implemented by adding a phase shift of 180°, while factor +1 means no additional phase. Each path is identified by a unique sequence.

The PCC technique can be applied if:

- the receiver detects the signals coherently

- the whole sequence is executed in a sufficiently short time such that the parameters to be measured are stationary

- the system is linear with respect to the individual signals.

The PCC technique can measure the signal paths via individual Transmit (TX) /Receive (RX) Modules (TRMs) or via groups of TRMs (either TX or RX paths, either polarization).

The average properties of rows or columns of TRMs can be measured by a short PCC sequence. The length of a PCC sequence is always a power of two. There are 20 rows of waveguides, therefore the PCC sequence has a minimum of 32 pulses. Although the 14 columns (14 tiles) could be measured by a PCC sequence of 16 pulses, it is assumed that a sequence length of 32 pulses is also used. All 20 rows are operated together, meaning the antenna is in a full operational state. The overall signal from all rows is received, digitized and packed into calibration packets. These packets are evaluated (on the ground) to determine the properties of the individual rows. The approach for measuring the average azimuth excitation coefficient is similar to the elevation pattern, using columns of TRMs instead of rows.

The PCC-32 measurements described above need approximately 129 pulses. Additional warm-up pulses may also be needed. Such a large number of calibration pulses represent a significant interruption in image generation when operated within the image acquisition of the stripmap mode. For intermediate calibration pulses in stripmap mode, and also for calibration pulses related to each sub-swath measurement in the ScanSAR modes, a shorter sequence is needed. The shortest possible PCC sequence is based on two measurements, however this procedure introduces PCC-inherent error contributions. These latter errors are to be expected, although they are significantly smaller than those due to leakage signals.

For the antenna model, the reference patterns of all beams are derived for radiometric correction of the SAR data. The active antenna of the SAR instrument allows a multitude of different antenna beams with their associated gain patterns. All these patterns are described by the mathematical antenna model which provides the antenna patterns as functions of the commanded amplitudes and phases within the front end EFEs and within the tile amplifiers. The quality of the patterns is ensured by the on-board temperature compensation controlled by the tile control units. The internal calibration signals measure the actual phases and amplitudes and allow verifying the correct function and performance of all included elements. The antenna model is established on-ground, based on pattern tests at various integration levels up to the complete antenna.

RF Characterization Mode:

The RF characterization mode is a self-standing mode and is not associated with the individual imaging data-takes. It is operated at least once per day during a convenient point within the long duration of wave mode.

The RF characterization mode verifies in-flight the correct function and characteristics of the individual TRMs. Operating it two or more times at different temperatures during the cool-down phases between the high dissipating imaging modes can provide in-orbit characterization versus temperature where necessary. The RF characterization mode performs measurements with internal signals and is designed to achieve a number of goals. The RF calibration mode will:

- cover all those measurements needed in-orbit but which are not required for each individual data-take

- provide data sets to assess the instrument health and performance as far as possible

- verify the correct function of the individual TRMs, both within the front-end and the tile amplifiers

- verify the excitation coefficients for the TX and RX patterns to ensure the validity of the antenna model.

This mode is based on the same measurement types as the internal calibration. The mode has to address the individual TRMs while operating the full antenna in representative thermal conditions and with nominal power consumption. This can be achieved using the PCC technique. As a standalone mode, it is not forced to use the signal parameters of a dedicated imaging mode, but instead an optimized set of parameters can be used. The calibration mode is to be operated for both TX polarizations. The receiver will measure both polarizations in any case.

Sentinel1_Auto13

Figure 163: In-orbit calibration plan for Sentinel-1 versus 12 days repeat cycles (image credit: (image credit: DLR, Ref. 243)

 

External Calibration

External calibration derives the calibration constant by measurement of corner reflector targets and homogeneous areas such as rainforest with exactly known backscatter coefficients. This is necessary as it will not generally be possible to know all parameters with sufficient accuracy prior to the in-flight measurements.

Sentinel1_Auto12

Figure 164: In-orbit external calibration (image credit: ESA)

External calibration comprises five steps as shown below.

1) Radiometric Calibration: Radiometric calibration is applied to correct for the bias of SAR data products. The required absolute calibration factor is derived by measuring the SAR system against reference point targets with well-known radar cross section. Due to the high demand on the radiometric accuracy of 1 dB (3&#963;) in all four operational modes, it is recommended to measure at least one beam of each mode against the SENTINEL-1 transponders deployed at different locations. Each selected beam will be measured during two passes (ascending and descending). Furthermore, two receive polarization combinations per operation mode are to be measured simultaneously. By measuring SENTINEL-1 against the three transponders for selected beams, the radiometric calibration can be performed within a limited number of repeat cycles. The absolute calibration factor of all other beams is then derived by applying the antenna model.

2) Antenna Model Verification: Antenna model verification ensures the provision of precise reference patterns of all operation modes and the gain offset between different beams. Verification of the antenna model is performed for selected beams, at least one with low, one with mid- and one with high incidence angle, all with the same polarization condition. In addition, some of the beams are selected for measuring the second polarization condition. Assuming acquisitions for each of the selected beams, using the receiver mode of the transponders and by using acquisitions over rainforest, antenna model verification can be performed within a few cycles.

3) Geometric Calibration: Geometric calibration is applied to assign the SAR data to the geographic location on the Earth's surface. Using well surveyed reference targets, the internal delay of the instrument and systematic azimuth shifts can be derived. For this purpose the acquired scenes are measured simultaneously against point targets deployed and precisely surveyed.

4) Antenna Pointing Determination: Antenna pointing determination is performed to achieve correct beam pointing of the antenna. The determination of the antenna pointing by the receiver mode of the transponders is performed using notch patterns in azimuth with different incidence angles (near, mid- and far). Using three transponders with a receiver function within one cycle (two passes) sufficient measurements can be acquired to derive the required accuracy. The appropriate antenna pattern is measured across the rainforest and using ground receivers.

5) Inter-Channel Phase Calibration: As the signal travels through different receive channels for H and V polarization, it may experience different gains, phase offsets and even different time delays. Inter-channel phase accuracy is calibrated using the SENTINEL-1 transponders that return the signal with H and V polarization components, and which therefore allow a direct phase comparison between H and V channels. The antenna model to be derived on the ground describes the antenna patterns with high accuracy. This antenna model is verified for a limited set of elevation beams via measurements over a homogeneous target, i.e. over rainforest. The azimuth beams will be measured using the receiver function of the SENTINEL-1 transponder.

 

Independent calibration verification:

In addition to the commissioning of Sentinel-1A executed by ESA, an independent verification of the system calibration will be executed for the first time by an external institution. For this purpose, the complete calibration chain was developed and established by DLR, starting with an efficient calibration concept, a detailed in-orbit calibration plan, the SW-tools for analyzing and evaluating all the measurements up to the calibration targets serving as accurate reference. 249)

DLR calibration facility: The Sentinel-1 calibration strategy requires a facility that is well-equipped with ground calibration hardware as well as software tools for analyzing and evaluating all the measurements. For this purpose, DLR/MRI (Microwave and Radar Institute) has been developed and established the following reliable and accurate ground equipment:

• Accurate and remote controlled ground targets like the DLR's novel corner reflectors as depicted in Figure 165 and the novel transponders as depicted in Figure 166, precisely surveyed for geometric and radiometric calibration. Using the receiver unit of the transponder, the pointing and the pattern of the antenna in azimuth direction can be measured during an overflight.

Sentinel1_Auto11

Figure 165: DLR's novel corner reflector which is remote controlled (image credit: DLR)

Sentinel1_Auto10

Figure 166: DLR's novel transponder, designed and developed for Sentinel-1A (image credit: DLR)

• Different analysis and evaluation tools have been modified w.r.t. the Sentinel-1A characteristics, like:

- Internal Calibration Module for analyzing the stability of the instrument and deriving several instrument offsets like the channel imbalance.

- Antenna Characterization Module for deriving the actual pointing of Sentinel-1A and verifying the antenna model in-flight

- CALIX, a software tool for point target analysis and deriving the absolute calibration factor. Furthermore by geometric analysis of accurately surveyed targets the internal delay of the instrument and the dating of the SAR data can be determined.

- TAXI, the Institute's experimental TanDEM-X interferometric processor, which will be used for interferometric analysis and for phase analysis of the TOPS mode of Sentinel-1A.

Test site selection: The next important point is concerned with the coverage of Sentinel-1A, because the coverage defines the number of visible measurements across a test site and drives consequently the schedule. Considering all aspects described before, the coverage of Sentinel-1A across the DLR calibration field in South Germany has been investigated for all beams being selected for in-flight measurements, as depicted in Figure 167 by the blue hatched swathes. The red framed area indicates a region covering all beams. Hence, deploying the transponders within this area, reference targets are available providing simultaneously a point target for both polarization channels of Sentinel-1A. The position of the corner reflectors is mainly driven by the edges of the swaths and the small vignettes of the wave mode (indicated by the black framed boxes).

Sentinel1_AutoF

Figure 167: Coverage of Sentinel-1A for all beams being selected for in-flight measurements (SM1, SM2, IW1, EW3, IW3, SM5, WV1) across the DLR calibration field deployed in South Germany (image credit: DLR)

Hence, the test site shown in Figure 167, composed of three transponders and three corner reflectors, enclosing an area of about 85 km x 20 km, is sufficient to cope with the tight requirements of commissioning Sentinel-1A, i.e all measurements required for calibrating the whole Sentinel-1A system can be performed within the commissioning phase of three months.

 


 

Copernicus Program Ground Segment

The ground segment is composed of the CGS (Core Ground Segment), the" Collaborative Ground Segment" and the Copernicus contributing missions' ground segments.

The Core ground segment monitors and controls the Sentinels spacecraft, ensures the measurement data acquisition, processing, archiving and dissemination to the final users. In addition, it is responsible for performing conflict-free mission planning according to a predefined operational scenario, and it ensures the quality of the data products and the performance of the space borne sensors by continuous monitoring, calibration and validation activities, guaranteeing the overall performance of the mission. 250)

Sentinel1_AutoE

Figure 168: Copernicus Ground Segment Architecture (image credit: ESA)

The Copernicus Ground Segment is complemented by the Sentinel Collaborative Ground Segment, which was introduced with the aim of exploiting the Sentinel missions even further. This entails additional elements for specialized solutions in different technological areas such as data acquisition, complementary production and dissemination, innovative tools and applications, and complementary support to calibration & validation activities.

For Copernicus operations, ESA has defined the concept and architecture for the Copernicus Core ground segment, consisting of a FOS (Flight Operations System) and a PDGS (Payload Data Ground Segment). Whereas the flight operations and the mission control of Sentinel-1 and -2 is performed by ESOC (ESA's European Space Operations Center in Darmstadt, Germany), the operations of Sentinel-3 and the Sentinel-4/-5 attached payloads to meteorological satellites is performed by EUMETSAT.

The EC (European Commission), supported by its agencies, is in charge to implement the Copernicus Services. The Commission is defined to be the owner and financing organization of Copernicus. The technical implementation is granted to other European organizations, namely ESA, EUMETSAT, EEA (European Environment Agency), ECMWF (European Centre for Medium-Range Weather Forecasts) and others. - Complemented by ESA programs and national contributions, ESA has the responsibility to build and operate a dedicated space segment (Sentinels) and the ground segment of Copernicus. 251)

The EC has also defined an overall Copernicus data policy, declaring the Sentinel mission data free and open. 252) This decision is reflecting the experience made with similar missions in the US (e.g. Landsat) and the new possibilities of the Internet. It will stimulate the use of Earth observation data, but also may challenge commercial suppliers, selling data similar to those of the Sentinels. The Copernicus data policy is also based on the European INSPIRE (Infrastructure for Spatial Information in the European Community) directive, which harmonizes the policy and electronic access to geographic information within Europe.

The majority of the Earth observation data for these services will come from a fleet of dedicated Copernicus satellites: the Sentinels. The features of the Copernicus Sentinel missions are depicted in Table 18. The series of satellites guarantees continuity of the ERS/ENVISAT missions and adds further features and parameters. Moreover, always two Sentinels of each series should be in orbit at any time, increasing the coverage for many applications. Applications and services will also benefit from a supply from other European national and commercial GMES Contributing Missions (GCM), managed in Copernicus by the ESA GSCDA (GMES Space Component Data Access) system.

Copernicus Mission

Launch

Sensor complement

Objective

Sentinel-1

2014

C-SAR (C-band SAR)

ERS/ENVISAT SAR data continuity for Land and Ocean surveillance; interferometry

Sentinel-2

2014

MSI (Multispectral Instrument)

Deliver high resolution optical information of all land-masses of the Earth, complementing e.g. Landsat & SPOT series.

Sentinel-3

2016

OLCI (Ocean and Land Color Instrument) SLSTR (Sea and Land Surface Temp. Radiometer) SRAL (Ku/C-band Radar Altimeter) MWR (Micro-Wave Radiometer)

Global daily land and sea parameter observation POD (Precise Orbit Determination)

Sentinel-4 (on MTG in GEO)

2019

UVN (UV-VIS-NIR) instrument

Monitoring of air quality, stratospheric ozone, solar radiation, and climate monitoring.

Sentinel-5 (on MetOp SG in LEO)

2020

UVNS (UV-VIS-NIR-SWIR) instrument

Atmospheric composition, cloud and aerosol for air quality and climate applications

Sentinel-5P (Precursor)

2016

TROPOMI (Tropospheric Monitoring Instrument)

Atmospheric composition, cloud and aerosol for air quality and climate applications

Table 18: Copernicus Sentinel missions characteristics

The management of the payload data from the Sentinel missions is performed by the CGS (Core Ground Segment) defined by ESA. The CGS consists of a series of X-band data acquisition stations, which will capture all global Sentinel-1/-2/-3 mission data (Sentinel-4/-5 will use dedicated EUMETSAT data acquisition facilities for its next generation geostationary and polar orbiting satellites). These stations are designed for dumping all data recorded on the satellites on-board data recorders, as well as generating near real time products (1-3h after sensing) directly at the stations. The PDGS will also make use of the EDRS (European Data Relay Satellite). This PPP (Public Private Partnership) between ESA and ASTRIUM GmbH, operates a communication payload on two geostationary satellites. The primary link between the Sentinels and the geostationary satellites is a LCT (Laser Communication Terminal), built by Tesat Space, Backnang, Germany and provided as contribution-in-kind by Germany to the Sentinel-1 and -2 satellite series. The downlink from the geostationary satellites is performed via Ka-band to dedicated stations and to user terminals (Ref. 251). 253)

The acquired mission data is then transferred to Sentinel PACs (Processing and Archiving Centers). The PACs are designed to take specifically care for a certain Sentinel/instrument project. For security and redundancy reasons, each Sentinel data set is hosted by two PACs (EUMETSAT is assigned to act as the second PAC for the Sentinel-3 mission data). The PACs generate systematically base level products from all acquired data, archive them in a mission archive and electronically distribute them to the Copernicus users.

The products and performance of each Sentinel is monitored by MPCs (Mission Performance Centers). The entire data flow is managed by a PDMC (Payload Data Management Center), hosted by ESA at ESRIN, Frascati, Italy. The transport and circulation of the data is performed via terrestrial networks. The GMES WAN therefore connects all PDGS elements with links, having appropriate bandwidth.

In 2011, ESA started a series of procurement actions to select European providers to offer their facilities for the set-up and operations of the PDGS elements. Figure 169 displays the structure of the PDGS and the outcome of the selection of the providers.

Sentinel1_AutoD

Figure 169: Overall structure of Copernicus Payload Data Ground Segment for Sentinels-1 to -3 (Status May 2013), image credit: ESA (Ref. 251)

Within this competitive selection process, ESA has awarded the DLR/DFD ( German Remote Sensing Data Center) with the set-up and operations of the PACs for Sentinel-1 and Sentinel-3 (OLCI part). T-Systems, Germany, is assisting DLR in the network parts of the PACs. In addition and under separate procurement, DFD designs, builds and operates the payload data ground segment) for the Sentinel-5 Precursor mission.

High-level tasks of the DLR Sentinel PAC are:

- receive Sentinel data from CGSs via the GMES WAN

- ingest these data into the STA (Short-Term Archive) and MTA (Mid-Term Archive) of the Sentinel PGDS

- ingest these data in a LTA (Long-Term Archive) for a period of more than 7 years

- perform consolidation and re-assembly of level-0 data received from CGS facilities

- perform systematic and request-driven processing of Sentinel data to higher-level products

- host Sentinel data products within a layered architecture of on-line dissemination elements that will facilitate the direct access of end-users via public networks

- share and exchange any locally processed data with a 2nd partner PAC for the purpose of redundancy.

According to the GSC (GMES Space Component) operations concept, the Sentinel PDGS will become operationally embedded in the GSCDA (GMES Space Component Data Access) System that ESA implements in support of data access to GMES/Copernicus Service Projects and their users.

Sentinel1_AutoC

Figure 170: Overall structure of the Sentinel-1 (S1) and Sentinel-3-OLCI PACs at DFD in Oberpfaffenhofen (image credit: DLR)

Sentinel-5P: The Sentinel-5 Precursor satellite will deliver a key set of atmospheric composition, cloud and aerosol data products for air quality and climate applications. The sensing instrument TROPOMI together with the operational level 1 and level 2 processors will bring a significant improvement in the precision as well as temporal and spatial resolution of derived atmospheric constituents. Sentinel-5 Precursor is planned for launch in 2016.

For the Sentinel-5P mission, DLR/DFD was selected by ESA for the development and operation of the entire PDGS (Payload Data Ground Segment), which covers the whole chain of payload data handling on ground: data reception, processing, archiving, near-real-time and offline delivery to end users. In addition, DLR/IMF (Institut für Methodik der Fernerkundung - Remote Sensing Technology Institute) was selected for the development of retrieval algorithms and operational processors for a number of key atmospheric trace gases and cloud products.

Sentinel-5P will continue the strong DFD heritage on development/operations of processors and ground segments for atmospheric missions started with GOME-1/ERS-2, SCIAMACHY/ENVISAT, and GOME-2 on the MetOp series. The Sentinel-5P PDGS - as well as the LTA for Sentinel-1 and Sentinel 3 OCLI - will be based on the DFD development of DIMS (Data and Information Management System). DIMS will be configured for the Sentinel 5P workflows and mission specific extensions for the demanding throughput and storage requirements (Ref. 251).

In summary, DLR/DFD is involved in the Core and collaborative ground segment of the Copernicus program. It has been developing PDGS (Payload Data Ground Segment) elements and will operate PACs (Processing and Archiving Centers) for Sentinels and national data acquisition stations, both in X-band and using EDRS acquisition services.

 

Sentinel-1 FOS (Flight Operations Segment)

The main responsibilities of the FOS at ESA encompass satellite monitoring and control, including execution of all platform activities and the commanding of the payload schedules. The principal components of the FOS are (Ref. 253): 254)

1) The Ground Station and Communications Network, which performs TT&C (Telemetry, Tracking and Commanding) operations within the S-band frequency. A single S-band ground station will be used throughout all mission phases, complemented by additional TT&C stations as launch and early operations (LEOP) and backup stations.

2) The FOCC (Flight Operations Control Center), which includes:

• the Sentinel Mission Control System, which supports telecommand coding and transfer and housekeeping telemetry (HKTM) data archiving and processing

• the Sentinel Mission Planning System which supports command request handling, the planning and scheduling of satellite operations and the scheduling of payload operations as prepared by the PDGS Mission Planning System

• the specific Sentinel Satellite Simulators, which support procedure validation, operator training and the simulation campaign before each major phase of the mission

• the Sentinel Flight Dynamics System, which supports all activities related to attitude and orbit determination and prediction, the preparation of slew and orbit maneuvers, satellite dynamics evaluation and navigation

• The Sentinel Key Management Facilities, which support the management of the telecommand security functions.

3) A General Purpose Communication Network, which provides the services for exchanging data with any other external system during all mission phases.

Sentinel1_AutoB

Figure 171: Simplified view of the Sentinel-1 Ground Segment (image credit: Astrium SAS)

Sentinel1_AutoA

Figure 172: Overall Layout of the Sentinel-1 Core PDGS (image credit: Astrium SAS)

The selected geographical locations and operators for the Sentinel-1 PDGS centers are (Ref. 253):

• KSAT for X-band reception (CGS) in Svalbard (Norway) and Alaska

• INTA for X-band reception in Maspalomas (Spain)

• E-Geos for X-band reception in Matera (Italy)

• Astrium Services for the PAC (Processing and Archiving Center) in Farnborough (UK)

• DLR for the PAC in Oberpfaffenhofen (Germany)

• CLS for the MPC (Mission Performance Center) operations in Brest (France).

• PDMC (Payload Data Management Center) will be located at ESRIN and be operated by the European Space Agency.

• The POD (Precise Orbit Determination) service will be provided by GMV (Spain).

Sentinel1_Auto9

Figure 173: Illustration of Sentinel-1 ground segment configuration (image credit: ESA, Ref. 167)

 

CPOD (Copernicus Precise Orbit Determination) Service

The CPOD service is part of the PDGS (Payload Data Ground Segment) of the Sentinel missions. A GMV-led consortium of Spain is operating the CPOD being in charge of generating precise orbital products and auxiliary data files for their use as part of the processing chains of the respective Sentinel PDGS. 255)

Figure 174 shows the different elements that interact with the CPOD service. On top we have the Sentinels satellites, all of them with two GPS Receivers on-board (Sentinel-3 also has a LRR and DORIS). The raw L0 data is downloaded at least once per orbit to one of the Ground Stations used (particularly Svalbard, but also Maspalomas and Matera are used). The raw L0 data that contains the GPS and attitude data is circulated to the Sentinels PDGS and from there it is made available to the CPOD Service Center, which will generate orbital products with different timelines.

Sentinel1_Auto8

Figure 174: Overview of the CPOD service elements (image credit: GMV, ESA)

The first three Sentinel missions require orbital products in NRT (Near Real Time), with latencies as low as 30 minutes, in STC (Short Time Critical), with latencies of 1.5 days and in NTC (Non-time Critical) with latencies of 20-30 days. The accuracy requirements are very challenging, targeting 5 cm in 3D for Sentinel-1 and 2-3 cm in radial direction for Sentinel-3.

Mission

Orbit Product

Product Category

Latency Requirement

Position Accuracy (RMS orbit)

S-1

NRT

Restituted

Within 3 hours (from the reception of GNSS data)

< 10 cm (2D)

S-2

NRT

Restituted

90 minutes before Sentinel-2 A/B ANX is crossed

< 10 m (2D) 3-sigma

S-2

NRT

Restituted

Within 30 minutes (from the reception of GNSS data)

< 3 m (3D) 3-sigma

S-3

NRT

Restituted

Within 30 minutes (from the reception of GNSS data)

10 cm threshold with a target of 8 cm (radial)

S-3

STC

Preliminary

Within 1,5 days (36 hr)

4 cm threshold with a target of 3 cm (radial)

S-1

NTC

Precise

Within 20 days

5 cm (3D)

S-3

NTC

Precise

Within 28 days (i.e. 2 days before NTC science product delivery)

3 cm threshold with a target of 2 cm (radial)

Table 19: Summary of timeliness and accuracy requirements 256)

The CPOD Service has been developed and it is being operated by a GMV-led consortium with a system running at GMV premises to provide orbital products for the Sentinel missions with different timeliness: NRT, STC , NTC and reprocessing REP. Additionally the Sentinel-3 POD IPF (Instrument Processing Facility), a software package developed as part of the CPOD Service, will run at the Sentinel-3 PDGS (on both, the Marine Center and Core Ground Station) generating NRT orbital products for the Sentinel-3 mission.

The accuracy of the orbital products is being assessed by a number of external validation institutions, all of them being part of the Copernicus POD QWG (Quality Working Group). The main purpose of the Copernicus POD QWG is to monitor the performance of the operational POD products (both the orbit products as well as the input tracking data) and to define potential and future enhancements to the orbit solutions.

The different Sentinel FOSs (Flight Operation Segments) provide orbital products (restituted and predicted) plus maneuver and mass history information. CNES provides also orbital products and DORIS data for Sentinel-3, and it receives GPS RINEX (Receiver Independent Exchange Format) files from the CPOD Service Center.

Veripos Ltd is the source of accurate GPS orbits and clocks for NRT and STC latencies and IGS for NTC and REP latencies. The CPOD also has an in-house back-up of Veripos based on magicGNSS, which provides NRT GPS orbits and clocks. For Sentinel-3, ILRS (International Laser Ranging Service) and DORIS data will also be used. Finally, the CPOD Service interacts with the CPOD QWG and a number of external validation centers.

The Copernicus POD Service has been developed and it is operated by GMV, but it interacts with different entities, both public and private, that act as clients, users and subcontractors. Following are the current main members of the Copernicus POD Service:

- ESA/ESRIN (European Space Research Institute) Frascati, Italy. This center leads the development of the different PGDSs, and in particular, the Sentinel-1 and -2 PDGS are located here.

- ESA/ESOC (European Space Operation Center), Darmstadt, Germany. This center hosts the FOS (Flight Operations Segment) of Sentinel-1, -2, and -3 missions during the commissioning phase and also during the Routine Operation phase except for Sentinel-3 mission, which is handed over to EUMETSAT.

- EUMETSAT (European Organization for the Exploitation of Meteorological Satellites), Darmstadt, Germany. This center hosts the FOS ( Flight Operations Segment) of Sentinel-3 mission during the Routine Operation Phase, and also the so-called Marine Center PDGS of Sentinel-3.

- CNES (Centre National d'Études Spatiales), Toulouse, France provides accurate orbits and platform data files for the Sentinel-3 mission. CNES has also contributed with the DORIS instrument, and as so, it also provides RINEX DORIS files to the Copernicus POD Service.

- GMV Innovating Solutions is the prime of the Copernicus POD Service. It has developed and it is operating the Service from its headquarters in Tres Cantos, near Madrid (Spain). It is responsible also of the overall management and the evolutions of the system.

- POSITIM UG provides expertise in the LEO POD field, prototypes improvements in algorithms and manages, on behalf of ESA/GMV, the Quality Working Group.

- DLR (Deutsches Zentrum für Luft- und Raumfahrt) Oberpfaffenhofen, Germany provides expertise in the LEO POD and GNSS fields. Additionally, it contributes with orbital products for external validation of products.

- TUM (Technische Universität München) provides expertise in the LEO POD field. Additionally, it contributes with orbital products for external validation of products.

- AIUB (Astronomisches Institut, Universität Bern), Bern, Switzerland contributes with orbital products for external validation of products.

- TU Delft (Technische Universiteit Delft), Delft, The Netherlands contributes with orbital products for external validation of products.

- VERIPOS Ltd, Aberdeen, UK is the provider of accurate GPS orbits and clocks in NRT and STC timeliness for it use in the GNSS POD processing.

There are two places where the operational orbits are computed. The so-called CPOD Service Center, located in GMV's premises, is in charge of computing all orbital products of Sentinel-1 and -2 and all STC and NTC products of Sentinel-3. The Sentinel-3 POD IPF (Instrument Processing Facility) is in charge of computing the Sentinel-3 NRT orbital products and it will be running at two locations, the Marine center (located in EUMETSAT, Darmstadt) and the Core Ground Station (located in Svalbard).

Orbital accuracy results:

• Sentinel-1A was launched on April 3, 2014. After 6 months of commissioning, the CPOD Service started the ROP (Routine Operation Phase) in October 2014. Since then, every four months the quality of the service is assessed, including the accuracy of the orbital products. For this, a specific period of time is selected for re-processing by the external validation institutions (i.e. AIUB, DLR, ESOC, TU Delft and TUM). This exercise has been performed twice since the beginning of the ROP phase.

• Sentinel-2A was launched on June, 23, 2015. The commissioning phase is expected to finish by mid/end October 2015, so the ROP (Routine Operation Phase) is expected to begin in November 2015. During the commissioning phase the orbit accuracy has been assessed by the same means used with Sentinel-1A, selecting a period of time to be re-processed by the external validation institutions (Ref. 255).

In the case of Sentinel-1A, the institutions compute offline accurate orbits and provide them to GMV for cross-comparison. It has been shown that systematically the accuracy requirements are fulfilled without major problems. Figure 175 shows the results of the last comparison campaign of January 2016; it shows the 3D RMS per day, during 10 days in January 2016, between the operational Sentinel-1 NTC solution (CPOD) and the daily solutions provided by each institution. Additionally, there is a combined solution (COMB) computed as a weighted average of all individual solutions. It can be seen that the differences are systematically below the required 5 cm (Ref. 256).

Sentinel1_Auto7

Figure 175: Sentinel-1A orbit comparisons (3D RMS; cm) between CPOD and external solutions; red line is threshold (image credit: GMV)

In addition, all NRT and NTC products are compared routinely against an offline ESOC solution (which used the same POD SW, NAPEOS, but of a different version and using different configuration and inputs). The following plots (Figures 176 and 177) show the differences with respect to ESOC from October 2015 to January 2016, where it can be seen that systematically the differences are well below the threshold. The cases above the threshold are typically due to maneuvers and data gaps.

Sentinel1_Auto6

Figure 176: Sentinel-1A Restituted Orbital Product vs. ESOC (2D RMS) from 1st October 2015 until 31st January 2016 (image credit: GMV)

Sentinel1_Auto5

Figure 177: Sentinel-1A Precise Orbital Product vs. ESOC (3D RMS) from 1st October 2015 to 31st January 2016 (image credit: GMV)

In the case of Sentinel-2A, the accuracy results are similar to those of Sentinel-1A. Figure 178 shows the results of the last comparison campaign of January 2016; it shows the 3D RMS per day, during 10 days in January 2016, between the operational Sentinel-2 NTC solution (CPOD) and the daily solutions provided by each institution. Additionally there is a combined solution (COMB) computed as a weighted average of all individual solution. It can be seen that the differences are systematically below 5 cm, like in the case of Sentinel-1A.

Sentinel1_Auto4

Figure 178: Sentinel-2A orbit comparisons (3D RMS; cm) between CPOD and external solutions (image credit: GMV, Ref. 256)

 


 

Copernicus / Sentinels EDRS system operations:

EDRS (European Data Relay Satellite) will provide a data relay service to Sentinel-1 and -2 and initially is required to support 4 Sentinels simultaneously. Each Sentinel will communicate with a geostationary EDRS satellite via an optical laser link. The EDRS GEO satellite will relay the data to the ground via a Ka-band link. Optionally, the Ka-band downlink is planned to be encrypted, e.g. in support to security relevant applications. Two EDRS geo-stationary satellites are currently planned, providing in-orbit redundancy to the Sentinels. 257)

EDRS will provide the same data at the ground station interface as is available at the input to the OCP (Optical Communications Payload) on-board the satellites, using the same interface as the X-band downlink. The EDRS transparently adapts the Sentinels data rate and format to the internal EDRS rate and formats, e.g. EDRS operates at bit rates of 600 Mbit/s and higher.

With EDRS, instrument data is directly down-linked via data relay to processing and archiving centers, while other data continues to be received at X-band ground stations. The allocation of the data to downlink via X-band or EDRS is handled as part of the Sentinel mission planning system and will take into account the visibility zones of the X-band station network and requirements such as timeliness of data.

Sentinel1_Auto3

Figure 179: Sentinel missions - EDRS interfaces (image credit: ESA)

 

Copernicus / Sentinel data policy:

The principles of the Sentinel data policy, jointly established by EC and ESA, are based on a full and open access to the data:

• anybody can access acquired Sentinel data; in particular, no difference is made between public, commercial and scientific use and in between European or non-European users (on a best effort basis, taking into consideration technical and financial constraints);

• the licenses for the Sentinel data itself are free of charge;

• the Sentinel data will be made available to the users via a "generic" online access mode, free of charge. "Generic" online access is subject to a user registration process and to the acceptation of generic terms and conditions;

Following registration, the user will have the possibility to immediately download a test data set that simulates the data products that will be generated by Sentinel-1. Following launch, registered users will be granted early access to Sentinel-1 data samples, even before the full operational qualification of the products is completed.

Registration is open to all users via simple on-line self-registration accessible via the Sentinel Data Hub. 258)

• additional access modes and the delivery of additional products will be tailored to specific user needs, and therefore subject to tailored conditions;

• in the event security restrictions apply to specific Sentinel data affecting data availability or timeliness, specific operational procedures will be activated.

ESA Member States approved these principles in September 2009. 259) 260) 261) 262) 263)

 

Sentinel-1 operational products:

• Level-0 products: Compressed, unprocessed instrument source packets, with additional annotations and auxiliary information to support the processing. 264)

• Level-1 products:

- Level-1 Slant-Range Single-Look Complex Products (SLC): Focused data in slant-range geometry, single look, containing phase and amplitude information.

- Level-1 Ground Range Detected Geo-referenced Products (GRD): Focused data projected to ground range, detected and multi-looked. Data is projected to ground range using an Earth ellipsoid model, maintaining the original satellite path direction and including complete geo-reference information.

• Level-2 Ocean products: Ocean wind field, swell wave spectra and surface currents information as derived from SAR data.

Product generation policy

Product type

Access mode

Timeliness

Systematic Global (for all acquired data)

L0 L1 GRD L2 Ocean

Subscription

3 hours from observation (NRT data) 24 hours from observation (standard)

Free online access from archive

> 24 hours from observation

Systematic Regional (for a subset of acquired data)

L1 SLC (Single-Look Complex)

Subscription

3 hours from observation (NRT data) 24 hours from observation (standard)

Free online access from archive

> 24 hours from observation

Systematic Local (for a subset of data acquired over ocean in the visibility of a Core Ground Station)

L0

Subscription

< 1 hour from observation

Table 20: Sentinel-1 Operational products access policy

Acquisition mode

Product type

Resolution class

Resolution (range x azi) (m)

Pixel spacing (range x azi) (m)

No of looks (range x azi)

ENL

SM (Stripmap Mode)

SLC

-

1.7 x 4.3 to 3.6 x 4.9

1.5 x 3.6 to 3.1 x 4.1

1 x 1

1

GRD

FR

9 x 9

4 x 4

2 x 2

3.9

HR

23 x 23

10 x 10

6 x 6

34.4

MR

84 x 84

40 x 40

22 x 22

464.7

IW

(Interferometric Wide Swath)

SLC

-

2.7 x 22 to 3.5 x 22

2.3 x 17.4 to 3 x 17.4

1

1

GRD

HR

20 x 22

10 x 10

5 x 1

4.9

MR

88 x 89

40 x 40

22 x 5

105.7

EW (Extra Wide Swath)

SLC

-

7.9 x 42 to 14.4 x 43

5.9 x 34.7 to 12.5 x 34.7

1 x 1

1

GRD

HR

50 x 50

25 x 25

3 x 1

3

MR

93 x 87

40 x 40

6 x 2

12

WV (Water Vapor)

SLC

-

2.0 x 4.8 and 3.1 x 4.8

1.7 x 4.1 and 2.7 x 4.1

1 x 1

1

GRD

MR

52 x 51

25 x 25

13 x 13

139.7

Table 21: Planned operational ESA Sentinel-1 products - L1 characteristics 265)

• For GRD (Ground Range Detected) products, the resolution corresponds to the mid range value at mid orbit altitude, averaged over all swaths.

• For SLC (Slant-Range Single-Look Complex) products SM/IW/EW products, the resolution and pixel spacing are provided from lowest to highest incidence angle. For SLC WV products, the resolution and pixel spacing are provided for beams WV1and WV2.

• For SLC SM/IW/EW products, the resolution and pixel spacing are provided from lowest to highest incidence angle. For SLC WV products, the resolution and pixel spacing are provided for beams WV1and WV2.

 


 

Preparatory campaigns:

In the context of the Copernicus program, ESA is conducting a number of coordinated preparatory activities (studies, campaigns, etc.) to demonstrate/validate the observation concepts (as well as many other system aspects) that are being planned for the various Sentinel missions. The following campaigns are in particular dedicated in support of Sentinel-1 (and -2, AgriSAR) applications.

AgriSAR 2009:

The AgriSAR 2009 campaign of ESA took place in April 2009. The objective is to evaluate how frequent multi-polarization acquisitions provided by Sentinel-1 will improve applications such as land-cover mapping and crop monitoring. To accomplish this ambitious task, ESA has asked MDA Geospatial Services to acquire multi-temporal, quad-polarization RADARSAT-2 imagery throughout the 2009 growing season over three test sites. The chosen sites are located in Flevoland in the Netherlands, Barrax in Spain and Indian Head in mid-west Canada.

In addition to the contribution from MDA Geospatial Services, the campaign included also a number of European and Canadian scientists to help with ground activities. These activities included the collection and analysis of information about land cover, crop type, crop condition and other parameters such as soil moisture. Of particular interest were the new algorithms and methods required to extract land-cover information from a dense temporal series of SAR images and follow how the crops develop. 266)

Sentinel1_Auto2

Figure 180: The color composite of a RADARSAT-2 polarimetric radar image acquired over the Flevoland test site in the Netherlands on April 4, 2009 (image credit: ESA)

Sentinel1_Auto1

Figure 181: Polarimetric RADARSAT-2 SAR image of the Barrax test site in Spain on April 9, 2009 (image credit: ESA)

IceSAR 2007:

The IceSAR airborne campaign (3 weeks in March 2007), which took place near Longyearbyen in Svalbard (Norway), was conducted by AWI (Alfred Wegner Institut), Bremerhaven, DLR/HR (Microwave and Radar Institute), and ESA. The radar configuration consisted of a C-band instrument with VV and VH polarizations, very similar to the future Sentinel-1 sensor. The C-band SAR was flown on the DO-228 aircraft of DLR (E-SAR instrument with C- and X-band capability). In addition, the Polar-2 aircraft of AWI was flown carrying the AWI infrared line scanner during the IceSAR campaign in coordination with the radar aircraft. 267) 268)

Sentinel1_Auto0

Figure 182: An airborne SAR sea-ice image taken over Storfjorden, Svalbard on March, 16, 2007 (image credit: ESA)

AgriSAR 2006:

The AgriSAR campaign of ESA took place in the summer of 2006 (Apr. 18 - Aug. 2, 2006) - representing an ambitious large-scale attempt to assess the performance of the Sentinel-1 (C-band SAR) and Sentinel-2 (Optical Multispectral) for land applications. The campaign was unique in scope and scale representing frequent airborne SAR coverage during the entire crop-growing season, from sowing to harvest. 269) 270) 271)

The main test site was Demmin (Durable Environmental Multidisciplinary Monitoring Information Network), an agricultural site located in Mecklenburg-Vorpommern in North-East Germany, approximately 150 km north of Berlin. Main crop types in the area are winter wheat, barley, maize, rape and sugar beet. The DLR (German Aerospace Center) E-SAR system was flown over the Demmin test site more than 14 times between the months of April and July. Weekly in-situ measurements were taken on the ground in selected fields throughout the same period.

In addition to SAR coverage, optical data using the Canadian CASI instrument from ITRES Research and the Spanish AHS from the National Institute for Aerospace Technology (INTA), were acquired during critical phases of the growing season in June and July. The June acquisitions were extended to include a forest and grassland site in the central Netherlands, used by the EU EAGLE project.

In total, over 15 research institutes from Germany, Spain, Italy, Belgium, The Netherlands, Britain, Canada and Denmark participated in the campaign.

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49) "Preparing for more radar vision," ESA, March 10, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel
-1/Preparing_for_more_radar_vision

50) "Approxching launch: student CubeSats integrated on theit orbital deployer," ESA, March 17, 2016, URL: http://www.esa.int/Education/CubeSats_-_Fly_Your_Satellite
/Approaching_launch_Student_CubeSats_
integrated_in_their_orbital_deployer

51) Carmelo Carrascosa, Fernando E. Alemán, Francisco J. Atapuerca, Andrea Pietropaolo, Giacomo Taini, Berthyl Duesmann, "Orbit Analysis and Orbit Control Strategy for Sentinel-1 Mission," Proceedings of the 59th IAC (International Astronautical Congress), Glasgow, Scotland, UK, Sept. 29 to Oct. 3, 2008, IAC-08.C1.4.2

52) Dirk Geudtner, Rámon Torres, Paul Snoeij, Malcolm Davidson, "Sentinel-1 System Overview," ESA/ESTEC, URL: http://earth.eo.esa.int/workshops/fringe2011/files/Sentinel-1%20System_Fringe_final_1.pdf

53) J. Roselló Guasch, P. Silvestrin, M. Aguirre, L. Massotti, "Navigation needs for ESA's Earth Observation missions," Proceedings of the 7th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, May 4-7, 2009, IAA-B7-1401

54) Josef Aschbacher, Thomas Beer, Antonio Ciccolella, Giancarlo Filippazzo, Maria Milagro, Alessandra Tassa, "Copernicus - Moving from development to operations," ESA Bulletin, No 157, Feb. 2014, pp. 30-37, URL: http://www.esa.int/About_Us/ESA_Publications/ESA_Bulletin_157_Feb_2014

55) "Iraq flood," ESA, Earth observation image of the week, 1 February 2019, URL: http://m.esa.int/spaceinimages/Images/2019/02/Iraq_flood

56) "Copernicus Sentinel-1 maps Norway in motion," ESA, 10 January 2019, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus
/Sentinel-1/Copernicus_Sentinel-1_maps_Norway_in_motion

57) "Copernicus Sentinel-1 data fuel Norwegian ground motion service," ESA, 10 January 2019, URL: https://sentinels.copernicus.eu/web/sentinel/news/-/article/copernicus-
sentinel-1-data-fuel-norwegian-ground-motion-service

58) "Mexico City," ESA Earth observation image of the week, 30 November 2018, URL: http://m.esa.int/spaceinimages/Images/2018/11/Mexico_City

59) "Oil spill spread," ESA, 10 October 2018, URL: http://m.esa.int/spaceinimages/Images/2018/10/Oil_spill_spread

60) "Mediterranean slick," ESA, 8 October 2018, URL: http://m.esa.int/spaceinimages/Images/2018/10/Mediterranean_slick

61) "Central Italy," ESA, Earth observation image of the week, 28 September 2018, URL: http://m.esa.int/spaceinimages/Images/2018/09/Central_Italy

62) "Northeast Ethiopia," ESA, Earth observation image of the week, 14 September 2018, URL: http://m.esa.int/spaceinimages/Images/2018/09/Northeast_Ethiopia

63) "Earth from Space: Northeast Ethiopia," ESA video program, 14 September 2018, URL: http://m.esa.int/spaceinvideos/Videos/2
018/09/Earth_from_Space_Northeast_Ethiopia

64) "Giant iceberg escapes," ESA, 13 September 2018, URL: http://m.esa.int/spaceinimages/Images/2018/09/Giant_iceberg_escapes

65) "NASA's ARIA Project Generates Satellite-Derived Map of Ground Deformation from Earthquake beneath Lombok, Indonesia," NASA/JPL, 8 August 2018, URL: https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA22491

66) "Sentinel-1 maps flash floods in Laos," ESA, 30 July 2018, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/
Copernicus/Sentinel-1/Sentinel-1_maps_flash_floods_in_Laos

67) "Dam breach in the Xe-Pian Xe-Namnoy lake area," ESA, 27.07.2018, URL: http://m.esa.int/spaceinimages/Images/2018/07
/Dam_breach_in_the_Xe-Pian_Xe-Namnoy_lake_area

68) "It's all go in summer for Greenland's glaciers," ESA, 13 July 2018, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/It_s_all_go_in_summer_for_Greenland_s_glaciers

69) Adriano Lemos, Andrew Shepherd, Malcolm McMillan, Anna E. Hogg, Emma Hatton, Ian Joughin, "Ice velocity of Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm, 2015–2017, from Sentinel 1-a/b SAR imagery ," The Cryosphere, Volume 12, Issue 6, 18 June 2018, https://doi.org/10.5194/tc-12-2087-2018, URL: https://www.the-cryosphere.net/12/2087/2018/tc-12-2087-2018.pdf

70) "Jakobshavn Isbrae ice flow," ESA, 13 July 2018, URL: http://m.esa.int/spaceinimages/Images/
2018/07/Jakobshavn_Isbrae_ice_flow

71) Dirk Geudtner, Nuno Miranda, Ignacio Navas-Traver, Francisco Vega Ceba, Pau Prats, Nestor Yague-Martinez, Heiko Breit, Francesco de Zan, Yngvar Larsen, Andrea Recchia, David Small, Adrian Schubert, Itziar Barat, "Sentinel-1A/B SAR and InSAR Performance," EUSAR 2018 (12th European Conference on Synthetic Aperture Radar), Aachen, Germany, June 4-7, 2018

72) "Sentinel-1 warns of refugee island flood risk," ESA, 29 May 2018, URL: https://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/
Sentinel-1/Sentinel-1_warns_of_refugee_island_flood_risk

73) "Barely an island," ESA, 29 May 2018, URL: http://m.esa.int/spaceinimages/Images/2018/05/Barely_an_island

74) "Mission Status Report 207 - Reference Period: 22 May 2018 – 28 May 2018," ESA, May 2018, URL: https://sentinel.esa.int/documents/247904/3339966/Sentinel-1-Mission_Status_Report_207-Period-22-28_May_2018.pdf

75) "Latest Mission Status Reports," ESA, May 2018, URL: https://sentinel.esa.int/web/sentinel/missions/sentinel-1/mission-status

76) "Radar shows large areas of Texas oil acreage heaving and sinking at large rates," Oil Gas Daily, 22 March, 2018, URL: http://www.oilgasdaily.com/reports/Radar_
images_show_large_swath_of_Texas_oil_patch_is
_heaving_and_sinking_at_alarming_rates_999.html

77) Jin-Woo Kim, Zhong Lu, "Association between localized geohazards in West Texas and human activities, recognized by Sentinel-1A/B satellite radar imagery," Scientific Reports, Published: online: 16 March 2018, 8:4727, DOI:10.1038/s41598-018-23143-6, URL: https://www.nature.com/articles/s41598-018-23143-6.pdf

78) "Bering Strait," ESA Earth observation image of the week, 23 Feb. 2018, URL: http://m.esa.int/spaceinimages/Images/2018/02/Bering_Strait

79) "Orange County," ESA image of the week, Dec. 15, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/12/Orange_County

80) "Thurston Island, Antarctica," ESA, Earth observation image of the week, 24 Nov. 2017, URL: http://m.esa.int/spaceinimages/Images/2017/11/Thurston_Island_Antarctica

81) "Satellites guide ships in icy waters through the cloud," ESA, 7 Nov. 2017, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Satellites
_guide_ships_in_icy_waters_through_the_cloud

82) "Halloween crack," ESA31 Oct. 2017, URL: http://m.esa.int/spaceinimages/Images/2017/10/Halloween_crack

83) "Sentinel-1 sees through hurricanes," ESA, 25 Oct. 2017, URL: http://www.esa.int/Our_Activities/Observing_
the_Earth/Copernicus/Sentinel-1/Sentinel
-1_sees_through_hurricanes

84) "Sagaing Division, Myanmar," ESA Earth observation image of the week, 20 Oct. 2017, URL: http://m.esa.int/spaceinimages/Images/2017
/10/Sagaing_Division_Myanmar

85) "NASA Damage Map Aids Puerto Rico Hurricane Response," NASA/JPL, 28 Sept. 2017, URL: https://www.jpl.nasa.gov/news/news.php?release=2017-252

86) https://www.jpl.nasa.gov/spaceimages/details.php?id=pia21964

87) "Giant berg on the move," ESA, 20 Sept. 2017, URL: http://m.esa.int/spaceinimages/Images
/2017/09/Giant_berg_on_the_move

88) "Sentinel-1 speeds up crop insurance payout," ESA, 17 August 2017, URL: http://www.esa.int/Our_Activities/Observing_the_Earth
/Copernicus/Sentinel-1/Sentinel-1_speeds_up_crop_insurance_payouts

89) "Sentinel satellite captures birth of behemoth iceberg," ESA, July 12, 2017, URL: http://m.esa.int/Our_Activities/Observing_the_
Earth/Copernicus/Sentinel-1/Sentinel_satellite
_captures_birth_of_behemoth_iceberg

90) "Depth of ice crack," ESA, 6 July 2017, URL: http://m.esa.int/spaceinimages/Images/2017/06/Depth_of_ice_crack

91) "Landslide on the radar," ESA, June 13, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/06/Landslide_on_the_radar

92) "Negribreen on the move," ESA, May 12, 2017, URL: http://www.esa.int/Our_Activities/Observing_the_
Earth/Copernicus/Sentinel-1/Negribreen_on_the_move

93) "Satellites track Antarctic ice loss over decades," ESA, 2 May 2017, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Satelli
tes_track_Antarctic_ice_loss_over_decades

94) Anna E. Hogg, Andrew Shepherd, Stephen L. Cornford, Kate H. Briggs, Noel Gourmelen, Jennifer Graham, Ian Joughin, Jeremie Mouginot, Thomas Nagler, Antony J. Payne, Eric Rignot, Jan Wuite, "Increased ice flow in Western Palmer Land linked to ocean melting," Geophysical Research Letters, Vol. 44, 2017, doi:10.1002/2016GL072110, URL of abstract: http://onlinelibrary.wiley.com/doi/10.1002/2016GL072110/abstract

95) http://www.esa.int/Highlights/Week_In_Images_17_21_April_2017

96) "How the Copernicus Emergency Management Service supported responses to major earthquakes in Central Italy," ISPRA, April 21, 2017, URL: http://www.copernicus.eu/news/how-copernicus-emergency-
management-service-supported-responses
-major-earthquakes-central-italy

97) "Sentinel-1 supports detection of illegal oil spills," Geospatial World, April 7, 2017, URL: https://www.geospatialworld.net/news-posts/sentinel-
1-supports-detection-illegal-oil-spills/

98) https://sentinels.copernicus.eu/web/sentinel/news/-/article/
sentinel-1-supports-detection-of-illegal-oil-spills

99) "Urban monitoring boosted by new data processor," ESA, April 4, 2017, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/
Urban_monitoring_boosted_by_new_data_processor

100) "TimeScan product: Germany," ESA, April 4, 2017, URL: http://www.esa.int/spaceinimages/Images/
2017/04/TimeScan_product_Germany

101) "TimeScan product: Pearl River Delta," ESA, April 3, 2017, URL: http://www.esa.int/spaceinimages/Images/2017
/04/TimeScan_product_Pearl_River_Delta

102) "Alert, Canada,", ESA Earth observation image of the week , March 31, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/03/Alert_Canada

103) "Cryovex and Karen: Catching Up," ESA, March 28, 2017, URL: http://blogs.esa.int/campaignearth/2017/03/28/cryovex-and-karen-catching-up/

104) "San Joaquin Valley is Still Sinking," NASA Earth Observatory, March 5, 2017, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89761

105) Tom G. Farr, Cathleen E. Jones, Zhen Liu, "Progress Report: Subsidence in California, March 2015 – September 2016," URL: http://www.water.ca.gov/waterconditions/docs/2017/JP
L%20subsidence%20report%20final%20for%20p
ublic%20dec%202016.pdf

106) "Lake Success, California," ESA, Earth observation image of the week, February 24, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/02/Lake_Success_California

107) "Sentinels warn of dangerous ice crack," ESA, Feb. 16, 2017, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus
/Sentinels_warn_of_dangerous_ice_crack

108) "Relocation of Halley Research Station," BAS Press Release, 6 Dec. 2016, URL: https://www.bas.ac.uk/media-post
/relocation-of-halley-research-station/

109) "Satellites monitor landslide in the Alps," ESA, Feb. 3, 2017, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/
Satellites_monitor_landslide_in_the_Alps

110) "Larsen Crack," ESA, Jan. 30, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/01/Larsen_crack

111) "Satellites confirm sinking of San Francisco tower," ESA, Nov. 25, 2016, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Satellites_confirm_sinking_of_San_Francisco_tower

112) "Millennium Tower sinking," ESA, Nov. 24, 2016, URL: http://m.esa.int/spaceinimages/Images/
2016/11/Millennium_Tower_sinking

113) "San Francisco displacement," ESA, Nov. 24, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/11/San_Francisco_displacement

114) "Bay Area displacement," ESA, Nov. 24, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/11/Bay_Area_displacement

115) "Oslo train station on the move," ESA, Nov. 24, 2016, URL: http://m.esa.int/spaceinimages/Images/
2016/11/Oslo_train_station_on_the_move

116) "Virunga Mountains," ESA Earth observation image of the week, Nov. 11, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/11/Virunga_Mountains

117) "Sentinel satellites reveal east–west shift in Italian quake," ESA, Nov. 3, 2016, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Sentinel_satellites_reveal_east_west_shift_in_Italian_quake

118) "European seismic zones", ESA, Oct. 28, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/10/European_seismic_zones

119) "Earthquake area in Italy," ESA, Oct. 28, 2016, URL: http://m.esa.int/spaceinimages/Images/
2016/10/Earthquake_area_in_Italy

120) "Ground displacement from Italy's earthquake," ESA, Aug. 28, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/08/Ground
_displacement_from_Italy_s_earthquake

121) "Copernicus Sentinel-1B handed over for operations," ESA, Sept. 16, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/
09/Copernicus_Sentinel-1B_handed_over_for_operations

122) "China's Poyang Lake in radar vision," ESA Earth observation image of the week, Sept. 16, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/09/Poyang_Lake

123) "Copernicus Sentinel-1A satellite hit by space particle," ESA, Aug. 31, 2016, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/
Sentinel-1/Copernicus_Sentinel-1A_satellite_hit_by_space_particle

124) "Sentinel-1 satellites combine radar vision," ESA, June 22, 2016, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/
Copernicus/Sentinel-1/Sentinel-1_satellites_combine_radar_vision

125) Pierre Potin, Betlem Rosich, Patrick Grimont, Nuno Miranda, Ian Shurmer, Alistair O'Connell, Ramón Torres, Mike Krassenburg, "Sentinel-1 Mission Status," Proceedings of EUSAR 2016, 11th European Conference on Synthetic Aperture Radar, Hamburg, Germany, June 6-9, 2016

126) Ramón Torres, Svein Løkås, David Bibby, Dirk Geudtner, "Sentinel-1B LEOP and Commissioning Results,"Proceedings of EUSAR 2016, 11th European Conference on Synthetic Aperture Radar, Hamburg, Germany, June 6-9, 2016

127) Dirk Geudtner, Pau Prats, Nestor Yague-Martinez, Ignacio Navas-Traver, Itziar Barat, Ramón Torres, "Sentinel-1 SAR Interferometry Performance Verification," Proceedings of EUSAR 2016, 11th European Conference on Synthetic Aperture Radar, Hamburg, Germany, June 6-9, 2016

128) "Sentinel-1 helping Cyclone Roanu Relief," ESA, May 26, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/
Copernicus/Sentinel-1/Sentinel-1_helping_Cyclone_Roanu_relief

129) "Antarctic Peninsula ice flow," T. Nagler , H. Rott, M. Hetzenecker, J. Wuite, "Monitoring ice motion of the Antarctic and Greenland ice sheets at high spatial and temporal resolution by means of Sentinel-1 SAR," Living Planet Symposium, 2016, Prague, Czech Republic, May 9-13, 2016, URL of abstract: http://www.esa.int/spaceinimages/Images/2016/
05/Antarctic_Peninsula_ice_flow

130) "Zachariae glacier," ESA, image of the week series, May 6, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/05/Zachariae_glacier

131) Alan Buis, "In Greenland, Another Major Glacier Comes Undone," NASA/JPL, Nov. 12, 2015, URL: http://www.jpl.nasa.gov/news/news.php?feature=4771

132) "Sentinel-1B delivers," ESA, April 28, 2016, URL: http://www.esa.int/Our_Activities/Observing_
the_Earth/Copernicus/Sentinel-1/Sentinel-1B_delivers

133) "Sentinel-1B spreads its wings," ESA, April 27, 2016: URL: http://www.esa.int/Our_Activities/Observing_
the_Earth/Sentinel-1B_spreads_its_wings

134) "Student satellites fly freely on their orbit in space," ESA, April 26, 2016, URL: http://www.esa.int/Education/CubeSats_-_Fly_Your_Satellite/Student_satellites_fly_freely_on_their_orbit_in_space

135) "Soyuz demonstrates Arianespace mission flexibility," Space Daily, April 26, 2016, URL: http://www.spacedaily.com/reports/Soyuz_demonstrates
_Arianespace_mission_flexibility_999.html

136) "Dasht-e Kavir," ESA, Earth observation image of the week, April 22, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/04/Dasht-e_Kavir

137) "Sentinel-1 counts fish," ESA, April 21, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Sentinel-1_counts_fish

138) "Sentinel-1A detects fishing cages," ESA, April 14, 2016, URL: http://www.esa.int/spaceinimages/Images
/2016/04/Sentinel-1A_detects_fishing_cages

139) "Irish mosaic," ESA, Earth observation image of the week, April 15, 2016: URL: http://www.esa.int/spaceinimages/Images/2016/04/Irish_mosaic

140) "Nansen gives birth to two icebergs," ESA, April 14, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Nansen_gives_birth_to_two_icebergs

141) "Bernese Alps," ESA, image of the week, April 8, 2016, URL: http://saint/spacings/Images/2016/04/Bernese_Alps

142) "Colors of Sweden," ESA, Feb. 5, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/02/Colours_of_Sweden

143) "Deal sealed for new Sentinel-1 satellites," ESA, Dec. 15, 2015, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Deal_sealed_for_new_Sentinel-1_satellites

144) "Dutch mosaic," ESA, Earth observation image of the week, Dec. 4, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/12/Dutch_mosaic

145) "Manicouagan Crater, Canada," ESA, Earth observation image of the week, Oct. 30, 2015, URL: http://www.esa.int/spaceinimages/
Images/2015/10/Manicouagan_Crater_Canada

146) "Azore Islands," ESA, Earth observation image of the week, Oct. 9, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/10/Azore_islands

147) "Chile earthquake on the radar," ESA, Sept. 21, 2015, URL: http://www.esa.int/spaceinimages/Images/
2015/09/Chile_earthquake_on_the_radar

148) "Mission Status Report 68 for the period August 11-17, 2015," EC, ESA, URL: https://sentinel.esa.int/documents/247904/1752934/
Sentinel-1-Mission_Status_Report_68-Period_11-17_August_2015.pdf

149) "Sentinel-1 Observation Scenario," ESA, 2015, URL: https://sentinels.copernicus.eu/web/sentinel/missions
/sentinel-1/observation-scenario

150) Alexis Mouche, Bertrand Chapron, Harald Johnsen, Fabrice Collard, Romain Husson, He Wang, Gilles Guitton, Fabrice Ardhuin, "Sentinel-1 results: Sea state applications," Proceedings of the IGARSS (International Geoscience and Remote Sensing Symposium) 2015, Milan, Italy, July 26-31, 2015

151) R. Lanari, P. Berardino, M. Bonano, F. Casu, C. De Luca, S. Elefante, A. Fusco, M. Manunta, M. Manzo, C. Ojha, A. Pepe, E. Sansosti, I. Zinno, "Sentinel-1 results: SBAS-DInSAR processing chain developments and land subsidence analysis," Proceedings of the IGARSS (International Geoscience and Remote Sensing Symposium) 2015, Milan, Italy, July 26-31, 2015

152) "Southern Bavaria," ESA, Earth observation image of the week, July 24, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/07/Southern_Bavaria

153) "Central California, USA," ESA, Earth observation image of the week, June 26, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/06/Central_California_USA

154) "Tianjin, China," ESA Earth observation image of the week, June 5, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/06/Tianjin_China

155) "Update: Disaster relief – DLR provides aerial images of Kathmandu," DLR/EOC, April 30, 2015, URL: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-13487/#/gallery/19391

156) "Nepal earthquake displacement," ESA, April 30, 2015, URL: http://www.esa.int/spaceinimages/Images
/2015/04/Nepal_earthquake_displacement

157) "Nepal Earthquake on the Radar," ESA, April 29, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
/Sentinel-1/Nepal_earthquake_on_the_radar

158) "Kathmandu grading map," ESA, April 29, 2015, URL: http://www.esa.int/spaceinimages/
Images/2015/04/Kathmandu_grading_map

159) "Florida, United States of America," ESA, image release on April 24, 2015, URL: http://www.esa.int/spaceinimages/Images
/2015/04/Florida_United_States_of_America

160) "happy birthday, Sentinel-1A," ESA, April 3, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
/Sentinel-1/Happy_birthday_Sentinel-1A

161) "Irkutsk and Lake Baikal," ESA image, featured on the Earth from Space video program, April 3, 2015, URL: http://www.esa.int/spaceinimages/
Images/2015/04/Irkutsk_and_Lake_Baikal

162) "Earth shifts in color," A gallery of InSAR images is presented at the 2015 Fringe Workshop, held at ESA/ESRIN in March 23-27, 2015, ESA, March 27, 2015, URL: http://www.esa.int/Our_Activities/Observing
_the_Earth/Highlights/Earth_shifts_in_colour

163) "Aral Sea," ESA image in the series 'Earth observation image of the week,' released on March 27, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/03/Aral_Sea

164) "Pine Island Glacier on Sentinel-1A's radar," ESA, March 25, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/03/Pine
_Island_Glacier_on_Sentinel-1A_s_radar

165) ESA, March 20, 2015, 'Our week in images,' URL: http://www.esa.int/Highlights/Week_In_Images_16_20_March_2015

166) "UK joins Sentinel collaborative ground segment," ESA, March 19, 2015, URL: http://www.esa.int/Our_Activities/Observing
_the_Earth/Copernicus/UK_joins_Sentinel
_Collaborative_Ground_Segment

167) http://www.esa.int/Highlights/Week_In_Images_02_06_March_2015

168) Pierre Potin, "Sentinel-1 Mission," POLinSAR 2015, ESA/ESRIN, Frascati, Italy, Jan. 26-30, 2015, URL: http://seom.esa.int/insarap/files/INSARAP-2014_Sentinel-1_Mission_Status_PPotin.pdf

169) "Lisbon, Portugal," ESA, Feb. 6, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/02/Lisbon_Portugal

170) "Satellites catch Austfonna shedding ice," ESA, Jan. 23, 2014, URL: http://www.esa.int/Our_Activities/Observing_the_Earth
/Satellites_catch_Austfonna_shedding_ice

171) Malcolm McMillan, Andrew Shepherd, Noel Gourmelen, Amaury Dehecq, Amber Leeson, Andrew Ridout, Thomas Flament, Anna Hogg, Lin Gilbert, Toby Benham, Michiel van den Broeke, Julian A. Dowdeswell, Xavier Fettweis, Brice Noël, Tazio Strozzi, "Rapid dynamic activation of a marine-based Arctic ice cap," Geophysical Research Letters, Vol. 41, Dec. 23, 2014, doi:10.1002/2014GL06225, URL: http://onlinelibrary.wiley.com/doi/10.1002/2014GL062255/full

172) "Mexico City subsidence," ESA, Dec. 11, 2014, URL: http://www.esa.int/spaceinimages/Images/2014/12/Mexico_City_subsidence

173) "Romania," ESA, image in the 'Earth from Space video program' series, Dec. 5, 2014: URL: http://www.esa.int/spaceinimages/Images/2014/12/Romania

174) "Sentinel-1 maps Fogo eruption," ESA, Dec. 2, 2014, URL: http://www.esa.int/spaceinimages/Images
/2014/12/Sentinel-1_maps_Fogo_eruption

175) "Laser link offers high-speed delivery," ESA, Nov. 28, 2014, URL: http://www.esa.int/Our_Activities/Observing_the_Earth
/Copernicus/Sentinel-1/Laser_link_offers_high-speed_delivery

176) "Super laser revolutionizes data communications in space," DLR, Nov. 28, 2014, URL: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/
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179) http://www.esa.int/spaceinimages/Images
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180) "Tokyo Bay, Japan," ESA, image in the 'Earth from Space video program' series, Nov. 21, 2014, URL: http://www.esa.int/spaceinimages/Images
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186) "Radar vision maps Napa Valley earthquake," ESA, Sept. 2, 2014, URL: http://www.esa.int/Our_Activities/Observing_
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190) "Rio de Janeiro, Brazil," ESA, Earth from Space video program, July 11, 2014, URL: http://www.esa.int/spaceinimages/Images/2014/07/Rio_de_Janeiro_Brazil

191) "Mount Pinatubo, Philippines," ESA, July 4, 2014, URL: http://www.esa.int/spaceinimages/
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192) "Sentinel-1A aids Balkan flood relief," ESA, May 28, 2014, URL: http://www.esa.int/Our_Activities/Observing_the_
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193) "Lake Constance (Bodensee)," ESA, May 30, 2014, URL: http://www.esa.int/spaceinimages/Images/2014/05/Lake_Constance

194) "Greece guaranteed access to Sentinel data," ESA, May 12, 2014, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/
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195) "Copernicus Sentinels Serving Society and the Environment," Athens, Greece, May 12-13, 2014, URL: http://congrexprojects.com/2014-events/Copernicus/program

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198) "Radar image of the Netherlands," ESA, April 25, 2014, URL: http://www.esa.int/spaceinimages/Images/
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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