Copernicus: Sentinel-1 — The SAR Imaging Constellation for Land and Ocean Services
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.
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
- 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
- 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).
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.
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)
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)
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).
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)
Figure 4: Architecture of the avionics subsystem (image credit: TAS-I)
Table 4: Sentinel-1 attitude steering modes (Ref. 79)
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.
Legend of Figure 6:
• DSHA (Data Storage & Handling Assembly)
• TXA (Telemetry X-band transmission Assembly)
• XBAA (X-band Antenna Assembly)
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).
Figure 7: Architecture of the TXA (image credit: TAS)
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.
Figure 8: Sentinel-1 satellite block diagram (TAS-I, ESA, Ref. 15)
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.
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.
Figure 10: Isometric views of the deployed satellite (image credit: TAS-I)
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.
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)
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.
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.
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. 101).
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)
Note: As of July 2019, the previously single large Sentinel-1 file has been split into two files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the Sentinel-1 mission and its imagery in the period 2019
• July 12, 2019: A week after two strong earthquakes struck near the city of Ridgecrest in Southern California, NASA scientists and engineers continue to analyze satellite data for information on fault slips and ruptures. Their observations are helping local authorities assess damage and will also provide useful information to engineers for designing resilient structures that can withstand ruptures like the ones created by the latest quakes. 55)
- The ARIA (Advanced Rapid Imaging and Analysis) team at NASA's Jet Propulsion Laboratory in Pasadena, California, created this map depicting areas that are likely damaged as a result of the recent major earthquakes. The color variation from yellow to red indicates increasingly more significant surface change, or damage. The map covers an area of 155 by 186 miles (250 x 300 km), shown by the large red polygon. Each pixel measures about 30 m across.
- To make the map, the team used SAR (Synthetic Aperture Radar) images from the European Space Agency's Copernicus Sentinel-1 satellites from before and after the sequence of quakes - July 4 and July 10, 2019, respectively. The map may be less reliable over vegetated areas but can provide useful guidance in identifying damaged areas.
- NASA's Disasters Program is in communication with the California Earthquake Clearinghouse, which is coordinating response efforts with the California Air National Guard, the U.S. Geological Service and the Federal Emergency Management Agency. NASA analysts are using data from satellites to produce visualizations of land deformation and potential landslides, among other earthquake impacts, and are making them available to response agencies. NASA's Disasters Program promotes the use of satellite observations in predicting, preparing for, responding to and recovering from disasters around the world. - The ARIA Team's analysis was funded by NASA.
Figure 17: NASA's ARIA team produced this map of earthquake damage in Southern California from the recent temblors in July 2019. The color variation from yellow to red indicates increasingly more significant surface change, or damage (image credit: NASA/JPL-Caltech, ESA)
• July 12, 2019: ESA and the Asian Development Bank have joined forces to help the Indonesian government use satellite information to guide the redevelopment following the earthquake and tsunami that devastated the provincial capital of Palu and surroundings last year. 56)
Figure 18: On 28 September 2018, the Indonesian island of Sulawesi was struck by a 7.5 magnitude earthquake followed by a tsunami that devastated the provincial capital of Palu, which lies at the head of a long narrow bay. This map shows the ground motion during the six months following the event and was obtained by processing Copernicus Sentinel-1 images acquired between October 2018 and April 2019. Results overlay a true-color composite from the Copernicus Sentinel-2 mission. ESA and the Asian Development Bank have joined forces to help Indonesian authorities to use and interpret maps such as this to guide redevelopment plans (image credit: ESA, the image contains Copernicus Sentinel data (2018–19), processed by Planetek Rheticus Service)
- On 28 September 2018, the Indonesian island of Sulawesi was struck by a 7.5 magnitude earthquake. The epicenter was on the island's northwest coast – 77 km north of Palu, which lies at the head of a long narrow bay. The quake triggered a tsunami that swept huge surges of water – as high as 10 m – along the bay and swamped the city.
- The combination of the earthquake, tsunami, soil liquefaction and landslides claimed well over 2000 lives, destroyed homes, buildings, infrastructure and farmland in several districts.
Figure 19: On 28 September 2018, the Indonesian island of Sulawesi was struck by a 7.5 magnitude earthquake followed by a tsunami that devastated the provincial capital of Palu, which lies at the head of a long narrow bay. This terrain motion map uses Copernicus Sentinel-1 images acquired between October 2018 and April 2019 and provides information about the stability of individual buildings (image credit: ESA, the image contains Copernicus Sentinel data (2018–19), processed by Planetek Rheticus Service)
- With the authorities and relief organizations having spent the last nine months dealing with the aftermath, the shift is now into the recovery phase. This includes the daunting job of rebuilding the areas that were decimated by the disaster – and the Asian Development Bank and ESA have joined forces to help the Indonesian government with the task in hand.
- Through ESA's program to support sustainable development, the aim here is to provide environmental information products derived from Earth observation data and training in their use to Indonesia through the Asian Development Bank.
- The project, ‘Earth Observation for Sustainable Development – Disaster Risk Reduction', is led by the Spanish company Indra with the Italian SME Planetek as a partner along with the French Geological Survey BRGM who is the scientific advisor of ESA's Geohazard Exploitation Platform, an initiative that provides a cloud-processing service to support geological hazard mapping.
- The main purpose of sharing these information products is to help the authorities better understand the hazards associated with seismic activity, flooding and landslides so they can make more informed decisions in elaborating a redevelopment master plan.
- Data from the Copernicus Sentinel-1 radar mission can detect ground movement of millimeters in and across wide areas and, therefore, provides a detailed picture of land deformation.
Figure 20: Following the earthquake and tsunami that hit the Indonesian island of Sulawesi in September 2018, ESA and the Asian Development Bank have been helping the authorities better understand the hazards associated with seismic activity, flooding and landslides through the use of satellite data. The project included a week-long training course in Jakarta, which explored services from ESA's Geohazards Exploitation Platform. Ground displacement rate maps of Jakarta that use information from the Copernicus Sentinel-1 mission, as shown here, were used in the course. In this case displacement is largely a result of groundwater extraction. Values correspond to line-of-sight velocities. Local displacement patterns reach about 12 cm/year. The inset zooms-in over Jakarta's harbor and is overlaid by displacement rates higher than 1.5 cm/year (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, GEP, CNR-IREA & BRGM)
- Ground-motion maps of before and after the earthquake have been produced through Planetek's automatic cloud-based ‘Rheticus Displacement' monitoring service. Accurate to a few millimeters, these maps are based on Copernicus Sentinel-1 radar data and are helping the authorities evaluate the effect that the disaster has had on the land surface stability.
- In addition to these information products, the project also included a week-long course in Jakarta organized by the Asian Development Bank and the Indonesian National Institute of Aeronautics and Space. Attended by more than 60 representatives from numerous Indonesian institutions, experts from Indra, Planetek and BRGM explained technical details, methodologies and usage of these satellite data products.
Figure 21: Learning about satellite data. Organized by the Asian Development Bank and the Indonesian National Institute of Aeronautics and Space, a week-long course was held in Jakarta to help authorities use satellite data to understand ground deformation following the earthquake and tsunami that hit the Indonesian island of Sulawesi in September 2018. The course was attended by more than 60 representatives from numerous Indonesian authorities. Experts from Indra, Planetek and BRGM explained the technical details and methodologies of using these satellite data products. Lecturers Michael Foumelis (BRGM), Alberto Lorenzo Alonso (Indra) and Vincenzo Massimi (Planetek) are sitting fifth, sixth and seventh from the left, respectively (image credit: LAPAN)
- Paolo Manunta, who helps ESA with on-site support to the Asian Development Bank, noted, "Users explained that they are particularly interested in the ground deformation maps – they offer great insight into how the land surface has changed and are essential for Indonesia to redevelop effectively."
- The team has also suggested that the Indonesian government additionally use ESA's online Geohazard Exploitation Platform, which is designed to support the users looking at seismic risks, volcanoes, subsidence and landslides. It allows the seamless browsing, access and processing of vast amounts of satellite data, plus the software tools to extract useful knowledge.
- The workshop included discussions on how space technology can support hazard and risk mapping in Indonesia and the user feedback obtained will serve as input for discussions between ESA, the Japanese Space Agency and the Asian Development Bank on how to further improve Earth observation for international development.
• June 21, 2019: The Copernicus Sentinel-1 mission takes us over the Lena River Delta, the largest delta in the Arctic. At nearly 4500 km long, the Lena River is one of the longest rivers in the world. The river stems from a small mountain lake in southern Russia, and flows northwards before emptying into the Arctic Ocean, via the Laptev Sea. 57)
- The river is visible in bright yellow, as it splits and divides into many different channels before meandering towards the sea. Sediments carried by the waters flow through a flat plain, creating the Lena River Delta. Hundreds of small lakes and ponds are visible dotted around the tundra.
- The delta's snow-covered tundra is frozen for most of the year, before thawing and blossoming into a fertile wetland during the brief polar summer – a 32,000 km2 haven for Arctic wildlife. Swans, geese and ducks are some of the migratory birds that breed in the productive wetland, which also supports fish and marine mammals.
- In 1995, the Lena Delta Reserve was expanded, making it the largest protected area in Russia.
Figure 22: This false-color image was captured on 14 January 2019, the peak of the Arctic winter, and shows a large amount of ice in the waters surrounding the delta. Cracks can be seen in the turquoise-colored ice at the top of the image, and several icebergs can also be seen floating in the Arctic waters to the right. Snow can also be seen in yellow on the mountains at the bottom of the image. This image is also featured in this week's edition of the Earth from Space program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• April 12, 2019: The Copernicus Sentinel-1 mission takes us over the busy maritime traffic passing through the English Channel. 58)
- Many vessels crossing at the narrowest part of the English Channel can be seen in the far right of the image. Connecting Dover in England to Calais in northern France, the Strait of Dover is another major route, with over 400 vessels crossing every day. The shortest distance across the Channel is just 33 km, making it possible to see the opposite coastline on a clear day.
- The cities of London and Paris, other towns and buildings and even wind turbines in the English Channel are visible in white owing to the strong reflection of the radar signal.
Figure 23: 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. Here, hundreds of radar images spanning 2016 to 2018 over the same area have been, compressed into a single image. The sea surface reflects the radar signal away from the satellite, making water appear dark in the image. This contrasts metal objects, in this case ships, which appear as bright dots in the dark water. Boats that passed the English Channel in 2016 appear in blue, those from 2017 appear in green, and those from 2018 appear in red. Owing to its narrowness, as well as its strategic connection of the Atlantic Ocean and the North Sea, the Channel is very busy with east-west ship traffic. Because of the volume of vessels passing through daily, a two-lane scheme is used, in order to avoid collisions. The two lanes can easily be detected in the image. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2016-18), processed by ESA, CC BY-SA 3.0 IGO)
• March 29, 2019: Separating the Black Sea and the Sea of Marmara, the strait is one of the busiest maritime passages in the world, with around 48,000 ships passing through every year. Daily traffic includes international commercial shipping vessels and oil tankers, as well as local fishing and ferries. Ships in the strait can be seen in the image as multi-colored dots. Three bridges are also visible spanning the strait and connecting the two continents. 59)
- 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. The multi-temporal remote sensing technique combines two or more radar images over the same area to detect changes occurring between acquisitions.
- In the far-left of the image of Figure 24, the aqua-green patches of land show the changes in the fields between the three satellite acquisitions.
- Turkey's most populous city, Istanbul (population of around 15 million residents in its metropolitan area) , can be seen on both sides of the Bosphorus (mostly spelled as Bosporus). The city appears in shades of white owing to the stronger reflection of the radar signal from buildings, which contrasts with the dark black color of the inland lakes and surrounding waters.
Figure 24: Captured by the Copernicus Sentinel-1 mission, this image shows the narrow strait that connects eastern Europe to western Asia: the Bosphorus in northwest Turkey. The image contains satellite data stitched together from three radar scans acquired on 2 June, 8 July and 13 August 2018. 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)
• March 27, 2019: It is thought that well over a million people have been affected by what is probably the worst storm on record to hit the southern hemisphere. Making landfall on 15 March 2019, Cyclone Idai ripped through Mozambique, Malawi and Zimbabwe, razing buildings to the ground, destroying roads and inundating entire towns, villages and swathes of farmland. The human death toll is still unknown. While humanitarian efforts continue, people are now also facing the mammoth task of picking up the pieces and cleaning up after this devastating storm. 60)
- Images from Copernicus Sentinel-1 contributed to activations triggered in the Copernicus Emergency Management Service and the International Charter Space and Major Disasters. Both services take advantage of observations from several satellites and provide on-demand mapping to help civil protection authorities and the international humanitarian community in the face of major emergencies.
Figure 25: This Copernicus Sentinel-1 image indicates where the flood waters are finally beginning to recede west of the port city of Beira in Mozambique. The image merges three separate satellite radar images from before the storm on 13 March, from one of the days when the floods were at their worst on 19 March, and as the waters are beginning to drain away on 25 March. The blue-purple color indicates where floodwater is receding, while areas shown in red are still underwater (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• March 20, 2019: Copernicus Sentinel-1 acquired this radar image of the oil slick, the large, dark patch visible in the center of the image, stretching about 50 km. Marine vessels are identifiable as smaller white points, which could be those assisting in the clean-up process. 61)
- Oil is still emerging from the ship now lying at a depth of around 4500 meters. French authorities trying to reduce the impact of pollution along the coast.
- Satellite radar is particularly useful for monitoring the progression of oil spills because the presence of oil on the sea surface dampens down wave motion. Since radar basically measures surface texture, oil slicks show up well – as black smears on a grey background.
Figure 26: Captured on 19 March at 17:11 GMT (18:11 CET) by the Copernicus Sentinel-1 mission, this image shows the oil spill from the Grande America vessel. The Italian container ship, carrying 2200 tons of heavy fuel, caught fire and sank in the Atlantic, about 300 km off the French coast on 12 March (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• March 20, 2019: As millions of people in Mozambique, Malawi and Zimbabwe struggle to cope with the aftermath of what could be the southern hemisphere's worst storm, Copernicus Sentinel-1 is one of the satellite missions being used to map flooded areas to help relief efforts. 62)
Figure 27: Millions of people in Mozambique, Malawi and Zimbabwe are struggling to cope with the aftermath of what could be the southern hemisphere's worst storm: Cyclone Idai. This image is from Copernicus Sentinel-1 and shows the extent of flooding, depicted in red, around the port town of Beira in Mozambique on 19 March. This mission is also supplying imagery through the Copernicus Emergency Mapping Service to aid relief efforts (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
- Cyclone Idai swept through this part of southeast Africa over the last few days, leaving devastation in its wake. Thousands of people have died and houses, roads and croplands are under water.
- It is currently thought that well over two million people in the three countries have been affected, but the extent of destruction is still unfolding.
- It is currently thought that well over two million people in the three countries have been affected, but the extent of destruction is still unfolding.
Figure 28: Captured by the Copernicus Sentinel-3 mission, this image shows Cyclone Idai on 13 March 2019 west of Madagascar and heading for Mozambique. Here, the width of the storm is around 800–1000 km, but does not include the whole extent of Idai. The storm went on to cause widespread destruction in Mozambique, Malawi and Zimbabwe. With thousands of people losing their lives, and houses, roads and croplands submerged, the International Charter Space and Major Disasters and the Copernicus Emergency Mapping Service were triggered to supply maps of flooded areas based on satellite data to help emergency response efforts (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA)
- In order to plan and execute this kind of emergency response it is vital to understand exactly which areas have been affected – especially as accessing people cut off is extremely challenging.
- Satellites orbiting Earth can provide indispensable up-to-date information to observe such events, as shown here on the right from the Copernicus Sentinel-3 mission, and, importantly, to map flooded areas for response teams facing these dire situations.
- The disaster triggered activations in both the Copernicus Emergency Mapping Service and the International Charter Space and Major Disasters.
- Both services take advantage of observations from several satellites and provide on-demand mapping to help civil protection authorities and the international humanitarian community in the face of major emergencies.
- The image of Figure 27 is from Copernicus Sentinel-1 and shows the extent of flooding, depicted in red, around the port town of Beira in Mozambique on 19 March. The image of Figure 29 uses the mission to map the flood for relief response through the Copernicus Emergency Mapping Service.
- 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.
Figure 29: Tropical Cyclone Idai made landfall on 14 March 2019 close to the port city of Beira in Mozambique. This map, which was generated through the Copernicus Emergency Management Service, uses information from the EC's Copernicus Sentinel-1 mission on 19 March (bright blue), and Italy's Cosmo-SkyMed satellite on 16 March (light blue) to map the floods to aid relief efforts. More maps of floods caused by Cyclone Idai are available at the Copernicus Emergency Management Service website (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), Cosmo-SkyMed, processed by GAF AG/e-GEOS/CMEMS)
• March 14, 2019: The Bering Strait is a sea passage that separates Russia and Alaska. It is usually covered with sea ice at this time of year – but as this image captured by the Copernicus Sentinel-1 mission on 7 March 2019 shows, it is virtually ice-free. 63)
- The extent of sea ice in the Bering Sea has dropped lower than it has been since written records began in 1850, and is most likely because of warm air and water temperatures. On average, the fluctuating sea ice in this region increases until early April, depending on wind and wave movement.
- To travel between Arctic and Pacific, marine traffic passes through the Bering Strait. Owing to the reduction of ice in the region, traffic has increased significantly.
- The Copernicus Sentinel-1 satellites provide images to generate maps of sea-ice conditions for safe passage in the busy Arctic waters, as well as distinguish between thinner, more navigable first-year ice and thicker, more hazardous ice. Each satellite carries an advanced radar instrument to image Earth's surface through cloud and rain, regardless of whether it is day or night.
Figure 30: The Bering Strait is a narrow passage - around 80 km wide - connecting the Pacific and Arctic Oceans. The few patches of sea ice are shown in light-blue colors. According to the National Snow & Ice Data Center in Boulder, CO, between 27 January to 3 March 2019, sea-ice extent decreased from 566,000 km2 to 193,000 km2. Sea ice was also exceptionally low last year, but it has been reported that this March the extent of sea ice is the lowest in the 40-year satellite record (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• March 14, 2019: The Copernicus Sentinel-1 radar mission shows how cracks cutting across Antarctica's Brunt ice shelf are on course to truncate the shelf and release an iceberg about the size of Greater London – it's just a matter of time. 64)
- The Brunt ice shelf is an area of floating ice bordering the Coats Land coast in the Weddell Sea sector of Antarctica.
Figure 31: Using radar images from the Copernicus Sentinel-1 mission the animation shows two lengthening fractures: a large chasm running northwards and a split, dubbed Halloween Crack, that has been extending eastwards since October 2016. They are now only separated by a few kilometers. The image show two lengthening fractures: a large chasm, Chasm 1, running northwards and a split, dubbed Halloween Crack, that has been extending eastwards since October 2016. They are now only separated by a few kilometers. Halloween Crack runs from an area known as McDonald Ice Rumples, which is where the underside of the otherwise floating ice sheet is grounded on the shallow seabed. This pinning point slows the flow of ice and crumples the ice surface into waves. The Copernicus Sentinel-1 mission carries radar, which can return images regardless of day or night and this allows us year-round viewing, which is especially important through the long, dark, austral winter months (video credit: ESA, the video contains modified Copernicus Sentinel data (2016–19), processed by ESA)
- The Brunt ice shelf is at its maximum extent during the satellite era and compared to images collected by Argon declassified intelligence satellite photographs in 1963 and maps made by Frank Worsley during the Endurance expedition into the Weddell Sea in 1915.
Figure 32: Changing locations of Brunt calving. A comparison of the Brunt ice shelf calving front locations over the last 100 years, based on 1915 and 1958 historical survey data from the Endurance expedition (Worsley 1921) and the International Geophysical Year, respectively, followed by the location in satellite images from Landsat in 1973 and 1978, ESA's, Envisat in 2011, and Copernicus Sentinel-1 in 2019. A comparison of the images indicates that the Brunt ice shelf is at its maximum 20th Century extent (image credit: ESA, the image contains modified Copernicus Sentinel-2 data (2019), courtesy Stef l'Hermitte TU Delft)
- History shows that the last event was in 1971 when a portion of ice calved north of the Ice Rumples and in what appears to have been a previous iteration of today's Halloween Crack which is separating along lines of weakness.
- Mark Drinkwater, Head of ESA's Earth and Mission Science Division, says, "Importantly, tracking the entire ice shelf movement reveals a lot going on north of the Halloween Crack, where the shelf flows in a more northerly direction. Meanwhile, this divergence is splitting the northern and southern parts of the shelf along the Halloween Crack. Interestingly, the animation also reveals a widening split right across the Ice Rumples, which may also put the structural integrity of this northern outer segment into question. We have been observing the Brunt ice shelf for decades and it is constantly changing. Early maps made in the 1970s indicate that the ice shelf was more like a mass of small icebergs welded together by sea ice."
Figure 33: Cracks cutting across Antarctica's Brunt ice shelf are on course to truncate the shelf and release an iceberg about the size of Greater London. The Brunt ice shelf is an area of floating ice bordering the Coats Land coast in the Weddell Sea sector of Antarctica (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
Legend to Figure 33: This Copernicus Sentinel-2 image from 7 February 2019 shows two lengthening fractures: a large chasm running northwards and a split, dubbed Halloween Crack, that has been extending eastwards since October 2016. They are now only separated by a few kilometers. The Halloween Crack runs from an area known as McDonald Ice Rumples, which is where the underside of the otherwise floating ice sheet is grounded on the shallow seabed. This pinning point slows the flow of ice and crumples the ice surface into waves. Routine monitoring by satellites with different observing capabilities offer unprecedented views of events happening in remote regions like Antarctica, and how ice shelves manage to retain their structural integrity in response to changes in ice dynamics, air and ocean temperatures.
- As the ice flows down the steep coastal area and across the grounding line into the floating ice shelf, it fractures into a series of regular blocks. The structural integrity of the shelf relies on the fractures being filled over decades by marine ice and snow. Since Copernicus Sentinel-1 radar penetrates through the surface snow, this pattern of fractures is revealed to give Brunt its skeletal-like appearance.
- When the chasm and cracks around McDonald ice rumples finally intersect, it is likely that the northern end of the calved iceberg remains pinned by its grounding point, leaving the southern end of the berg to swing out into the ocean.
- Although it may be the biggest berg observed to break off Brunt, compared to the recent Larsen ice shelf iceberg A68, for example, it won't be a particularly large one. However, the concern is that this calving could allow the ice left behind to flow more freely towards the ocean.
- "We are now poised for this eventual calving, which could have consequences for the ice shelf as a whole. After the 1971 calving, ice shelf velocities are reported to have doubled from 1 to 2 m/day. So we will be carefully monitoring the ice shelf with the combination of both Copernicus Sentinel-1 and Copernicus Sentinel-2, which carries an optical instrument, to see how the dynamics influence the integrity of the remaining ice sheet," continues Dr Drinkwater.
- With the ice shelf currently deemed unsafe, the British Antarctic Survey (BAS) has closed up their Halley VI research station, which was repositioned south of Halloween Crack and east of the chasm in 2017.
- The station used to be operational all year round, but this is the third winter running that it has had to close because of potential danger.
- There has been a permanent research station on Brunt since the late 1950s, but in 2016–17 the base was dragged 23 km to its current, more secure location. If it had not been moved, it would now be on the seaward side of the chasm.
- Routine monitoring by satellites with different observing capabilities offer unprecedented views of events happening in remote regions like Antarctica, and how ice shelves manage to retain their structural integrity in response to changes in ice dynamics, air and ocean temperatures.
- The Copernicus Sentinel-1 mission carries radar, which can return images regardless of day or night and this allows us year-round viewing, which is especially important through the long, dark, austral winter months. A recent image from the Copernicus Sentinel-2 mission provides complementary information.
• February 22, 2019: When Mount Agung, a volcano on the island of Bali in Indonesia erupted in November 2017, the search was on to find out why it had stirred. Thanks to information on ground deformation from the Copernicus Sentinel-1 mission, scientists now have more insight into the volcano's hidden secrets that caused it to reawaken. 65)
Figure 34: Copernicus Sentinel-1 InSAR data shows ground uplift on the flank of Mount Agung, which is on the island of Bali in Indonesia. The data show uplift between August and November 2017, prior to the eruption of Mount Agung on 27 November. The eruption was preceded by a wave of small earthquakes. A team led by Bristol University's School of Earth Sciences in the UK used radar data from the Copernicus Sentinel-1 radar mission and the technique of InSAR to map ground motion, which may indicate that fresh magma is moving beneath the volcano. Their research provides the first geophysical evidence that Agung and the neighboring Batur volcano may have a connected plumbing system (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by University of Bristol/COMET)
- After lying dormant for more than 50 years, Mount Agung on the Indonesian holiday island of Bali rumbled back to life in November 2017, with smoke and ash causing airport closures and stranding thousands of visitors.
- Fortunately, it was preceded by a wave of small earthquakes, signalling the imminent eruption and giving the authorities time to evacuate around 100,000 people to safety.
- The prior event in 1963, however, claimed almost 2000 lives and was one of the deadliest volcanic eruptions of the 20th century. Knowing Agung's potential for devastation, scientists have gone to great lengths to understand this volcano's reawakening.
- And, Agung has remained active, slowly erupting on and off since 2017.
- Bali is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. A clue came from the fact that Agung's 1963 eruption was followed by a small eruption at its neighboring volcano, Batur, 16 km away.
- A paper published recently in Nature Communications describes how a team of scientists, led by the University of Bristol in the UK, used radar data from the Copernicus Sentinel-1 mission to monitor the ground deformation around Agung. 66)
- Their findings may have important implications for forecasting future eruptions in the area, and indeed further afield.
Figure 35: As an advanced radar mission, Sentinel-1 satellites can image the surface of Earth through cloud and rain and regardless of whether it is day or night. This makes it an ideal mission, for example, for monitoring the polar regions, which are in darkness during the winter months and for monitoring tropical forests, which are typically shrouded by cloud. Over oceans, the mission will provide imagery to generate timely maps of sea-ice conditions for safe passage, to detect and track oil spills and to provide information on wind and waves, for example. Over land, Sentinel-1's systematic observations will be used, for example, to track changes in the way the land is used and to monitor ground movement. Moreover, this new mission is designed specifically for fast response to aid emergencies and disasters such as flooding and earthquakes (video credit: ESA/ATG medialab)
- They used the remote sensing technique of InSAR (Interferometric Synthetic Aperture Radar), where two or more radar images over the same area are combined to detect slight surface changes.
- Tiny changes on the ground cause differences in the radar signal and lead to rainbow-colored interference patterns in the combined image, known as a SAR interferogram. These interferograms can show how land is uplifting or subsiding.
- Juliet Biggs from Bristol University's School of Earth Sciences, said, "Using radar data from the Copernicus Sentinel-1 radar mission and the technique of InSAR, we are able to map any ground motion, which may indicate that fresh magma is moving beneath the volcano."
- In the study, which was carried out in collaboration with the Center for Volcanology and Geological Hazard Mitigation in Indonesia, the team detected uplift of about 8–10 cm on Agung's northern flank during the period of intense earthquake activity prior to the eruption.
- Fabien Albino, also from Bristol's School of Earth Sciences and who led the research, added, "Surprisingly, we noticed that both the earthquake activity and the ground deformation signal were five kilometers away from the summit, which means that magma must be moving sideways as well as vertically upwards. - Our study provides the first geophysical evidence that Agung and Batur volcanoes may have a connected plumbing system. This has important implications for eruption forecasting and could explain the occurrence of simultaneous eruptions such as in 1963."
- Part of European Union's fleet of Copernicus missions, Sentinel-1 is a two-satellite constellation that can provide interferometric information 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.
- ESA's Copernicus Sentinel-1 mission manager, Pierre Potin, noted, "We see the mission is being used for a multitude of practical applications, from mapping floods to charting changes in ice. Understanding processes that are going on below the ground's surface – as demonstrated by this new research – is clearly important, especially when these natural processes can put people's lives and property at risk."
- While the European Union is at the helm of Copernicus, ESA develops, builds and launches the dedicated Sentinel satellites. It also operates some of the missions and ensures the availability of data from third party missions contributing to the Copernicus program.
Figure 36: This image of Mount Agung on the Indonesian island of Bali was captured on 2 July 2018 by the Copernicus Sentinel-2 mission (the image was released on 22 February 2019, offering a ‘camera-like' view of the Agung and Batur volcanoes). After being dormant for 50 years, Mount Agung erupted in November 2017. It has continued to erupt on and off since then – a bright orange spot can be seen in the volcano's crater. Recent research provides evidence that Agung and the neighboring Batur volcano, visible northwest of Agung, may have a connected magma plumbing system (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• 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. 67)
- 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.
Figure 37: 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. 68)
- 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.
Figure 38: 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 39: 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. 69)
Legend to Figure 39: 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.
Figure 40: 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. 69)
- "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.