Minimize Copernicus: Sentinel-3

Copernicus: Sentinel-3 — Global Sea/Land Monitoring Mission including Altimetry

Spacecraft     Launch    Mission Status     Sensor Complement    Ground Segment    References

The Sentinel-3 (S3) mission of ESA and the EC is one of the elements of the GMES (Global Monitoring for Environment and Security) program, which responds to the requirements for operational and near-real-time monitoring of ocean, land and ice surfaces over a period of 20 years. The topography element of this mission will serve primarily the marine operational users but will also allow the monitoring of sea ice and land ice, as well as inland water surfaces, using novel observation techniques.The Sentinel-3 mission is designed as a constellation of two identical polar orbiting satellites, separated by 180º, for the provision of long-term operational marine and land monitoring services. The operational character of this mission implies a high level of availability of the data products and fast delivery time, which have been important design drivers for the mission. 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14)

The Sentinel-3 program represents a series of operational spacecraft over the envisioned service period to guarantee access to an uninterrupted flow of robust global data products.

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 15)

The main observation objectives of the mission are summarized in the following list:

• Ocean and land color observation data, free from sun-glint, shall have a revisit time of 4 days (2 days goal) and a quality at least equivalent to that of Meris instrument on Envisat. The actual revisit obtained over ocean at the equator (worst case) is less than 3.8 days with a single satellite and drops below 1.9 days with 2 satellites, phased 180° on the same orbital plane.

• Ocean and land surface temperature shall be acquired with at least the level of quality of AATSR on Envisat, and shall have a maximum revisit time of 4 days with dual view (high accuracy) observations and 1 day with single view. Achieved performance is shown to be significantly better, even with a single satellite (dual view: 3.5 days max, 1.8 days average).

• Surface topography observations shall primarily cover the global ocean and provide sea surface height (SSH) and significant wave height (SWH) to an accuracy and precision at least equivalent to that of RA-2 on Envisat. Additionally, Sentinel-3 shall provide surface elevation measurements -in continuity to CryoSat-2 - over ice regions covered by the selected orbit, as well as measurements of in-land water surfaces (rivers and lakes).

In addition, Sentinel-3 will provide surface vegetation products derived from synergistic and co-located measurements of optical instruments, similar to those obtained from the Vegetation instrument on SPOT, and with complete Earth coverage in 1 to 2 days.

The EU Marine Core Service (MCS) and the Land Monitoring Core Service (LMCS), together with the ESA GMES Service Element (GSE), have been consolidating those services where continuity and success depends on operational data flowing from the Sentinels.

The operational character of the mission implies a high level of availability of the data products and fast delivery time, which have been important design drivers for the mission.

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Figure 1: Artist's rendition of the deployed Sentinel-3 spacecraft (image credit: ESA/ATG medialab) 16)

Legend to Figure 1: Sentinel-3 is arguably the most comprehensive of all the Sentinel missions for Europe’s Copernicus programme. Carrying a suite of state-of-the-art instruments, it provides systematic measurements of Earth’s oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics and provide critical information for ocean and weather forecasting.

Spacecraft:

The Sentinel-3 spacecraft is being built by TAS-F (Thales Alenia Space-France). A contract to this effect was signed on April 14, 2008. The spacecraft is 3-axis stabilized, with nominal pointing towards the local normal and yaw steering to compensate for the Earth rotation affecting the optical observations. The spacecraft has a launch mass of about 1150 kg, the height dimension is about 3.9 m. The overall power consumption is 1100 W. The design life is 7.5 years, with ~100 kg of hydrazine propellant for 12 years of operations, including deorbiting at the end.

AOCS (Attitude and Orbit Control Subsystem): The spacecraft is 3-axis stabilized based on the new generation of avionics for the TAS-F LEO (Low Earth Orbit) platform. The AOCS software of the GMES/Sentinel-3 project is of PROBA program heritage. NGC Aerospace Ltd (NGC) of Sherbrooke, (Québec), Canada was responsible for the design, implementation and validation of the autonomous GNC (Guidance, Navigation and Control) algorithms implemented as part of the AOCS software of PROBA-1, PROBA-2, and PROBA-V. 17)

Spacecraft launch mass, design life

~1150 kg, 7.5 years (fuel for additional 5 years)

Spacecraft bus dimensions

3.9 m (height) x 2.2 m x 2.21 m

Spacecraft structure

Build around a CFRP (Carbon Fiber Reinforced Plastics) central tube and shear webs

AOCS (Attitude and Orbit Control Subsystem)

- 3 axis stabilization
- Gyroless in nominal mode, thanks to a high performance
- Multi-head star tracker (HYDRA) and GNSS receiver.
- Use of thrusters only in Orbit Control Mode.

Pointing type

Geodetic + yaw steering

Absolute pointing error
Absolute measurement error

< 0.1º
< 0.015º

Thermal control

- Passive control with SSM radiators
- Active control of the bus centralized on the SMU (Satellite Management Unit)
- Autonomous thermal control management for most of the sensors.

EPS (Electrical Power Subsystem)

- Unregulated power bus, with a Li-ion battery and GaAs solar array.
- Solar Array 1 wing, 3 panels , 10.5 m2, power of 2300 W EOL,
- Average power consumption in nominal mode: up to 1100 W

Mechanisms

- Stepper motor SADM (Solar Array Drive Mechanism)
- Synchronized solar array hold-down and deployment mechanism

Propulsion

- Monopropellant (hydrazine) operating in blow-down mode
- Two sets of four 1 N thrusters/propellant mass: ~100 kg

Data handling and software

Centralized SMU running applications for all spacecraft subsystems processing tasks, complemented by a PDHU (Payload Data Handling Unit) for instruments data acquisition and formatting before transmission to the ground segment.

Operational autonomy

27 days

Table 2: Overview of Sentinel-3 spacecraft parameters

Data handling architecture: The requirements for the Sentinel-3 data handling architecture call for: a) minimized development risks, b) system at minimum cost, c) operational system over 20 years. This has led to design architecture as robust as possible using a single SMU (Satellite Management Unit) computer as the platform controller, a single PDHU (Payload Data-Handling Unit) for mission data management, and to reuse existing qualified heritage. 18)

The payload accommodates 6 instruments, sources of mission data. The 3 high rate instruments provide mission data directly collected through the SpaceWire network, while the low rate instruments are acquired by the central computer for distribution through the SpaceWire network to the mass memory. The PDHU acquires and stores all mission data for latter multiplexing, formatting, encryption and encoding for download to the ground.

The payload architecture is built-up over a SpaceWire network (Figure 2) for direct collection of high rate SLSTR, OLCI and SRAL instruments and indirect collection of low rate MWR, GNSS and DORIS instrument data plus house-keeping data through the Mil-Std-1553 bus by the SMU, all data being acquired from SpaceWire links and managed by the PDHU.

The mission data budget is easily accommodated thanks to the SpaceWire performance. Each SpaceWire link being dedicated to point-to-point communication without interaction on the other links (no routing), the frequency is set according to the need plus a significant margin. The PDHU is able to handle the 4 SpaceWire sources at up to 100 Mbit/s.

All mission data sources (OLCI, SLSTR, SRAL and SMU) provide data through two cold redundant interfaces and harnesses. The PDHU, being critical as the central point of the mission data management, implements a full cross-strapping between nominal and redundant sources interfaces and its nominal and redundant sides.

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Figure 2: SpaceWire architecture of the Sentinel-3 spacecraft (image credit: TAS-F)

The PDHU SpaceWire interfaces are performed thanks to a specific FPGA, the instrument’s ones are based on the ESA Atmel SMCS-332, while the SMU interfaces are implemented by an EPICA ASIC circuit developed by Thales Alenia Space.

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Figure 3: Schematic view of a full cross-strap redundancy within the PDHU (image credit: TAS-F, Ref. 18)

RF communications: The S-band is used for TT&C transmissions The S-band downlink rate is 123 kbit/s or 2 Mbit/s, the uplink data rate is 64 kbit/s. The X-band provide the payload data downlink at a rate of 520 Mbit/s. An onboard data storage capacity of 300 Gbit (EOL) is provided for payload data.

Four categories of data products will be delivered: ocean color, surface topography, surface temperature (land and sea) and land. The surface topography products will be delivered with three timeliness levels: NRT (Near-Real Time, 3 hours), STC (Standard Time Critical, 1-2 days) and NTC (Non-Time Critical, 1 month). Slower products allow more accurate processing and better quality. NRT products are ingested into numerical weather prediction and seastate prediction models for quick, short term forecasts. STC products are ingested into ocean models for accurate present state estimates and forecasts. NTC products are used in all high-precision climatological applications, such as sealevel estimates.

The resulting analysis and forecast products and predictions from ocean and atmosphere adding data from other missions and in situ observations, are the key products delivered to users. They provide a robust basis for downstream value-added products and specialized user services.

Introduction of new technology: A newly developed MEMS rate sensor (gyroscope), under the name of SiREUS, will be demonstrated on the AOCS of Sentinel-3. The gyros will be used for identifying satellite motion and also to place it into a preset attitude in association with optical sensors after its separation from the launcher, for Sun and Earth acquisition. Three of the devices will fly inside an integrated gyro unit, each measuring a different axis of motion, with a backup unit ensuring system redundancy. Each unit measures 11 cm x 11 cm x 7 cm, with an overall mass of 750 grams. 19)

The SiREUS device is of SiRRS-01 heritage, a single-axis rate sensor built by AIS (Atlantic Inertial Systems Ltd., UK), which is using a ’vibrating structure gyro’, with a silicon ring fixed to a silicon structure and set vibrating by a small electric current. The SiRRS-01 MEMS gyro has been used in the automobile industry. These devices are embedded throughout modern cars: MEMS accelerometers trigger airbags, MEMS pressure sensors check tires and MEMS gyros help to prevent brakes locking and maintain traction during skids. - In a special project, ESA selected the silicon-based SiRRS-01 to have it modified for space use (and under the new name of SiREUS).

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Figure 4: Photo of the MEMS rate sensor (image credit: ESA)

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Figure 5: Alternate view of the Sentinel-3 spacecraft and the accommodation of the payload (image credit: ESA)

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Figure 6: Photo of the Sentinel-3A spacecraft in the cleanroom of Thales Alenia Space in Cannes, France with the solar wings attached (image credit: ESA, A. Le Floc’h) 20)



Status of project development

• May 04, 2020: During these unprecedented times of the COVID-19 lockdown, trying to work poses huge challenges for us all. For those that can, remote working is now pretty much the norm, but this is obviously not possible for everybody. One might assume that like many industries, the construction and testing of satellites has been put on hold, but engineers and scientists are finding ways of continuing to prepare Europe’s upcoming satellite missions such as the next Copernicus Sentinels. 21)

- Despite COVID-19, a milestone has been reached for the Copernicus Sentinel-3 mission, with the transport of the ‘D’ satellite platform from Thales Alenia Space in Rome, Italy, to Cannes in France.

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Figure 7: The Copernicus Sentinel-3D arrives in Cannes (image credit: Thales Alenia Space)

- There are currently two Sentinel-3 satellites in orbit: Sentinel-3A and Sentinel-3B. They work as a pair to measure systematically Earth’s oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics, and to provide essential information in near-real time for ocean and weather forecasting.

- To ensure continuity, they will eventually be replaced by Sentinel-3C and Sentinel-3D. Therefore, work is ongoing to prepare these next satellites.

- Nic Mardle, ESA’s Copernicus Sentinel-3 project manager, said, “At the start of the restrictions the Thales team in Italy worked particularly hard to try to complete everything for Sentinel-3D before a full lockdown was imposed. Single shifts with no hand-over allowed two teams to continue working on the satellite with no risk of infecting each other.

- “They were almost complete when the full shutdown of the facilities was announced, but this did not stop the Thales teams in Italy and in France and us at ESA, as we all continued by working remotely to get though the all-important ‘Delivery Review Board’.

- As soon as Thales’ facilities could be accessed again, the teams completed the few final activities including the packing and shipment preparations and finalized the necessary approvals from Italian and French governments, so that the satellite platform could be transported by road from Italy to France.

- Sentinel-3D arrived safely at the Cannes facilities in the night of 21 April and was unpacked by the Thales-Alenia Cannes team with the remote support from their colleagues in Rome.

- Nic added, “Activities are definitely more complicated in this period, but all teams are working together to facilitate the continuation of the program in the most efficient and pragmatic way, finding solutions to the new problems caused by the impacts the virus, while ensuring that the health and safety of the teams involved is ensured.”

- Josef Aschbacher, ESA’s Director of Earth Observation Programs, noted, “Everybody is working under extremely difficult circumstances and I’m really happy to see that work continues to prepare numerous new missions.

- “This is not only vital to ensure the continuity of measurements of our planet from space to understand and monitor environmental changes that are affecting society worldwide, but also we need to keep demonstrating new space technologies for the future. And, with COVID-19 affecting the economy so badly, we are making every effort to keep the space industry and downstream ventures in business.”

• April 13, 2018: The team of propulsion experts has spent two days carrying out the tricky task of fuelling the Copernicus Sentinel-3B satellite with 130 kg of hydrazine and pressurizing the tank for its life in orbit. 22) 23)

- Since hydrazine is extremely toxic, only specialists remained in the cleanroom for the duration. A doctor and security staff waited nearby with an ambulance and fire engine ready to respond to any problems.

- The satellite is scheduled for liftoff on 25 April from Russia’s Plesetsk Cosmodrome at 17:57 GMT (19:57 CEST).

- In orbit it will join its identical twin, Sentinel-3A, which was launched in 2016. This pairing of satellites provides the best coverage and data delivery for Copernicus.

- Sentinel-3B is the seventh Sentinel satellite to be launched for Copernicus. Its launch will complete the constellation of the first set of Sentinel missions for Europe’s Copernicus program.

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Figure 8: Fuelling of the Sentinel-3B spacecraft (image credit: Thales Alenia Space)

• March 23, 2018: With the Sentinel-3B satellite now at the Plesetsk launch site in Russia and liftoff set for 25 April, engineers are steaming ahead with the task of getting Europe’s next Copernicus satellite ready for its journey into orbit. 24)

- After arriving at the launch site on 18 March, the satellite has been taken out of its transport container and is being set up for testing. Kristof Gantois, ESA’s Sentinel-3 engineering manager, said, “The satellite’s journey from France was hampered slightly by the freezing winter weather here in Russia, but it’s now safe in the milder cleanroom environment.

- Sentinel-3B will join its twin, Sentinel-3A, in orbit. The pairing of identical satellites provides the best coverage and data delivery for Europe’s Copernicus program – the largest environmental monitoring program in the world.

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Figure 9: Following its arrival at Russia’s Plesetsk launch site, the Copernicus Sentinel-3B satellite has been removed from its transport container. The satellite will now be prepared for liftoff, scheduled for 25 April 2018. Its identical twin, Sentinel-3A, has been in orbit since February 2016. The two-satellite constellation offers optimum global coverage and data delivery. The mission has been designed to measure systematically Earth’s oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics. It will provide essential information in near-realtime for ocean and weather forecasting (image credit: ESA)

• February 2, 2018: After being put through its paces to make sure it is fit for life in orbit around Earth, the Copernicus Sentinel-3B satellite is ready to be packed up and shipped to Russia for liftoff. 25)

- Its twin, Sentinel-3A, has been in orbit since February 2016, systematically measuring our oceans, land, ice and atmosphere. The information feeds a range of practical applications and is used for monitoring and understanding large-scale global dynamics.

- The pairing of identical satellites provides the best coverage and data delivery for Europe’s Copernicus program – the largest environmental monitoring program in the world.

- Sentinel-3B has spent the last year at Thales Alenia Space’s premises in Cannes, France, being assembled and tested, and now it is fit and ready for its journey to the Plesetsk launch site in northern Russia.

- This included putting it in a vacuum chamber, exposing it to extreme temperatures, and we have also simulated the vibrations it will be subjected to during launch. - With liftoff expected to be confirmed for the end of April, the satellite will start its journey to Russia in March.

- Both Sentinel-3 satellites carry a suite of cutting-edge instruments to supply a new generation of data products, which are particularly useful for marine applications. For example, they monitor ocean-surface temperatures for ocean and weather forecasting services, aquatic biological productivity, ocean pollution and sea-level change. — Sentinel-3B also marks a milestone in Europe’s Copernicus program.

- With the Sentinel-1 and Sentinel-2 pairs already in orbit monitoring our environment, the launch of Sentinel-3B means that three mission constellations will be complete. In addition, Sentinel-5P, a single-satellite mission to monitor air pollution, has been in orbit since October 2017.

- While the Sentinel-1 and Sentinel-2 satellites circle Earth 180° apart, the configuration for Sentinel-3 will be slightly different: the 140° separation will help to measure ocean features such as eddies as accurately as possible.

- Prior to this, however, they will fly just 223 km apart, which means that Sentinel-3B will be a mere 30 seconds behind Sentinel-3A.

- Flying in tandem like this for around four months is designed to understand any subtle differences between the two sets of instruments – measurements should be almost the same given their brief separation.

- ESA’s ocean scientist, Craig Donlon, explains, “Our Sentinel-3 ocean climate record will eventually be derived from four satellites because we will be launching two further Sentinel-3s in the future.

- “We need to understand the small differences between each successive satellite instrument as these influence our ability to determine accurate climate trends. The Sentinel-3 tandem phase is a fantastic opportunity to do this and will provide results so that climate scientists can use all Sentinel-3 data with confidence.”

• December 5, 2017: EUMETSAT has confirmed the readiness of its teams and the new version of its ground segment to support the launch and commissioning of the Copernicus Sentinel-3B satellite in a two-satellite configuration with Sentinel-3A. 26)

- The new version of the ground segment includes enhancements and upgrades necessary to exploit a dual Sentinel-3 system. Its acceptance follows a comprehensive campaign of verification and validation tests.

- During the commissioning of Sentinel-3B, the two Sentinel-3 satellites will fly in close formation, 30 seconds apart. In this phase, ESA will manage Sentinel-3B flight operations, and EUMETSAT will be progressively ramping up its flight control activity to prepare the hand-over, while continuing to perform flight operations of Sentinel-3A.

- The close formation flight will allow to compare thoroughly the measurements from all instruments aboard Sentinel-3A and –B, ensuring the best consistency between the products from the two satellites.

- The completion of commissioning will lead to a handover of the Sentinel-3B satellite from ESA to EUMETSAT once the latter has been moved to it final orbital position, at a 140º phasing from Sentinel-3A, to form the full Sentinel-3 constellation. The 140° phasing was chosen to optimize global coverage and ensure optimized sampling of ocean currents by the combined altimeters on board Sentinel-3A and -3B.

- Thus the Sentinel-3 constellation will also realize the best possible synergy with the cooperative Jason-3 high precision ocean altimeter mission, another Copernicus marine and climate mission exploited by EUMETSAT on behalf of the European Union.

- Under the Copernicus data policy, all Sentinel-3 marine data and products are available on a full, free and open basis to all users through EUMETSAT’s Near Real Time dissemination channels EUMETCast, the Copernicus Online Data Access and EUMETview.

• June 1, 2017: While the Copernicus Sentinel-3A satellite is in orbit delivering a wealth of information about our home planet, engineers are putting its twin, Sentinel-3B satellite through a series of vigorous tests before it is shipped to the launch site next year. It is now in the thermal–vacuum chamber at Thales Alenia Space’s facilities in Cannes, France. This huge chamber simulates the huge swings in temperature facing the satellite in space. Once this is over, the satellite will be put through other tests to prepare it for liftoff in the spring 2018. Both Sentinel-3 satellites carry the same suite of cutting-edge instruments to measure oceans, land, ice and atmosphere. 27)

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Figure 10: Sentinel-3B being placed in the thermal/vacuum chamber in Cannes, France (image credit: Thales Alenia Space)

• January 14, 2016: Following the Christmas break, the Sentinel-3A satellite has been taken out of its storage container and woken up as the campaign to prepare it for launch resumes at the Russian Plesetsk Cosmodrome. Liftoff is set for 4 February. 28)

• Nov. 20, 2015: The Sentinel-3A spacecraft has left France bound for the Plesetsk launch site in Russia and launch in late December. An Antonov aircraft carries the precious cargo to Arkhangelsk in Russia after a stopover in Moscow to clear paperwork. 29)

• Oct. 15, 2015: Before the latest satellite for Copernicus is packed up and shipped to the Plesetsk Cosmodrome in Russia for launch at the end of the year, the media and specialists were given the chance to see this next-generation mission center-stage in the cleanroom. The event was hosted by Thales Alenia Space in Cannes, France, where engineers have spent the last few years building and testing Sentinel-3A. 30)

• In December 2014, the Sentinel-3A spacecraft is now fully integrated, hosting a package of different instruments to monitor Earth’s oceans and land. After spending many months carefully piecing the satellite together, it is now being tested in preparation for launch towards the end of 2015. 31)

- Environmental tests will start in early 2015.

• In July 2014, the OLCI instrument was delivered and mounted onto the satellite.


Launch: The Sentinel-3A spacecraft was launched on February 16, 2016 (17.57 GMT) on a Rockot/Briz-KM vehicle of Eurockot Launch Services (a joint venture between Astrium, Bremen and the Khrunichev Space Center, Moscow). The launch site was the Plesetsk Cosmodrome in northern Russia. The satellite separated 79 minutes into the flight. 32) 33)

ESA awarded the contract to Eurockot Launch Services on Feb. 9, 2012. 34)

There are three spacecraft in this series: Sentinel-3A, -3B, and -3C. The second satellite is expected to be launched ~18 months after the first one.

Orbit: Frozen sun-synchronous orbit (14 +7/27 rev./day), mean altitude = 815 km, inclination = 98.6º, LTDN (Local Time on Descending Node) is at 10:00 hours. The revisit time is 27 days providing a global coverage of topography data at mesoscale.

With 1 satellite, the ground inter-track spacing at the equator is 2810 km after 1 day, 750 km after four days, and 104 km after 27 days.

For the altimetry mission, simulations show that this orbit provides an optimal compromise between spatial and temporal sampling for capturing mesoscale ocean structures, offering an improvement on SSH mapping error of up to 44% over Jason - due to improved spatial sampling (Figure )- and 8% over the Envisat 35-day orbit - due to better temporal sampling. After a complete cycle, the track spacing at the equator is approximately 100 km.

The Sentinel-3 mission poses the most demanding POD (Precise Orbit Determination) requirements, specially in the radial component, not only in post-processing on-ground, but also in real-time. This level of accuracy requires dual-frequency receivers. The main objective of the mission is the observation with a radar altimeter of sea surface topography and sea ice measurements (see columns 3, 4, 5 in Table 3).

Targets

Real-time

< 3 hours

< 1-3 days

< 1 month

Radial orbit error (rms)

< 3 m

< 8 cm

< 3 cm

< 2 cm

Application

Support tracking mode changes

Atmospheric dynamics

Ocean

Global change

Table 3: Error budget requirements in Sentinel-3 as a function of time wrt measurement 35)


Launch: The Sentinel-3B satellite of ESA and the EC was launched on 25 April 2018 (17:57 GMT) on a Rockot/Briz KM vehicle of Eurockot from the Plesetsk Cosmodrome, Russia. 36) 37)

The second satellite will be placed in the same orbit with an offset of 140º; this phasing improves interleave between S-3A and S-3B for better SRAL meso-scale sampling of 4-7 days. 38)

Commissioning will include a 4-5 month tandem flight. A tandem phase operation of the A/B pair with ~30 s separation in time between satellites on near identical ground-track for ~4-5 months will be flown during Phase E1.

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Figure 11: Tandem phase operations overview (EUMETSAT, ESA, Ref. 38)

With two satellites flying simultaneously, the following coverage will be achieved (Ref. 11):

- Global Ocean color data is recorded with OLCI and SLSTR in less than 1.9 days at the equator, and in less than 1.4 days at latitudes higher than 30º, ignoring cloud effects.

- Global Land color data is recorded with OLCI and SLSTR in less than 1.1 days at the equator, and less than 0.9 days in latitudes higher than 30º.

- Global Surface temperature data is recorded in less than 0.9 days at the equator and in less than 0.8 days in latitudes higher than 30º.

- Continuous altimetry observations where global coverage is achieved after completion of the reference ground track of 27 days.


Note: As of May 2020, the previously single large Sentinel-3 file has been split into three files, to make the file handling manageable for all parties concerned, in particular for the user community.

This article covers the Sentinel-3 mission and its imagery in the period 2020

Sentinel-3 mission and its imagery in the period 2019

Sentinel-3 imagery in the period 2018-2016



Status of the Sentinel-3 mission in 2020 + 2021

• April 15, 2022: The Scandinavian Peninsula, which comprises Sweden and Norway, is approximately 1850 km long. It extends southward from the Barents Sea in the north, the Norwegian sea to the west and the Gulf of Bothnia and the Baltic Sea to the east. Denmark, Finland, Latvia and Lithuania are also visible in this week’s image. 39)

- Along the left side of the peninsula, the jagged fjords lining Norway’s coast can be spotted from space. Many of these fjords were carved out by the thick glaciers that formed during the last ice age. The largest and deepest fjord on Norway’s coast, called Sognefjord, lies in southwest Norway and is 1308 m deep.

- Sweden’s topography consists mainly of flat, rolling lowlands dotted with lakes. Lake Vänern and Lake Vättern, the largest lakes of Sweden, are clearly visible at the bottom of the peninsula. The lakes do not freeze completely during the winter months. To the northeast of the peninsula lies Finland with more than 55,000 lakes – most of which were also created by glacial deposits.

- During March, much of northern Europe and Scandinavia had been affected by a strong high-pressure weather system, which also allowed for this almost cloud-free acquisition. On 19 March in Tirstrup, Denmark, the atmospheric pressure reached 1051.6 hPa, the highest value ever recorded in March.

- Carrying a suite of cutting-edge instruments, Copernicus Sentinel-3 measures Earth’s oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics. It provides essential information in near-real time for ocean and weather forecasting.

- With a focus towards our oceans, Sentinel-3 measures the temperature, colour and height of the sea surface as well as the thickness of sea ice, while, over land, the mission maps the way land is used, provides indices of vegetation state and measures the height of rivers and lakes.

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Figure 12: The Copernicus Sentinel-3 mission captured this impressive shot of the almost cloud-free Scandinavian Peninsula on 20 March, 2022. The image is a mosaic of 2 descending orbits with a difference of around 60 minutes between them, hence the observable striping at the top of the image. The image is also featured on the Earth from Space video programme (image credit: ESA)

• January 20, 2022: In July 2017, a giant iceberg, named A-68, snapped off Antarctica’s Larsen-C ice shelf and began an epic journey across the Southern Ocean. Three and a half years later, the main part of iceberg, A-68A, drifted worryingly close to South Georgia. Concerns were that the berg would run aground in the shallow waters offshore. This would not only cause damage to the seafloor ecosystem but also make it difficult for island wildlife, such as penguins, to make their way to the sea to feed. Using measurements from satellites, scientists have charted how A-68A shrunk towards the end of its voyage, which fortunately prevented it from getting stuck. However, the downside is that it released a colossal 152 billion tonnes of freshwater close to the island, potentially having a profound effect on the island’s marine life. 40)

- When A-68 was spawned, it had a surface area of more than twice the size of Luxemburg – one of the largest icebergs on record.

- It lost a chunk of ice almost immediately after being calved, resulting in the larger berg being renamed A-68A, and its offspring became A-68B. In April 2020, A-68A lost another chunk subsequently called A-68C.

- Antarctic icebergs are named from the Antarctic quadrant in which they were originally sighted, then a sequential number, and then if the iceberg breaks, a sequential letter is added.

- For the first two years of its life, A-68A stayed in the cold waters of the Weddell Sea close to its parent ice shelf. Here, it experienced little in the way of melting. However, once the berg began its northward journey across the Drake Passage, it travelled through increasingly warm waters and began to melt.

- Altogether, the A-68A iceberg thinned by 67 metres from its initial thickness of 235 metres, with the rate of melting rising sharply as the berg drifted in the Scotia Sea around South Georgia.

- A paper published in Remote Sensing of Environment describes how researchers from the Centre for Polar Observation and Modelling in the UK and the British Antarctic Survey combined measurements from different satellites to chart how A-68A changed in area and thickness throughout its life cycle. 41)

Figure 13: A68’s journey. Journey of the A68A iceberg from the Larsen C Ice Shelf at the Antarctic Peninsula, across the Weddell Sea, through the deep ocean of Scotia Sea and approaching South Georgia at the end of its lifetime. The warming ocean conditions led to the thinning and shrinking of the berg. Elevation and ocean depth are based on IBCSO and GEBCO data (Arndt et al., 2013; GEBCO Compilation Group, 2019) and ocean temperature is derived from the World Ocean Atlas (WOA, Boyer et al., 2018). Iceberg positions and length are taken from the Antarctic Iceberg Tracking Database (Budge and Long, 2018) and iceberg thickness is calculated from satellite altimetry data (video credit: CPOM/GEBCO Compilation Group/WOA/Antarctic Tracking Database)

- The journey of A-68A was charted using observations from five different satellite missions.

- To track how the area of A-68A changed, they used optical imagery from the Copernicus Sentinel-3 mission and from the MODIS instrument on the US Terra mission, along with radar data from the Copernicus Sentinel-1 mission. While the Sentinel-1 radar imagery offers all-weather capability and higher spatial resolution, MODIS and Sentinel-3 optical imagery have higher temporal resolution but cannot be used during the polar night and on cloudy days.

- To measure changes in the iceberg’s freeboard, or the height of the ice above the sea surface, they used data from ESA’s CryoSat mission and from the US ICESat-2 mission. Knowing the freeboard of the ice means that the thickness of the entire iceberg can be calculated.

- Tommaso Parrinello, ESA’s CryoSat Mission Manager, said, “Our ability to study every move of the iceberg in such detail is thanks to advances in satellite techniques and the use of a variety of measurements. Imaging satellites record the shape of the iceberg and data from altimetry missions like CryoSat add another important dimension as they measure the height of surfaces – which is essential for calculating changes in volume.”

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Figure 14: Visualising the amount of freshwater released from A-68A. The image here shows just how much water this is: a cube measuring approximately 5.3 x 5.3 km positioned over Manhattan (image credit: CPOM/ESA/Google basemap)

- The new study reveals that A-68A collided only briefly with the sea floor and broke apart shortly afterwards, making it less of a risk in terms of blockage. By the time it reached the shallow waters around South Georgia, the iceberg’s keel had reduced to 141 metres below the ocean surface, shallow enough to just avoid the seabed which is around 150 metres deep.

- If an iceberg’s keel is too deep it can get stuck on the sea floor. This can be disruptive in many ways; the scour marks can destroy fauna, and the berg itself can block ocean currents and predator foraging routes.

- However, a side effect of the melting was the release of a colossal 152 billion (152 x 109) tonnes of freshwater close to the island – a disturbance that could have a profound impact on the island’s marine habitat.

- When icebergs detach from ice shelves, they drift with the ocean currents and wind, releasing cold fresh meltwater and nutrients as they melt. This process influences the local ocean circulation and fosters biological production around the iceberg.

- Anne Braakmann-Folgmann, PhD candidate at the CPOM (Centre for Polar Observation and Modelling) and lead author of the study said, “This is a huge amount of meltwater, and the next thing we want to learn is whether it had a positive or negative impact on the ecosystem around South Georgia.

- “Because A-68A took a common route across the Drake Passage, we hope to learn more about icebergs taking a similar trajectory, and how they influence the polar oceans.”

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Figure 15: A-68A’s position on 17 December 2020 (British Antarctic Survey/ESA)

• August 3, 2021: This map shows the temperature of the land surface on 2 August 2021. It is clear to see that surface temperatures in Turkey and Cyprus have reached over 50°C, again. A map we published on 2 July shows pretty much the same situation. The Mediterranean has been suffering a heatwave for some weeks, leading to numerous wildfires. Turkey, for example, is reported to be amid the country’s worst blazes in at least a decade. 42)

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Figure 16: This map was generated using data from Copernicus Sentinel-3’s Sea and Land Surface Temperature Radiometer. While weather forecasts use predicted air temperatures, this satellite instrument measures the real amount of energy radiating from Earth – and depicts the real temperature of the land surface (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

- The Copernicus Sentinel-3 satellites also carry camera-like instruments, which captured smoke billowing from the fires in Turkey on 30 July.

• August 2, 2021: Captured by the Copernicus Sentinel-3 mission on 30 July 2021, this image shows smoke billowing from several fires along the southern coast of Turkey. Turkey has been battling deadly wildfires since last week. 43)

- Southeast Europe is currently experiencing extremely high temperatures. Greece is reported to be expecting an all-time European record today of 47°C. The heatwave, the result of a heat dome, has seen temperatures reach above 40°C in many areas, and meteorologists expect the weather will continue this week, making it the most severe heatwave since the 1980s.

- Fires have also been raging in Spain, Italy and Greece, some of which have led to the Copernicus Emergency Mapping Service being triggered. The mapping service uses data from satellites to aid response to disasters such as wildfires and floods.

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Figure 17: Smoke billows from fires in Turkey observed by the Sentinel-3 mission. Over the weekend, tourists and local residents had to be evacuated from Bodrum and Marmaris, with some fleeing by boat as the flames crept closer to the shoreline (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

• July 7, 2021: For the hundreds of millions of people living in coastal regions around the world, rising seas driven by climate change pose a direct threat. In order for authorities to plan appropriate protection strategies, accurate information on sea-level rise close to the coast is imperative. For various reasons, these measurements are difficult to get from satellites. However, new ESA-funded research demonstrates how a specific way of processing satellite altimetry data now makes it possible to determine sea-level change in coastal areas with millimeter per year accuracy, and even if the sea is covered by ice. 44)

- Using the Baltic Sea as a target for the research, this new processing technique, which shows regional differences in sea-level rise, drastically improves and extends previous sea-level trend maps. The results reveal that between 1995 and 2019, sea level has risen at an annual rate of 2–3 mm in the south, along the German and Danish coasts, compared to 6 mm in the northeast, in the Bay of Bothnia.

- As our atmosphere and oceans continue to warm because of climate change, sea levels are likely to continue to rise for many decades to come. The 2019 report from the United Nations Intergovernmental Panel on Climate Change (IPCC) paints a grave picture of the problems we face because of sea-level rise. The Special Report on the Ocean and Cryosphere in a Changing Climate states that global mean sea level is likely to rise between 0.29 m and 1.1 m by the end of this century. This is the worst projection of sea-level rise ever made by the IPCC.

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Figure 18: Captured by the Copernicus Sentinel-3 mission on 30 May 2021, this image shows the Baltic Sea and coastlines of the surrounding countries of Denmark, Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Poland, and Germany. Sea-level rise is a major global concern, and using satellites carrying radar altimeters to map sea-level change close to the coast is difficult, especially along complex coastlines such as those seen here. The main problem is because mountains, bays and offshore islands distort the radar signal that is reflected back to the satellite. Another problem is sea ice, which covers parts of the oceans in winter, is impenetrable to radar. However, new research demonstrates how a specific way of processing satellite now makes it possible to determine sea-level change in coastal areas with millimeter per year accuracy, and even if the sea is covered by ice (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

- However, as with any average, the term ‘global mean sea level rise’ does not tell the whole story. Sea level is not rising at the same rate everywhere. Along coasts, for example, sea level rise can exceed the global mean because of complex ocean dynamics nearer land.

- While the French–USA series of Jason satellite missions, ESA’s Envisat and CryoSat missions, and the Copernicus Sentinel-3 satellites have provided essential data to track sea-level rise in the open ocean, mapping rise nearer the coastline is more difficult. This is because mountains, bays and offshore islands distort the radar signal that is reflected back to the satellite. Another problem is sea ice, which covers parts of the oceans in winter, is impenetrable to radar.

- Florian Seitz, Director of the German Geodetic Research Institute at the Technical University of Munich (TUM), said, “To protect people and infrastructure – for example by building flood protection structures, securing ports or making dikes higher – we need reliable forecasts on sea-level trends.”

- Through ESA’s Earth Observation Science for Society Baltic Sea Level project (Baltic SEAL), a team of researchers at the Technical University of Munich worked with international partners to develop algorithms to process measurement data from a range of satellite altimetry sensors to yield precise and high-resolution measurements of sea-level changes in coastal areas and in leads between the sea ice.

- The researchers chose the Baltic Sea as the model region. “Data from this region are especially suitable for developing new methods because multiple factors make analysis difficult such as the complex shape of the coastline, sea ice and wind. At the same time, there are plenty of local sea level measurements to corroborate the results,” said project leader Marcello Passaro.

- “An analytical method that works in the Baltic Sea can be easily adapted to other regions.”

- To handle hundreds of millions of radar measurements taken between 1995 and 2019 from satellite missions including the Jason series, Envisat, CryoSat and Copernicus Sentinel-3, the team developed a multi-stage process. In the first step, they calibrated the measurements from the various satellite missions so that they could be combined. With specially developed algorithms, they were then able to detect signals from the ice-covered seawater in the radar reflections produced along cracks and fissures, called leads. This made it possible to determine sea levels for the winter months. With new computational methods they also achieved better resolution of radar echoes close to land.

- As a result, it is now possible to measure sea level in coastal areas and compare the results with local tidal records. The processed data were then fitted to a fine grid with a resolution of 6–7 km using an algorithm developed by the team. The result is a highly precise dataset covering the entire Baltic Sea region.

- The data show the regional effects of the rise in sea level between 1995 and 2019. Sea level has risen at an annual rate of 2–3 mm in the south, along the German and Danish coasts, compared to 6 mm in the northeast, in the Bay of Bothnia. The cause of this large rise is strong south-westerly winds that drive the waters to the north and eastward. This above-average increase in sea level does not pose a threat to coastal dwellers, however, because since the end of the last Ice Age the land here has been rising by up to 1 cm a year as a result of post-glacial rebound.

- The researchers have also created a comprehensive dataset for the North Sea region. The sea level here is rising by 2.6 mm per year, and by 3.2 mm in the German Bight. Local trends can be determined using the dataset and the user manual – both of which are freely accessible online.

- “With the data, researchers can verify their climate models, for example, and public authorities can plan suitable protective measures,” says Dr Seitz.

- ESA’s Jérôme Benveniste added, “The Baltic SEAL project has produced excellent results, demonstrating the value of Earth observation for society. This new way of processing satellite radar altimetry data is really going to help authorities to take appropriate measure to protect citizens and infrastructure from sea-level rise. We are also keenly awaiting the high-resolution data that will come from the new Copernicus Sentinel-6 mission, which also promises to map sea-surface height close to the coastline, which uses an additional new processing algorithm called Fully-Focused Synthetic Aperture Radar to drastically increase the retrieved resolution.”

- The Baltic SEAL dataset is available at balticseal.eu

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Figure 19: The map shows mean sea-level rise in the North and Baltic Sea (millimeters per year), calculated using satellite altimetry data between 1995 and 2019 (image credit: TUM/ESA)

• July 2, 2021: Scorching temperatures hit both Greece and Turkey this week, leading to the temporary closure of the Acropolis – Greece’s most visited monument. 45)

- This map shows the land surface temperature of Greece and surrounding countries on 30 June. The data show that surface temperatures reached over 50°C in many locations including the northwest of Athens and many regions in Turkey. The blue spots visible near Albania are clouds.

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Figure 20: The map has been generated using the Copernicus Sentinel-3’s Sea and Land Surface Temperature Radiometer. Whereas weather forecasts use predicted air temperatures, the satellite measures the real amount of energy radiating from Earth – therefore this map better represents the real temperature of the land surface (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

• July 1, 2021: While heatwaves are quite common during the summer months, the scorching heatwave hitting parts of western Canada and the US has been particularly devastating – with temperature records shattered and hundreds of people falling victim to the extreme heat. 46)

- Canada broke its temperature record for a third consecutive day: recording a whopping 49.6°C on 29 June in Lytton, a village northeast of Vancouver, in British Columbia.

- Portland, Oregon, also broke its all-time temperature record for three days in a row.

- The extent of the heatwave can be seen in the map of Figure 21, which shows the land surface temperature of parts of Canada and the US on 29 June. The data show that surface temperatures in Vancouver and Portland reached 43°C, and Calgary recorded 45°C. The hottest temperatures recorded are in the state of Washington (visible in deep red) with maximum land surface temperatures of around 69°C.

- The persistent heat over parts of western Canada and parts of the US has been caused by a heat dome stretching from California to the Arctic. Temperatures have been easing in coastal areas, but there has been little respite for the inland regions.

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Figure 21: The map has been generated using data from the Copernicus Sentinel-3 mission. While weather forecasts typically use air temperatures, the Sea and Land Surface Temperature Radiometer onboard Sentinel-3 measures the energy radiating from Earth’s surface. Therefore, the map shows the actual temperature of the land’s surface pictured here, which can be significantly hotter or colder than air temperatures. The light blue in the image represents either snow and ice or cloud coverage. Snow and ice can be seen, for example, in the mountain ranges of Canada and Mount Rainier in the US, while some clouds can be seen on the Pacific Coast and in the bottom right of the map (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

• May 28, 2021: All five of North America’s Great Lakes are pictured in this spectacular image captured by the Copernicus Sentinel-3 mission: Lake Superior, Michigan, Huron, Erie, and Ontario. 47)

- The Great Lakes are a chain of deep freshwater lakes. With a combined area of around 244,000 km2, the lakes represent the largest surface of freshwater in the world – covering an area exceeding that of the United Kingdom.

- Around 100,000 years ago, a major ice sheet formed over most of Canada and part of the US. As it formed, giant glaciers flowed into the land carving out valleys and levelling mountains. As higher temperatures began to melt the ice sheet, meltwater filled the holes left by the glaciers.

- Many of these holes today still contain water and formed the thousands of lakes across central USA and Canada. The biggest remnants of this process are the Great Lakes. The lakes drain roughly from west to east and empty into the Atlantic Ocean.

- Lake Superior, the northernmost and westernmost lake, is the largest and deepest of the Great Lakes. It drains into Lake Huron via the St. Marys River at an average rate of 2000 m3/s. Lake Michigan lies south of Lake Superior and connects with Lake Huron through the six km-wide channel Straits of Mackinac in the north. Lake Huron is the second largest of the Great Lakes and is bounded by Michigan, US, on the north and by Ontario, Canada, to the east.

- Lake Erie is the shallowest and southernmost of the Great Lakes. Green algal blooms are visible on the lake. These toxic blooms have been a problem for the lake in recent years. Caused by heightened levels of phosphorus – found in fertilizers and common household products – finding its way into the water, these blooms have caused harm to the lake’s fish population.

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Figure 22: In this image, captured on 15 March 2020, a large quantity of ice and snow coverage is visible north of the lakes, yet the amount of ice cover on the lakes is minimal – extremely unusual for the ice season which typically runs from 1 December through 30 April. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

- Parts of the Great Lakes typically freeze every winter. As Earth’s climate changes, rising air and water temperatures have led to less ice cover on many lakes in North America, including the Great Lakes.

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Figure 23: Ice cover on the Great Lakes can fluctuate dramatically from year to year, depending on several patterns of climate variability. Years with lower-than-normal ice cover appear to have become more frequent during the past two decades. The graph indicates that 1979 was the year with the highest ice coverage (94.7%), while 2002 had the lowest maximum ice coverage (11.8%) meaning that the Great Lakes were almost ice-free for the entire year [image credit: ESA (Data source: NOAA GLERL)]

- Sentinel-3 is a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus environmental monitoring program. Each satellite’s instrument package includes an optical sensor to monitor changes in the color of Earth’s surfaces. It can be used, for example, to monitor ocean biology and water quality.

• April 21, 2021: Oceans play a vital role in taking the heat out of climate change, but at a cost. New research supported by ESA and using different satellite measurements of various aspects of seawater along with measurements from ships has revealed how our ocean waters have become more acidic over the last three decades – and this is having a detrimental effect on marine life. 48)

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Figure 24: Ocean acidification. As atmospheric carbon dioxide rises, Earth’s oceans are absorbing more carbon, changing the chemistry of ocean water. Observations from satellites can be used to measure parameters that indicate changing ocean water, such as temperature, salinity and chlorophyll content. Satellite and in-situ surface observations are combined using a machine learning technique to generate global monthly maps that characterize the changing chemistry of the ocean. Ocean acidification is shown by the steady fall in seawater pH values over the last 30 years (image credit: ESA Planetary Visions)

- Oceans not only soak up around 90% of the extra heat in the atmosphere caused by greenhouse gas emissions from human activity such as the burning of fossil fuel, but also draw down about 30% of the carbon dioxide we pump into the atmosphere. While this sounds like a good thing, these processes are making seawater more acidic.

- Decreasing seawater pH, or ocean acidification, leads to a reduction in the carbonate ions that calcifying organisms, such as shellfish and corals, need to build and maintain their hard shells, skeletons and other calcium carbonate structures. If the seawater pH dips too low, shells and skeletons can even begin to dissolve.

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Figure 25: Sea butterfly. Ocean acidification is altering bio-geo-chemical cycles and having a detrimental effect on ocean life. Pteropods, tiny marine snails known as ‘sea butterflies’, are an example of a particularly vulnerable species, where shell damage has been observed already in portions of the Arctic and Southern Ocean. Pteropods are hugely important in the polar food web, serving as a key food source for important fisheries species, such as salmon and cod (image credit: NOAA)

- While this poses serious consequences for some forms of marine life, there are potential damaging knock-on effects for the marine ecosystem as a whole. For example, the pteropod, or sea butterfly, is being affected by ocean acidification as the change in seawater pH can dissolve their shells. They may only be little sea snails, but they are important food for organisms ranging from tiny krill to huge whales.

- There are also other far-reaching consequences for us all because the health of our oceans is also important for regulating the climate, and essential for aquaculture and food security, tourism, and more.

- Being able to monitor changes in ocean acidification is therefore important for climate and environmental policy-making, and for understanding the implications for marine life.

- Measurements of seawater pH can be taken from ships, but these are readings are sparse and difficult to use to monitor change. However, variations in marine carbonate chemistry tend to be closely related to variations in temperature, salinity, chlorophyll concentration and other variables, many of which can be measured by satellites that have near-global coverage.

- A paper published recently in Earth System Science Data describes how scientists working in the OceanSODA project used measurements from ships and from satellites to show how ocean waters have become more acidic over the last three decades. 49)

Figure 26: Using satellites to understand ocean acidification. OceanSODA-Satellite-based observations of ocean acidification (video credit: ETH Zürich, animation by ESA Planetary Visions)

- Luke Gregor, from ETH Zurich’s Institute of Biogeochemistry and Pollutant Dynamics and co-author of the paper, explained, “We used both in-situ and satellite measurements of sea-surface temperature, salinity and chlorophyll to derive changes in surface-ocean alkalinity and carbon dioxide concentrations, from which pH and calcium carbonate saturation state and other properties of ocean acidification can be computed.

- “To capture the complex relationship between changes in these variables and oceanic carbon, we used the power of machine learning.

- “This provided us with one of the first global-scale observation-based views of the surface-ocean carbonate system from 1985 to 2018. The results show a strong and gradual increase in the acidity of the ocean as it continues to absorb atmospheric carbon dioxide. Along with the increase in the ocean’s acidification, there is an associated decrease in the availability of the carbonate ion concentration, making it harder for organisms to grow their shells and skeletons.”

- The team used a range of different satellite data, including sea-surface temperature data from the Sea and Land Surface Temperature Radiometer carried on the Copernicus Sentinel-3 satellites and from the Advanced Very High Resolution Radiometer carried on Europe’s MetOp satellites and on the US National Oceanic and Atmospheric Administration’s POES satellites. This dataset came through ESA’s Climate Change Initiative.

- Information on chlorophyll was also thanks to a multi-sensor blended dataset through ESA’s GlobColour project and included data from the OLCI (Ocean and Land Color Instrument) on the Copernicus Sentinel-3 satellites.

- Information on ocean salinity was realized through a climate reanalysis dataset called SODA3.

- Dr Gregor noted, “Having this wealth of satellite data allows us to really understand what has been happening to our vast oceans over the last 30 years. Moreover, it is essential that we continue to use satellite data to the monitor oceans to further understand the resilience and sensitivity of coral reefs and other marine organisms to the increasing threats of ocean acidification.”

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Figure 27: Ocean acidification weakens coral reef skeletons. Coral reefs build their skeletons to harvest light more effectively. As our oceans become more acidic, these skeletons become weaker, making coral reefs more susceptible to breaking when waves pass over. This is just one of the impacts of ocean acidification on coral reefs (image credit: Pexels, F. Ungaro)

• February 11, 2021: Storm Darcy hit the Netherlands in the evening of Saturday 6 February as it pushed its way through much of northern Europe. Strong winds and bitter cold, which initiated a ‘code red’ weather warning, brought the country to an almost standstill as most public transport was cancelled the following day – by which time most of the country was under around 10 cm of snow. The snowfall also caused disruption to parts of the UK and Germany. 50)

- Although the snow stopped falling a day or so later, temperatures have remained below freezing, reawakening the Dutch passion for ice-skating. The Netherlands is home to the century-old ‘Elfstedentocht’, a 200-kilometer race on natural ice through 11 towns and cities in the northern province of Friesland. It was last held in 1997, but the current COVID pandemic restrictions mean that this historic race, which can attract thousands of participants and hundreds of thousands of spectators, is not permitted this year.

- Climate change is thought to be having an impact on the chances of conditions being right for an Elfstedentocht – the canal ice has to be at least 15 cm thick. According to the Dutch Meteorological Institute, KNMI, a century ago, there was a 20% chance every year of it being cold enough to organise the race, this has now decreased to an 8% chance.

- Copernicus Sentinel-3 is a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus environmental monitoring programme. Each satellite carries the same suite of four sensors. This image, showing snow cover in the Netherlands, northern France, Belgium, Luxembourg, Denmark, part of the UK and part of Germany, was captured by the mission’s ocean and land cover instrument.

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Figure 28: As this image captured today, 11 February, by Copernicus Sentinel-3 shows, the Netherlands remains pretty much snow-covered thanks to days of sub-zero temperatures following the country’s first major snowstorm in a decade (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

• January 13, 2021: The heavy snowfall that hit Spain a few days ago still lies heavy across much of the country as this Copernicus Sentinel-3 satellite image shows. 51)

- Storm Filomena hit Spain over the weekend, covering a large part of the country in thick snow. Madrid one of the worst affected areas (see satellite image), was brought to a standstill with the airport having to be closed, trains cancelled and roads blocked.

- People in central Spain are struggling as a deep freeze follows the heavy snow. Yesterday, the temperature plunged to –25°C in Molina de Aragón and Teruel, in mountains east of Madrid – Spain's coldest night for at least 20 years.

- Copernicus Sentinel-3 is a two-satellite mission. Each satellite carries a suite of cutting-edge instruments to measure systematically Earth’s oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics. For example, with a swath width of 1270 km, the ocean and land color instrument, which acquired the two tiles for this image, provides global coverage every two days.

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Figure 29: While the idea of snuggling under a blanket in the cold winter months is very appealing, the blanket that covers half of Spain is not remotely comforting. This satellite image, captured on 12 January at 11:40 CET, shows how much of the country is still facing hazardous conditions following the snow that fell at the weekend – the heaviest snowfall the country has had in five decades (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)

• December 18, 2020: A large block of ice has broken off the northern tip of the A-68A iceberg as seen in new images captured by the Copernicus Sentinel-3 mission. 52)

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Figure 30: New images captured by the Copernicus Sentinel-3 mission revealed that the A-68A iceberg has spun around in a clockwise direction, moving one end of the berg closer to the shelf and into shallow waters. In doing so, the berg could have scraped the seafloor, measuring less than 200 m deep, causing an enormous block of ice to snap off the iceberg’s upper tip (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

- Satellite missions have been used to track the A-68A berg on its journey since 2017, when it broke off the Larsen C ice shelf in Antarctica. Over the past weeks, the A-68A iceberg has drifted alarmingly close to the remote island of South Georgia, where scientists feared that the iceberg could ground in the shallow waters offshore and threaten wildlife.

- New satellite images revealed yesterday that the iceberg has spun around in a clockwise direction, moving one end of the berg closer to the shelf and into shallow waters. In doing so, the berg could have scraped the seafloor, measuring less than 200 m deep, causing an enormous block of ice to snap off the iceberg’s northern tip.

- The new chunk of ice is around 18 km long and approximately 140 km2, around the same size as Seville, Spain, and can be seen detached from the main A-68A iceberg in the images. Despite its small appearance in the images, the new piece of ice is so large it will most likely be named A-68D by the US National Ice Center in the coming days. Two other chunks of ice that previously broke off were named A-68B and A-68C.

- The main A-68A iceberg is now approximately 3700 km2 with a length of around 135 km. Having lost many other pieces of ice over the past weeks, A-68A has now lost its title as the world’s largest iceberg. First place now passes onto the A-23A iceberg, which is currently stuck in the Weddell Sea, with a size of almost 4000 km2.

- It is still unclear where the main A-68A iceberg will now travel. Carried by currents, it could continue its journey around the island of South Georgia as many other previous icebergs have done in the past, moving in a southeast direction, before turning north.

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Figure 31: A-68A’s position on 17 December. New images have revealed that the A-68A iceberg has spun around in a clockwise direction, moving one end of the berg closer to the shelf and into shallow waters. In doing so, the berg could have scraped the seafloor, measuring less than 200 m deep, causing an enormous block of ice to snap off the iceberg’s upper tip (image credit: British Antarctic Survey/ESA)

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Figure 32: A-68A’s journey. The map shows the different positions of the berg over the course of its three-year journey. The map also includes historic iceberg tracks, based on data from a number of satellites including ESA’s ERS-1 and ERS-2 as part of the Antarctic Iceberg Tracking Database, and shows that A-68A is following this well-trodden path (image credit: ESA, the map contains modified Copernicus Sentinel data (2020), processed by ESA; Antarctic Iceberg Tracking Database)

• December 17, 2020: The snow-covered Alps are featured in this image captured by the Copernicus Sentinel-3 mission. 53)

- Just south of the Alps, the typical winter fog and haze can be seen over the Po Valley. The haze is most likely to be a mix of both fog and smog, trapped at the base of the Alps owing to both its topography and atmospheric conditions. Patches of snow can also be seen on the island of Corsica, Croatia and at the bottom of the Apennines in central Italy.

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Figure 33: Heavy snowfall in the Alps has been recorded over the past weeks, with up to 3 m of snow recorded in some parts of the Austrian and Italian Alps. On 14 December, the OLCI (Ocean and Land Color Instrument) onboard the Sentinel-3 mission acquired this image of snow cover and low cloud coverage around the Alps. According to EUMETSAT, the snow came in two bouts. The first occurred during the weekend of 5-6 December and was stronger, influencing the western part of the Alps, while the second, on 8 and 9 December, brought snow to central and eastern Alps, and was not as abundant as the first. The skies then cleared after 10 December, allowing this image to be captured. The first bout of snow lead to road blocks, power outages throughout South Tyrol and avalanche warnings, according to Der Spiegel (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

• October 30, 2020: All 1200 islands that make up the Republic of Maldives are featured in this spectacular image captured by the Copernicus Sentinel-3 mission. 54)

- The ocean and color instrument onboard the Copernicus Sentinel-3 mission has a swath width of 1270 km which allows us to enjoy this wide view of the Maldive Islands and its surroundings. A popular tourist destination, the Maldives lie in the Indian Ocean, around 700 km southwest of the southernmost tip of mainland India, visible in the top-right of the image.

- The nation consists of a chain of small coral islands that are grouped into clusters of atolls – visible as circular or oval-shaped reef structures in the middle of the image. Scattered across 90,000 km2 of ocean, the Maldives are one of the most geographically dispersed countries in the world. The islands extend more than 820 km from north to south and around 130 km from east to west.

- Different cloud formations can be seen dotted around the image, the difference in appearance is most likely due to the different height above the surface. The Maldive archipelago is frequently covered by clouds, making this almost cloud-free image quite rare.

- One of the world’s lowest-lying countries, more than 80% of the Maldives’ land is less than one meter above mean sea level, making its population of over 500,000 people extremely vulnerable to sea swells, storm surges and severe weather. The Special Report on the Ocean and Cryosphere in a Changing Climate on sea level rise states that the global mean sea level is likely to rise to around 1 m by the end of this century, which could ultimately cover the majority of the nation.

- Scheduled for launch on 10 November from the Vandenberg Air Force Base in California, the Copernicus Sentinel-6 Michael Freilich satellite is the first of two identical satellites to be launched sequentially to provide accurate measurements of sea-level change.

- In order to better understand how rising seas will impact humanity, scientists and researchers need long climate records. Copernicus Sentinel-6 will take on the role of radar altimetry reference mission, continuing the long-term record of measurements of sea-surface height started in 1992 by the French-US Topex Poseidon and then the Jason series of satellite missions. By continuing this time series, Sentinel-6 will allow for further climate research and help scientists monitor the effects of climate change.

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Figure 34: Most atolls of the Maldives consist of a large, ring-shaped coral reef supporting numerous small islands. In this image, captured on 29 March 2020, the Huvadhu Atoll and Addu Atoll are partially covered by clouds (visible in the bottom of the image). This image is also featured on the Earth from Space video program (image credit: ESA the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

• October 23, 2020: The Copernicus Sentinel-3 mission takes us over the Ganges Delta – the world’s largest river delta. 55)

- Covering an area of around 100 000 km2, the Ganges Delta lies in both Bangladesh and the State of West Bengal in India. The delta is formed mainly by the large, sediment-laden waters of the Ganges and Brahmaputra rivers (Figure 35).

- The Ganges river carries fertile soil and nutrients, which it deposits across its vast delta floodplain. The river flows for over 2400 km from the Himalayas before emptying into the Bay of Bengal – the world’s largest bay. It is here where the murky colored waters mix with the darker colored waters of the Indian Ocean.

- The delta is largely covered with a swamp forest, known as the Sundarbans, and can be seen in dark green near the coast with several rivers snaking through it. The Sundarbans, which translates as 'beautiful forest' in Bengali, are the world’s largest mangrove forest and provide a critical habitat for numerous species, including the Bengal tiger and the Indian python.

- The city of Kolkata (formerly Calcutta) is visible near the Sundarbans in the lower-center of the image. With over 14 million inhabitants, Kolkata is one of India’s largest cities and is the dominant urban center of eastern India. Dhaka, the capital of Bangladesh, can be seen in the lower-right of the image, just north of the Buriganga river. Dhaka is Bangladesh’s most populous city and is one of the largest metropolises in South Asia.

- With a population of over 100 million people, the delta is one of the most densely populated deltas in the world and is extremely vulnerable to climate change. The residents of this region are particularly at risk from repeated catastrophic floods due to heavy runoff of meltwater from the Himalayas, intense rainfall during the monsoon season and from accelerated sea-level rise exacerbated by land subsidence.

- Sea-level rise is a global issue, but regional differences in sea-level rise put some places at risk more than others. In the coming decades, Asia is likely to feel the worst effects because of the number of people living in low-lying coastal regions. Bangladesh, India, China, Vietnam, Indonesia and Thailand are home to the greatest number of people who today live on land that could be threatened by permanent inundation by 2100.

- It is vital that the changing height of the sea surface continues to be closely monitored over the coming decades. Set to launch next month, the Copernicus Sentinel-6 mission will be key in undertaking this important role until at least 2030. Renamed in honor of the former director of NASA’s Earth Science Division, the Copernicus Sentinel-6 Michael Freilich satellite is the first ESA-developed satellite to be given a ride into space on the SpaceX Falcon 9 rocket, the world’s first orbital class reusable rocket.

- Since the satellite arrived at Vandenberg Air Force Base in California on 24 September, it has been transferred to the SpaceX Payload Processing Facility, unpacked and undergone a series of tests to make sure all will be well during the rigors of liftoff and during its five-plus years in orbit around Earth.

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Figure 35: The river bed of the Ganges can be seen in the left of the image, while Brahmaputra can be seen to the right. The snow-covered Himalayas can be seen at the top of the image. This image of Sentinel-3, captured on 31 March 2020, is also featured on the Earth from Space video program (image credit: ESA the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

• September 22, 2020: Earth’s oceans help to slow global warming by absorbing carbon from our atmosphere – but fully observing this crucial process in the upper ocean and lower atmosphere is difficult, as measurements are taken not where it occurs, the sea surface, but several meters below. New research uses data from ESA, NASA and NOAA satellites to rectify this, and finds that far more carbon is absorbed by the oceans than previously thought. 56)

Much of the carbon dioxide emitted by human activity does not stay in the atmosphere but is taken up by oceans and land vegetation – so-called ‘carbon sinks’.

There are ongoing efforts to collect and compile in situ measurements of the ocean sink in the form of the SOCAT ( Surface Ocean CO2 Atlas), which contains over 28 million international observations of our oceans and coastal seas from 1957 to 2020. By delving into SOCAT’s vast database, scientists can identify how much carbon is being sucked out of the atmosphere and stored by our seas.

Figure 36: Characterizing how carbon flows between ocean and atmosphere. According to new research, the amount of carbon absorbed by the ocean is being underestimated by up to 0.9 Gigatons a year. This animation reflects the findings. The map to the left shows the mean monthly ocean-to-atmosphere carbon flux (corrected for cool water and salty sea surface), with carbon flowing into the ocean (i.e. a negative flux) represented in blue (and vice versa, with red regions representing where carbon is being emitted from the ocean into the atmosphere). The graph to the right shows the annual integrated global net carbon flux between the atmosphere and oceans from 1992 to 2018 with no corrections (yellow line), surface temperature corrections only (red line), and corrected for cool water and salty sea surface (blue line), video credit: University of Exeter College of Life and Environmental Sciences 57)

“However, there’s a catch: the measurements are not made right at the ocean surface where they are needed, but from a few meters down,” explains Andrew Watson of the University of Exeter, UK, lead author of the new study. Although the difference may be mere meters, the sea surface temperature changes with depth – and so, too, does its associated ability to absorb carbon from the atmosphere.

“Previous studies have ignored the small temperature differences between the surface of the ocean and the sampling depth, but we know that this has a significant impact on how carbon is held by the oceans in terms of salinity, solubility, stability, and so on,” adds Andrew. “But satellites can measure the temperature more or less exactly at the ocean surface – and when we do this, we find it makes a big difference.”

By applying satellite corrections to SOCAT data from 1992 to 2018 to account for temperature differences between the surface and at a few meters’ depth, the researchers find a substantially higher ocean uptake of carbon dioxide than previously thought. They were able to do this thanks to data from a suite of satellites such as ESA’s Envisat, NOAA’s AVHRR, EUMETSAT’s MetOp series, and the Copernicus Sentinel-3 mission, firstly as part of the OceanFlux research project (part of ESA’s Science for Society program) and then continued within two EU-funded projects.

The corrected figures reveal that the net flux of carbon into the oceans is underestimated by up to 0.9 Gigatons of carbon per year – a significant amount that, at times, doubles uncorrected values.

Figure 37: Depicting carbon flux between the ocean and atmosphere. This animation reflects the findings, showing the mean monthly ocean-to-atmosphere carbon flux (corrected for cool water and salty sea surface) from 1992 to 2019. Carbon flowing into the ocean (i.e. a negative flux) is represented in blue, with red regions representing where carbon is being emitted from the ocean into the atmosphere (a positive flux), video credit: University of Exeter College of Life and Environmental Sciences

“These results are consistent with independent estimates of the size of the oceanic carbon sink – those based on global ocean surveys by research ships,” adds co-author Jamie Shutler, also of the University of Exeter. “Now that these two separate estimates of the size of the carbon dioxide ocean sink agree pretty well, we can view and use their results with greater confidence, and trust that they are most likely giving us an accurate picture of what is going on.”

Andrew and Jamie were both part of a Europe-wide research team – including researchers from Heriot-Watt University and UHI, Scotland – that previously used SOCAT data to estimate how carbon flows into and out of our oceans with unprecedented accuracy. They found that, in 2010 alone, three Gigatons of carbon were drawn into the ocean: about a third of the emissions caused by human activity. This finding contrasted with previous estimates of a quarter, leading Andrew, Jamie and colleagues to conclude – as in this study – that the oceans’ role in capturing atmospheric carbon is being underestimated.

While this may bring positive benefits in terms of reducing atmospheric warming due to climate change, as more carbon dioxide is being removed from the air, the oceans are impacted by the carbon they absorb. They become more acidic, which threatens the health of marine ecosystems and makes it increasingly difficult for ocean life to survive.

“The importance of our oceans in both regulating climate and supporting biodiversity cannot be overstated,” adds ESA’s Craig Donlon. “Across all of ESA’s Earth observation activities, our aim is to fully account for the role of our oceans in terms of the carbon cycle. This key result, together with others built on the dedication and excellent collaboration of the ESA OceanFlux team, gives us a solid basis for that, and will help us to more accurately characterize and better understand our planet’s changing climate.”

• September 18, 2020: 'Medicane' Ianos. Medicanes are similar in form to hurricanes and typhoons, but can form over cooler waters. While hurricanes move east to west, medicanes move from west to east. 58)

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Figure 38: The Copernicus Sentinel-3 mission captured this image of the Mediterranean hurricane, or 'Medicane,' crossing the Ionian Sea and approaching Greece yesterday 17 September at 10:48 CEST. Medicane Ianos, set to make landfall over Greece today, is expected to bring hurricane-force winds and heavy rain (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

- Sentinel-3 is a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus environmental monitoring program. Each satellite’s instrument package includes an optical sensor to monitor changes in the color of Earth’s surfaces.

• September 11, 2020: The Western US states have been battling close to 100 wildfires, blanketing the majority of the west coast in smoke. Captured on 10 September, this Copernicus Sentinel-3 image shows the extent of the smoke plume which, in some areas, has caused the sky to turn orange. 59)

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Figure 39: In this image, multiple fires can be seen in the states of California, Washington and Oregon – the areas hit hardest by the blazes – producing the thick plume of smoke which can be seen travelling westwards. Based on additional data from the Copernicus Sentinel-3 mission, as of yesterday, the smoke was visible travelling 2000 km west of the active fires (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

- The cities of Portland, Eureka, Eugene, San Francisco and Sacramento are all blanked in smoke. In the top of the image, the cities of Vancouver and Seattle are visible.

- Sentinel-3 is a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus environmental monitoring program. Each satellite’s instrument package includes an optical sensor to monitor changes in the color of Earth’s surfaces. It can be used, for example, to monitor ocean biology and water quality.

• August 28, 2020: As we eagerly await the return of our Earth from Space program next Friday, today the Copernicus Sentinel-3 mission shows us a rare, cloud-free view of Iceland captured on 14 August 2020. 60)

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Figure 40: Cloud-free Iceland. The large, white area visible on the island is a national park that encompasses the Vatnajökull Glacier. Covering an area of around 8400 km2 with an average ice thickness of more than 900 m, Vatnajökull is not only classified as the biggest glacier in Iceland, but the biggest in Europe. The white, circular patch in the center of the country is Hofsjökull, the country’s third largest glacier and its largest active volcano. The elongated white area west of Hofsjökull is Langjökull, Iceland’s second largest ice cap. Reykjavík, the capital and largest city of Iceland, is located on the Seltjarnarnes Peninsula, in southwest Iceland. In the top-left of the image, several sea ice swirls can be seen off the coast of Greenland (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

• August 27, 2020: Over the past months, the Arctic has experienced alarmingly high temperatures, extreme wildfires and a significant loss of sea ice. While hot summer weather is not uncommon in the Arctic, the region is warming at two to three times the global average – impacting nature and humanity on a global scale. Observations from space offer a unique opportunity to understand the changes occurring in this remote region. 61)

- According to the Copernicus Climate Change Service, July 2020 was the third warmest July on record for the globe, with temperatures 0.5°C above the 1981-2010 average. In addition, the Northern Hemisphere saw its hottest July since records began — surpassing the previous record set in 2019.

- The Arctic has not escaped the heat. On 20 June, the Russian town of Verkhoyansk, which lies above the Arctic Circle, recorded a staggering 38°C. Extreme air temperatures were also recorded in northern Canada. On 11 August, Nunavut’s Eureka Station, located in the Canadian Arctic at 80 degrees north latitude, recorded a high of 21.9°C – which were reported as being the highest temperature ever recorded so far north.

- Although heatwaves in the Arctic are not uncommon, the persistent higher-than-average temperatures this year have potentially devastating consequences for the rest of the world. Firstly, the high temperatures fuelled an outbreak of wildfires in the Arctic Circle. Images captured by the Copernicus Sentinel-3 mission show some of the fires in the Chukotka region, the most north-easterly region of Russia, on 23 June 2020.

- Wildfire smoke releases a wide range of pollutants including carbon monoxide, nitrogen oxides and solid aerosol particles. In June alone, the Arctic wildfires were reported to have emitted the equivalent of 56 megatons of carbon dioxide, as well as significant amounts of carbon monoxide and particulate matter. These wildfires affect radiation, clouds and climate on a regional, and global, scale.

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Figure 41: This map shows the land surface temperature of the Eureka region in the Canadian territory of Nunavut on 11 August 2020. This map has been generated using data from Copernicus Sentinel-3’s Sea and Land Surface Temperature Radiometer (SLSTR). While weather forecasts use near surface air temperatures, Sentinel-3 measures the amount of energy radiating from Earth’s surface (image credit: ESA, the map contains modified Copernicus Sentinel (2020), processed by ESA, CC BY-SA 3.0 IGO)

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Figure 42: This image of Siberian fires was captured on 23 June 2020 by the OLCI instrument on board the Copernicus Sentinel-3 mission. Part of Sakha, Chukotka and the Magadan Oblast is pictured here. Sea-ice can be seen to the north while smoke dominates the bottom part of the image with a number of active fires visible in the center (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)

- The Arctic heatwave also contributes to the thawing of permafrost. Arctic permafrost soils contain large quantities of organic carbon and materials left over from dead plants that cannot decompose or rot, whereas permafrost layers deeper down contain soils made of minerals. The permanently frozen ground, just below the surface, covers around a quarter of the land in the northern hemisphere.

- When permafrost thaws, it releases methane and carbon dioxide into the atmosphere – adding these greenhouse gases to the atmosphere. This, in turn, causes further warming, and further thawing of the permafrost – a vicious cycle.

- According to the UN’s Intergovernmental Panel on Climate Change Special Report, permafrost temperatures have increased to record-high levels from the 1980s to present. Although satellite sensors cannot measure permafrost directly, a recent project by ESA’s Climate Change Initiative (CCI), combined in situ data with satellite measurements of land-surface temperature and land cover to estimate permafrost extent in the Arctic.

- The thaw of permafrost is also said to have caused the collapse of the oil tank that leaked over 20,000 tons of oil into rivers near the city of Norilsk, Russia, in May.

- The Siberian heatwave is also recognized to have contributed to accelerating the sea-ice retreat along the Arctic Russian coast. Melt onset was as much as 30 days earlier than average in the Laptev and Kara Seas, which has been linked, in part, to persistent high sea level pressure over Siberia and a record warm spring in the region. According to the Copernicus Climate Change Service, the Arctic sea ice extent for July 2020 was on a par with the previous July minimum of 2012 – at nearly 27% below the 1981-2020 average.

- ESA’s Mark Drinkwater comments, “Throughout the satellite era, polar scientists pointed to the Arctic as a harbinger of more widespread global impacts of climate change. As these interconnected events of 2020 make their indelible marks in the climate record, it becomes evident that a ‘green’ low-carbon Europe is alone insufficient to combat the effects of climate change.”

- Without concerted climate action, the world will continue to feel the effects of a warming Arctic. Because of the Arctic’s harsh environment and low population density, polar orbiting space systems offer unique opportunities to monitor this environment. ESA has been monitoring the Arctic with its Earth-observing satellites for nearly three decades. Satellites not only can monitor changes in this very sensitive region, but can also facilitate navigation and communications, improve Arctic maritime security, and enable more effective management of sustainable development.

- ESA’s Director for Earth Observation, Josef Aschbacher, adds, “Whilst the first generation of Copernicus Sentinels today offer excellent global data, their combined Arctic observation capabilities are limited in scope. As part of the preparation of Copernicus 2.0, three new high priority candidate missions: CIMR, CRISTAL and ROSE-L, and next-generation Sentinels are being prepared by ESA.

- “Together with the Copernicus CO2M mission, these new missions will provide new pan-Arctic, year-round monitoring and CO2 emissions data to support the EU Green Deal and further boost the Copernicus climate change monitoring and service capabilities.”

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Figure 43: This map shows the Arctic sea ice extent on 25 August 2020. The orange line shows the 1981 to 2010 median extent for that day. The grey circle in the middle indicates a lack of data (image credit: NSIDC/processed by ESA)

• August 20, 2020: Amid the blistering California heatwave, which is in its second week, there are around 40 separate wildfires across the state. Record high temperatures, strong winds and thunderstorms have created the dangerous conditions that have allowed fires to ignite and spread. The fires are so extreme in regions around the San Francisco Bay Area that thousands of people have been ordered to evacuate. 62)

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Figure 44: Captured on 19 August 2020, this Copernicus Sentinel-3 image shows the extent of the smoke from fires currently ablaze in California, USA (image credit: ESA, the image contains Copernicus Sentinel (2020), processed by ESA, CC BY-SA 3.0 IGO)

• June 8, 2020: Today marks World Oceans Day, a day that aims to raise awareness in protecting and restoring our oceans and its resources. Today, and every day, Earth observing satellites continuously watch over the ocean to monitor and protect our environment. 63)

- Covering more than 70% of Earth’s surface, the oceans are what makes this our Blue Planet. Our seas influence the climate, produce the oxygen we breathe, serve as a means of transport and a major source of food and resources.

- But they are under stress from climate change, pollution and ocean acidification – all of which affect ecosystems and biodiversity. Satellite data increase our scientific understanding and support a range of environmental monitoring services in support of ocean conservation. From water saltiness to wave height, through sea level, sea ice and phytoplankton, satellites take stock of the ocean in many different ways.

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Figure 45: In this image, captured by the Copernicus Sentinel-3 mission, the green algae blooms swirling around the Baltic Sea are visible. The Baltic Sea faces many serious challenges, including toxic pollutants, deep-water oxygen deficiencies and toxic blooms of cyanobacteria affecting the ecosystem, aquaculture and tourism (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

- Satellite data can track the growth and spread of harmful algae blooms in order to alert and mitigate against damaging impacts for tourism and fishing industries. Learn more about the seas that surround us and how satellite monitoring helps protect them.

• May 8, 2020: Lying in the North Atlantic Ocean, Greenland is the world’s largest island and is home to the second largest ice sheet after Antarctica. Greenland’s ice sheet covers more than 1.7 million km2 and covers most of the island. 64)

- Ice sheets form in areas where snow that falls in winter does not melt entirely over the summer. Over thousands of years, layers of snow pile up into thick masses of ice, growing thicker and denser as the new snow and ice layers compress the older layers.

- Ice sheets are constantly in motion. Near the coast, most of the ice moves through relatively fast-moving outlets called ice streams, glaciers and ice shelves.

- In this image (Figure 46), sea ice and icebergs can be seen in the Nares Strait – the waterway between Greenland and Canada’s Ellesmere Island, visible top left in the image. On the tip of Ellesmere Island lies Alert – the northernmost known settlement in the world. Inhabited mainly by military and scientific personnel on rotation, Alert is about 800 km from the closest community, which is roughly the same distance from Alert to the North Pole.

- Scientists have used data from Earth-observing satellites to monitor Greenland’s ice sheet. According to a recent study, both Greenland and Antarctica are losing mass six times faster than they were in 1990s. Between 1992 and 2017, Greenland lost 3.8 trillion tons of ice – corresponding to around 10 mm contribution to global sea-level rise.

- Melting ice sheets caused by rising temperatures and the subsequent rising of sea levels is a devastating consequence of climate change, especially for low-lying coastal areas. The continued satellite observations of the Greenland ice sheet are critical in understanding whether ice mass loss will continue to accelerate and the full implications of this anticipated change.

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Figure 46: Northwest Greenland is featured in this icy image captured by the Copernicus Sentinel-3 mission. In the top center of this image, captured on 29 July 2019, the Petermann glacier is visible. Petermann is one of the largest glaciers connecting the Greenland ice sheet with the Arctic Ocean. Upon reaching the sea, a number of these large outlet glaciers extend into the water with a floating ‘ice tongue’. Icebergs occasionally break or ‘calve’ off these tongues. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

• March 6, 2020: The Copernicus Sentinel-3 mission takes us over part of the Canadian Arctic Archipelago. Most of the archipelago is part of Nunavut – the largest and northernmost territory of Canada. 65)

- The archipelago covers an area of around 1,500,000 km2 and consists of 94 major islands and more than 36,000 minor ones. The archipelago is bound by the Beaufort Sea to the west and by Hudson Bay and the Canadian mainland to the south – largely obscured by clouds in this image.

- The various islands of the Canadian Arctic Archipelago are separated by a series of waterways collectively known as the Northwest Passage. In the past, the Northwest Passage has been impassable owing to its thick, year-round sea ice.

- However, owing to significant changes in the Arctic climate, summer sea ice has decreased substantially and has led to an increasing number of vessels navigating through this once-impossible route.

- According to the National Snow and Ice Data Center (NSIDC), the sea ice extent in July 2019 declined at an average daily rate of 105,700 km2 – exceeding the 1981 to 2010 average rate of 86,800 km2 per day.

- This image (Figure 47) was captured in the days when several wildfires were burning in the Arctic, specifically Siberia. In this image, a wildfire can be seen on mainland Canada, along the Mackenzie River, and smoke plumes are visible blowing westwards.

- Banks Island – the westernmost island of the Arctic Archipelago – is visible in the center of the image. The island has a large population of Arctic foxes, as well as caribou, polar bears and wolves. A number of glacial lakes can be seen in emerald green on the east side of the island.

- Victoria Island lies to the east of Banks Island, and can be identified with its deeply indented coast. With an area of around 200,000 km2, Victoria Island is only slighter smaller than the island of Great Britain.

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Figure 47: In this image of Sentinel-3, captured on 27 July 2019, sea ice can be seen in the waterways of the Canadian Archipelago, as well as broken-up sea ice in the Beaufort Sea. Numerous, large ice floes are seen at the southern margin of the pack ice, and can be seen drifting southwards. As the pack ice drifts and encounters warmer waters, the ice is more prone to rapid melting. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

• January 17, 2020: The Copernicus Sentinel-3 mission takes us over the Japanese archipelago – a string of islands that extends about 3000 km into the western Pacific Ocean. 66)

- While the archipelago is made up of over 6000 islands, this image focuses on Japan's four main islands (Figure 48).

- Honshu’s land mass comprises approximately four-fifths of Japan’s total area. Honshu’s main urban areas of Tokyo, Nagoya, and Osaka are clearly visible in the image. The large grey area in the east of the island, near the coast, is Tokyo, while the smaller areas depicted in grey are the areas around Nagoya and Osaka.

- Honshu is also home to the country’s largest mountain, Mount Fuji. A volcano that has been dormant since it erupted in 1707, Mount Fuji is around 100 km southwest of Tokyo and its snow covered summit can be seen as a small white dot.

- The Sea of Japan, also referred to as the East Sea, (visible to the west of the archipelago) separates the country from the east coast of Asia. The turquoise waters surrounding the island of Hokkaido can be seen at the top of the image, while the waters in the right of the image have a silvery hue because of sunglint – an optical effect caused by the mirror-like reflection of sunlight from the water surface back to the satellite sensor.

- Sentinel-3 is a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus environmental monitoring program. Each satellite’s instrument package includes an optical sensor to monitor changes in the color of Earth’s surfaces. It can be used, for example, to monitor ocean biology and water quality.

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Figure 48: While the archipelago is made up of over 6000 islands, this image focuses on Japan's four main islands. Running from north to south, Hokkaido is visible in the top right corner, Honshu is the long island stretching in a northeast–southwest arc, Shikoku can be seen just beneath the lower part of Honshu, and Kyushu is at the bottom. This image, which was captured on 24 May 2019, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

• January 9, 2020: Ferocious bushfires have been sweeping across Australia since September, fuelled by record-breaking temperatures, drought and wind. The country has always experienced fires, but this season has been horrific. A staggering 10 million hectares of land have been burned, at least 24 people have been killed and it has been reported that almost half a billion animals have perished. 67)

- Photographs and film footage have without doubt left the world shocked, but the view from space shows the scale of what Australians are having to deal with.

- New South Wales has been worst hit. The Copernicus Sentinel-3 image of Figure 50 shows smoke pouring from numerous fires in the state on 3 January.

Figure 49: While this image was captured by the mission’s OLCI (Ocean and Land Color Instrument), which offers camera-like images, the mission’s SLSTR (Sea and Land Surface Temperature Radiometer) instrument can record fire hotspots. This instrument works like a thermometer in the sky, measuring thermal infrared radiation to take the temperature of Earth’s land surfaces. The instrument’s two dedicated fire channels are used to compile the World Fire Atlas. The animation here shows how the number of fires increased between October 2019 and January 2020. The measurements were taken by the Copernicus Sentinel-3A satellite at night only, and since the spatial resolution is limited to 1 km, the animation, as shocking as it is, actually underestimates the number of fires (image credit: ESA, the image contains modified Copernicus Sentinel data (2019-2020), processed by ESA)

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Figure 50: This Copernicus Sentinel-3 image shows smoke pouring from numerous fires in New South Wales on 3 January 2020 (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)



Sensor complement (optical payload, topographic payload)

In the context of GMES (Global Monitoring for Environment and Security), the objectives of the Sentinel-3 mission, driven by ESA and the user community, encompass the commitment to consistent, long-term collection of remotely sensed data of uniform quality in the areas of sea / land topography and ocean color. Measurements over oceans will be provided jointly with other operational missions, such as the Jason series, to contribute to the realization of a permanent Global Ocean Observing System (GOOS). Regarding ice, it is foreseen to monitor land ice (also denoted as ice sheet) including ice margins and sea ice. At last, measurements over rivers and lakes will help in the water level monitoring of spots of interest throughout the world.

Sentinel-3 will support primarily services related to the marine environment, such as maritime safety services that need ocean surface-wave information, ocean-current forecasting services that need surface-temperature information, and sea-water quality and pollution monitoring services that require advanced ocean color products from both the open ocean and coastal areas. Sentinel-3 will also serve numerous land, atmospheric and cryospheric application areas such as land-use change monitoring, forest cover mapping and fire detection. 68)

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Figure 51: Sentinel-3 spacecraft with payload layout (image credit: ESA)

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Figure 52: FOVs (Field of Views) of the Sentinel-3 instruments (image credit: ESA)


Optical payload (OLCI, SLSTR)

The optical payload consists of the OLCI and SLSTR instruments. They provide a common quasi-simultaneous view of the Earth to help develop synergistic products. 69) 70) 71)

The primary mission objective of the optical payload is to ensure the continuation of the successful Envisat observations of MERIS for ocean color and land cover and AATSR for sea surface temperature. In addition, due to the overlapping field of view from both optical sensors, new applications will emerge from the combined exploitation of all spectral channels.

OLCI (Ocean and Land Color Instrument):

OLCI is a medium resolution pushbroom imaging spectrometer of MERIS heritage, flown on Envisat, but with a slightly modified observation geometry: the FOV (Field of View) is tilted towards the west (~ 12º away from the sun), minimizing the sun-glint effect over the ocean and offering a wider effective swath (~ 1300 km, overall FOV of 68.6º). The sampling distance is 1.2 km over the open ocean and 0.3 km for coastal zone and land observations. The instrument mass is ~ 150 kg, a size of 1.24 m x 0.83 m x 1.32 m, the power demand is 124 W; it has been designed and developed at Thales Alenia Space España.

The FOV of OLCI is divided between five cameras on a common structure with the calibration assembly. Each camera has an optical grating to provide the minimum baseline of 16 spectral bands required by the mission together with the potential for optional bands for improved atmospheric corrections.

The OLCI bands are optimized to measure ocean color over open ocean and coastal zones. A new channel at 1.02 µm has been included to improve atmospheric and aerosol correction capabilities. Two additional channels in the O2A absorption line (764.4 and 767.5 nm, in addition to the existing channel at 761.25 nm) are included for improved cloud top pressure (height) with an additional channel at 940 nm in the H2O absorption region, to improve water vapor retrieval. A channel at 673 nm has been added for improved chlorophyll fluorescence measurement.

Band No

λ center
(nm)

Bandwidth
(W/m2 sr µm)

Lmin
(W/m2 sr µm)

Lref
(W/m2 sr µm)

Lsat
(W/m2 sr µm)

SNR@Lref

Oa1

400

10

21.60

62.95

413.5

2188

Oa2

412.5

10

25.93

74.14

501.3

2061

Oa3

442.5

10

23.96

65.61

466.1

1811

Oa4

490

10

19.78

51.21

483.3

1541

Oa5

510

10

17.45

44.39

449.6

1488

Oa6

560

10

12.73

31.49

524.5

1280

Oa7

620

10

8.86

21.14

397.9

997

Oa8

665

10

7.12

16.38

364.9

883

Oa9

673.75

7.5

6.87

15.70

443.1

707

Oa10

681.25

7.5

6.65

15.11

350.3

745

Oa11

708.25

10

5.66

12.73

332.4

785

Oa12

753.75

7.5

4.70

10.33

377.7

605

Oa13

761.25

2.5

2.53

6.09

369.5

232

Oa14

764.375

3.75

3.00

7.13

373.4

305

Oa15

767.5

2.5

3.27

7.58

250.0

330

Oa16

778.75

15

4.22

9.18

277.5

812

Oa17

865

20

2.88

6.17

229.5

666

Oa18

885

10

2.80

6.00

281.0

395

Oa19

900

10

2.05

4.73

237.6

308

Oa20

940

20

0.94

2.39

171.7

203

Oa21

1020

40

1.81

3.86

163.7

151

Table 4: OLCI band specifications, in cyan MERIS heritage, in yellow additional bands 72)

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Figure 53: The OLCI instrument supports a re-definition of its spectral bands through a programmable acquisition design to support a high-degree of flexibility during the mission (image credit: ESA)

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Figure 54: Schematic view of the OLCI instrument configuration (image credit: ESA)

Each camera is constituted of a Scrambling Window Element to comply with the polarization requirement, a COS (Camera Optical Sub-assembly) for the spectral splitting of the different wavelengths, a FPA (Focal Plane Assembly) with a CCD for the signal detection and a VAM (Video Acquisition Module) for the monitoring of the analog signal. The optical sub-assembly of each camera includes its own grating and provides the 21 spectral bands required by the mission in the range 0.4-1.0 µm. 73)

The control of the instrument assembly is realized by a CEU (Common Electronic Unit), which assumes the function of instrument control, power distribution and digital processing.

A calibration assembly, including a rotation wheel with five different functions for normal viewing, dark current, spectral and radiometric calibrations insures the calibration of the instrument. The calibration wheel has 5 positions: 74)

• The Earth Observation aperture

• The Shutter, blocking incoming light it allows dark offset acquisition (and gives the calibration zero)

• The nominal radiometric diffuser, from which calibration gains are derived

• The reference radiometric diffuser, dedicated to the monitoring of the nominal diffuser ageing

• The spectral diffuser allowing spectral calibration at 3 wavelengths.

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Figure 55: Schematic view of the OLCI observation geometry with the 5 camera assembly (image credit: ESA)

Compared to ENVISAT, the following improvements have been implemented:

• Along-track SAR capability for coastal zones, inland water and sea-ice altimetry

• Off-nadir tilted field of view for OLCI cameras to minimize sun-glint contamination (i.e. loss of ocean color data)

• New spectral channels in OLCI and SLSTR allowing improved retrieval of geophysical products and detection of active fire

• Synergy products (e.g. vegetation) based on combination of OLCI and SLSTR data (OLCI swath fully covered by SLSTR swath).

In each camera unit, Earth light enters a calibration assembly which includes filters as well as spectral calibration sources which are PTFE (Polytetrafluorethylen, also known as Teflon) sun diffusers to track spectral calibration, gain calibration and instrument aging effects. Next, light passes through the scrambling window assembly featuring a scrambling window and an inverse filter.

The camera optics subassembly houses all optics needed for the separation of spectral bands and focusing the light onto the detector. After passing through the ground imager optics, the light is dispersed by a diffraction grating and passed onto the CCD detector system building the centerpiece of the focal plane assembly.

The spectrometer generates a dispersed image of the entrance slit onto a two-dimensional detector where one dimension is the spatial extension of the slit and the other is the spectral dispersion of the slit image created by the grating.

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Figure 56: OLCI optical design (image credit: ESA)

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Figure 57: Photo of the OLCI engineering model (image credit: ESA, TAS)