Copernicus: Sentinel-3 — Global Sea/Land Monitoring Mission including Altimetry
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.
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.
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.
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)
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.
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.
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).
Figure 4: Photo of the MEMS rate sensor (image credit: ESA)
Figure 5: Alternate view of the Sentinel-3 spacecraft and the accommodation of the payload (image credit: ESA)
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:
• 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. 21) 22)
- 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.
Figure 7: 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. 23)
- 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.
Figure 8: 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. 24)
- 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. 25)
- 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. 26)
Figure 9: 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. 27)
• 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. 28)
• 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. 29)
• 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. 30)
- 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. 31) 32)
ESA awarded the contract to Eurockot Launch Services on Feb. 9, 2012. 33)
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).
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. 37)
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.
Figure 10: Tandem phase operations overview (EUMETSAT, ESA, Ref. 37)
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.
Status of the Sentinel-3 mission
• September 7, 2018: The Copernicus Sentinel-3A satellite takes us over the North Sea, revealing a significant algae bloom covering most of the southern part. One of Europe's most productive fisheries, the North Sea covers an area of 570, 000 km2 and is linked to the Atlantic by one of the world's busiest shipping regions – the English Channel. 38)
- The image of Figure 11 covers a large section of Scandinavia, including Norway, the south of Sweden, and Denmark, stretching down to Germany and the Netherlands in the bottom right. On the left of the image we can see the east coast of Scotland and the Northern Isles, comprising two archipelagos – Orkney and Shetland. This image is also featured on the Earth from Space video program. 39)
- Harmful algal blooms caused by excessive growth of marine algae have occurred in the North Sea and the English Channel area in recent years, with satellite data being used to track their growth and spread. These data can then be used to help develop alert systems to mitigate against damaging impacts for tourism and fishing industries.
- Harmful blooms, which pose a threat to various forms of water life, are thought to carry an annual cost of over 900 million euros to these industries in the EU.
- Helping to map algal blooms and providing critical information for marine operations are just some of the ways that the two-satellite Sentinel-3 is used for Europe's Copernicus environmental monitoring program. Since 2016, Sentinel-3A has been measuring our oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics. In April 2018, it was joined by its twin satellite Sentinel-3B.
Figure 11: This true-color image taken using Sentinel-3's OLCI (Ocean and Land Color Instrument) shows a significant algae bloom. The image was captured on 27 May 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• August 24, 2018: The Copernicus Sentinel-3A satellite took the temperature at the top of Hurricane Lane as it headed towards Hawaii's Big Island on 22 August 2018. Lane weakened to a Category 3 storm on 23 August, just before it hit Hawaii. Still a powerful storm, it has brought torrential rain to the Big Island. The island is still reeling from months of devastating lava flows from the Kilauea volcano and is now coping with heavy rain and flooding. The brightness temperature of the clouds at the top of the storm, some 12–15 km above the ocean, range from about –80°C near the eye of the storm to about 15°C at the edges (Figure 12). 40)
- Hurricanes are one of the forces of nature that can be tracked only by satellites, providing up-to-date imagery so that authorities know when to take precautionary measures. Satellites deliver information on a storm's extent, wind speed and path, and on key features such as cloud thickness, temperature, and water and ice content. Sentinel-3's Sea and Land Surface Temperature Radiometer measures energy radiating from Earth's surface in nine spectral bands.
Figure 12: The Copernicus Sentinel-3 mission takes the temperature of Hurricane Lane on 22 August as it headed for Hawaii (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• July 20, 2018: With Europe in the grip of a heatwave and little rain, the scorched ground and dry vegetation is succumbing to fire. Fires have now broken out as far as the Arctic Circle, in Sweden. This animation shows images from the Copernicus Sentinel-2 (Figure 14) and Sentinel-3 (Figure 13) missions. Sentinel-2 carries a high-resolution MSI (Multispectral Imager) and Sentinel-3 carries a suite of instruments including an OLCI (Ocean and Land Color Instrument). The missions offer complementary views of Earth to help monitor environmental change and events such as these fires. 41)
- The fires have led to the authorities evacuating some villages and appealing for help from other countries, and concerns that the current record temperatures and drought are linked to climate change.
- There are said to be around 50 fires now burning in the country. Through July there have been three times as many fires as there were last year.
- Jonas Olsson from the Swedish Meteorological and Hydrological Institute is reported to have said, "It's very, very dry in most of Sweden. The flows in the rivers and lakes are exceptionally low, except in the very northern part of the country. We have water shortages. Rainfall has only been around a seventh of the normal amount, the lowest since record-keeping began in the late 19th century."
- While the focus is clearly on trying to extinguish these fires, the Copernicus Sentinel missions offer an eye in the sky to identify where fires have broken out. This is especially valuable in areas that are sparsely populated.
Figure 13: The wider view, which stretches from the west coast of Norway to central Sweden, was captured by Sentinel-3 on 17 July 2018. Here, smoke can be seen billowing from several fires (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA)
Figure 14: The closer view was captured on the same day (17 July) by Sentinel-2. Here, flames and smoke from two of the fires can be seen clearly, along with smoke from other fires in the vicinity (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA)
• July 13, 2018: The Copernicus Sentinel-3A satellite takes us over Shanghai, China. One of the most populous cities in the world and home to over 24 million people, the city is visible in the lower right of the image just above the Yangtze River mouth. As a significant global financial center it is also the site of the world's busiest container ports because of its strategic location on the Yangtze River delta. 42)
- The Taihu Lake is shown in green in the lower right part of the image. In 2007, an algal bloom on the lake caused major problems with water supplies in the neighboring city of Wuxi. Such algal blooms may well be linked to the discharge of phosphates found in fertilizers used in industry and agriculture into the water.
- Steps have been taken to limit the use of such fertilizers in a bid to reduce algal blooms, which can significantly alter the ecology of the environment below the surface and pose a threat to various forms of water life.
Figure 15: This true color image taken using Sentinel-3A's OLCI (Ocean and Land Color Instrument) shows the huge amount of sediment carried into the ocean along the coast. The image covers an area of over 1200 km side length, showing Beijing at the center-top, the salt flats close to the Mongolian border in the top left, and North Korea, with its capital, Pyongyang, just visible in the top right of the image. A large number of urban settlements represented as grey flecks are interspersed with agricultural fields, dominating the central part of the image (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• June 19,2018: The key to monitoring Earth's changing environment and to guaranteeing a consistent stream of satellite data to improve our daily lives is to take the same measurements over the course of decades. But how do you know that measurements from successive satellites, even though identical in build, are like for like? The answer, for the Copernicus Sentinel-3 mission, is to engage in some nifty orbital flying. 43)
- Sentinel-3 is a two-satellite mission to supply the coverage and data delivery needed for Europe's Copernicus environmental monitoring program.
- Launched in 2016, Sentinel-3A has been measuring our oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics and to provide critical information for marine operations, and more.
- Its twin, Sentinel-3B, was launched in April 2018 and is having its instruments calibrated and being commissioned for service. Once Sentinel-3B is operational, the two satellites will orbit Earth 140° apart.
- Now, however, the satellites have been positioned much closer together, flying a mere 30 seconds apart. Travelling at 7.4 km/s, the separation equates to a distance of 223 km. - The reason for this is to see how their instruments compare.
- Even though the two Sentinel-3 satellites are identical, each carrying a radar altimeter, a radiometer and an imaging spectrometer, there's a chance that their instruments could behave slightly differently. It is important that any differences are carefully accounted for otherwise the information they deliver could be misinterpreted as changes happening on Earth's surface.
- Given the satellites' current brief separation, their measurements should be virtually the same. This tandem phase is also important for the future Sentinel-3 satellites.
- 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 four-month 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."
- ESA's Sentinel-3 project manager, Bruno Berruti, said, "Following liftoff and the usual checks, the operations team has been expertly flying Sentinel-3B so that it gradually flies closer to Sentinel-3A. We recently reached the magic separation of 30 seconds and I am happy to say that we are now officially in the tandem phase. This will last around four months, after which the two satellites will be gently moved apart until they reach their operational separation of 140°. This is different to the other Sentinel missions, but for our mission it is better to measure ocean features such as eddies as accurately as possible."
- ESA's Sentinel-3 mission manager, Susanne Mecklenburg, added, "So far, we are really happy with the results of the tandem phase. Measurements from the satellites' instrument packages seem to be very much aligned, but we will be analyzing the results very carefully over the next months to make sure we account for any minor differences."
Figure 16: Sentinel-3 tandem mission comparison (image credit: ESA, the images contain modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• June 8, 2018: For World Oceans Day, the Copernicus Sentinel-3A satellite takes us over the Atlantic Ocean and the Republic of Cabo Verde. Several of the small islands that make up the archipelago of Cabo Verde can be seen peeking out from beneath the clouds (Figure 17). These 10 volcanic islands, with a total area of about 4000 km 2, lie in the Atlantic Ocean about 570 km off the west coast of Senegal and Mauritania, which frame the image on the right. 44) 45)
- The most striking thing about this image, however, is the dust and sand being carried by the wind towards Cabo Verde from Africa. The sand comes mainly from the Sahara and Sahel region. Owing to Cabo Verde's position and the trade winds, these storms are not uncommon and can disrupt air traffic.
- However, this sand also fertilizes the ocean with nutrients and promotes the growth of phytoplankton, which are microscopic plants that sustain the marine food web. The iron in the dust is particularly important. Without iron mammals cannot make haemoglobin to transport oxygen around the bloodstream and plants cannot make chlorophyll to photosynthesize. Research has shown that around 80% of iron in samples of water taken across the North Atlantic originates from the Sahara. It can be assumed, therefore, that life in the deep ocean depends on this delivery of fertilizer from one of the world's most parched regions.
- World Oceans Day takes place on 8 June each year and celebrates the ocean, its importance in all our lives, and how we can protect it.
- Historically, the name "Cape Verde" has been used in English for the archipelago and, since independence in 1975, for the country. In 2013, the Cape Verdean government determined that the Portuguese designation Cabo Verde would henceforth be used for official purposes, such as at the United Nations, even in English contexts. Cape Verde is a member of the African Union.
Figure 17: The Sentinel-3A satellite captured this image on 30 May 2018 (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• June 5, 2018: Launched on 25 April 2018, Sentinel-3B has already delivered some impressive first images from its ocean and land color instrument, from its altimeter and from the optical channels of its radiometer. With the radiometer's thermal-infrared channels now turned on, the satellite completes its set of firsts with an image that depicts thermal signatures over southern Italy, the Mediterranean Sea and Sicily – with the hotspot of Mount Etna clearly visible. This image shows the ‘brightness temperature', which corresponds to radiation emitted from the surface. Further processing is needed to turn this into an actual temperature map. The land surface is shown in red–orange colors, corresponding to a brightness temperature range of 296–320K. The blue colors over the ocean correspond to a range of 290–295K. The dark blue–black areas correspond to clouds, which are opaque to thermal-infrared radiation and so prevent a view of the ocean or land surface. 46)
- Mount Etna, Europe's largest and most active volcano in Europe, appears much hotter than the surrounding land. In a state of almost continuous unrest, the volcano is currently classified as having ‘minor activity'.
- Over the oceans, the Sentinel-3 radiometer is important for providing SST (Sea Surface Temperature) measurements for oceanographic and weather forecasting centers. Over land, the instrument can be used, in particular, to monitor urban heat islands and wildfires.
- Sentinel-3B joins its identical twin, Sentinel-3A, in orbit. This pairing of satellites increases coverage and data delivery for the European Union's Copernicus environment program.
Figure 18: The infrared channels of Sentinel-3B's radiometer have been turned on and reveal the hotspot of Mount Etna in Sicily (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• May 11, 2018: Sentinel-3B has also delivered first data from its altimeter, SRAL (SAR Radar Altimeter), – which means that all of the instruments are working well. 47)
Figure 19: The altimeter has measured the height of Lake Van in east Turkey, close to the boarder of Iran. This brackish lake is the largest body of water in Turkey. The image shows two tracks, about 7 km apart, across the lake: one from the Sentinel-3A satellite on 26 April 2018 and one from Sentinel-3B on 9 May. They measure the lake to be 1647 m above sea level and clearly show the transition from land to water (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA)
- Sentinel-3B will not be fully commissioned for service for another five months or so, but even at this early stage in its life in orbit, these data compare well with those of its fully-operational twin, Sentinel-3A. The altimeter is particularly important for measuring changes in sea level, but as this example shows, the instrument also contributes to monitoring the height of lake water through the Copernicus Global Land Service. It is also used to measure the height of ice.
• May 11, 2018: The high-precision sea level anomaly measurements from SRAL (Synthetic Aperture Radar Altimeter) on Sentinel-3B enhance the Copernicus altimeter constellation of Sentinel-3A and Jason-3, along with Jason-2. 48)
Figure 20: The altimeter measurements, all acquired on 8 May 2018 over the Atlantic Ocean and the north American coastline, clearly match well at crossing points and the map of sea level anomalies produced by the Copernicus Marine Environment Monitoring Service (CMEMS), image credit: EUMETSAT, CMENS
- Pierre Yves Le Traon, Scientific Director at Mercator Ocean, which operates the Copernicus Marine Environment Monitoring Service (CMEMS), said receiving data from altimeters on two Sentinel-3 satellites will bring benefits to marine safety and industries.
- "The joint use of Sentinel-3A and Sentinel-3B high precision altimeters will improve capabilities of CMEMS to forecast waves and ocean currents at fine scale," Le Traon said. "This is highly needed for the applications we service, such as marine safety, maritime transport and offshore operations."
• May 10, 2018: The SLSTR (Sea and Land Surface Temperature Radiometer) is particularly sophisticated, measuring energy radiating from Earth's surface in nine spectral bands, including visible and infrared. It also includes dedicated channels for measuring fires. This early image came from its optical channels. 49)
- SLSTR measures the energy radiating from the Earth's surface in nine spectral bands, including visible and infrared. The thermal channels will be switched on once the instrument has completed outgassing water vapor, and the infrared channels have been cooled to the operating temperatures. 50)
- Sentinel-3B is currently flying in tandem with its twin, Sentinel-A, which was launched in 2016, so that their observations can be cross calibrated. The spacecraft are part of a series of Sentinel satellites under the umbrella of the EU's Copernicus program, which takes a continuous "health check" of our planet.
Figure 21: The SLSTR instrument on Sentinel-3B captured this image on 9 May 2018. It shows a low pressure system over the UK and Ireland, France, the Bay of Biscay, Spain and part of north Africa. Vegetation appears in red (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by EUMETSAT)
• May 9, 2018: Less than two weeks after it was launched, the Copernicus Sentinel-3B satellite has delivered its first images of Earth. Exceeding expectations, this first set of images include the sunset over Antarctica, sea ice in the Arctic and a view of northern Europe. 51)
- The very first image, captured on 7 May at 10:33 GMT , shows the transition between day and night over the Weddell Sea in Antarctica. The satellite also captured swirls of sea ice off Greenland on the same day. Another in this first set of images offers a rare cloud-free view of northern Europe. They were taken by OLCI (Ocean and Land Color Instrument) on Sentinel-3B.
Figure 22: The first image of OLCI on Sentinel-3B was captured on 7 May 2018 (10:33 GMT). The image shows the sunset over the Weddell Sea off the coast of Antarctica. While the line between day and night is clearly visible, bright streaks glint on the clouds from the sunset. OLCI, features 21 distinct bands, a resolution of 300 m and a swath width of 1270 km. The instrument can be used to monitor aquatic biological productivity and marine pollution, and over land it can be used to monitor the health of vegetation (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by EUMETSAT, CC BY-SA 3.0 IGO)
Figure 23: One of the Copernicus Sentinel-3B's first images of OLCI features Greenland. Captured on 7 May 2018 at 13:20 GMT, the image shows sea ice swirled into eddies caused by the wind and ocean currents (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by EUMETSAT, CC BY-SA 3.0 IGO)
- Josef Aschbacher, ESA's Director of Earth Observation Programs, said, "The launch of Sentinel-3B completed the first batch of Sentinels that we are delivering for Copernicus. We finished the launch and early orbit phase in a record time and we are now getting on with the task of commissioning the satellite for service. These first images from the ocean and land color instrument already show how the satellite is set to play its role in providing a stream of high-quality environmental data to improve lives, boost the economy and protect our world."
- Over oceans, OLCI measures the temperature, color and height of the sea surface as well as the thickness of sea ice. These measurements are used, for example, to monitor changes in Earth's climate and for more hands-on applications such as for monitoring marine pollution. Over land, this innovative mission monitors wildfires, maps the way land is used, checks vegetation health and measures the height of rivers and lakes.
Figure 24: This OLCI image of cloud-free Northern Europe on Sentinel-3B was captured on 8 May 2018 at 09:33 GMT. Features over land and water can been seen clearly such as different types of land cover, snow and also a plume of phytoplankton in the North Sea (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by EUMETSAT, CC BY-SA 3.0 IGO)
• April 27, 2018: This mosaic of cloud-free images from the Copernicus Sentinel-3A satellite spans the entire continent of Europe, and more. The view stretches from Iceland in the northwest across to Scandinavia and Russia in the northeast, and from the northern tips of Norway and Finland to as far south as Algeria, Libya and Egypt. 52)
- While the satellite's OLCI (Ocean and Land Color Instrument) depicts the green of summer in many parts of Europe, the dryness that summer brings, particularly to the south, can also be seen in parts of Spain, Italy and Turkey, for example.
- This week, aerospace fans have had their eyes firmly set on the ILA Berlin Air Show in Germany. Berlin lies in the center of the image (Figure 25). Here, participants have been learning about new space technologies as well as being treated to latest results from satellite missions such as ESA's Gaia, which has been used to chart the position, brightness and motion of more than a billion stars. With the second Sentinel-3 satellite, Sentinel-3B, lifting off from Russia this week, the focus has also been this latest Copernicus mission.
- Like Gaia maps stars thousands of light-years away to understand the Universe, the Sentinel-3 mission observes our home planet to understand large-scale environmental dynamics. Based on a constellation of two identical satellites, the Sentinel-3 mission carries a suite of instruments to measure our oceans, land and ice.
- Over land, this innovative mission is being used to map the way land is used, provide indices of vegetation, monitor wildfires and measure the height of rivers and lakes. Over oceans it measures the temperature, color and height of the sea surface as well as the thickness of sea ice.
Figure 25: The image, which is made up of scenes captured between 1 March 2017 and 30 July 2017, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by Sinergise/ESA)
• April 26, 2018: With the launch of Sentinel-3B, the first set of Sentinels for Copernicus is now in orbit delivering an almost mind-boggling amount of data. While this wealth of information advances environmental monitoring, it also opens up huge business opportunities. To help bring these data to market, ESA and SAP have joined forces to create the World Space Alliance. SAP (Systems, Applications & Products in Data Processing) is a German-based (HQs in Walldorf) European multinational software corporation that makes enterprise software to manage business operations and customer relations. 53)
- ESA and SAP first teamed up two years ago to close the gap between traditional Earth observation and the digitalized business world. Building on this fruitful partnership, the two organizations today signed another agreement to strengthen the use of digital technologies and Earth observation data for a range of business sectors.
- Josef Aschbacher, Director of Earth Observation Programs at ESA, said, "Data from the Sentinels are, of course, open and freely available to everybody, but through our partnership with SAP we are working on making data products that businesses can easily tap into."
- The World Space Alliance will be powered by the SAP Cloud Platform. In turn, ESA also benefits from the platform's big-data handling and dissemination capabilities. The data it uses will come primarily from the Copernicus Sentinel missions, but also from other satellite missions that contribute to Copernicus.
- The agreement was signed at the ILA Berlin Air Show on 26 April 2018, this new agreement paves the way to strengthen the use of digital technologies and Earth observation data for a range of business sectors.
• April 26, 2018: ESA's mission control team keeping a close watch on the launch and progress of Sentinel-3B as it joined its identical twin, Sentinel-3A, to complete a constellation that will provide global monitoring of Earth's oceans, land, ice and atmosphere for Europe's Copernicus environmental monitoring program. 54)
- Europe's Copernicus program now has three complete two-satellite constellations in orbit plus an additional single satellite, Sentinel-5P, a mission to monitor air pollution.
- At the end of the commissioning phase, encompassing the first five months in orbit to test the functionality of the satellite, ESA will hand over operations of the satellite to EUMETSAT. ESA and EUMETSAT manage the mission jointly with ESA producing land products and EUMETSAT marine products for application through the Copernicus services.
Table 4: About the Tandem Phase of the Sentinel-3 mission (Craig Donlon, the Mission Scientist for the Copernicus Sentinel-3 and Sentinel-6 Satellites at ESA) 55)
- In two years since its launch, the Sentinel-3A satellite has delivered over 500 Terabytes of data about the Earth's oceans, land, ice and atmosphere. Its free and open data has allowed us to improve our understanding of large-scale global dynamics beyond expectations. Now, after two years of a solo journey, the Sentinel-3A finally has a twin – Sentinel-3B (Ref. 55).
• April 25, 2018: Just 92 minutes after liftoff, Sentinel-3B sent its first signals to the Kiruna station in Sweden. Data links were quickly established by teams at ESA's operations center in Darmstadt, Germany, allowing them to assume control of the satellite (Ref. 35).
- During the three-day launch and the early orbit phase, controllers will check that all the satellite's systems are working and begin calibrating the instruments to commission the satellite. The mission is expected to begin routine operations after five months.
- "This is the seventh launch of a Sentinel satellite in the last four years. It is a clear demonstration of what European cooperation can achieve and it is another piece to operating the largest Earth observation program in the world, together with our partners from the European Commission and EUMETSAT," said ESA Director General Jan Wörner.
- With this launch, the first set of Sentinel missions for the European Union's Copernicus environmental monitoring network are in orbit, carrying a range of technologies to monitor Earth's land, oceans and atmosphere.
- ESA's Director of Earth Observation Programs, Josef Aschbacher, said, "With Sentinel-3B, Europe has put the first constellation of Sentinel missions into orbit – this is no small job and has required strong support by all involved. It allows us to get a very detailed picture of our planet on a daily basis and provides crucial information for policy makers. "It also offers lots of opportunities for commercial companies to develop new innovative services. And, the free and open data policy allows every citizen to have updates for their own use. When we designed such a satellite constellation 20 years ago not everyone was convinced Europe could do that. I am glad to see this has become reality and that it is now a large European success story."
• April 13, 2018: EUMETSAT collects and disseminates data from three instruments carried by the Sentinel-3 satellites. They are: OLCI (Ocean and Land Color Instrument), SLSTR (Sea and Land Surface Temperature Radiometer), and SRAL (Synthetic Aperture Radar Altimeter). The SRAL instrument has been designed to deliver accurate measurements of sea surface height, significant wave height and surface wind speeds over the world's oceans. 56)
- Sea level rise is an important indicator of climate change. Globally, the sea level has been rising by an average of just over 3mm per year for the past 20 years. However, the rise is not uniform – it varies considerably around the world. Additionally, the rate of sea level rise is increasing by about 1mm per year each decade. This suggests that by the end of the century the sea level could have risen by as much as 65cm more than current projections.
- EUMETSAT Project Scientist and Altimetry Expert Remko Scharroo said the SRAL measures an array of important data in addition to sea level. "Sea surface height data from the satellite's altimeter have significantly improved our capability to analyze and forecast ocean currents," Scharroo said. "This is essential for the applications we serve such as marine safety, ship routing and predicting the fate of marine pollution events. Another set of data maps significant wave height, which again is important information needed for ship safety. Finally, the SRAL also provides accurate topography measurements over sea ice, ice sheets, rivers and lakes."
- The successful launch of Sentinel-3B at the end of April will represent the full deployment of the Sentinel-3 mission. Sentinel-3A was launched in February 2016 and has been delivering observations for two years. The two satellites are needed to provide the full set of measurements required by users.
- This includes for use in ocean meteorology, which is all about capturing significant wave height, wind speed and sea level measurements. Altimetry ensures the monitoring of ocean currents and eddies which carry a lot of energy throughout the ocean and interact with the atmosphere, thereby influencing the weather.
- An important example is the forecasting of hurricanes. Altimeters can help derive the latent heat in oceans. "You might argue that the SLSTR instrument does the same thing, that it measures heat in the ocean," Scharroo said. "But these are two different types of measurements entirely. "While sea surface temperature covers the total top layer of the ocean, it does not tell you much about the structure below. For this, you need altimeter measurements. Water expands when it's hot. The more heat penetrate the depth of the oceans, the higher the sea level rises and that will give you vital information about the column of water underneath. In short, the SLSTR provides information about the surface but not about the column of water underneath or the latent heat."
- Scharroo said both measurements were valid and important. "There is no competition between the instruments, believe me," he said. "It is in synergy that they work best."
Figure 26: Typical measurements of the instruments SRAL and SLSTR (image credit: EUMETSAT)
• April 9, 2018: EUMETSAT operates the Sentinel-3 satellites on behalf of the EU and delivers the marine mission. 57)
- Ocean Color data can be used for a wide variety of purposes. They can help to track and forecast harmful algal blooms, which can endanger humans, marine or freshwater life and aquaculture. These data also support the monitoring of coastal water quality, by tracking eutrophication, nuisance blooms, sedimentation and erosion.
- Ocean color data are also of a truly global importance as they help monitor climate change: ocean color is one of the so-called Essential Climate Variables (ECV) listed by the WMO (World Meteorological Organization) that help detect changes in biological activity in the ocean's surface layer.
- Ewa Kwiatkowska, EUMETSAT Remote Sensing Scientist explains: "Phytoplankton take up carbon dioxide (CO2) during photosynthesis, making the ocean the most important carbon sink. Alternatively, ocean color data can be used to monitor the annual global uptake of CO2 by phytoplankton on a global scale."
- Observations of ocean color support many industries, including fisheries and aquaculture, because of the phytoplankton role at the base of the aquatic food chain. They also support studies of the Earth system, for instance through monitoring El Niño/La Niña events and their impacts on ocean living ecosystems.
- She added: "Ocean color data can aid reporting obligations of the European Union's legislation within Marine Strategy Framework Directive and Water Framework Directive, the goal of which is to achieve or maintain Good Environmental Status of the seas by the year 2020."
- To ensure a steady flow of these vital data, two Sentinels are a must as Kwiatkowska explains. "Harmful outbreaks of algal bloom, require constant and consistent monitoring and forecasting from the OLCI instrument. With a cloud cover and gaps in coverage between successive orbits, there could be a discontinuity in the observations – with possibly detrimental effects.
- She continued "Also, there is a need to time phytoplankton blooms for ecosystem forecasts and to detect trends in eutrophication, where water body gets over-enriched with an excess amount of nutrients. This process induces growth of plants and algae and due to the biomass load, may result in oxygen depletion of the water body."
Figure 27: A typical OLCI ocean color image of Sentinel-3A (image credit: NASA Earth Observatory, image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response)
• April 6, 2018: The Copernicus Sentinel-3A satellite takes us over southern Siberia and the world's largest freshwater lake: Lake Baikal. Imaged on 14 March 2017, this deep lake is covered by ice. The entire lake is typically covered between January and May and in some places the ice can be more than 2 m thick. 58) 59)
- Holding around 23 000 km3 of water, Lake Baikal is the largest freshwater lake by volume in the world. It contains about 20% of the world's fresh surface water, which is more than all of the North American Great Lakes put together. Baikal water is extraordinarily clean, transparent and saturated with oxygen. The high transparency is thanks to numerous aquatic organisms purifying the water and making it similar to distilled water.
- At 25 million years, this remarkable lake is also the oldest in the world. It is known as the Galapagos of Russia because its age and isolation have produced rich and unusual water wildlife, which is of exceptional value to evolutionary science. Occasionally, new species are discovered and it has been estimated that we know of only 70–80% of all the species inhabiting the lake. For these reasons, in 1996 it was listed as a UNESCO World Heritage Site. The lake is surrounded by mountain-taiga landscapes, which are also protected to preserve their natural state.
Figure 28: This false-color image was acquired on 14 March 2018 with Sentinel-3A (image credit: ESA, this image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• March 9, 2018: The Copernicus Sentinel-3A satellite carries a suite of state-of-the art sensors that deliver a wealth of information to monitor our changing world, but this image was captured with its OLCI (Ocean and Land Color Instrument) . With a swath-width of 1270 km, this instrument delivers images that can span several countries, as we see here. 60)
- From east to west, the image features the islands of Corsica and Sardinia in the Mediterranean Sea, Italy and across the Adriatic Sea to Croatia, Bosnia and Herzegovina, Serbia, and to the western edges of Romania. To the north and partly obscured by clouds, lie Germany, Switzerland, Austria and the Alps.
- South of the Alps, haze hovers over Italy's Po Valley. Following the Po River to the east, the sediment it carries can be seen entering the Adriatic Sea. In fact, sediments line most of the eastern coast of Italy, giving it a greenish blue frame, while the western coast is mostly sediment-free.
- As the colors in this image suggest, the camera can be used to monitor ocean ecosystems and vegetation on land – all of which will bring significant benefits to society through more informed decision-making.
- Sentinel-3A will soon be joined in orbit by its twin Sentinel-3B, which is scheduled for liftoff from Russia on 25 April. 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.
Figure 29: This image was captured by Sentinel-3A on 28 September 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA, CC BY-SA 3.0 IGO)
• February 28, 2018: Italy is usually associated with relatively warm weather, but this week it, too, has fallen victim to the cold snap nicknamed the Beast from the East. 61)
- Freezing temperatures carried on winds from Siberia have brought snow to much of Europe, causing widespread disruption. As this image captured on 27 February by the Copernicus Sentinel-3A satellite shows, Italy in southern Europe was not spared. Temperatures in Rome (bottom right of the image) are normally between 6°C and 14°C, but this week it has been down to –5°C during the night, and it is the first time the city has seen snowfall in six years. Naples also had its heaviest snowfall in decades.
Figure 30: Sentinel-3A image of northern Italy, acquired on 27 Feb. 2018, showing in partucular the snow-capped Apennine mountain range (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• February 9, 2018: The Copernicus Sentinel-3A satellite takes us over the Atlantic Ocean close to Spain and Portugal where the sky not only features clouds but also crisscross tracks from maritime vessels. 62)
- The familiar condensation trails – or contrails – we see in the sky usually come from aircraft, so it might seem strange that ships can also occasionally leave their mark in the sky. This rarely seen maritime twist on aircraft contrails was captured by Sentinel-3A on 16 January 2018. Known as ship tracks, these narrow cloud streaks form when water vapor condenses around small particles that ships emit in their exhaust fumes. They typically form when low-lying stratus and cumulus clouds are present and when the air surrounding the ship is calm.
- Like aircraft contrails, ship tracks may also play a role in our climate by reducing the amount of sunlight that reaches Earth's surface or conversely by trapping the Sun's radiation in our atmosphere – but this remains an uncertain aspect of climate science.
- The Copernicus Sentinel-3A satellite carries a suite of sensors including OLCI (Ocean and Land Color Instrument), which was used to capture this image of Figure 31.
Figure 31: Sentinel-3A image of the Atlantic Ocean off the coast of Portugal and Spain, captured on 16 January 2018, showing ship track contrails in the clouds. Although the Strait of Gibraltar is a busy shipping lane, with numerous ships travelling in and out of the Mediterranean Sea, there are no ship tracks visible here in the image. Most tracks are several hundred of kilometers off shore (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• January 11, 2018: Wave information is crucial for people working at sea, to be able to navigate and operate safely. A new product based on satellite altimeter data detailing ‘Significant Wave Height' now enables this. 63)
- High waves are not only dangerous but can threaten delicate procedures at sea, so wave information is paramount for operating safely and efficiently. For instance, in oil and gas offshore platform operations, historic data and forecasts of wave heights are vital for the safety of personnel, equipment and the environment.
- Marine renewable energy operations and site studies require similar information on waves and ship routing can also be improved by such forecasts.
- In physical oceanography, the SWH (Significant Wave Height) is defined traditionally as the mean wave height (trough to crest) of the highest third of the waves. This mathematical definition of ocean wave height is intended to express the height that would be estimated by a trained observer, capturing the most significant waves over the water surface.
- Satellite wave measurements come from two main sources: altimetry and SAR (Synthetic Aperture Radar). The SWH can be obtained through altimetry and directional and spectral information with SAR.
- CMEMS (Copernicus Marine Environment Monitoring Service) released the first realtime global wave product based on satellite data, broadening its offer—previously based on numerical wave forecast models. Released in the summer of 2017, this new product from satellite altimeter data contains the Significant Wave Height from Jason-3 and from the Copernicus Sentinel-3A satellite altimeter data, provided within three hours after data acquisition.
- It provides quality-filtered and inter-calibrated along-track high-resolution SWH (one measurement every 0.7 km, or every second). These measurements contribute to global ocean coverage along the satellite ground tracks with 0.7 km resolution.
- Such satellite wave products represent actual measurements of the waves, covering the entire Earth, regularly and homogeneously over several years. They often offer a better portrayal of extreme events, which numerical models tend to under estimate.
- In-situ wave data, typically provided by buoys, are similarly very helpful but in many open-water areas such moored buoys are not available, mainly due to the technical difficulty and cost of installing and maintaining them in deep ocean, far from the coast (Figure 32).
Figure 32: In-situ wave data, typically provided by buoys, are very helpful to validate satellite wave products but in many areas of open water such buoys are not available, because of the difficulty and costliness of installation and maintenance (image credit: INSITU TAC /CMEMS)
- Sentinel-3A's wave data are also assimilated into numerical realtime wave models to provide wave forecasts with better accuracy. For example, assimilation into the CMEMS global wave forecast model has a strong impact in the north-west of the Pacific Ocean related to the typhoon season and in the Gulf of Mexico after Hurricane Harvey (Figure 33).
- Dr Romain Husson, responsible for wave products at CLS for CMEMS, says, "In the first quarter of 2018, CMEMS will also deliver wave products derived from Sentinel-1A and -1B's SAR instruments. With respect to altimetry, SAR has the unique ability to measure the wave period and direction on top of the SWH and is particularly well suited for long waves, sometimes also referred to as swell."
Figure 33: Sentinel-3A wave data assimilation in the CMEMS global wave forecast model has a strong impact in the north-west of the Pacific Ocean related to the typhoon season and in the Gulf of Mexico after Hurricane Harvey. Analysis increment (in meters) of SWH after 1-day of assimilation of Sentinel-3A wave data in the CMEMS Global Wave Model MFWAM (starting date on 29 August, 2017 at 06:00 UTC to 30 August, 2017 at 0:00 UTC), image credit: ESA, the image contains Copernicus Sentinel data (2017)/ processed by Météo France/CMEMS
• December 22, 2017: EUMETSAT has released a series of videos that provide training on how to access, download and manipulate Sentinel-3 marine data from its Copernicus Online Data Access (CODA) platform. - A set of three Copernicus Sentinel-3 marine user handbooks has also been published. They will enable end users to become familiar with the main features of products based on data coming from instruments onboard Sentinel-3. 64)
• December 21, 2017: Monitoring large, remote bodies of water is logistically challenging, time consuming and expensive. Responding quickly to events that pose a risk to human health has been almost impossible, given the size of some lakes and seas. An innovative satellite data service is now able to change things around. 65)
- Based on satellite remote-sensing data, CyanoLakes RealTime is an online monitoring and mapping service, designed by leading specialist scientists at CyanoLakes (Pty) Ltd. It significantly improves water and health authorities' ability to monitor, respond to and manage cyanobacteria, algal blooms and water weeds in both fresh and salt waters.
- Cyanobacteria blooms pose a serious health threat to humans and animals and are increasingly common due to pollution and a warming climate. Eutrophication can devastate natural ecosystems and increases the cost of water treatment.
- In October 2014, Mark Matthews won the Copernicus Masters Ideas Challenge for applications using satellites. He developed an algorithm able to distinguish between cyanobacteria and algae, which was recognized as a breakthrough in research and innovation, and also solved many of the challenges associated with using satellite data for routine monitoring applications.
- With his new algorithm, Dr. Matthews envisaged an online information service providing daily warnings on the health risks from cyanobacteria blooms. This would allow water and health authorities an unprecedented ability to monitor in near-real time for cyanobacteria and algal blooms, ultimately protecting the general public from this kind of pollution.
Figure 34: Products from Sentinel-3 and MERIS: The products from the maximum peak height algorithm include cyanobacteria, floating cyanobacteria also known as scum, and floating aquatic vegetation (image credit: the image contains MERIS imagery modified by CyanoLakes Pty Ltd.)
- In 2015, after being awarded with a research grant by the Water Research Commission, CyanoLakes (Pty) Ltd began working on a prototype for South Africa.
- The South African Department of Water and Sanitation became the first user of the prototype, using the information to fill gaps in their monitoring database and for reporting.
Figure 35: Cyanobacteria risk level map: The cyanobacteria risk level map of the CyanoLakes RealTime prototype service for 102 water bodies in South Africa (image credit: CyanoLakes (Pty) Ltd.)
- In January 2017, following the public release of data from the Copernicus Sentinel-3 satellite, the prototype started to be used in near realtime operations, enabling a variety of solutions for many fields.
- These applications included filling information gaps in data-poor regions for water scientists and engineers, improving the safety of water sport events, providing aquaculture operators with warnings of harmful algal blooms to reduce economic losses, and wide-scale monitoring and mapping of cyanobacteria blooms and eutrophication for water and health authorities.
Figure 36: Near real-time monitoring of chlorophyll-a: The CyanoLakes RealTime detailed viewer showing chlorophyll-a concentrations for the Vaal Dam, South Africa, on 08 October 2017 (image credit: the image contains modified Copernicus Sentinel data (2017), processed by CyanoLakes Pty Ltd.)
- The OLCI (Ocean and Land Color Instrument) on Sentinel-3A is currently the only sensor in space with the necessary spectral bands, radiometric sensitivity, spatial resolution and coverage for near realtime services related to the detection of cyanobacteria.
- Using the prototype service, the Department of Water and Sanitation was able to monitor the massive outbreak of the invasive water hyacinth at Hartbeespoort dam, which occurred during 2016–17.
- Dr Matthews said, "Sentinel-3 is the backbone of the CyanoLakes RealTime service, given its unique instrument characteristics. Without it, we could not provide our service to the market. We are excited about the launch of Sentinel-3B in 2018 because it will allow us to provide an even better service, with daily updates to clients anywhere around the globe."
Figure 37: Near real-time monitoring of water hyacinth: The CyanoLakes RealTime detailed viewer is showing water hyacinth (magenta) at Hartbeespoort Dam, South Africa, on 11 October 2017 (image credit: the image contains modified Copernicus Sentinel data (2017), processed by CyanoLakes Pty Ltd.)
• November 3, 2017: From the fourth most populous city to the rugged Outback, the Sentinel-3A satellite gives us a wide-ranging view over Australia's southwestern corner. This perspective from space clearly illustrates human's influence on our environment: the agricultural landscape that dominates in the lower-left is suddenly interrupted by the more densely vegetated national parks and forests.
- The city of Perth is located on the coast along the left edge of the image (Figure 38). About 150 km north of Perth sits ESA's tracking station at New Norcia, where a 35 m diameter radio dish communicates with deep-space missions such as Rosetta and Mars Express.
- Moving further inland, grasslands give way to the deserts of Australia's vast and remote interior – known as the Outback – with a landscape dominated by red soil and sparse vegetation. Several large salt lakes are visible across the image in white, including the appropriately named Lake Disappointment by explorer Frank Hann in search of fresh water (top of image).
- Clouds over the ocean obstruct our view of the southern coast, but the lack of cloud cover over the interior desert pronounces the dry climate, which is a consequence of global wind patterns.
- Sentinel-3 offers a ‘bigger picture' for Europe's Copernicus program by systematically monitoring Earth's oceans, land, ice and atmosphere to understand large-scale global dynamics.
- While the satellite mission carries a suite of cutting-edge instruments, this image, also featured on the Earth from Space video program, was captured on 9 April 2017 by the satellite's OLCI (Ocean and Land Color Instrument), which helps to monitor ocean ecosystems, supports crop management and agriculture, and provides estimates of atmospheric aerosol and clouds.
Figure 38: Sentinel-3A image of western Australia, acquired on 9 April 2017 with OLCI (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• October 12, 2017: The Copernicus Sentinel-3A satellite captured this image on 11 October 2017 (Figure 39), when Hurricane Ophelia was about 1300 km southwest of the Azores islands and some 2000 km off the African coast. 66)
- Originally classified as a tropical storm, it has been upgraded to a hurricane. The US National Hurricane Center said that Ophelia could become even stronger in the next days.
Figure 39: The image was acquired at 12:45 GMT on 11 Oct. 2017 by the satellite's OLCI instrument (image credit: the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• On 28 August, 2017, EUMETSAT's near-real-time dissemination service went to the next level when EUMETSAT's CODA (Copernicus Online Data Access) service, became operationally available to users via the new single-sign on option. 67)
- It ensures that CODA users can access both Copernicus and data from EUMETSAT's Earth observation portal with one username and password.
- In combination with EUMETCast - a flexible multicasting service delivering the unified data streams from Copernicus and EUMETSAT's own missions, as well as EUMETview - an interactive visualization service especially for satellite imagery, EUMETSAT's data services provide solutions for a variety of different needs:
a) Sourcing Copernicus Data with CODA: EUMETSAT's CODA service is a rolling archive featuring a month's worth of Sentinel-3 data through an uncomplicated web interface as well as a scripting service, which allows users to automate bulk data downloads (within certain parameters).
After an extensive pilot phase, the CODA service is now fully available to users. CODA is particularly relevant for the ocean and remote sensing scientists, but its benefits reach beyond the scientific community. Developers in the public and private sector, be it for products or information services, can use CODA to develop innovative applications.
Hayley Evers King (Plymouth Marine Laboratory) summarizes her experience: "CODA is ideal for our daily business. It allows us to investigate specific areas and locate data for a particular region anywhere on the globe. This is, for example, useful when spotting algae blooms. The handling is particularly easy and follows a streamlined, user-friendly process. CODA allows us to select data without needing much experience. This is immensely helpful."
b) Data dissemination via EUMETCast: The vast majority of marine data from the Copernicus-3A satellite, operated by EUMETSAT on behalf of the European Union, are now available on EUMETCast. With this milestone, EUMETSAT's flexible multicasting service now delivers unified data streams to Copernicus users integrating observations from Copernicus and its own missions. This new marine data stream, involving products from Sentinel-3A, Jason-3, Metop and Meteosat creates a broad range of opportunities for the downstream development of applications, services and – ultimately – added value in Europe.
For Hayley Evers King (Plymouth Marine Laboratory) EUMETCast is important because "... it allows us to routinely and quickly access large amounts of data. We use it together with CODA and EUMETview; having these various sources of data access will increase the number of users for Copernicus data."
• August 25, 2017: The Copernicus Sentinel-3A satellite saw the temperature at the top of Hurricane Harvey on 25 August 2017 at 04:06 GMT as the storm approached the US state of Texas. The brightness temperature of the clouds at the top of the storm, some 12–15 km above the ocean, range from about –80°C near the eye of the storm to about 20°C at the edges. 68)
- Hurricanes are one of the forces of nature that can be tracked only by satellites, providing up-to-date imagery so that authorities know when to take precautionary measures. Satellites deliver information on a storm's extent, wind speed and path, and on key features such as cloud thickness, temperature, and water and ice content.
Figure 40: SLSTR (Sea and Land Surface Temperature Radiometer) image of Hurricane Harvey, acquired on 25 Aug. 2017 at 04:06 GMT, approaching the coast of Texas (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• August 11, 2017: Southern Europe is in the grip of a relentless heatwave, fuelling wildfires and water shortages. Information from the Copernicus Sentinel-3A satellite has been used to map the sweltering heat across the region. 69)
- The map of Figure 41 shows that on 7 August 2017, temperatures of the land surface rose above 40°C – not an usual occurrence over the last weeks. Much of Italy, including Rome, Naples, Florence, Sardinia and Sicily has been suffering these highs. With numerous towns and cities on the ministry of health's maximum heat alert, the Italians have aptly dubbed the heatwave ‘Lucifer'. Extreme temperatures have also been recorded in Spain and Portugal, the Balkans and Greece.
- As well as wildfires and water shortages, the heat has also led to some tourist attractions being closed, ill health and even some fatalities, and the drought is also threatening crops.
- The map uses data from the satellite's SLSTR (Sea and Land Surface Temperature Radiometer), which measures energy radiating from Earth's surface in nine spectral bands – the map therefore represents temperature of the land surface, not air temperature which is normally used in forecasts. The white areas in the image are where cloud obscured readings of land temperature.
Figure 41: Southern Europe is in the grip of a heatwave, fuelling wildfires and water shortages. Information from the Copernicus Sentinel-3A satellite has been used to map the sweltering heat across the region (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• July 6, 2017: With the Copernicus Sentinel-3A satellite fully fledged and its data freely available, the task of monitoring and understanding our changing planet has been made that much easier. Seeing the effect spring has on our plant life is just one of its many uses. — Launched in February 2016 and carrying a suite of instruments, Sentinel-3 is the most complex of all the Sentinel missions. 70)
- As the workhorse mission for Europe's environmental monitoring Copernicus program, it measures Earth's oceans, land, ice and atmosphere systematically so that large-scale global changes can be monitored and understood. While Sentinel-3 offers this ‘big picture', it can also be used to monitor smaller-scale environmental issues such as urban heat islands.
- Sentinel-3 is well on the way to being at the heart of operational oceanography, but it also provides unique and timely information about changing land cover and vegetation health.
- For instance, the animation of Figure 42 uses information from the satellite's ocean and land color instrument to measure changing amounts of chlorophyll in plants. Here we clearly see the progress of spring greening in the northern hemisphere, for example.
Figure 42: The Copernicus Sentinel-3A's ocean and land color instrument can ‘see' chlorophyll in vegetation. The animation shows how chlorophyll, which is essential in photosynthesis, around the world changed between 1 April and 27 May 2017. While tropical rainforests can be seen to maintain a high degree of chlorophyll, the animation clearly shows the progress of spring greening in the northern hemisphere. This is particularly evident in the eastern part of the USA. It also captures the progress of agricultural planting for summer crops across China where planting normally takes place between March and May. Here various stages of growth are captured. The chlorophyll index ranges from 1 to 6.5 (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by University of Southampton–J. Dash/Brockman Consult (S3-MPC))
- Since its initial commissioning, when the satellite and instruments were meticulously fine-tuned, Sentinel-3A has been in a ‘ramp up' phase. - This means that over the last year, while the satellite was being prepared for its life as a fully operational mission, only ‘direct instrument' data were available. Another step in the processing chain is needed to translate them into more tangible information for users worldwide.
- This milestone has now been passed so that the best quality data possible are now freely available from the satellite's ocean and land color instrument and from the sea and land surface temperature sensor, which measures energy radiating from Earth's surface.
- This level of data from its other instrument – a radar altimeter, which measures the height of the sea surface, rivers, lakes and land – have been available since last December.
- ESA's Sentinel-3 mission manager, Susanne Mecklenburg, explained, "Sentinel-3 is an extremely complex mission, and I'm very proud to say that it's delivering on its promise.
Figure 43: Feeling the heat: Sentinel-3's Sea and Land Surface Temperature Radiometer includes dedicated channels for measuring fires. This will help to map carbon emissions from burnt biomass and to assess damage and estimate recovery of burnt areas. Information to help manage forest fires will be available using Sentinel-3 measurements combined with meteorological forecasting data. In addition, forests can be monitored systematically to assess risk and develop efficient plans to prevent forest fires (image credit: ESA/ATG medialab)
- "We have been working closely with our colleagues at Eumetsat to make sure it is ready to deliver top-quality data. This is important because while Eumetsat operates the satellite, both organizations manage the mission together.
- "ESA is responsible for the land data products and Eumetsat for the marine products – all of which are made available for the Copernicus services and other users. Measurements made by the satellite's color instrument over land now offer users key information to monitor the health of our vegetation, which is essential for agricultural practices, and to help plan resources. This also complements other missions such as the Copernicus Sentinel-2 and Proba-V. Together, they will be a powerful tool to map our changing lands."
- Sentinel-3 shows how Earth's surface temperature changes, which is also important for weather forecasting and for monitoring climate change. Over land, measurements can be used for urban planning, for example.
- Later in the year, data products will also be available for monitoring fires.
Figure 44: Sentinel-3A senses Earth's heat: Information from Sentinel-3A's radiometer, which measures radiation emitted from Earth's surface, reveal how the temperature of Earth's land changes between July and November 2016. Measurements are in kelvin (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by UK National Center for Earth Observation/University of Leicester)
• June 23, 2017: Sentinel-3 gives us a nearly cloud-free view of France and the surrounding countries (Figure 45). Much of the landscape is covered with agricultural features. In fact, farmers manage nearly half of Europe's land area. While agriculture brings benefits for economy and food security, it puts the environment under pressure. Satellites can help to map and monitor land use, and the information they provide can be used to improve agricultural practices. 71)
- On the right side of the image we can see the snow-covered Alps, while the Pyrenees mountains are visible near the bottom.
- To the west of the Alps a green area of mountains and plateaus is visible, called the Massif Central. The region has more than 400 volcanoes, considered by scientists to be extinct.
- On the right side of the image, the light brown area flanked by dark areas is the Rhine River forming part of France's border with Germany. The dark area to the east is the Black Forest, while the dark area to the west are the Vosges Mountains.
- Just above the center of the image, we can see Paris – the site of ESA's headquarters as well as the Paris Air & Space Show taking place this week.
Figure 45: This image of France was captured by the Copernicus Sentinel-3A satellite's OLCI (Ocean and Land Color Instrument) on 7 April 2017. OLCI monitors ocean ecosystems, supports crop management and agriculture, and provides estimates of atmospheric aerosol and clouds – all of which bring significant benefits through more informed decision-making (image credit: ESA, this image contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO)
• April 27, 2017: The Copernicus Sentinel-3A satellite brings us over the Bering Sea, north of the Alaska Peninsula, on 26 March. Seasonal sea ice dominates the upper part of the image. Ice plays an important role in the sea's ecosystem. Growing algae attach to the bottom of the ice; when the ice melts in the spring, it leaves behind a layer of nutrient-rich freshwater on which the algae thrive. Organisms higher up the food chain then eat the algae. 72)
- In the top-right corner of Figure 46, we can see part of Alaska's mainland blanketed with snow, as well as Nunivak Island appearing like a massive piece of floating ice. At the center of the image are the islands of Saint Paul and Saint George – part of the Pribilof Islands. An estimated two million seabirds nest on these islands annually.
- The swirling clouds on the right side of the image are the result of a meteorological phenomenon known as a von Kármán vortex street. As wind-driven clouds pass over the Unimak Island on the right edge of the image, they flow around the high volcanoes to form the large spinning eddies that can clearly be seen in the image.
Figure 46: A Sentinel-3A image of the Bering Sea, acquired on March 26, 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA , CC BY-SA 3.0 IGO)
• March 10, 2017: A Sentinel-3 image in the Russian Far East and of the Kamchatka Peninsula is provided , located between the Pacific Ocean to the east and the Sea of Okhotsk to the west, where clouds blend with the ice and snow beneath from the bird's-eye view (Figure 47). One of the fascinating features is the pattern of floating sea ice, appearing in light blue. Along the left, one can see cracks in the ice covering the water. In the middle/right, small pieces of fragmented ice, driven by wind and currents, create the swirls of blue along the coast of the Kamchatka Peninsula. 73)
- Kamchatka, a 1250 km long peninsula with an area of 270, 000 km2, has a landscape covered with volcanoes due to its location along the highly active Pacific ‘Ring of Fire'. There are about 160 volcanoes on the peninsula, 29 of which are still active. The central mountain range running down the spine of the peninsula, is visible in the image, while the eastern range is mostly covered by clouds. Between them lies the central valley, appearing somewhat brown from the lack of snow cover.
- It is no surprise that the area is often referred to as the ‘land of fire and ice'. Owing to minimal development, the peninsula is known for its abundance of large brown bears. Other common animals include foxes, wolves, reindeer and wolverines.
Figure 47: The OLCI (Ocean and Land Color Instrument) on Sentinel-3A image of the Kamchatka Peninsula (on the right side) was acquired on Feb. 15, 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA)
• December 13, 2016: Launched in February 2016 with a suite of cutting-edge instruments, Sentinel-3A is arguably the most comprehensive of all the Copernicus Sentinel missions. Since then, the satellite has been thoroughly tested and fine-tuned. This led to the release of its first Earth color data in October and first radiometer data last month. Now, the public also have access to data from its radar altimeter. 74)
- Sentinel-3A's topography package will bring a step change in satellite altimetry, measuring the height of the sea surface, waves and surface wind speed over the oceans. It also provides accurate topography measurements over sea ice, ice sheets, rivers, lakes and land. Over the oceans, the radar altimeter contributes information for forecasting, which is essential for safe maritime operations, for example. Monitoring sea-level change and diminishing Arctic ice is also important for monitoring the effects brought about by climate change.
- As the image of Antarctica shows (Figure 48), the radar altimeter is also important for measuring changes in the height of land ice. The data may seem relatively sparse at the moment, but this is because they only show a few days' readings. Accurately measuring changes in the height of the huge ice sheets that blanket Antarctica and Greenland is important for climate research and understanding sea-level change.
- ESA's CryoSat mission currently measures changes in ice height and paved the way for Sentinel-3's radar altimeter. Importantly, Sentinel-3's radar altimeter is the first to provide 100% coverage over all of Earth's surfaces in ‘synthetic aperture radar' mode. For accuracy, Sentinel-3's topography package also includes a microwave radiometer that is used to correct measurements from the radar altimeter affected by water vapor in the atmosphere.
- While changes in ice height may be relatively slow, the radar altimeter will also be used to measure changes that can be more abrupt, such as the height of water in lakes and rivers.
- The Sentinel-3 mission is managed jointly by ESA and EUMETSAT. The day-to-day operations of the Sentinel-3A satellite are carried out by EUMETSAT. ESA, as the developer of the mission, continues to monitor its health and performance. ESA is responsible for the land data products and EUMETSAT for the marine products – all of which are made available for application through Copernicus services.
Figure 48: The SRAL (SAR Radar Altimeter) of the Sentinel-3A spacecraft measured the height of the Antarctic ice sheet (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by UCL–MSSL)
• November 17, 2016: Following the release of Sentinel-3A's first Earth color data, the public now have access to data from the satellite's radiometer, which measures energy radiating from Earth's surface in nine spectral bands. Arguably the most comprehensive of all the Copernicus Sentinel missions, Sentinel-3A carries a suite of state-of-the-art instruments to systematically measure Earth's oceans, land, ice and atmosphere. 75)
- Since it was launched in February 2016, the satellite has been thoroughly tested and fine-tuned. This led to the release of first-level data from its OLCI (Ocean and Land Color Instrument) in October and now data from the SLSTR (Sea and Land Surface Temperature Radiometer) are also available.
- Information from the radiometer will be used to create global maps of SST (Sea Surface Temperature) for ocean and weather forecasting. Over land, the instrument will be used, for example, to detect heat stress, which is useful for improving agricultural practices and monitoring urban heat islands. As cities continue to expand, understanding how heat islands develop is important for planners and developers.
- Importantly, the radiometer has dedicated channels for measuring fires. This will help to assess damage and estimate recovery of burned areas.
- Further processing is needed to turn this kind of data (Figure 49) into actual ocean- and land-surface temperature maps. These next-stage data will start to be released in early 2017. Nevertheless, differences between the land, coasts and sea can be seen clearly in this brightness temperature image. — Data from the satellite's radar altimeter will be made available in December.
- While the day-to-day operations of the Sentinel-3A satellite are carried out by EUMETSAT, the mission is managed jointly by ESA and EUMETSAT. ESA is responsible for the land data products and EUMETSAT for the marine products – all of which are made available for application through Copernicus services.
Figure 49: The image, which stretches from northern France and Belgium to Italy and western Greece, is an example of first-level data from the radiometer. It shows ‘brightness temperature', which corresponds to radiation emitted from the surface (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by ESA)
• October 20, 2016: Today, the Copernicus Sentinel-3A satellite has taken another step towards being fully ‘operational' as the first data from its OLCI (Ocean and Land Color Instrument) are made available to monitor the health of our planet. Following its launch in February, the satellite and instruments have been thoroughly tested and fine-tuned – leading to this important milestone. - Carrying a suite of instruments, Sentinel-3A is arguably the most complex of all the Copernicus Sentinels. 76) 77)
- It has been designed to measure Earth's oceans, land, ice and atmosphere to monitor large-scale global dynamics and to provide critical near-realtime information for numerous ocean, land and weather applications.
- The Sentinel-3 validation team, a group of expert users, has been receiving sample products since May. Their feedback is essential to both ESA and EUMETSAT to ensure the data are of the highest quality, as is needed for the myriad of operational applications that the mission will serve.
- At the ‘end of commissioning' review in July, it was noted that a couple of points had to be addressed before the first data were officially released to the public.
- Susanne Mecklenburg, ESA's Sentinel-3 mission manager, said, "It is imperative that these first-level data are the best quality possible so we are being extremely careful. It is now very gratifying to see data from the satellite's Ocean and Land Color Instrument being released to users worldwide. "Data from the other two instruments – the SLSTR (Sea and Land Surface Temperature Radiometer) and SRAL (SAR Radar Altimeter) – will be made available in November and December, respectively."
- Offering new eyes on Earth, the OLCI (Ocean and Land Color Instrument) will monitor the global oceans, and inland waters, including phytoplankton, water quality, harmful algal blooms, sediment transport in coastal areas, El Niño and La Niña events, and climate change. It will also support observations of vegetation and crop conditions, as well as provide estimates of atmospheric aerosol and clouds – all of which bring significant benefits to society through more informed decision-making.
- While the operations of the Sentinel-3A satellite are carried out by EUMETSAT, the mission is managed jointly by ESA and EUMETSAT. ESA is responsible for the land data products and EUMETSAT for the marine products – all of which are made available for application through Copernicus services.
- Hilary Wilson, EUMETSAT's Sentinel-3 project manager, said, "The release of Sentinel-3A's first operational data is the culmination of a lot of hard work by ESA, EUMETSAT and the expert user teams. It represents an important milestone for the Copernicus Marine Environment Monitoring Service and also for the wider marine monitoring community. Routine operations of the satellite have been proceeding smoothly since EUMETSAT took over this responsibility in July and we are now focusing on bringing the remaining marine products to this community."
Figure 50: These two images, taken on 13 June 2016 and 22 August by Sentinel-3A's OLCI (Ocean and Land Color Instrument), show differences in ice cover in northeast Greenland. Differences in sea ice off the coast are clear to see. (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA). 78)
• October 2016: Commissioning phase results of the Sentinel-2A Optical Payloads. 79)
Table 5: Optical CalVal activities of the Sentinel-3A spacecraft launch on Feb. 16, 2016 from Plesetsk/Russia Cosmodrome
With the successful launch of Sentinel-3A, a new era for the Copernicus Services has started offering data over oceans and lands with unprecedented coverage. Together with Sentinel-3B, its twin satellite scheduled for launch in 2017, and later on with the launch/replacement of the Sentinel-3C and D units, a 20-year period of continuous observations is guaranteed. Among the five instruments embarked, the OLCI and SLSTR optical payload ensure the continuity of the ENVISAT mission with very much improved performance. During the calibration validation (CalVal) phase functional, performance, product verification and validation were performed confirming the overall excellent performance of the optical payload.
Figure 51: This image of Europe was taken by Sentinel-3A's OLCI on 16 October 2016. The framed part of the image shows, for example, how its 1270 km-wide swath captures an area stretching from Spain to Italy. The ‘zoom in', depicted in Figure 52, shows the French landscape in detail and changes in water color off the south coast. The OLCI features 21 distinct bands in the 400–1020 µm spectral region tuned to specific ocean color, vegetation and atmospheric correction measurement requirements. As well as its wide swath, it has a spatial resolution of 300 m for all measurements, overlapping the satellite's SLSTR (Sea and Land Surface Temperature Radiometer) swath (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
Figure 52: Zoom in image from Figure 51. The islands of Corsica and Sardinia can be seen in the west with coast of Tuscany and the island of Elba to the northeast. The waters along the east coast of Corsica and along the Italian coast are colored by discharge from the land following recent heavy rainfall (image credit: ESA, the image contains modified Copernicus Sentinel data (2016) processed by EUMETSAT) 80)
• September 30, 2016: The SLSTR (Sea and Land Surface Temperature Radiometer) visible channels onboard Sentinel-3A were turned on from 2nd March 2016 and the infrared channels on the 23rd March 2016. The first level 1 (L1b) data was released to expert and validation users on the 14th June 2016, with the level 2 (L2) data similarly released on the 21st June 2016. A successful commissioning review was held on the 12th July 2016, following this EUMETSAT resumed operations of the Sentinel-3A satellite. EUMETSAT processes Sentinel-3 marine data and products at its Sentinel-3 Marine Center, for real time delivery to end-users. 81)
- SST (Sea Surface Temperature) from SLSTR provides increased global coverage than AATSR due to an increased swath width (up to 1400 km) for both nadir only and dual (740 km) view scans. An example of the daily SST global coverage from Sentinel-3A for one day is shown in Figure 53.
Figure 53: Global map of Sentinel-3A SLSTR Sea Surface Temperature (day and night-time) for 17th September 2016 (image credit: EUMETSAT, ESA)
• Sept. 20, 2016: Wildfires break out in the boreal forests of eastern Russia most summers, but 2016 has been particularly bad, with numerous blazes since July. The image of Figure 54, which was taken by the Copernicus Sentinel-3A satellite on 14 September, shows smoke billowing from a string of fires northwest of Lake Baikal in Siberia. These huge smoke plumes stretch over 2000 km. It is thought that drier conditions associated with warmer weather – this June being the hottest on record – have contributed to the unusually large number of fires. 82)
Figure 54: As numerous wildfires continue to burn in Siberia, the Copernicus Sentinel-3A satellite has captured images of huge smoke plumes, acquired on Sept. 14, 2016, stretching 2000 km and winds blowing the smoke to the west (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
• July 13, 2016: Getting the bigger picture on the health of our planet drew another step closer today as Europe's Sentinel-3A satellite was handed over to EUMETSAT for operations. -Since it was launched in February, the satellite and its instruments have been meticulously fine-tuned to make sure that everything is fit and ready for the task in hand: to systematically map Earth's surface for a myriad of services related to both the oceans and land. 83) 84)
- ESA's Bruno Berruti has been responsible for taking Sentinel-3A from the drawing board and into orbit ready for service. He said, "As the last phase of the ‘project', the handover signals the end to an intense five months during which we ensured the satellite and instruments are all working well so that they can start delivering routine data."
- "After only five months of commissioning, we have already released samples for most types of data products. The coming months will see a gradual ramp-up of our processing and data dissemination activities to make sure that the user community is served in the best possible way. The intention is to release first operationally qualified data products to all users in September."
- So while Sentinel-3A is well on the road to start delivering data that is expected to make unique contribution to the paradigm shift in monitoring our planet, ESA remains busy preparing its identical twin for launch in 2017.
Figure 55: The animation shows the difference in the day and night temperatures of the land surface. These daytime measurements were taken by Sentinel-3A's radiometer on 20 June 2016 and the night time readings were taken on 21 June (image credit: ESA, the image contains modified Copernicus Sentinel data (2016))
Figure 56: Baltic swirls - captured by Sentinel-3A on 23 June 2016, this image shows an algae bloom in the Baltic Sea. The image was captured with its OLCI (Ocean and Land Color Instrument), which provides biogeochemical measurements to monitor, for example, concentrations of algae, suspended matter and chlorophyll in seawater. The colored tracks in the image are temperature measurements from a zeppelin, which was used as part of HZG (Helmholtz-Zentrum Geesthacht) Clockwork Ocean project. Satellite imagery was used to help locate these eddies (image credit: ESA, the image contains modified Copernicus Sentinel data (2016)/HZG)
• April 6, 2016: Despite only being in orbit a matter of weeks, Sentinel-3A has already delivered some impressive first images. With the thermal-infrared channels now turned on, the satellite completes its set of firsts with a view of ocean features off the coast of Namibia. 85)
- The first image from the Sentinel-3A SLSTR (Sea and Land Surface Temperature Radiometer) thermal-infrared channels depicts thermal signatures over a part of western Namibia and the South Atlantic Ocean. This image shows the ‘brightness temperature', which corresponds to radiation emitted from the surface. Further processing is needed to turn this into an actual temperature map. The Namibian land surface is shown in red–orange colors, corresponding to a temperature range 301–319 K. The blue colors over the ocean correspond to a temperature range of 285–295 K. The black areas correspond to clouds, which are opaque to thermal-infrared radiation and so prevent a view of the ocean or land surface.
- Cold water is seen along the Namibian coast upwelling from deeper waters. The Benguela current flows north along the west coast of South Africa driven by southeasterly winds creating coastal upwelling. Many eddies and meanders are generated in this complex system and these small-scale features are captured beautifully by SLSTR. Understanding changes in the pattern of these waters is important for fisheries, for example.
Figure 57: Thermal signature of the Namibian coastline observed by SLSTR on Sentinel-3A (image credit: ESA, the image contains modified Copernicus Sentinel data (2016))
• April 1, 2016: The new Sentinel-3A satellite recently began providing data from orbit. This very early image recorded on 3 March 2016, takes us over the River Nile and Delta and the surrounding desert areas of northeast Africa and parts of the Middle East. Very distinct is Egypt, a country connecting northeast Africa with the Middle East, home to millennia-old monuments still sitting along the lush Nile valley. 86)
- In the center of the image, the capital city Cairo with the Nile snaking northwards is clearly visible, along with the Red Sea just further east. Also evident are the islands of Cyprus further north in the Mediterranean Sea and parts of Crete on the very left. Portions of southern Turkey are also visible including some islands of the Aegean Sea.
Figure 58: This SLSTR (Sea and Land Surface Temperature Radiometer) image of Sentinel-3A was acquired on March 3, 2016 showing the River Nile and the extensive Nile Delta (image credit: ESA, the image contains modified Copernicus Sentinel data , processed by ESA)
Legend to Figure 58: The false color image of SLSTR measures the energy radiating from Earth's surface in nine spectral bands, including visible and infrared bands.
• March 8, 2016: The three instruments on the Sentinel-3A satellite are now offering a tantalizing glimpse of what's in store for Europe's Copernicus environmental monitoring effort. The latest images, which feature Europe and Antarctica, come from the sensor that records Earth's radiant energy. Launched just three weeks ago, Sentinel-3A carries a suite of cutting-edge instruments to provide systematic measurements of Earth's oceans, land, ice and atmosphere. This information will feed into numerous Copernicus services to monitor and manage our environment. 87)
- The SLSTR (Sea and Land Surface Temperature Radiometer) measures the energy radiating from Earth's surface in nine spectral bands, including visible and infrared. In addition to providing the temperature of the land and sea surface, dedicated channels will search for fires. This will help to map carbon emissions from burnt biomass and to assess damage and estimate recovery of burned areas. The first images come from the visible channels because the thermal-infrared channels have yet to be activated (Figure 59).
- Another of the images from its visible channels of SLSTR shows a long crack running through the ice shelf to the east of the Antarctic Peninsula (Figure 60).
- An additional false-color image, captured on 2 March, features a large part of Europe, demonstrating the instrument's 1400 km-wide swath. It also shows vegetated areas in red as well as storm Jake over the UK (Figure 61).
Figure 59: This is one of the first images from Sentinel-3A's SLSTR (Sea and Land Surface Temperature Radiometer), acquired with the instrument's visible channels on 3 March 2016 at 11:23 GMT (image credit: Copernicus data (2016))
Legend to Figure 59: This false-color image features the Spanish Canary Islands, the Portuguese island of Madeira and the northwest coast of Africa. The vegetated islands appear red in contrast to the Western Sahara, which has little vegetation. The snow-capped peak of Mount Teide on the island of Tenerife is clearly visible. Both SLSTR and Sentinel-3's OLCI (Ocean and Land Color Instrument) will be used to monitor plant health. As the SLSTR scans Earth's surface, it senses visible light and infrared light (heat) in a number of different spectral channels. The thermal infrared channels will soon be working when the instrument has finished outgassing the water vapor. This is necessary because the infrared channels must be cooled to operate properly. The SLSTR will measure global sea- and land-surface temperatures every day to an accuracy of better than 0.3ºC.
Figure 60: Another early image of SLSTR shows a long crack running through the ice shelf to the east of the center part of the Antarctic Peninsula. The crack is about 2 km wide, but widens to 4 km or more in some places. There are also finer cracks and structures visible in the ice shelf. Structure in the cloud, cloud shadows and details of the land emerging from the ice can also be seen. The image was acquired on 3 March 2016 at 11:53 GMT with the instrument's visible channel (image credit: Copernicus data (2016)
Figure 61: Acquired with the SLSTR instrument's visible channels on 2 March 2016 at 10:04 GMT, this false-color image features a large part of Europe showing vegetated areas in red. Moreover, the image demonstrates the instrument's 1400 km-wide swath. The image also clearly shows storm Jake over the UK (image credit: Copernicus data (2016))
• March 4, 2016: Just after the SRAL (SAR Radar Altimeter) instrument on Sentinel-3A, it traced the height of the sea surface over a stretch of the North Atlantic, some of the most dynamic ocean waters in the world. Showing features relating to the Gulf Stream, the track compares very well with the background map of sea-surface height. The map (Figure 62), produced by the CMEMS (Copernicus Marine Environment Monitoring Service), comprises near-realtime data for one day from the CryoSat-2, Jason-2 and SARAL/AltiKa satellites. 88)
- The altimeter is designed to deliver accurate measurements of sea-surface height, significant wave height and surface-wind speeds over the world's oceans for Copernicus ocean forecasting systems and for monitoring sea-level change.
- Pierre-Yves Le Traon from Mercator Ocean said, "These first results are very promising and illustrate the great potential Sentinel-3 has for the CMEMS. Sea-surface height data from the satellite's altimeter will, for example, significantly improve our capability to analyze and forecast ocean currents. This is essential for the applications we serve such as marine safety, ship routing and predicting the fate of marine pollution events."
- The altimeter has heritage from the CryoSat-2 and Jason-2 missions. This first image is in low-resolution mode but it will provide measurements at a resolution of approximately 300 m in the along-track direction after processing. SRAL will be the first satellite altimeter to provide 100% coverage over all of Earth's surfaces in ‘synthetic aperture radar mode', directly resulting from experience with CryoSat-2.
Figure 62: This is the first track measured by Sentinel-3A's SRAL (SAR Radar Altimeter) immediately after it was switched on. The track, which captures features in the Gulf Stream current, compares well to the background data that comprises near-realtime data from the CryoSat-2, Jason-2 and Altika satellites (image credit: Copernicus data (2016)/CMEMS)
• March 2, 2016: Featuring Spain, Portugal and North Africa, this is one of the first images from the Sentinel-3A satellite. The image was taken by the satellite's OLCI (Ocean and Land Color Instrument) on 1 March 2016 and clearly shows the Strait of Gibraltar between the Atlantic and Mediterranean. Swirls of sediment and algae in the seawater can be seen along the southwest coast of Spain and along the coast of Morocco. The instrument picks out Morocco's dry desert and snow-covered peaks of the Atlas Mountains and greener vegetated northern areas of Spain. 89)
Figure 63: OLCI image of Sentinel-3 acquired on March 1, 2016 showing the Strait of Gibraltar, Spain Portugal and North Africa (image credit: ESA)
• Feb. 25, 2016: Each year, about a quarter of the carbon dioxide we release into the atmosphere ends up in the ocean, but how it happens is still not fully understood. The Sentinel-3A satellite is poised to play an important role in shedding new light on this exchange. 90)
- Initially, the fact that the oceans are absorbing a significant amount of the carbon dioxide we pump into the atmosphere by burning biomass and fossil fuels would appear to be a good thing. However, as more carbon dioxide dissolves into the oceans, it leads to ocean acidification, making it difficult for some marine life to survive.
- Monitoring and understanding the carbon cycle is important because carbon is the fundamental building block of all living organisms. Also, the process of carbon moving between the oceans, atmosphere, land and ecosystems helps to control our climate.
- Over the last four years an international team of scientists and engineers have been using satellites along with measurements from ships and pioneering cloud computing techniques to study how carbon dioxide is transferred from the atmosphere into the oceans. Their work reveals that the seas around Europe absorb an astonishing 24 million tonnes of carbon each year. This is equivalent in weight to two million double decker buses or 72 000 Boeing 747s. 91)
- The team are making their data and cloud computing tools, the ‘FluxEngine', available to the international scientific community so that other groups can analyse the data for themselves.
• Feb. 25, 2016: Working around the clock, mission teams have brought Sentinel-3A through the critical LEOP (Launch and Early Orbit Phase) in just 49 hours, much earlier than planned and a record for such a complex satellite. LEOP was completed on Feb. 18. All operations were executed on time, and the satellite and ground systems performed perfectly during the whole period. 92)
- The speedy completion of LEOP means that the five-month commissioning phase has already started, and Sentinel-3 project and operations teams will start validating the correct functioning of spacecraft and its payload. -In parallel, teams at ESA/ ESRIN in Frascati are working on configuring and validating the complex data delivery channels and bringing these into full service.
- In the afternoon of 23 February, Sentinel-3A tested its first delivery of science data, downlinking test data from the few instruments already switched on, including the SLSTR (Sea and Land Surface Temperature Radiometer). The 10-minute downlink was conducted using the satellite's X-band radio transmitter, confirming its ability to deliver high-rate data via the mission's designated ground station, at Svalbard on the Norwegian archipelago of Spitsbergen.
• After a first burn starting about five minutes after liftoff and a second about 70 minutes later, Rockot's upper stage delivered Sentinel-3A into its planned orbit, 815 km above Earth. The satellite separated 79 minutes into the flight (Ref. 31).
- The first signal from Sentinel-3A was received after 92 minutes by the Kiruna station in Sweden. The telemetry links and attitude control were then established by controllers at ESA/ESOC in Darmstadt, Germany, allowing them to monitor the health of the satellite.
- The mission is the third of six families of dedicated missions that make up the core of Europe's Copernicus environmental monitoring network. Copernicus relies on the Sentinels and contributing missions to provide data for monitoring the environment and supporting civil security activities. Sentinel-3 carries a series of cutting-edge sensors to do just that.
Figure 64: Operations image of the week: The men and women now flying Sentinel-3A comprise a ‘team of teams' who specialize in areas such as mission operations, flight dynamics and ground stations (image credit: ESA) 93)
Legend to Figure 64: This ‘team of teams' involves some 50 engineers and scientists at ESOC, including spacecraft engineers, specialists working on tracking stations and the sophisticated ‘ground segment' – the hardware and software used to control the satellite and distribute its data – and experts working in flight dynamics, software and networks, as well as simulation and training teams.
Representatives from ESA's Sentinel project team, as well as several operations engineers integrated within the Flight Control Team and shared with EUMETSAT, are also working to ensure the success of this crucial mission.