Copernicus: Sentinel-2 — The Optical Imaging Mission for Land Services
Sentinel-2 is a multispectral operational imaging mission within the GMES (Global Monitoring for Environment and Security) program, jointly implemented by the EC (European Commission) and ESA (European Space Agency) for global land observation (data on vegetation, soil and water cover for land, inland waterways and coastal areas, and also provide atmospheric absorption and distortion data corrections) at high resolution with high revisit capability to provide enhanced continuity of data so far provided by SPOT-5 and Landsat-7. 1) 2) 3) 4) 5) 6) 7) 8)
Table 1: Copernicus is the new name of the former GMES program 9)
The overall GMES user requirements of the EU member states call for optical observation services in the areas of Global Climate Change (Kyoto Protocol and ensuing regulations), sustainable development, European environmental policies (e.g. spatial planning for Soil Thematic Strategy, Natura 2000 and Ramsar Convention, Water Framework Directive), European civil protection, common agricultural policy, development and humanitarian aid, and EU Common Foreign & Security Policy.
To meet the user needs, the Sentinel-2 satellite data will support the operational generation of the following high level products like:
• Generic land cover, land use and change detection maps (e.g. CORINE land cover maps update, soil sealing maps, forest area maps)
• Maps of geophysical variables (e.g. leaf area index, leaf chlorophyll content, leaf water content).
The mission is dedicated to the full and systematic coverage of land surface (including major islands) globally with the objective to provide cloud-free products typically every 15 to 30 days over Europe and Africa. To achieve this objective and to provide high mission availability, a constellation of two operational satellites is required, allowing to reach a 5-day geometric revisit time. The revisit time with only one operational satellite as it will be the case at the beginning of the deployment of the system is 10 days. - In comparison, Landsat-7 provides a 16-day geometric revisit time, while SPOT provides a 26-day revisit, and neither of them provides systematic coverage of the overall land surface.
The following list summarizes the top-level system design specifications derived from the user requirements:
• Sentinel-2 will provide continuity of data for services initiated within the GSE (GMES Service Element) projects. It will establish a key European source of data for the GMES Land Fast Track Monitoring Services and will also contribute to the GMES Risk Fast Track Services.
• The frequent revisit and high mission availability goals call for 2 satellites in orbit at a time, each with a 290 km wide swath using a single imaging instrument
• Continuous land + islands carpet mapping imaging within the latitude range of -56º to +83º (the selected orbit excludes imagery from Antarctica)
• 10 m, 20 m, and 60 m spatial resolution (in the VNIR to SWIR spectral range) to identify spatial details consistent with 1 ha MMU (Minimum Mapping Unit)
• An accurate geolocation (< 20 m) of the data is required (without GCPs) and shall be produced automatically to meet the timeliness requirements. The geolocation accuracy of Level 1 b imagery data w.r.t. WGS-84 (World Geodetic System - 1984) reference Earth ellipsoid of better than 20 m at 2σ confidence level without need of any ground control points is required.
• Very good radiometric image quality (combination of onboard absolute and on ground vicarious calibration).
• The mission lifetime is specified as 7.25 years and propellant is to be sized for 12 years, including provision for de-orbiting maneuvers at end-of-life.
• 2 weeks of satellite autonomy and maximum decoupling between flight operations and mission exploitation
Table 2: Sentinel-2 fast track service compliance to land user requirements
To provide operational services over a long period (at least 15 years following the launch of the first satellites), it is foreseen to develop a series of four satellites, with nominally two satellites in operation in orbit and a third one stored on ground as back-up.
In partnership: The Sentinel-2 mission has been made possible thanks to the close collaboration between ESA, the European Commission, industry, service providers and data users. Demonstrating Europe’s technological excellence, its development has involved around 60 companies, led by Airbus Defence and Space in Germany for the satellites and Airbus Defence and Space in France for the multispectral instruments. 10)
The mission has been supported in kind by the French space agency CNES to provide expertise in image processing and calibration, and by the German Aerospace Center DLR that provides the optical communication payload, developed by Tesat Spacecom GmbH.
This piece of technology allows the Sentinel-2 satellites to transmit data via laser to satellites in geostationary orbit carrying the European Data Relay System (EDRS). This new space data highway allows large volumes of data to be relayed very quickly so that information can be even more readily available for users.
Seven years in the making, this novel mission has been built to operate for more than 20 years. Ensuring that it will meet users’ exacting requirements has been a challenging task. Developing Sentinel-2 has involved a number of technical challenges, from early specification in 2007 to qualification and acceptance in 2015.
The satellite requires excellent pointing accuracy and stability and, therefore, high-end orbit and attitude control sensors and actuators. The multispectral imager is the most advanced of its kind, integrating two large visible near-infrared and shortwave infrared focal planes, each equipped with 12 detectors and integrating 450,000 pixels.
Pixels that may fail in the course of the mission can be replaced by redundant pixels. Two kinds of detectors integrate high-quality filters to isolate the spectral bands perfectly. The instrument’s optomechanical stability must be extremely high, which has meant the use of silicon carbide ceramic for its three mirrors and focal plane, and for the telescope structure itself.
The geometric performance requires strong uniformity across the focal planes to avoid image distortion. The radiometric performance excluded any compromise regarding stray light, dictating a tight geometry and arrangement of all the optical and mechanical elements. The instrument is equipped with a calibration and shutter mechanism that integrates a large spectralon sunlight diffuser.
Each satellite has a high level of autonomy, so that they can operate without any intervention from the ground for periods of up to 15 days. This requires sophisticated autonomous failure analysis, detection and correction on board.
The ‘carpet mapping’ imaging plan requires acquisition, storage and transmission of 1.6 TB per orbit. This massive data blast results from the combination of the 290 km swath with 13 spectral channels at a spatial resolution as high as 10 m.
In addition, the optical communication payload using the EDRS data link is a new technology that will improve the amount and speed of data delivery to the users. This was very recently demonstrated by Sentinel-1A, which also carries an optical communication payload.
Land in focus: Ensuring that land is used sustainably, while meeting the food and wood demands of a growing global population – a projected eight billion by 2020 – is one of today’s biggest challenges. The Copernicus land service provides information to help respond to global issues such as this as well as focusing on local matters, or ‘hotspots’, that are prone to specific challenges.
However, this service relies on very fast revisit times, timely and accurate satellite data in order to make meaningful information available to users – hence, the role of Sentinel-2. Through the service, users will have access to information about the health of our vegetation so that informed decisions can be made – whether about addressing climate change or how much water and fertilizer are needed for a maximum harvest.
Sentinel-2 is able to distinguish between different crop types and will deliver timely data on numerous plant indices, such as leaf area index, leaf chlorophyll content and leaf water content – all of which are essential to accurately monitor plant growth. This kind of information is essential for precision farming: helping farmers decide how best to nurture their crops and predict their yield.
While this has obvious economic benefits, this kind of information is also important for developing countries where food security is an issue. The mission’s fast geometric revisit of just five days, when both satellites are operational, and only 10 days with Sentinel-2A alone, along with the mission’s range of spectral bands means that changes in plant health and growth status can be easily monitored.
Sentinel-2 will also provide information about changes in land cover so that areas that have been damaged or destroyed by fire, for example, or affected by deforestation, can be monitored. Urban growth also can be tracked.
The Copernicus services are managed by the European Commission. The five ‘pan-European’ themes covering 39 countries are addressed by the land service, including sealed soil (imperviousness), tree cover density, forest type, and grasslands. There is currently insufficient cloud-free satellite data in high resolution with all the necessary spectral bands that cover Europe fast enough to monitor vegetation when it is growing rapidly in the summer. Sentinel-2 will fill this gap.
This multi-talented mission will also provide information on pollution in lakes and coastal waters at high spatial resolution and with frequent coverage. Frequent coverage is also key to monitoring floods, volcanic eruptions and landslides. This means that Sentinel-2 can contribute to disaster mapping and support humanitarian aid work.
Leading edge: The span of 13 spectral bands, from the visible and the near-infrared to the shortwave infrared at different spatial resolutions ranging from 10 to 60 m on the ground, takes global land monitoring to an unprecedented level.
The four bands at 10 m resolution ensure continuity with missions such as SPOT-5 or Landsat-8 and address user requirements, in particular, for basic land-cover classification. The six bands at 20 m resolution satisfy requirements for enhanced land-cover classification and for the retrieval of geophysical parameters. Bands at 60 m are dedicated mainly to atmospheric corrections and cirrus-cloud screening.
In addition, Sentinel-2 is the first civil optical Earth observation mission of its kind to include three bands in the ‘red edge’, which provide key information on the vegetation state.
Thanks to its high temporal and spatial resolution and to its three red edge bands, Sentinel-2 will be able to see very early changes in plant health. This is particularly useful for the end users and policy makers to detect early signs of food shortages in developing countries (Ref. 10).
Table 3: Facts and figures
In April 2008, ESA awarded the prime contract to Airbus Defence and Space (former EADS-Astrium GmbH) of Friedrichshafen, Germany to provide the first Sentinel-2A Earth observation satellite. In the Sentinel-2 mission program, Astrium is responsible for the satellite’s system design and platform, as well as for satellite integration and testing. Astrium Toulouse will supply the MSI (MultiSpectral Instrument), and Astrium Spain is in charge of the satellite’s structure pre-integrated with its thermal equipment and harness. The industrial core team also comprises Jena Optronik (Germany), Boostec (France), Sener and GMV (Spain). 11) 12) 13) 14)
Sentinel-2 uses the AstroBus-L of EADS Astrium, a standard modular ECSS (European Cooperation for Space Standards) compatible satellite platform compatible with an in-orbit lifetime of up to 10 years, with consumables sizeable according to the mission needs. The platform design is one-failure tolerant and the standard equipment selection is based on minimum Class 2 EEE parts, with compatibility to Class 1 in most cases. The AstroBus-L platform is designed for direct injection into LEO (Low Earth Orbit). Depending on the selection of standard design options, AstroBus-L can operate in a variety of LEOs at different heights and with different inclinations. An essential feature of AstroBus-L is the robust standard FDIR (Failure Detection, Isolation and Recovery) concept, which is hierarchically structured and can easily be adapted to specific mission needs.
Figure 1: Artist's rendition of the Sentinel-2 spacecraft (image credit: ESA, Airbus DS)
The satellite is controlled in 3-axes via high-rate multi-head star trackers, mounted on the camera structure for better pointing accuracy and stability, and gyroscopes and a GNSS receiver assembly. The AOCS (Attitude and Orbit Control Subsystem) comprises the following elements: 18)
• A dual frequency GPS receiver (L1/L2 code) for position and time information
• A STR (Star Tracker) assembly for precise attitude information (use of 3 STRs)
• A RMU (Rate Measurement Unit) for rate damping and yaw acquisition purposes
• A redundant precision IMU (Inertial Measurement Unit) for high-accuracy attitude determination
• Magnetometers (MAG) for Earth magnetic field information
• CESS (Coarse Earth Sun Sensors) for coarse Earth and Sun direction determination
• 4 RW (Reaction Wheels) and 3 MTQ (Magnetic Torquers)
• RCS (Reaction Control System) a monopropellant propulsion system for orbit maintenance with 1 N thrusters
The different tasks of the AOCS are defined the following modes:
• Initial Acquisition and Save Mode (rate damping, Earth acquisition, yaw acquisition, steady-state)
• Normal Mode (nominal and extended observation)
• Orbit Control Mode (in- and out-of-plane ΔV maneuvers).
Figure 2: Overview of the AOCS architecture (image credit: EADS Astrium)
The geolocation accuracy requirements of < 20 m for the imagery translate into the following AOCS performance requirements as stated in Table 4.
For Sentinel-2 it was decided to mount both the IMU and the star trackers on the thermally controlled sensor plate on the MSI. So the impact of time-variant IMU/STR misalignment on the attitude performance can be decreased to an absolute minimum. Furthermore, the consideration of the time-correlated star tracker noises by covariance tuning was decided.
Figure 3: Sentinel-2 spacecraft architecture (image credit: Astrium GmbH)
Figure 4: Block diagram of the Sentinel-2 spacecraft (image credit: EADS Astrium)
The EPS (Electric Power Subsystem) consists of:
• Solar Array (one deployable and rotatable single wing with three panels). Total array area of 7.1 m2. Use of 2016 triple junction GaAs solar cells with integrated diode. Total power of 2300 W (BOL) and 1730 W (EOL). The mass is < 40 kg.
• SADM (Solar Array Drive Mechanism) for array articulation. Use of a two phase stepper motor with µ-stepping to minimize parasitic distortions during MSI operation, motor step angle 1.5º. Mass of < 3.2 kg.
• PCDU (Power Control and Distribution Unit). PCDU with one unregulated 28 V ±4 V main power bus. Mass of < 21.6 kg; the in-orbit life is 12.25 years.
• Li-ion batteries with 8 cells in series. Total capacity of 102 Ah @ EOL. Mass = 51 kg.
Figure 5: Block diagram of the electrical power subsystem (image credit: EADS Astrium)
The OBC is based on the ERC32 PM (Processor Module) architecture. The PLDHS (Payload Data Handling System) provides source data compression from 1.3 Gbit/s to 450 Mbit/s [state-of-the-art lossy compression (wavelet transform)].
The spacecraft mass is ~ 1200 kg, including 275 kg for the MSI instrument, 35 kg for the IR payload (optional) and 80 kg propellant (hydrazine). The S/C power is 1250 W max, including 170 W for the MSI and < 100 W for the IR payload. The spacecraft is designed for a design life of 7.25 years with propellant for 12 years of operations, including deorbiting at EOL (End of Life).
Table 5: Overview of some spacecraft parameters
Figure 6: Schematic view of the deployed Sentinel-2 spacecraft (image credit: EADS Astrium)
Figure 7: The Sentinel-2 spacecraft in launch configuration (image credit: ESA)
Payload data are being stored in NAND flash memory technology SSR (Solid State Recorder) based on integrated CoReCi (Compression Recording and Ciphering) units of Airbus DS, available at various capacities. The CoReCi is an integrated image compressor, mass memory and data ciphering unit designed to process, store and format multi-spectral video instrument data for the satellite downlink. The mass memory utilizes high performance commercial Flash components, ESA qualified and up-screened for their use in space equipment. This new Flash technology allows mass and surface area used in the memory to be reduced by a factor of nearly 20 when compared with the former SD-RAM (Synchronous Dynamic Random Access Memory) based equipment. The first CoReCi unit has been successfully operating on SPOT-6 since September 2012. Sentinel-2A is carrying a CoReCi unit. 19) 20)
The MRCPB (Multi-Résolution par Codage de Plans Binaires) compression algorithm used is a wavelet transform with bit plane coding (similiar to JPEG 2000). This complex algorithm is implemented in a dedicated ASIC, with speeds of up to 25 Mpixel/s. Alternatively this unit can be supplied with a CCSDS compression algorithm using a new ASIC developed with ESA support. The ciphering is based on the AES algorithm with 128 bit keys. The modularity of the design allows the memory capacity and data rate to be adapted by adjusting the number of compressor and memory boards used.
• February 27, 2017: The ninth Vega light-lift launcher is now complete at the Spaceport, with its Sentinel-2B Earth observation satellite installed atop the four-stage vehicle in preparation for a March 6 mission from French Guiana. 21)
• January 12, 2017: Sentinel-2B arrived at Europe’s spaceport in Kourou, French Guiana on 6 January 2017 to be prepared for launch. After being moved to the cleanroom and left for a couple of days to acclimatise, cranes were used to open the container and unveil the satellite. Over the next seven weeks the satellite will be tested and prepared for liftoff on a Vega rocket. 22)
• November 15, 2016: Sentinel-2B has successfully finished its test program at ESA/ESTEC in Noordwijk, The Netherlands. The second Sentinel-2 Airbus built satellite will now be readied for shipment to the Kourou spaceport in French Guiana begin January 2017. It is scheduled for an early March 2017 lift-off on Vega. 23)
- Offering "color vision" for the Copernicus program, Sentinel-2B like its twin satellite Sentinel-2A will deliver optical images from the visible to short-wave infrared range of the electromagnetic spectrum. From an altitude of 786 km, the 1.1 ton satellite will deliver images in 13 spectral bands with a resolution of 10, 20 or 60 m and a uniquely large swath width of 290 km.
• June 15, 2016: Airbus DS completed the manufacture of the Sentinel-2B optical satellite; the spacecraft is ready for environmental testing at ESA/ESTEC. The Sentinel-2 mission, designed and built by a consortium of around 60 companies led by Airbus Defence and Space, is based on a constellation of two identical satellites flying in the same orbit, 180° apart for optimal coverage and data delivery. Together they image all Earth’s land surfaces, large islands, inland and coastal waters every five days at the equator. Sentinel-2A was launched on 23 June 2015, its twin, Sentinel-2B, will follow early next year. 24)
- The Sentinel-1 and -2 satellites are equipped with the Tesat-Spacecom’s LCT (Laser Communication Terminal). The SpaceDataHighway is being implemented within a Public-Private Partnership between ESA and Airbus Defence and Space.
Figure 8: Sentinel-2B being loaded at Airbus Defence and Space’s satellite integration center in Friedrichshafen, Germany (image credit: Airbus DS, A. Ruttloff)
• April 27, 2015: The Sentinel-2A satellite on Arianespace’s next Vega mission is being readied for pre-launch checkout at the Spaceport, which will enable this European Earth observation platform to be orbited in June from French Guiana. — During activity in the Spaceport’s S5 payload processing facility, Sentinel-2A was removed from the shipping container that protected this 1,140 kg class spacecraft during its airlift from Europe to the South American launch site. With Sentinel-2A now connected to its ground support equipment and successfully switched on, the satellite will undergo verifications and final preparations for a scheduled June 11 liftoff. 25)
Figure 9: Sentinel-2A is positioned in the Spaceport’s S5 payload processing facility for preparation ahead of its scheduled June launch on Vega (image credit: Arianespace)
• April 23, 2015: The Sentinel-2A satellite has arrived safe and sound in French Guiana for launch in June. The huge Antonov cargo aircraft that carried the Sentinel-2A from Germany, touched down at Cayenne airport in the early morning of 21 April. 26)
• April 8, 2015: The Sentinel-2A satellite is now being carefully packed away in a special container that will keep it safe during its journey to the launch site in French Guiana. The satellite will have one final test, a ‘leak test’, in the container to ensure the propulsion system is tight. Bound for Europe’s Spaceport in French Guiana, Sentinel-2A will leave Munich aboard an Antonov cargo plane on 20 April. Once unloaded and unpacked, it will spend the following weeks being prepared for liftoff on a Vega rocket. 27)
• February 24, 2015: Sentinel-2A is fully integrated at IABG’s facilities in Ottobrunn, Germany before being packed up and shipped to French Guiana for a scheduled launch in June 2015. 28)
Figure 10: Photo of the Sentinel-2A spacecraft in the thermal vacuum chamber testing at IAGB's facilities (image credit: ESA, IABG, 2015)
• In August 2014, Airbus Defence and Space delivered the Sentinel-2A environmental monitoring satellite for testing . In the coming months, the Sentinel-2A satellite will undergo a series of environmental tests at IABG, Ottobrunn, Germany, to determine its suitability for use in space. 29) 30)
Figure 11: Sentinel-2A solar array deployment test at IABG (Airbus Defence & Space), image credit: ESA 31)
- Sentinel-2A is scheduled to launch in June 2015; Sentinel-2B, which is identical in design, is set to follow in March 2017. Together, these two satellites will be able to capture images of our planet’s entire land surface in just five days in a systematic manner.
Figure 12: Photo of the Sentinel-2A spacecraft at the satellite integration center in Friedrichshafen, Germany (image credit: Airbus DS, A. Ruttloff)
RF communications: The payload data handling is based on a 2.4 Tbit solid state mass memory and the payload data downlink is performed at a data rate of 560 Mbit/s in X-band with 8 PSK modulation and an isoflux antenna, compliant with the spectrum bandwidth allocated by the ITU (international Telecommunication Union).
Command and control of the spacecraft (TT&C) is performed with omnidirectional S-band antenna coverage using a helix and a patch antenna. The TT&C S-band link provides 64 kbit/s in uplink (with authenticated/encrypted commands) and 2 Mbit/s in downlink..
The requirements call for 4 core X-band ground stations for full mission data recovery by the GMES PDS (Payload Data System).
In parallel to the RF communications, an optical LEO-GEO communications link using the LCT (Laser Communication Terminal) of Tesat-Spacecom (Backnang, Germany) will be provided on the Sentinel-2 spacecraft. The LCT is based on a heritage design (TerraSAR-X) with a transmit power of 2.2 W and a telescope of 135 mm aperture to meet the requirement of the larger link distance. The GEO LCT will be accommodated on AlphaSat of ESA/industry (launch 2012) and later on the EDRS (European Data Relay Satellite) system of ESA. The GEO relay consists of an optical 2.8 Gbit/s (1.8 Gbit/s user data) communication link from the LEO to the GEO satellite and of a 600 Mbit/s Ka-band communication link from the GEO satellite to the ground. 34)
To meet the user requirements of fast data delivery, DLR (German Aerospace Center) is funding the OCP (Optical Communication Payload), i.e. the LCT of Tesat, – a new capability to download large volumes of data from the Sentinel-2 and Sentinel-1 Earth observation satellites - via a data relay satellite directly to the ground. A contract to this effect was signed in October 2010 between ESA and DLR. 35)
Since the Ka-band downlink is the bottleneck for the whole GEO relay system, an optical ground station for a 5.625 Gbit/s LEO-to-ground and a 2.8 Gbit/s GEO-to-ground communication link is under development.
Orbit: Sun-synchronous orbit, altitude = 786 km, inclination = 98.5º, (14+3/10 revolutions/day) with 10:30 hours LTDN (Local Time at Descending Node). This local time has been selected as the best compromise between cloud cover minimization and sun illumination.
The orbit is fully consistent with SPOT and very close to the Landsat local time, allowing seamless combination of Sentinel-2 data with historical data from legacy missions to build long-term temporal series. The two Sentinel-2 satellites will be equally spaced (180º phasing) in the same orbital plane for a 5 day revisit cycle at the equator.
The Sentinel-2 satellites will systematically acquire observations over land and coastal areas from -56° to 84° latitude including islands larger 100 km2, EU islands, all other islands less than 20 km from the coastline, the whole Mediterranean Sea, all inland water bodies and closed seas. Over specific calibration sites, for example DOME-C in Antarctica, additional observations will be made. The two satellites will work on opposite sides of the orbit (Figure 13).
• The first stage separated 1 min 55 seconds after liftoff, followed by the second stage and fairing at 3 min 39 seconds and 3 min 56 seconds, respectively, and the third stage at 6 min 32 seconds.
• After two more ignitions, Vega’s upper stage delivered Sentinel-2B into the targeted Sun-synchronous orbit. The satellite separated from the stage 57 min 57 seconds into the flight.
• Telemetry links and attitude control were then established by controllers at ESOC in Darmstadt, Germany, allowing activation of Sentinel’s systems to begin. The satellite’s solar panel has already been deployed.
• After this first ‘launch and early orbit’ phase, which typically lasts three days, controllers will begin checking and calibrating the instruments to commission the satellite. The mission is expected to begin operations in three to four months.
Sentinel-2B will join its sister satellite Sentinel-2A and the other Sentinels part of the Copernicus program, the most ambitious Earth observation program to date. Sentinel-2A and -2B will be supplying ‘color vision’ for Copernicus and together they can cover all land surfaces once every five days thus optimizing global coverage and the data delivery for numerous applications. The data provided by these Sentinel-2 satellites is particularly suited for agricultural purposes, such as managing administration and precision farming.
With two satellites in orbit it will take only five days to produce an image of the entire Earth between the latitudes of 56º south and 84º north, thereby optimizing the global coverage zone and data transmission for numerous applications.
To ensure data continuity two further optical satellites, Sentinel-2C and -2D, are being constructed in the cleanrooms of Airbus and will be ready for launch as of 2020/2021.
Figure 14: Illustration of the Sentinel-2B spacecraft in orbit (image credit: Airbus DS, Ref. 38)
Figure 15: This technical view of the Sentinel-2 satellite shows all the inner components that make up this state-of-the-art high-resolution multispectral mission (video credit: ESA/ATG medialab)
Figure 16: As well as imaging in high resolution and in different wavelengths, the key to assessing change in vegetation is to image the same place frequently. The Sentinel-2 mission is based on a constellation of two satellites orbiting 180° apart, which along with their 290 km-wide swaths, allows Earth’s main land surfaces, large islands, inland and coastal waters to be covered every five days. This is a significant improvement on earlier missions in the probability of gaining a cloud-free look at a particular location, making it easier to monitor changes in plant health and growth (video credit: ESA/ATG medialab)
Note: As of 30 April 2021, the Sentinel-2 file has been split into a total of five files. — As of May 2019, the previously single large Sentinel-2 file has been split into two additional files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the Sentinel-2 mission and its imagery in the period 2021
Mission status and some imagery of 2021
• July 30, 2021: The Copernicus Sentinel-2 mission takes us over Malé – the capital and most populous city in the Republic of Maldives, a small archipelagic state in the Indian Ocean. 40)
- The Republic of Maldives consist of a chain of around 1200 small coral islands that are grouped into clusters of atolls – scattered across 90,000 km2 of ocean. A number of these little islands can be seen in the image, with the turquoise colors depicting clear, shallow waters dotted by coral reefs which contrasts with the dark colors of the Indian Ocean.
- Malé, located at the southern edge of the North Malé Atoll, can be easily spotted in the right of the image. The island is small enough to walk around in approximately one hour, with most sights concentrated on its northern shore. Malé is both a trade and tourist center, connected with Sri Lanka and India by steamship lines, with several vessels visible in the image.
- With a population of more than 200,000 and an area of around 8 km2, Malé is one of the most densely populated cities in the world with the city covering almost the entire island.
- With more than 80% of the Maldives’ land standing less than one meter above average sea level, the Maldives has the lowest terrain of any country in the world. This makes the archipelago particularly vulnerable to sea-level rise.
- In response to this rising threat, the Maldives is working on enhancing the resilience of the country’s islands, which includes constructing the artificial island of Hulhumalé – visible northeast of the airport island of Hulhulé.
- The island has been constructed by pumping sand from the seafloor onto a submerged coral platform, that rises around 2 m above sea level. The reclaimed land provides some much-needed space, and will also help meet the industrial and commercial development of the Malé region.
Figure 17: Malé, located at the southern edge of the North Malé Atoll, can be easily spotted in the right of the image. The island is small enough to walk around in approximately one hour, with most sights concentrated on its northern shore. Malé is both a trade and tourist centre, connected with Sri Lanka and India by steamship lines, with several vessels visible in the image. This image, also featured on the Earth from Space video program, was captured by the Copernicus Sentinel-2 mission – a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
- Satellite data have shown that the global ocean has risen, on average, 3 mm a year over the last 25 years. Warming ocean waters, melting glaciers and diminishing ice sheets is making rising sea levels a real threat for low-lying islands such as the Maldives.
Figure 18: Sea level rise is a global issue, but in the coming decades Asia is likely to feel the worst effects because of the number of people living in low-lying coastal regions. Small island states could also face particularly devastating losses. For example, in the Maldives in the Indian Ocean about one-third of the population live on land that could be underwater before the end on the century. It is vital that the changing height of the sea surface continues to be closely monitored over the coming decades. The Copernicus Sentinel-6 Michael Freilich is the key mission undertaking this important role until at least 2030 (image credit: ESA/ATG medialab)
• July 23, 2021: The Tarso Toussidé volcanic massif in Chad is featured in this false-color composite image captured by the Copernicus Sentinel-2 mission. 41)
- Tarso Toussidé, capped by the Toussidé (potentially active) stratovolcano, is located in the western end of the Tibesti Mountains, in Chad. With an elevation of 3265 m above sea level, Toussidé is the second highest peak in Tibesti, after Emi Koussi.
- Toussidé has undergone a number of eruptions and lava flows, with the lava reaching lengths of 25 km and covering an area of 200 km2, appearing to have ‘stained’ the ground in the process. The volcano ejected tephra, fragments of rock and volcano glass, lava and ash. In the middle of the field lies Pic Toussidé, a lava dome which can be seen poking out of the caldera.
- Toussidé is said to be amongst the youngest volcanoes in Tibesti. A large number of fumaroles (openings in or near a volcano through which gases emerge) are active on its summit, exhaling mostly water vapor at temperatures of 40–60 °C – suggesting it is the only active Tibesti volcano.
- Just next to Toussidé, in the far-right of the image, lies the Trou au Natron caldera, which sits at an elevation of around 2450 m. A number of volcanic cones sit on the floor of the caldera, with numerous vents and hot springs on the caldera’s floor emitting hot steam.
- Much of the surface of the caldera is lined with a white crust of salts, including sodium carbonite. These crusts are usually formed when mineral-rich steam is emitted from small vents on the crater’s floor, and when this evaporates in the heat, the minerals are left behind.
- The caldera has an irregular diameter of around 6-8 km and is up to 1000 m deep, and is said to have been filled by a freshwater lake during the last glacial maximum.
- In the left of the image, the red shows sparse vegetation along the ephemeral creeks.
- Satellite imagery is a practical way to study remote areas such as the volcanic regions in the Tibesti Mountain Range. The Copernicus Sentinel-2 mission carries a multispectral imager with 13 spectral bands and has a wide swath coverage, delivering data on Earth’s land every five days.
Figure 19: This week’s edition of the Earth from Space program features a false-color composite image of the Tarso Toussidé volcanic massif, captured by the Copernicus Sentinel-2 mission. This image is also featured in the Earth from Space video program (image credit: ESA)
• July 16, 2021: The commercial and industrial center of Peru, Lima is located on the mostly flat terrain in the Peruvian coastal plain, within the valleys of the Chillón, Rímac and Lurín rivers. The city is bordered on the east by the foothills of the Andes Mountains and on the west by the Pacific Ocean. 42)
- Lima can be seen directly on the south bank of the Rímac River, which flows for around 200 km through the Lima Region, before emptying near Callao – a seaside city and port in the Lima metropolitan area (the largest metropolitan area of Peru).
- Lima’s historical center was declared a UNESCO World Heritage Site in 1988 owing to its large number of historical buildings dating from the Spanish colonial era. One of the most notable characteristics of Lima is the barren desert that surrounds the city, with the sand supporting little to no plant life, with the exception of where water has been artificially provided.
- Although Lima is located at a tropical latitude, the cool offshore Humboldt Current (also known as the Peru Current) produces a year-round temperate climate. The cooling of the coastal air mass produces thick cloud cover throughout winter and the dense sea mist, known locally as garúa, often rolls in to blanket the city. In this image, captured on 20 April 2020, several cloud formations can be seen dotted along the coast.
- Callao is Peru’s main seaport and home to its main airport, Jorge Chávez International Airport. Several small boats and vessels can be seen near the port. Callao has several islands: San Lorenzo Island (currently used as a military base), El Frontón (a former high security prison), the Cavinzas Islands, and the Palomino Islands, where numerous sea lions and sea birds live.
Figure 20: Lima, the capital and largest city of Peru, is featured in this Copernicus Sentinel-2 image, observed on 20 April 2020. This image is also featured on the Earth from Space video program (image credit: ESA)
• July 9, 2021: The Gulf of Martaban, an arm of the Andaman Sea located in southern Myanmar, is featured in this false-color image captured by the Copernicus Sentinel-2 mission. The image has been processed in a way that included the near-infrared channel – which makes vegetation appear bright red. 43)
- The gulf, also known as Gulf of Mottama, is named after the port city of Mottama, formerly known as Martaban. The Gulf of Martaban is considered a unique estuarine mudflat environment that is home to a great variety of flora and fauna. Fed by sediment and nutrients from three major rivers (Sittang, Salween and Yangon), the gulf supports a number of species including marine fish, 150 000 migratory birds as well as supporting the livelihood of tens of thousands of people.
- A notable characteristic of the gulf is that it has a tide-dominated coastline, with tidal ranges between six and seven meters. The mouth of the gulf, which is approximately 100 km wide, narrows into a funnel-shaped bay to produce a powerful tidal bore phenomenon that can reach heights of over a meter in the upper estuary. As a result, the tidal mudflats of the gulf are among the largest in the world.
- The city of Yangon is visible in the bottom-left of the image, at the convergence of the Yangon and Bago Rivers. With over seven million people, Yangon is Myanmar's most populous city and its most important commercial center. The city served as the country’s capital until 2006.
Figure 21: The Sittang River, visible in the right side of the image, originates near Mandalay, Myanmar, and flows southward for around 420 km before emptying into the gulf. Dense vegetation can be seen in bright red, particularly in the left of the image. The distinct rectangular shape, visible in the upper half of the image, is part of the Moeyungyi Wetland Wildlife Sanctuary, a designated Ramsar Site of International Importance. The site encompasses several artificial lakes and bodies (visible in black). One of the bodies of water appears in light blue most likely owing to eutrophication – the overabundance of algae, phosphorus and other plant nutrients. This image, acquired on 18 November 2020, is also featured in the Earth from Space video program
- Sentinel-2 is a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus program. The mission’s frequent revisits over the same area and high spatial resolution allow changes in water bodies to be closely monitored.
• July 2, 2021: The Frisian Islands stretch from the northwest of the Netherlands through Germany to the west of Denmark. Although they are considered a single physical feature, they are divided into West, East and North Frisian Islands – with the North Frisian Islands visible here. 44)
- The North Frisian Islands are split between Germany and Denmark. There are four larger islands that make up the archipelago: Sylt, Föhr, Amrum, and Pellworm.
- Sylt, the largest of the archipelago, is around 100 km2 and is known for its distinctive shape of its shoreline. Sylt extends in length more than 35 km and, in some places, is only 1 km wide. A sandy beach stretches across the islands’ west coast, however it has begun to erode owing to storm tides. The northernmost island of Germany, it is connected to the mainland by the Hindenburgdamm, an 11 km-long causeway.
- The Wadden Sea on the islands’ east side, between Sylt and the mainland, is part of the Schleswig-Holstein Wadden Sea National Park and has been a nature reserve and bird sanctuary since 1935.
- The islands of Föhr and Amrum are visible southeast of Sylt. The larger Föhr is called the ‘Green Island’ due to it being sheltered from the storms of the North Sea by its neighboring islands. The island of Amrum features an extended beach area along its west coast, which faces the open North Sea. The east coast borders to mud flats and tidal creeks of the Wadden Sea.
- The three white islands visible below Amrum are the North Frisian Barrier Islands. These sand banks, or shoals, act as a natural breakwater for the smaller islands closer to land. Just east of these lies the island of Pellworm.
- North of Sylt are the Danish islands of Rømø, Mandø, and, lastly, Fanø. In the top-left of the image, a large algal bloom is visible in emerald green. Harmful algal blooms caused by excessive growth of marine algae have occurred in the North Sea 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.
Figure 22: North Frisian Islands. Part of the Frisian Islands, a low-lying archipelago just off the coast of northern Europe, is visible in this image captured by the Copernicus Sentinel-2 mission. This image is also featured on the Earth from Space video program (image credit: ESA)
• June 30, 2021: For Asteroid Day, the Copernicus Sentinel-2 mission takes us over the Shoemaker Impact Structure (formerly known as Teague Ring) in Western Australia. 45)
- The almost circular shape of the Shoemaker impact site, visible in the bottom-right of the image, is approximately 30 km in diameter and is defined by concentric rings formed in sedimentary rocks (seen in dark brown). The precise age of the impact is unknown, but is estimated to be between 1000 and 600 million years ago – making it Australia’s oldest impact crater.
- Asteroid Day, the UN-endorsed global awareness campaign is back on 30 June with an exciting 5-hour live broadcast from 18:00 CET. With the help of leading experts, Asteroid Day Co-founder Dr. Brian May and the most engaging voices in science communications from around the world, the five hour program will bring the solar system’s smallest worlds to vivid life for audiences of all ages and backgrounds. For more information, visit ESA joins Asteroid Day for rocky live broadcast.
Figure 23: Located around 100 km northeast of the small town Wiluna, the Shoemaker Impact Structure was renamed in honor of Eugene Shoemaker, a planetary geologist and pioneer in impact crater studies. This false-color image was processed by selecting spectral bands that can be used for classifying geological features, allowing us to clearly identify the concentric rings in the image. The light blue areas are saline and ephemeral lakes including Nabberu, Teague, Shoemaker and other smaller ponds (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
• June 18, 2021: Sentinel-2 image of the week: 14-18 June 2021 showing the California drought. 46)
Figure 24: The Copernicus Sentinel-2 mission brings two images showing the impact of the severe drought affecting the state of California in the United States. The images cover the area over Angeles National Forest at the outskirts of the Greater Los Angeles metropolitan area and depict changes in water levels of several important water reservoirs as well as the state of the forest in June 2020 and 2021 (image credit: ESA, the image contains modified Copernicus Sentinel data (2020-2021), processed by ESA, CC BY-SA 3.0 IGO)
• June 18, 2021: The Tana River, Kenya’s longest river, is featured in this false-color image captured by the Copernicus Sentinel-2 mission. 47)
- The Tana River flows for around 1000 km from the Aberdare Mountains, west of Nyeri, running eastwards before veering south around the massif of Mount Kenya, and opening onto a wide valley, pictured here, where it meanders through a floodplain often subject to inundation. The river then continues its journey before entering the Indian Ocean at Formosa Bay, Kipini.
- The river is known for its extraordinary biodiversity, as it provides water and life for wild animals, nomads and their livestock, as well as for agricultural purposes.
- Some of the Tana’s tributaries as well as several smaller, seasonal rivers, known as lagas, that only flow during the rainy season, are visible flowing in an east-west direction in the image. The river beds support livestock and wildlife during the dry season owing to their ability to retain water.
Figure 25: This false-color image, captured on 25 February 2020, was processed in a way that included the near-infrared channel. This type of band combination from Copernicus Sentinel-2 is most commonly used to assess plant density and health, as plants reflect near-infrared and green light, while absorbing red. Since they reflect more near-infrared than green, dense, plant-covered land appears in bright red. This image is also featured on the Earth from Space video program, (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
- It is easy to pick out the narrow band of riparian forest visible along the banks of the river in the image. The riparian forest usually thrives year-round, although its extent is highly dependent on seasonal flooding and ground water recharge by the Tana.
- This image was captured during the area’s wet season, where the small tributaries of the Tana are highly visible and a significant amount of vegetation can be seen. If the image had been captured during the dry season (around June-September), the smaller tributaries and the vegetation growing around them would have dried up.
- The river flows alongside the town of Garissa, the capital of Garissa County, and is visible as a greyish patch of land on the east side of the river. Around 5 km south of Garissa lies the Bour-Algi Giraffe Sanctuary, home to around 1000 giraffes and endangered wildlife including the Rothschild giraffe and gerenuk – a long-necked antelope found in the region.
- Copernicus Sentinel-2 is a two-satellite mission. Each satellite carries a high-resolution camera that images Earth’s surface in 13 spectral bands. The mission is mostly used to track changes in the way land is being used and to monitor the health of vegetation.
• June 14, 2021: A new study using satellite evidence confirms that a rock and ice avalanche caused the Chamoli disaster in India earlier this year. The resulting mud and debris flood led to massive destruction downstream. 48)
- On 7 February 2021, the Chamoli district in the Uttarakhand region of India experienced a humanitarian tragedy when a large mass of rock and ice, around 27 million m3, was released from the steep mountain flank of the Ronti peak.
- This collapse caused a flow of debris to barrel down the Ronti Gad, Rishiganga, and Dhauliganga river valleys, causing significant destruction along the route, killing more than 200 people and destroying two major hydropower facilities that were under construction.
- In response to this, the International Charter 'Space and Major Disasters', a service that provides satellite images in response to natural and human-made emergencies, was activated. The service provides free access to very high-resolution satellite data such as from Worldview 1/2, Cartosat-1 and Pleiades.
- Combined with freely available images from Landsat and the Copernicus Sentinel-2 mission, scientists analyzed numerous images acquired before and after the event to quickly determine what was going on and quantify key measures of the event, for example its total volume, elevation differences and travel distances.
- This analysis allowed scientists to exclude that a glacier lake outburst flood had been the cause of the disaster. Instead, the study provides satellite evidence that the disaster was caused by a large mass of ice and rock dislodged from the slopes of Ronti Peak, starting as a giant landslide that transformed into a mud and debris flow causing destruction along its path.
Figure 26: This Copernicus Sentinel-2 image shows the aftermath of the Chamoli disaster on 7 February 2021. The dotted orange line shows the site of the collapse from the north slope of the Ronti peak. This collapse caused a flow of debris to barrel down the Ronti Gad, Rishiganga, and Dhauliganga river valleys, causing significant destruction along the route, killing more than 200 people and destroying two major hydropower facilities that were under construction (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
- The team of 53 scientists and experts came together online in the days following the disaster to re-construct the event and investigate the scope and impact of the flood caused by the landslide. Their study, published on 10 June in the journal Science, not only analyzed satellite imagery, but also seismic records and eye-witness videos to determine the timing of the event and produce computer models of the flow. 49)
- Lead author Dan Shugar, Associate Professor in the Department of Geoscience at the University of Calgary, commented, “The rapid increase in the number of satellites orbiting Earth allowed our team to understand the basics of what happened in a matter of hours. We now have access to satellites that image every part of Earth every day – sometimes even multiple times per day – and this has really revolutionized how we do this sort of science.”
- The results of the analysis were also sent to the governmental agencies of India to help them plan and support emergency assistance to the local teams.
- Two participants from ESA’s Climate Change Initiative, specifically the Glaciers_cci and Permafrost_cci projects, helped with the retrieval and analysis of satellite images which included Copernicus Sentinel-2, PlanetLab and Corona.
- Andreas Kääb, from the University of Oslo, was able to determine the volume and ice/rock mixing ratios based on his experience with such events from earlier studies. He explains, “The calculated 80% rock in the avalanche completely converted the 20% glacier ice into water over the 3200 m elevation difference from Ronti Peak to the Tapovan hydropower plant. This conversion is largely responsible for the devastating impact of the resulting mud and debris flood wave.”
- Among many other technical details, Copernicus Sentinel-2 images revealed that the crack near the bergschrund (a crevasse that forms where moving glacier ice separates from stagnant ice) of the steep hanging glacier opened already some years ago and that an ice avalanche from a neighboring glacier occurred in 2016. The images from 2016—2020 show the ice avalanche deposit largely melting away over this period.
- Frank Paul, from the University of Zurich is science lead of the Glaciers_cci project, and commented: “This study clearly shows that satellite data could play a larger role in future high mountain hazard assessments, in particular for evaluating large and inaccessible areas.”
- Andreas Kääb added “This specific event was extreme and basically unpredictable. However, rock avalanches are known to be highly mobile, far-reaching and devastating when they mix with snow and ice.”
- The researchers suggest that in a warmer climate such events might be happening more frequently, and that the full potential of satellite data and knowledge should be utilized to identify possibly dangerous regions.
Figure 27: Destroyed Tapovan Vishnugad hydroelectric plant after devastating debris flow on 7 February 2021 (image credit: Irfan Rashid, Department of Geoinformatics, University of Kashmir)
• June 11, 2021: Chongqing, the largest municipality in China, is featured in this Copernicus Sentinel-2 image. 50)
- Covering an area of over 80,000 km2, around the size of Austria, Chongqing is located in southwest-central China. Chongqing covers a large area crisscrossed by rivers and mountains. These are the Daba Mountains in the north, the Wu Mountains in the east, the Wuling Mountains in the southeast and the Dalou Mountains in the south.
- The city of Chongqing, one of the most important economic centers in China, is known as a ‘mountain city’ owing to its rugged terrain and steep gorges. Chongqing is a major manufacturing and transportation centre, and has become the biggest automobile manufacturing base in China.
Figure 28: The city of Chongqing lies at the confluence of the Yangtze and Jialing rivers, where the clashing colors of the rivers meet. The Yangtze river is visible in brown in the right of the image, while the green waters of the Jialing can be seen in the left. The rivers make Chongqing China's biggest port city in the southwest region. With a length of 6300 km, the Yangtze is the longest river in both China and Asia and the third longest river in the world. The Jialing River, rises in the Qin Mountains, and joins the Yangtze after a course of around 1190 km. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• June 4, 2021: The Copernicus Sentinel-2 mission takes us over Warsaw – the capital and largest city of Poland. 51)
- Warsaw straddles the Vistula (Wisla) River, the largest river in Poland. With a length of around 1000 km and a drainage basin of some 195 000 km2, the Vistula is an important waterway to the nations of Eastern Europe.
- The agricultural fields surrounding Warsaw, visible in the left of the image, are very distinctive with their small and highly fragmented shape. These unique agricultural structures are most likely due to the fact that many farms are private, with most fields covering a relatively small area (around 9 hectares on average).
- Divided into right and left bank portions by the river, Warsaw extends around 30 km from north to south and around 25 km from east to west. On the west bank of the river, lies Warsaw’s historical Old Town (Stare Miasto) which holds the most prominent tourist attractions and was designated a UNESCO World Heritage Site in 1980.
- East of the Vistula lies the Narodowy National Stadium, a retractable-roof stadium used for professional football, concerts and was used as the location of the United Nations Climate Change Conference (COP-19) in November 2013.
- Warsaw is also home to a prominent statue dedicated to the mathematician and astronomer Nicolaus Copernicus, which stands near the Polish Academy of Sciences. Copernicus was an important figure to humanity’s understanding of the universe. His theory of the heliocentric universe, the notion that Earth orbits the sun, went against the Ptolemy’s system which had been in place for a thousand years, which stated that Earth was at the centre of the solar system.
- Owing to Copernicus’ pioneering contribution to modern science, the European Union named their Earth observation programme after him. The programme provides accurate, timely and easily accessible information to monitor our planet and its environment, understand and mitigate the effects of climate change and ensure civil security.
Figure 29: Located in east-central Poland, Warsaw lies in the heartland of the Masovian Plain, around 280 km from the Baltic coastal city of Gdańsk. The city saw more than 85% of its buildings destroyed during World War II, yet, despite its hardships, Warsaw has risen from the ashes – earning itself the nickname 'Phoenix City.' This image, acquired on 1 July 2020, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
• May 21, 2021: The Copernicus Sentinel-2 mission takes us over Los Cabos – a municipality on the southern tip of Mexico's Baja California Peninsula. 52)
- Meaning ‘the capes’ in Spanish, Los Cabos is a region composed of mountains and coastal plains and is largely dry and rocky with over 320 days of sunshine each year. The area encompasses the two cities of Cabo San Lucas (visible in the bottom-left) and San José del Cabo (visible to the right).
- The area along the coast between the two cities, often referred to as the Los Cabos Resort Corridor or simply the Corridor, stretches around 30 km along the highway and features a plethora of beaches dotted primarily with hotels, resorts and golf courses.
- The peninsula ends with the Arch of Cabo San Lucas, known locally as ‘El Arco’ or ‘Land’s End.’ This distinctive land formation, carved by winds and waves, is where the Pacific Ocean meets the Gulf of California, also known as the Sea of Cortez.
- The Arch of Cabo San Lucas is adjacent to Lovers Beach (Playa del Amor) on the Sea of Cortez side and Divorce Beach (Playa del Divorcio) on the rougher Pacific Ocean side. The arch is a popular gathering area for sea lions and is frequented by tourists.
- A region of mountains dominate the landscape including the Sierra de la Laguna Mountain Range and the Sierra de San Lázaro, which are both formed of volcanic rock with peaks between 400 and 1000 m.
- The main river in the area is the San José River, visible in the right of the image, and flows north to south primarily during the summer rainy season. The river creates an estuary at its southern end, which is one of the largest in Mexico and is home to both native and migratory birds.
Figure 30: This image has been processed in a way that included the Copernicus Sentinel-2’s near-infrared channel, which makes vegetation appear bright red. As the image was acquired on 20 June 2020, the region is particularly dry with little vegetation visible. Los Cabos is dry and warm most of the year, with a short rainy season in late summer and early autumn. This image is also featured on the Earth from Space video program (image credit: ESA)
Los Cabos seasonal comparison
The Copernicus Sentinel-2 images of Figures 31 and 32 show a seasonal comparison over Los Cabos – a municipality on the southern tip of Mexico's Baja California Peninsula. Both images have been processed in a way that included Sentinel-2’s near-infrared channel, which makes vegetation appear bright red.
This type of band combination from Sentinel-2 is most commonly used to assess plant density and health, as plants reflect near-infrared and green light, while absorbing red. Since they reflect more near-infrared than green, dense, plant-covered land appears in bright red in the image.
Figure 31: This image was acquired on 20 June 2020, the region is particularly dry with little vegetation visible (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
Figure 32: This image was captured on 28 September 2020, during the region’s rainy season, and shows the high-density of vegetation in the area. This type of band combination from Sentinel-2 is most commonly used to assess plant density and health, as plants reflect near-infrared and green light, while absorbing red. Since they reflect more near-infrared than green, dense, plant-covered land appears in bright red in the image (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
• May 18, 2021: Hundreds of satellite images spanning over 25 years have been compiled to show the evolution of Greece’s ever-changing coastlines. 53)
- For decades, coastal areas have been subject to intense urbanization and population growth. These areas are some of the most dynamic on Earth and, unfortunately, suffer from severe coastal hazards owing to storm activity and sea level rise. Monitoring coastal areas is key to understanding the evolution of coastal dynamics and in helping authorities protect these environments.
- The Space for Shore project, funded by ESA, provides a variety of tools for coastal erosion monitoring using Earth observation products. The consortium is composed of technical experts from five European countries.
- Two key players of the consortium, Terraspatium and i-Sea, have processed hundreds of satellite images, including data from the Copernicus Sentinel-2 mission, from 1995—2020 to analyze over 900 km of coast in Greece – in the Peloponnese, Eastern Macedonia and Thrace regions.
- The results highlight the fragility of Greece’s coastline and indicate the likelihood of coastal erosion increasing in the coming years. Over the 1995—2020 period, around 40% of the coastlines analyzed have shown ‘progradation’ which is the seaward growth of beaches caused by the progressive build-up of sediment. The team found that nearly 10% of the studied coastal areas are subject to erosion greater than 3 m per year.
Figure 33: Coastlines in Greece mapped by Space for Shore. This map shows the coastlines in the Peloponnese, Eastern Macedonia and Thrace regions in Greece mapped by the Space for Shore project, funded by ESA (image credit: ESA)
- Deltas, estuaries and capes appear to be the most exposed areas with retreat that can reach 30 m per year. Erosion at river mouths are especially of great concern as this signifies a sediment deficit and suggests critical and long-lasting consequences for coasts deprived of sediment input from rivers.
Figure 34: This image shows coastline changes from 1995-2020 along the Peloponnese peninsula in southern Greece. Areas in red indicate strong erosion, while areas in green show strong accretion (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA/Space for Shore)
- As an example, the team studied Zakynthos Island, particularly the Laganas coastal area. Given that the beaches are frequently watched by ecologists who closely monitor the migration of loggerhead sea turtles, they found it to crucial to observe the bathymetry and the waterline of the coast to record changes in its environmental impact.
- Aurélie Dehouck, Head of i-Sea and coordinator of Space for Shore, commented, “Over the last 25 years, our analysis has revealed a strong variability in Greece’s coastlines, with extremely dynamic local changes.
Figure 35: This image shows shoreline changes near Kalogera Lagoon, along the Peloponnese peninsula in southern Greece. Areas in red indicate erosion between 1995 and 2020, while areas in green show strong accretion during the same time period. Coastline data from 1995 to 2020 has been overlaid onto a Copernicus Sentinel-2 image from 2021 (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA/Space for Shore)
- “From this assessment of intra-period variability, two foregone conclusions emerge: the need to monitor coastal dynamics on crossed timescales to better identify sediment movement, problematic depletions and coastal responses to high-energy events, and the need to constantly monitor in order to know the real status of beaches of which the issues of the present and the future are based.”
- “Through the Space for Shore project, a comprehensive set of in situ scientific measurements, combined with numerous retrospective remote sensing data were produced. Thus, an evidence-based up-to-date assessment framework for the extent of coastal erosion was provided, rendering it an extremely helpful and substantially incomparable toolkit to the coastal managers throughout the region, both for the present and future use,” commented Athanasios Nalmpantis from the Public Sector at the Region of Eastern Macedonia & Thrace.
- On 22 January 2021, the results of the Coastal Change from Space project were presented in an online webinar.
• May 14, 2021: The Copernicus Sentinel-2 mission takes us over Qeshm Island – the largest island in Iran. 54)
- Qeshm Island lies in the Strait of Hormuz, parallel to the Iranian coast from which it is separated by the Clarence Strait (Khuran). With an area of around 1200 km2, the island has an irregular outline and shape often compared to that of an arrow. The island is approximately 135 km long and spans around 40 km at its widest point.
- The Hara Forest Protected Area, a network of shallow waterways and forest, can be seen clearly in the image, between Qeshm Island and the mainland. Hara, which means ‘grey mangrove’ in the local language, is a large mangrove forest and protected area that brings more than 150 species of migrating birds during spring, including the great egret and the western reef heron. The forest also hosts sea turtles and aquatic snakes.
- The dome-shaped Namakdan mountain is visible in the southwest part of the island and features the Namakdan Cave – one of the longest salt caves in the world. With a length of six km, the cave is filled with salt sculptures, salt rivers and salt megadomes.
- The water south of Qeshm Island appears particularly dark, while lighter, turquoise colors can be seen in the left of the image most likely due to shallow waters and sediment content. Several islands can be seen in the waters including Hengam Island, visible just south of Qeshm, Larak Island and Hormuz Island which is known for its red, edible soil.
- Several cloud formations can be seen in the bottom-right of the image, as well as a part of the Musandam Peninsula, the northeastern tip of the Arabian Peninsula. The peninsula’s jagged coastline features fjord-like inlets called ‘khors’ and its waters are home to dolphins and other marine life.
- Data from the Copernicus Sentinel-2 mission can help monitor changes in urban expansion, land-cover change and agriculture monitoring. The mission’s frequent revisits over the same area and high spatial resolution also allow changes in inland water bodies to be closely monitored.
Figure 36: The Sentinel-2 image shows the largely arid land surfaces on both Qeshm Island and mainland Iran. The island generally has a rocky coastline except for the sandy bays and mud flats that fringe the northwest part of the island. This image is also featured on the Earth from Space video program (image credit: ESA the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
• May 07, 2021: The Copernicus Sentinel-2 mission takes us over Morbihan – a French department in the south of Brittany. 55)
- Morbihan takes its name from ‘Mor-Bihan’ which means ‘little sea’ in the Breton language. The Gulf of Morbihan, visible in the center of the image, is one of the most famous features of the coastline with numerous islands and islets. The gulf is around 20 km long from east to west and around 15 km wide from north to south. It opens onto the Bay of Quiberon by a narrow passage between Locmariaquer and Port-Navalo.
- Many ships and vessels can be seen in the bay. Several islands are visible in the image, including the small islands of Houat and Hœdic and the large Belle Île, which is visible in the bottom-left of the image. Belle Île is known for the sharp cliff edges visible on the southwest side, but also for its beaches and renowned opera festival.
- The town and sea port of Lorient is visible in the top-left of the image. The town is situated on the right bank of the Scorff River at its confluence with the Blavet on the Bay of Biscay. The island of Groix lies a few kilometers off Lorient. The island has high cliffs on its north coast and sandy beaches in secluded coves on the south coast.
- Morbihan is also known for its ‘Alignements de Carnac’ which consists of rows of around 3000 standing stones and megalithic tombs. The stones were said to be erected during the Neolithic period, around 4500 BC. Most of the stones are within the Breton village of Carnac, but some to the east are within La Trinité-sur-Mer.
- Fields dominate the French countryside as seen in this image captured on 13 September 2020. Brittany is known for its rich and varied agriculture including meats and dairy products, but also provides a variety of high quality fruit and vegetables including tomatoes, strawberries, peas and green beans.
- The Copernicus Sentinel-2 mission is designed to provide images that can be used to distinguish between different crop types as well as data on numerous plant indices, such as leaf area, leaf chlorophyll and leaf water – all essential to monitor plant growth accurately.
Figure 37: Brittany is an important cultural region in the northwest of France and is divided into four departments: Ille-et-Vilaine in the east, Côtes d'Armor in the north, Finistère in the west and Morbihan in the south. This image is also featured on the Earth from Space video program. (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
• April 30, 2021: Antofagasta, a port city in northern Chile, is featured in this image captured by the Copernicus Sentinel-2 mission. 56)
- The city stretches approximately 22 km along the coast, snuggled between the ocean and the arid mountains to the east. The largest city in northern Chile, Antofagasta has a population of around 400,000 people. The city’s early growth resulted from the discovery of nitrate deposits in 1866, while today the economy is mainly based on the exploitation of various minerals such as copper and sulphur.
- Located around 1000 km north of Santiago, Antofagasta is the capital of both the Antofagasta Province and Region. The Antofagasta province borders the El Loa and Tocopilla provinces to the north and the Pacific Ocean to the west.
- In the right of the image (Figure 38), large, emerald green geometric shapes are visible and are most likely evaporation ponds used in mining operations. These bright colors are in stark contrast with the surrounding desert landscape, which is largely devoid of vegetation, making them easily identifiable from space.
- The city of Antofagasta is also a communications centre on the Pan-American Highway, visible as distinctive black lines in the right of the image, and is also linked by rail to the mines, as well as Bolivia and Argentina.
- Antofagasta is located within the Atacama Desert which is considered one of the driest places on Earth, as there are some parts of the desert where rainfall has never been recorded. Antofagasta typically has a cold desert climate with abundant sunshine, with January being its warmest month.
Figure 38: This image, captured on 6 January 2021 by the Sentinel-2 mission, shows little cloud cover over the city and surrounding area but strong westerly winds have created distinct wave patterns over the ocean – visible all the way from space. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
• April 30, 2021: One tends to think of mountain glaciers as slow moving, their gradual passage down a mountainside visible only through a long series of satellite imagery or years of time-lapse photography. However, new research shows that glacier flow can be much more dramatic, ranging from about 10 meters a day to speeds that are more like that of avalanches, with obvious potential dire consequences for those living below. 57)
- Glaciers are generally slow-flowing rivers of ice, under the force of gravity transporting snow that has turned to ice at the top of the mountain to locations lower down the valley – a gradual process of balancing their upper-region mass gain with their lower-elevation mass loss. This process usually takes many decades. Since this is influenced by the climate, scientists use changes in the rate of glacier flow as an indicator of climate change.
- For some glaciers around the world this gradual flow can speed up, so that they advance several kilometers in just a few month or years, a process called glacier surging. After a surge, the glacier usually remains still and the displaced ice melts over a few decades.
- Although surges can block rivers and create lakes that may burst suddenly, these events don’t often pose any danger, as by their very nature, they tend to be in remote and sparsely-populated regions – a fact that means that these events are often only known about thanks to data and images from satellites.
- For several years now, scientists have known that a glacier can also actually detach from the mountain rock and gush down to the valley at speeds of up to 300 km an hour as a fluid ice-rock avalanche.
- However, a paper published recently in The Cryosphere (Ref. 58) describes how scientists working in ESA’s Climate Change Initiative Glaciers team has discovered, together with several colleagues, that these glacier detachments have happened much more often than had been known. Even more surprisingly, this is happening to glaciers resting on relatively flat beds. 58)
Figure 39: Glacier avalanches in the Sedongpu region, China. For several years now, scientists have known that a glacier can actually detach from the mountain rock and gush down to the valley at speeds of up to 300 km an hour as a fluid ice-rock avalanche. The image, based on data from the Copernicus Sentinel-2 mission, shows the traces of ice/rock avalanches that occurred in 2017 and 2018, resulting from vast flows of rock and ice that finally partly blocked a river in the valley below (image credit: ESA, the image contains modified Copernicus Sentinel-2 data (2017–18), processed by CCI Glacier team and ESA)
- Andreas Kääb, from the University of Oslo, explained, “We have known about debris flows originating from glaciers that break off at high elevations for several decades now, however, until relatively recently, we were extremely surprised to discover that glaciers resting on flatter beds can also detach as a whole.
- “These events are reported only rarely. In fact, they only really came to light in 2002 after a huge chunk of the Kolka glacier, which sits in a gently sloping valley on the Russian–Georgian border, detached and thundered down the valley at about 80 m/s, carrying around 130 million m3 of ice and rock that killed more than 100 people.
- “Using satellite data, we have now discovered that such events are more common than we could have ever imagined, and this might be a consequence of a changing climate.”
Figure 40: Glacier avalanches in Tibet’s Aru mountain range. In 2016, a glacier in Tibet’s Aru mountain range suddenly collapsed, killing 10 people and hundreds of livestock. A few months later, a second glacier in the same mountain range also unexpectedly collapsed. The image, based on data from the Copernicus Sentinel-1 mission, shows the traces left after these two avalanches. For several years now, scientists have known that glaciers can detach from the mountain rock like this and gush down to the valley at speeds of up to 300 km/hr as a fluid ice-rock avalanche (image credit: ESA, the image contains modified Copernicus Sentinel-2 data (2016), processed by CCI Glacier team and ESA)
- The team of scientists from all over the world used data from different satellites including the Copernicus Sentinel-1 and Sentinel-2 missions and the US Landsat mission as well as digital elevation models to document and analyze events that were already known about, but also to identify glacier detachments that had not been recorded so far.
- They studied 20 glacier detachments that occurred in 10 different regions, from Alaska to the Andes and from the Caucasus to Tibet.
Figure 41: Global occurrence of glacier detachments. New research shows that climate change might be having a more dramatic effect on mountain glaciers than thought, causing them to leave their bed and act more like avalanches (image credit: CCI Glacier team/ESA)
- Frank Paul, from the University of Zurich, said, “We analyzed the timing of events, calculated volumes, run-out distances, elevation ranges, permafrost conditions as well as possible factors triggering these glacier avalanches. Although we found some common characteristics, there are diverse circumstances that may have led to these events. However, we have concluded that, at least for some events, the effects of a warmer climate, such as permafrost thawing and meltwater infiltration, may well be to blame.”
- Andreas Kääb added, “The bottom line is that detachment of glaciers resting on flat bedrock are more common than we thought.
- “The current era of frequent high-resolution optical and radar data, not least from Sentinel-2 and Sentinel-1, has brought a step-change in detecting and understanding these events after they happen. Although we are still far away from having a prognostic tool to detect possible events before they happen, thanks to satellite data and this new understanding, we might be able to detect precursor signals in good time to potentially save lives.”
• April 23, 2021: The Copernicus Sentinel-2 mission takes us over the sediment-stained waters in Laizhou Bay, located on the southern shores of the Bohai Sea, on the east coast of mainland China. 59)
- The bay is the smallest of three main bays of the Bohai Sea, and is named after the city of Laizhou, visible to the east (Figure 42). Large quantities of sediment carried by the Yellow River, visible in the left of the image, discolor the waters of the bay and appear turquoise. This sediment can be seen throughout the waters in this image, even far from the coast.
- The Yellow River is China’s second longest river, with a length of over 5400 km, and is surpassed only by the Yangtze River. The river rises in the Bayan Har Mountains in Western China and flows through nine provinces before emptying into the Laizhou Bay. Its drainage basin is the third largest in the country, with an area of around 750,000 km2.
- The river is estimated to carry 1.6 billion tons of silt annually, carrying the majority to the sea. Owing to this heavy load of silt, the Yellow River deposits soil in stretches, ultimately elevating the river bed. Excessive sediment deposits have raised the river bed several meters above the surrounding ground, sometimes causing damaging floods.
- On the southern coast of Laizhou Bay, in the bottom of the image, flooded fields are visible and are most likely artificial fish farms. The city of Dongying, home to the second largest oilfield in China, is visible in the left of the image.
- Copernicus Sentinel-2 is a two-satellite mission. Each satellite carries a high-resolution camera that images Earth’s surface in 13 spectral bands. The mission is mostly used to track changes in the way land is being used and to monitor the health of vegetation.
Figure 42: This Sentinel-2 image, acquired on 26 February 2020, is also featured on the Earth from Space video program. This image was processed in a way that included the near-infrared channel, which makes vegetation appear bright red. The lush vegetation can be distinguished from the brown fields in the image, which are unharvested or not yet fully grown (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
• April 16, 2020: Volcanic eruptions on Saint Vincent have blanketed the Caribbean island in ash leading to over 16 000 residents to be evacuated from their homes. False-color images captured by the Copernicus Sentinel-2 mission show the aftermath of the explosive eruption that took place on 9 April 2021. 60)
- La Soufrière is an active stratovolcano on the Caribbean island of Saint Vincent in Saint Vincent and the Grenadines. A series of explosive events began in April 2021, forming a plume of volcanic ash reaching 8 km in height, and generating pyroclastic flows down the volcano’s south and southwest flanks.
- The images have been processed in a way that included the satellite’s near-infrared channel. This type of band combination is most commonly used to assess plant density and health, as plants reflect near-infrared and green light, while absorbing red. Since they reflect more near-infrared than green, dense, plant-covered land appears in bright red.
- In response to the eruption, the Copernicus Emergency Mapping Service was activated. The service uses satellite observations to help civil protection authorities and, in cases of disaster, the international humanitarian community, respond to emergencies.
Figure 43: This image was captured on 8 April, one day before the first main eruption (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
Figure 44: This image was taken on 13 April, and shows the northern part of the island covered in ash ((image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
• April 16, 2021: On 22 April 2021, on Earth Day, Thomas Pesquet is planned to return to the International Space Station for his second mission, Alpha. Ahead of his launch, the Copernicus Sentinel-2 mission takes us over Cape Canaveral, USA, in a region known as the Space Coast. 61)
- The cape area is part of the region known as the Space Coast, and is home to the Kennedy Space Center – including the space shuttle landing facility, a visitor’s center, Cape Canaveral Air Force Station and a space vehicle assembly building. Launch Complex 39A, visible along the coast (Figure 45), is where the Saturn V rocket carrying Apollo 11 began its voyage to the moon in 1969, carrying Neil Armstrong, Michael Collins, and Edwin ‘Buzz’ Aldrin.
- Before the space program was launched, Cape Canaveral was a stretch of barren, sandy scrubland. The cape was chosen for rocket launches owing to its close proximity to the equator. As the linear velocity of Earth’s surface is greatest towards the equator, the southerly location of the cape allows for rockets to take advantage of this by launching eastward – in the same direction as Earth’s rotation.
- The space center is included in the Merritt Island National Wildlife Refuge, visible in the top of the image, which occupies more than 550 km2 of estuaries and marshes. It preserves the habitat of around 1000 plant and 500 wildlife species, included several endangered species. The city of Cape Canaveral lies just south of the space center and around 8 km north of Cocoa Beach (visible in the bottom of the image).
- It is from here where French ESA astronaut Thomas Pesquet will be launched on his second mission to the International Space Station. Thomas will be the first ESA astronaut to fly on a SpaceX Crew Dragon launching on a Falcon 9 rocket, together with NASA astronauts Shane Kimbrough and Megan McArthur and JAXA astronaut Akihiko Hoshide. He will be the first European to launch from the US since 2011, when Roberto Vittori, from Italy, flew onboard space shuttle Endeavour to deliver the Alpha Magnetic Spectrometer.
- During his six-month mission, called Alpha, Thomas will spend much of his time on scientific research and will also be carrying out maintenance tasks as part of the station’s crew. Towards the end of his mission, he will serve as commander of the Station. He will be the fourth European to hold the post of commander, after ESA astronauts Frank De Winne, Alexander Gerst and Luca Parmitano.
Figure 45: Cape Canaveral is a cape and city in Brevard County, in east-central Florida. The cape is separated from the mainland by the Banana River, Merritt Island and the Indian River from east to west. This image, captured on 2 February 2021, is also featured on the Earth from Space video program (image credit: ESA)
• April 9, 2021: The Copernicus Sentinel-2 mission takes us over Bucharest – the capital and largest city of Romania. 62)
Figure 46: Bucharest lies on the southeast corner of the Romanian Plain, on the banks of the Dâmbovita River, a small tributary of the Danube. The city covers an area of around 225 km2, in an area once covered by the Vlăsiei forest, which, after it was cleared, gave way to a fertile flatland. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
- The city is characterized by a number of main squares from which streets and boulevards radiate. One of the main boulevards, Bulevardul Unirii, can be spotted in the middle of the city and leads the way to the Palace of Parliament.
- An icon of the country’s capital, this monumental building is the largest in Europe and the world’s second-largest administrative building after the Pentagon in the United States. It is home to the Parliament of Romania as well as the National Museum of Contemporary Art.
- Several lakes stretch across the northern part of the city, the most important of which are Lake Herăstrău, Lake Floreasca, Lake Tei, and Lake Colentina. In the centre of the capital is a small artificial lake – Lake Cişmigiu – surrounded by the Cişmigiu Gardens.
- Văcăresti Nature Park can be seen in the southern part of the city. Covering an area of around 190 hectares, the park contains the wetlands surrounding Lake Văcăresti and hosts close to 100 species of birds, half of which are protected.
- Agricultural fields dominate the rest of this week’s image. Romania is one of the biggest agricultural producers in the European Union, exporting mainly maize, wheat and other grains.
• April 8, 2021: Italy’s Mount Etna, Europe’s most active volcano, has recently been on explosive form, with 17 eruptions in less than three months. Instruments onboard three different satellites orbiting Earth have acquired imagery of the eruptions – revealing the intensity of the lava-fountaining eruptive episodes, known as paroxysms. 63)
Figure 47: This Copernicus Sentinel-2 animation shows the latest activity taking place in Mount Etna from 16 February 2021 until 2 April 2021 (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
- Located on the east coast of Sicily, Mount Etna is one of the world’s most active volcanoes. Its eruptions occur at the summit, where there are four craters: the Voragine and the Bocca Nuova, formed in 1945 and 1928 respectively, the Northeast Crater, the highest point on Etna (3330 m) and the Southeast Crater, which has recently been the most active of the four.
- Starting in February 2021, the Southeast Crater produced a series of intense lava fountains coloring the night sky in hues of orange and red. Over the course of the following weeks, the volcano produced lava fountains reaching as high as 1.5 km.
- These spectacular explosions are amongst the highest observed at the Southeast Crater in recent decades. In the past, lava fountains reaching the same height were only observed at the Voragine crater in December 2015 – with lava fountains of over 2000 m.
- Different satellites carry different instruments that can provide a wealth of complementary information to understand volcanic eruptions. Once an eruption begins, optical instruments can capture the various phenomena associated with it, including lava flows, mudslides, ground fissures and earthquakes.
- Atmospheric sensors on satellites can also identify the gases and aerosols released by the eruption, as well as quantify their wider environmental impact. The image below, captured by the Copernicus Sentinel-5P satellite, shows the sulphur dioxide concentrations visible travelling southwards towards Libya. Sulphur dioxide is released from a volcano when magma is relatively close to the surface.
Figure 48: Sulphur dioxide concentrations on 24 March 2021. Atmospheric sensors on satellites can also identify the gases and aerosols released by the eruption, as well as quantify their wider environmental impact. This image, captured by the Copernicus Sentinel-5P satellite, shows the sulphur dioxide concentrations visible travelling southwards towards Libya. Sulphur dioxide is released from a volcano when magma is relatively close to the surface (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
- After a week or so of remaining calm, Etna’s Southeast Crater re-awoke on the morning of 31 March with a loud explosion at around 07:00 CEST, followed by several puffs of ash and lava.
- According to the National Institute of Geophysics and Volcanology in Italy (INGV), the explosive activity increased in the late afternoon and during the night with lava flowing towards the Valle del Bove, with smaller flows advancing southwards. As of today, activity in the Southeast Crater remains calm.
• March 29, 2021: Climate change is having an undeniable influence on coastal areas. A substantial proportion of the world’s sandy coastlines are already eroding owing to increased storm surges, flooding and sea level rise. With our coastal environments in constant change, Earth observation satellites are being used to better strengthen our knowledge of changing coastlines. 64)
- For decades, coastal areas have been subject to intense urbanization and population growth. The European Union coastline is approximately 68,000 km long, more than three times longer than that of the United States. According to the European Environment Agency, almost half of the EU population lives less than 50 km from the sea, with the seaside being Europe’s most popular holiday destination.
- Coastal erosion is currently observed on many shorelines in Europe and will most likely worsen with rising sea levels. Monitoring coastal movement is key in understanding the evolution of coastal environments and these data can prove fundamental information to regional decision-makers.
- ESA has been developing an array of products to address these challenges. As part of ESA’s EO Science for Society program, the Coastal Change from Space project is providing important insights into global coastal changes. Using 25 years of satellite imagery, including data from the Copernicus Sentinel-1 and Sentinel-2 missions, the team has mapped 2800 km of coastline analyzed across four nations: The United Kingdom, Ireland, Spain and Canada.
Figure 49: This image shows the annual mean shoreline change in Start Bay, Devon. Areas in red indicate strong erosion, while areas in dark blue show strong accretion (image credit: ESA, the image contains modified Copernicus sentinel data (2018-19), processed by ESA/ARGANS Ltd.)
- As part of this project, a special process has been developed and applied to ensure each pixel from every image has a greatly improved accuracy on the ground, as well as identifying where the coastline is precisely located on a specific date.
- The frequent revisit rate of the Sentinel-1 and Sentinel-2 missions has enabled the changes to be observed as well as more permanent and extreme movements due to storm events. These results were then validated by a team of independent scientists from the four nations using results from field observations and local knowledge.
- Roberto Díaz Sánchez, from the Directorate General for the Coast and the Sea at the Ministry for the Ecological Transition and the Demographic Challenge, commented, “Taking part in this project has enlightened us in coastal surveillance from space. We are now firmly on the road to a new and promising coastal management paradigm, increasing our chances in successfully adapting our coasts to the effects of climate change.”
- The current dataset of over 30,000 individual images is now being used to help coastal scientists better understand their local processes.
Figure 50: This image shows the shoreline changes along the coast of Malgrat de Mar, Spain. Areas of erosion between 1994 and 2019 are visible in red, while areas of accretion between 1994 and 2019 are visible in blue. The 1994 coastline data is extracted from US Landsat data while the 2019 data is from the Copernicus Sentinel-2 mission (image credit: ESA, the image contains modified Copernicus sentinel data (2018-19), processed by ESA/ARGANS Ltd/Landsat)
- Mónica López, Spanish Delegate at ESA and Centre for the Development of Industrial Technology, said, “I would like to congratulate all of the team for the successful project which is focused in a very important topic for some countries, including Spain. I would like to remark a very positive aspect of the project which has been the high involvement of final users in all the phases of the project, mainly during validation and testing.”
- Koen Verbruggen, Director Geological Survey Ireland at the Department of Environment, Climate & Communications, added, “The datasets being produced under the ESA-funded Coastal Change from Space project have great potential application in Ireland and come at a very opportune time as we are establishing a National Coastal Change Management Strategy. The coastal change data can help us recognize areas of greatest change, and thus prioritize the allocation of resources at national and local levels.”
- The next stage in the journey will be to use this insightful datasets to improve the performance of models and join with other infrastructure and coastal zone morphological knowledge to improve forecasts and enable sensible mitigation strategies to be employed.
- On 22 January, the results of the Coastal Change from Space project were presented in an online webinar.
• March 26, 2021: The Gariep Dam, the largest dam in South Africa, is featured in this false-color image captured by the Copernicus Sentinel-2 mission. 65)
- The image of Figure 51 has been processed in a way that highlights vegetation in shades of green and water bodies in black. The water on the east side of the Gariep Dam appears in royal blue owing to a large quantity of sediments coming from the Orange River, therefore appearing brighter than the water flowing out of the west side of the dam.
- The Orange River plays an important role in the South African economy by providing water for irrigation and hydroelectric power. It rises in the Drakensberg mountains in Lesotho, flowing westwards through South Africa to the Atlantic Ocean.
- The river is said to be one of the world’s most turbid, and is estimated to deliver around 60 million tons of sediment each year to the western margin of South Africa. A significant quantity of this sediment is believed to be from soil erosion, an increasing environmental threat to sustainability in southern Africa.
- The bright green circular shapes along the Orange River are an example of center-pivot irrigation systems, where equipment rotates around a centre pivot and crops are fed with water from the centre of the arc.
- The rest of the image is dominated by bare soil and rocky terrain which appear in different shades of pink and red. Straight lines in the image are roads which connect this area to other parts of South Africa.
Figure 51: The Gariep Dam, visible in the bottom right of the image, lies along the Orange River, bordering the Free State and Eastern Cape provinces. The dam’s primary purpose is for irrigation, domestic and industrial use as well as power generation. The wall of the Gariep Dam, which is around 88 m high and 900 m long, holds back the Gariep Reservoir and, when full, the reservoir covers an area of around 360 km2. Sentinel-2 captured this image 30 January 2020, it is also featured on the Earth from Space video program (image credit: ESA)
• March 22, 2021: Clustered at the edge of the Crocodile River in Mpumalanga Province, South Africa, stand thousands of farms and small holdings growing fresh fruit and sugar cane. Water to irrigate the crops is taken from the river, but this slows its flow rate and leaves less for those downstream. 66)
- On World Water Day, how can the government achieve the sustainable use of water for the benefit of all South Africans? ESA has been working in partnership with two Dutch companies and a South African catchment management authority to find a solution.
- Some 20 year ago, in response to severe water shortages, the South African government passed the National Water Act, which is intended to restrict the amount of water farmers use for irrigation.
- However ensuring that farmers only take the water to which they are entitled is tricky.
- Maurits Voogt, who works for HydroLogic, a relatively small company based in Amersfoort in the Netherlands, says: “It is a major task to monitor and enforce the legal use of water in places where there are limited qualified personnel available, and the areas that need to be monitored are huge.
- “We have developed a smart, satellite-based water auditing service as part of ESA’s program ARTES ( Advanced Research in Telecommunications Systems). It allows water management authorities to monitor irrigated water use in large areas without actually needing to visit every single farm.
- “By doing so, the water auditing application helps them implement regulatory measures effectively, and thereby supports the sustainable use of water resource.”
Figure 52: Farms along Crocodile River. Captured by the Copernicus Sentinel-2 mission, this image shows farms next to the Crocodile River in Mpumalanga Province, South Africa. Farmers growing sugar cane and fresh fruit take water from the river to irrigate their crops, leaving less for those people living downstream. In response to severe water shortages, the South African government passed the National Water Act of 1998, which is intended to restrict the amount of water farmers use for irrigation (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
- The water auditing service uses evapotranspiration data calculated from satellite imagery by partner company eLEAF, based in Wageningen.
- Combined with rainfall data from rain gauges and satellites, this evapotranspiration data is used to calculate how much water is used for irrigation. The application automatically compares the water use with data taken from a national water use register that lists the amount of water allocated to each farm.
Figure 53: Circular cultivated areas along Crocodile River. Captured by the Copernicus Sentinel-2 mission, this image shows circular cultivated areas in farms next to the Crocodile River in Mpumalanga Province, South Africa. Farmers growing sugar cane and fresh fruit take water from the river to irrigate their crops, leaving less for those people living downstream. In response to severe water shortages, the South African government passed the National Water Act of 1998, which is intended to restrict the amount of water farmers use for irrigation (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
- In a pilot project, staff from HydroLogic and eLEAF used the technology to study irrigated water use for more than 50,000 fields covering some 40,000 km2 — about the area of the Netherlands.
- The team analyzed a handful of farms to confirm that the system could identify which farms had used large volumes of water compared to their neighbors.
- The costs of the pilot project were shared between ESA, eLEAF, Hydrologic and the Inkomati-Usuthu Catchment Management Authority, which is responsible for managing water resources in the region through which the Crocodile River flows.
- Following the demonstration project, the Inkomati-Usuthu Catchment Management Authority signed ongoing contracts for the water auditing service.
- Tendai Sawunyama, manager of resource planning and operations for the Inkomati-Usuthu Catchment Management Authority, says: “The application allows water managers to prioritize where to investigate for over-usage or illegal abstraction of water, and to make better decisions on where to place water meters. It can improve the understanding of water use and water allocation, and therefore help to create more sustainable water use in agriculture.”
- The water auditing application has been rolled out across South Africa to all catchment management authorities. It is now being modified to cater for the different user requirements needed by regional water authorities in Colombia and the Netherlands.
- It was developed with the support of ESA Space Solutions through the ESA Business Applications program.
• March 19, 2012: Ahead of the International Day of Forests, the Copernicus Sentinel-2 mission takes us over part of the Amazon rainforest in the Amazonas – the largest state in Brazil. 67)
- As its name implies, the Amazonas is almost entirely covered by the Amazon rainforest – the world’s largest tropical rainforest covering an area of around six million sq km. The Amazon is the world’s richest and most-varied biological reservoir, containing several million species of insects, birds, plants and other forms of life.
Figure 54: This image has been processed using the infrared channel of the Sentinel-2 satellite which makes the dense rainforest appear in bright green. This makes differences in vegetation coverage more evident than only using the visible channels of the satellite that our eyes are able to see. In this image, the Juruá River, the most-winding river in the Amazon basin, is visible. The river appears in shades of maroon and magenta as the reflected sunlight from the water’s surface consists of a mix of mainly blue and green, while the reflection in the near infrared is almost zero – leading to the colors we see here. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
- The Juruá river, which flows more than 3000 km before emptying into the Amazon River, is turbid with relatively high nutrient levels. The river rises in the highlands in east-central Peru before winding its way through lowlands in Brazil.
- Several crescent-shaped oxbow lakes can be seen flanking the river. Oxbow lakes are generally formed when rivers cut through a meander ‘neck’ to shorten its course, causing the old channel to be blocked off – migrating away from the lake and creating a more direct route.
- The Tarauacá River, a tributary of Juruá, can be seen in the left of the image. Eirunepé, a settlement established in the 19th Century as a hub for rubber production, is visible in the top-left of the image.
- The 21 March marks the International Day of Forests – a day which seeks to raise awareness on a range of benefits that sustainably managed forests can contribute to our lives. According to the United Nations, the world is losing 10 million hectares of forest each year, which accounts for 12-20% of the global greenhouse gas emissions that contribute to climate change.
- The Amazon rainforest is crucial for helping to regulate global warming as the forests absorb millions of tons of carbon emissions every year. As plants grow, they remove carbon dioxide from the atmosphere and store it as biomass. This is then released back to the atmosphere through processes such as deforestation for agriculture and wildfires.
- Tracking biomass changes is key to understanding the global carbon cycle and also for informing global climate models that help predict future change. Earth observation satellites have been instrumental in helping our understanding of this important process. New maps produced by ESA’s Climate Change Initiative, provide a global view of above ground biomass are pertinent in helping to support forest management, emissions reduction and sustainable development policy goals.
- ESA’s upcoming Biomass mission will provide crucial information about the state of our forests and how they are changing. The satellite will pierce through woodland canopies to perform a global survey of Earth’s forests over the course of Biomass’s mission.
• March 12, 2021: The Strait of Gibraltar connects the Mediterranean Sea with the Atlantic Ocean and separates southernmost Spain from northernmost Africa. The channel is 58 km long and narrows to 13 km in width between Point Marroquí (Spain) and Point Cires (Morocco). Ferries and vessels can be seen travelling across the strait and crossing between the two continents. 68)
- Water bodies, such as the Mediterranean Sea and the Atlantic Ocean, appear in dark blue or black while turbid waters, such as those visible along the Spanish coast in the top-left of the image, appear in cyan or light blue. This is most likely due to sediment-laden waters flowing from rivers into the sea. Inland water bodies, such as the Barbate Reservoir visible at the top of the image, can be spotted in various shades of azure owing to their turbidity.
- Several prominent cities can be seen in the image in grey. These include Tangier, the port and principal city of northern Morocco which lies just 27 km from the southern tip of Spain. Tétouan lies along the Martil Valley and can be seen in the bottom-right of the image. Its medina is a designated UNESCO World Heritage site since 1997.
- At the southern end of the Iberian Peninsula, the Bay of Gibraltar can be seen. The shoreline is densely populated and the shore is divided, from west to east, between the Spanish municipalities of Algeciras, Los Barrios, San Roque, La Línea de la Concepción and the British Overseas Territory of Gibraltar.
Figure 55: This false-color image, captured on 28 October 2020, was processed in a way that included the near-infrared channel. This type of band combination from Copernicus Sentinel-2 is most commonly used to assess plant density and health, as plants reflect near-infrared and green light, while absorbing red. Since they reflect more near-infrared than green, dense, plant-covered land appears in bright red. This image is also featured in the Earth from Space program (image credit: ESA)
• March 5, 2021: The Copernicus Sentinel-2 mission takes us over the Galápagos Islands – a volcanic archipelago situated some 1000 km west of Ecuador in the Pacific Ocean. 69)
- The archipelago consists of 13 major islands and a handful of smaller islands and islets scattered across approximately 60,000 km2 of ocean. Repeated volcanic eruptions and ongoing seismic activity have helped form the rugged mountain landscape of the islands. In this image, captured on 23 September 2020, several circular volcanic cones can be seen atop the islands.
- The largest island of the archipelago, Isabela (Albemarle), is visible in the center. Around 132 km in length, the island’s seahorse shape is the result of the merging of multiple large volcanoes into a single land mass. The five volcanoes seen on the island are (from north to south): Wolf Volcano, Darwin Volcano, Alcedo Volcano, Sierra Negra Volcano and Cerro Azul Volcano. Two of the island’s volcanoes, Ecuador and Wolf, lie directly on the Equator.
- At the southern end of the island, hills covered with forests can be seen in bright green, separating the Sierra Negra, the most active of the Galapagos volcanoes, from the sandy coastline (partially visible here owing to cloud cover). Tortuga Island, named for its distinct shape, can be seen southeast from Isabela. The tiny island is actually a collapsed volcano that is a nesting location for a variety of seabirds.
- The second largest island of the archipelago, Santa Cruz, can be seen to the right of Isabela. Its capital, Puerto Ayora (not visible), is the most populated urban center in the islands.
- The Galápagos Islands are best known for their diverse array of plant and animal species, many of which are endemic meaning they are not found anywhere else in the world. These include the giant Galapagos tortoise, the marine iguana, the flightless cormorant and the Galapagos penguin – the only species of penguin that lives north of the equator.
- These species were observed by Charles Darwin during the voyage of the HMS Beagle in 1835 and inspired his theory of evolution by natural selection. To preserve the unique wildlife on the islands, the Ecuadorian government made the entire archipelago a national park in 1959.
Figure 56: The archipelago consists of 13 major islands and a handful of smaller islands and islets scattered across approximately 60,000 km2 of ocean. Repeated volcanic eruptions and ongoing seismic activity have helped form the rugged mountain landscape of the islands. In this image, captured on 23 September 2020, several circular volcanic cones can be seen atop the islands. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
• February 26, 2021: The Copernicus Sentinel-2 mission takes us over Vancouver – the third largest city in Canada. 70)
- In this image, captured on 29 July 2019, an unusually large quantity of sediment can be seen gushing from the Fraser River into the Strait of Georgia. The Fraser River is the longest river within British Columbia rising at Fraser Pass in the Rocky Mountains and flows for over 1300 km before emptying into the strait. The river's annual discharge at its mouth is estimated to be around 3550 m3/s, and is said to discharge around 20 million tons of sediment into the ocean.
- Several ships and vessels can be easily spotted at the top of the image, in the Burrard Inlet, which separates the city of Vancouver from the slopes of the North Shore Mountains (not visible).
- Vancouver Island dominates the left-side of the image. Covering an area of over 31 000 km2, it is the largest island on the Pacific coast of North America. The island is heavily wooded and mountainous with several peaks of more than 2100 m.
- At the bottom of the image, marine stratocumulus clouds can be seen over the Strait of Juan de Fuca, which also marks the international boundary between Canada and the Unites States. These types of cloud formations could be related to the Puget Sound Convergence Zone – a frequent weather phenomena where northwest winds are split by the Olympic Mountains and then re-converge over Puget Sound, visible in the bottom-right of the image.
- Copernicus Sentinel-2 is a two-satellite mission. Each satellite carries a high-resolution camera that images Earth’s surface in 13 spectral bands. The mission is mostly used to track changes in the way land is being used and to monitor the health of our vegetation.
Figure 57: Vancouver, visible at the top of the image, lies between the Burrard Inlet, an arm of the Strait of Georgia, to the north, and the Fraser River delta to the south. Vancouver has the highest population density in Canada, with over 5400 people/km2, making it the fifth-most densely populated city in North America. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• February 19, 2021: After Etna’s powerful eruption on Tuesday 16 February, the volcano produced another spectacular display of fire – with tall lava fountains shooting into the night sky, reaching heights of around 700 m. The first eruption caused large lava flows to descend eastwards into the Valle del Bove, travelling for approximately 4 km, but the second major explosion on Thursday (Feb. 18) caused the lava also to run for about 1.3 km down the volcano’s southern flanks. 71)
- Ash from the eruptions covered the city of Catania and authorities have been monitoring developments in the nearby towns at the base of the volcano, including Linguaglossa, Fornazzo and Milo. The eruption also forced the temporary closure of Sicily’s Catania Airport, which often happens when the volcano is active.
- According to Volcano Discovery, which publishes frequent alerts about seismic activity, the volcano also saw activity earlier today, 19 February, with lava flows continuing to descend to the south and east. Mount Etna is the tallest active volcano in Europe and frequently erupts.
- Satellite data can be used to detect the slight signs of change that may foretell an eruption. Once an eruption begins, optical and radar instruments can capture the various phenomena associated with it, including lava flows, mudslides, ground fissures and earthquakes. Atmospheric sensors on satellites can also identify the gases and aerosols released by the eruption, as well as quantify their wider environmental impact.
Figure 58: Italy’s Mount Etna, one of the world’s most active volcanoes, has erupted twice in less than 48 hours, spewing a fountain of lava and ash into the sky. This image, captured yesterday 18 February 2021 at 09:40 GMT by the Copernicus Sentinel-2 mission, has been processed using the mission’s shortwave-infrared band to show the lava flow in bright red (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
• February 19, 2021: The Copernicus Sentinel-2 mission takes us over Lusaka – the capital and largest city of Zambia. 72)
- Lusaka, visible at the top of the image of Figure 59, is located on a high plateau in south-central Africa with an elevation of around 1200 m. With a population of over 2 million people, Lusaka is one of the fastest developing cities in southern Africa. Lusaka National Park is easily identifiable as a brown patch of land just southeast of the city. The 6700 hectare park hosts a variety of rare and endangered animals.
- Owing to Zambia’s humid sub-tropical climate, agriculture is the country’s main source of income and jobs. The circular shapes in the image, visible mostly southwest of Lusaka in light green, are an example of pivot irrigation, or center-pivot irrigation systems. This type of irrigation functions where equipment rotates around a central pivot and crops are fed with water from the centre of the arc.
- Water from the nearby Kafue River, visible cutting across the image from left to right, is used for irrigation and hydroelectric power. At 1600 km long, the Kafue River is the longest river lying solely within Zambia. The river flows across the flat plain called Kafue Flats (also known as Butwa) and meanders in a maze of swampy channels and lagoons.
- The flats, visible in dark brown in the far-left of the image, are a shallow flood plain around 240 km long and about 50 km wide, and are usually flooded to a depth of less than one meter in the rainy season.
- From here, the Kafue River continues its journey southeast, flowing through the Kafue Gorge before finally joining the Zambezi River, visible in the bottom-right of the image, near Chirundu, Zimbabwe.
Figure 59: Data from the Copernicus Sentinel-2 mission can help monitor changes in urban expansion, land-cover change and agriculture monitoring. The mission’s frequent revisits over the same area and high spatial resolution also allow changes in inland water bodies to be closely monitored. This image, which was captured on 29 July 2019, is also featured on the Earth from Space program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• February 12, 2021: For Valentine’s Day, the Copernicus Sentinel-2 mission takes us over Valentine Island in northern Western Australia. 73)
- The King Sound has one of the highest tides in Australia, and amongst the highest in the world, reaching a maximum tidal round of around 11 to 12 m. The Fitzroy River, one of Australia’s largest watercourses, along with the Lennard, Meda and Robinson Rivers, empty their muddy and sediment-laden waters into the Sound.
Figure 60: The tiny Valentine Island, visible in the top-left of the image, measures around 1.6 km in length and around 250 m wide. The island is located in the King Sound, a large gulf and inlet of the Indian Ocean in Australia’s Kimberley Region. The gulf is around 120 km long and averages about 50 km in width. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
Figure 61: These images show the result of the floods brought on by heavy rainfall that hit Western Australia in late 2020. The image on the left was captured on 11 November 2020, while the image on the right was taken around a month later, on 16 December 2020 (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
- The heavy rain caused a large amount of sediment to be discharged into the Sound, as seen in dark shades of brown which contrast with the clearer, turquoise-colored waters visible at the top. The sediment has also been transported and deposited around Valentine Island.
- A myriad of mangrove estuaries can be seen scattered around the coast. Australia is surrounded by around 11,000 km of mangrove-lined coast, located primarily on the northern and eastern coasts of the continent. Mangroves contribute many environmental benefits to coastal and estuarine ecosystems; they provide food and habitats for a wealth of wildlife such as birds and fish.
- As more people move closer to coastal zones, the risk to mangroves increases. Greater pressure is placed on the mangrove environment from both direct and indirect sources such as dumping of waste, fish farming, sea level rise and climate change.
- Satellite missions such as Copernicus Sentinel-2 allow us to capture spectacular images such as these from space. This year, some of our incredible images of Earth from Space are now available as posters in the ESA On Demand shop. From the Amazon, to the Baltic Sea, to Antarctica, browse our new, Earth-inspired wall art for your home or office. Surprise someone special this Valentine’s Day with the special-edition image of the heart-shaped Moorea Island.
• February 5, 2021: The Copernicus Sentinel-2 mission takes us over the algal blooms swirling around the Pacific Ocean, just off the coast of Japan. 74)
- Algae blooms refer to the rapid multiplying of phytoplankton – microscopic marine plants that drift on or near the surface of the sea. Excessive algal growth, or algal blooms, can become visible to the naked eye and collectively tint ocean waters, allowing us to detect these tiny organisms from space.
- Although algal blooms are a natural and essential part of life in the sea, human activity is also said to increase the number of annual blooms. Harmful algal blooms can be stimulated by environmental factors, such as light, warmer water temperatures and excessive nutrients.
- During the spring bloom season, nutrients such as nitrates and phosphates are more abundant in the surface waters. Without direct in situ measurements, it is difficult to distinguish the type of algae that cover the ocean here. Algae is then usually carried by winds and currents closer to the coast of Japan.
Figure 62: In the image pictured here, captured on 14 June 2019, high concentrations of algae can be seen around 130 km off Hokkaido Island, the second largest island of Japan. This particular algal bloom measured more than 500 km across and 200 km wide, with the area pictured here showing just a small portion of the bloom, around 100 km from north to south and around 110 km from east to west. This image is also featured in this week's Earth from Space Program (image credit: ESA)
Figure 63: In the Pacific Ocean, near Hokkaido, Japan the colder Oyashio Current converges from the north with the warmer Kuroshio Current, which flows from the south. When two currents with different temperatures and densities collide, they often create eddies – swirls of water drifting along the edge of the two water masses. The phytoplankton growing atop the surface waters become concentrated along the boundaries of these eddies and trace out the motions of the water (image credit: ESA)
- Phytoplankton play an important role in the food chain, but they also have an impact on the global carbon cycle by absorbing carbon dioxide on a scale equivalent to that of terrestrial plants. Primary production is often used to describe the synthesis of organic material from carbon dioxide and water through photosynthesis. Even small variations in primary productivity can affect carbon dioxide concentrations, as well as influencing biodiversity and fisheries.
- As ocean surfaces warm in response to increasing atmospheric greenhouse gases, phytoplankton productivity will need to be monitored both consistently and systematically.
- Satellite data can not only be used to track the growth and spread of harmful algae blooms in order to alert and mitigate against damaging impacts for tourism and fishing industries, but have also recently proven fundamental to providing a global view of phytoplankton and their role in, and response to, climate change.
• January 29, 2021: Ahead of World Wetlands Day, the Copernicus Sentinel-2 mission takes us over Lake Titicaca – one of the largest lakes in South America. 75)
- Covering an area of around 8300 km2, Lake Titicaca lies on the high Andes plateau and straddles the border between Peru (to the west) and Bolivia (to the east). It is considered the highest major body of navigable water in the world, as it sits at an elevation of 3800 m above sea level.
- The lake extends approximately 190 km from northwest to southwest and is 80 km across at its widest point. Tiquina, a narrow strait, actually separates the lake into two separate bodies of water. The larger subbasin in the northwest is called Lake Chucuito in Bolivia and Lake Grande in Peru, while the smaller in the southeast is referred to as Lake Huiñaymarca in Bolivia and Lake Pequeño in Peru.
- Many rivers drain into the lake, including the Ramis, one of the largest, visible in the northwest corner of the lake. The smaller Desaguadero river drains the lake at its southern end, which then flows south through Bolivia. This outlet only accounts for a small percentage of the lake’s excess water, as the rest is lost by evaporation caused by persistent winds and intense sunlight.
- Lake Titicaca is a designated Ramsar Site of International Importance, as the waters of Titicaca are essential to the wellbeing of millions of people who rely on the lake for agriculture, fishing and tourism, as well as water birds and animals that live along and on its shores.
- February 2 marks the anniversary of the signing of the Convention on Wetlands of International Importance, known as the Ramsar Convention, in Ramsar, Iran in 1971. World Wetlands Day aims to raise global awareness about the vital role of wetlands for our planet and population.
- From their vantage point of 800 km high, Earth-observing satellites provide data and imagery on wetlands that can be used to monitor and manage these precious resources sustainably. For example, both the Copernicus Sentinel-2 and Sentinel-3 missions have recently been used to monitor the variation of chlorophyll concentrations in the lake and help detect trends and hotspots over time.
Figure 64: Forty-one islands rise from Titicaca’s waters, the largest of which, Titicaca Island, or Isla del Sol in Spanish, can be seen just off the tip of the Copacabana Peninsula in Bolivia. Several green algal blooms can be seen in the lake, including in the lake’s northwest and southeast corners. Snow in the Andes mountain range can be seen in the top-right of the image. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
• January 22, 2021: Sardinia, the second-largest island in the Mediterranean Sea, is featured in this false-color image captured by the Copernicus Sentinel-2 mission. 76)
- Sardinia (also known as Sardegna) is situated between the Mediterranean Sea to the west and south and the Tyrrhenian Sea to the east. The island sits 200 km west of the Italian Peninsula, 200 km north of Tunisia and around 12 km south of the French island of Corsica, partially visible in the top of the image.
- Sardinia is a mainly mountainous region, with its highest point Mount La Marmora in the Gennargentu massif visible in the centre-right of the image. With over 1800 km of coastline, Sardinia is internally renowned for its beaches including those along the Emerald Coast, or Costa Smeralda, Alghero and Villasimius. The coasts, particularly in the east, are high and rocky, with long stretches of coastline with bays, inlets and various smaller islands located off the coast.
- The archipelago of La Maddalena, including the renowned islands of La Maddalena, Caprera and Santo Stefano, can be seen in the top-right of the image. Its islands are known for their pristine beaches and wild beauty. Cagliari, the island’s capital and largest city, lies on the southern coast of the island.
- Copernicus Sentinel-2 is designed to provide images that can be used to distinguish between different crop types as well as data on numerous plant indices, such as leaf area index, leaf chlorophyll content and leaf water content – all of which are essential to accurately monitor plant growth.
Figure 65: This image, which uses data from 11 October to 14 October 2019, has been processed using the shortwave infrared band and the near infrared band to highlight dense vegetation. Crops and vegetation appear in bright green in the image, while bare soil can be seen in various shades of orange and brown. Grasslands and croplands with a higher moisture content appear more vibrant in the image. As water is a strong absorber of infrared, inland water bodies are delineated and can be easily spotted in black. Much of the Sardinia’s arable land is devoted to cereal cultivation and fruit growing. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• January 15, 2021: The Copernicus Sentinel-2 mission takes us over the Tanezrouft Basin – one of the most desolate parts of the Sahara Desert. 77)
Figure 66: Tanezrouft is a region of the Sahara lying in southern Algeria and northern Mali. The hyperarid area is known for its soaring temperatures and scarce access to water and vegetation, a reason why it’s often referred to as the ‘Land of Terror’. There are no permanent residents that live here, only occasional Tuareg nomads. This image, also featured on the Earth from Space video program, was captured on 12 January 2020 by the Copernicus Sentinel-2 mission (image credit: ESA, the image contains modified Copernicus Sentinel data (2020), processed by ESA, CC BY-SA 3.0 IGO)
- The barren plain extends to the west of the Hoggar mountains and southeast of the sandy Erg Chech. The terrain shows evidence of water erosion that occurred many years ago, when the Sahara Desert’s climate was much wetter, as well as wind erosion caused by frequent sandstorms – exposing ancient folds in the Paleozoic rocks.
- The region is characterized by dark sandstone hills, steep canyon walls, salt flats (visible in white in the image), stone plateaus and seas of multi-storey sand dunes known as ‘ergs’. Concentric rings of exposed sandstone strata create a stunning pattern predominantly visible in the left of the image.
- White lines in the right of the image are roads that lead to In Salah – the capital of the In Salah Province and In Salah District. Just above the center-left of the image, an airstrip can be seen. An interesting, grid-like pattern can be seen in the bottom of the image and mostly consists of human-made clearings and roads.
• January 12, 2021: Captured by the Copernicus Sentinel-2 mission on 11 January 2021 at 12:14 CET, this image of Madrid in Spain appears to have been taken in black and white. In fact, it is a true-color image – but the heaviest snowfall in 50 years has blanketed the region, turning the landscape white. 78)
- Storm Filomena hit Spain over the weekend, blanketing parts of the country in thick snow and leaving half of the country on red alert. Madrid, one of the worst affected areas, was brought to a standstill with the airport having to be closed, trains cancelled and roads blocked.
Figure 67: Although this satellite image was taken after the storm had passed, it is clear to see that much snow still remains, especially in the outskirts of the city. For example, some runways at the airport, which is visible in the top-right of the image, are still covered by snow. The unusual cold weather on the Iberian Peninsula is expected to last until later this week with temperatures forecasted to plunge to –12ºC. The race is on to clear roads so that supplies of essential goods such as food supplies and Covid vaccines can be delivered (image credit: ESA, the image contains modified Copernicus Sentinel data (2021), processed by ESA, CC BY-SA 3.0 IGO)
Copernicus: Sentinel-2 continued
Sensor complement: (MSI)
MSI (Multispectral Imager):
The instrument is based on the pushbroom observation concept. The telescope features a TMA (Three Mirror Anastigmat) design with a pupil diameter of 150 mm, providing a very good imaging quality all across its wide FOV (Field of View). The equivalent swath width is 290 km. The telescope structure and the mirrors are made of silicon carbide (SiC) which allows to minimize thermoelastic deformations. The VNIR focal plane is based on monolithic CMOS (Complementary Metal Oxide Semiconductor) detectors while the SWIR focal plane is based on a MCT (Mercury Cadmium Telluride) detector hybridized on a CMOS read-out circuit. A dichroic beamsplitter provides the spectral separation of VNIR and SWIR channels. 79) 80) 81) 82) 83) 84) 85)
Airbus DS (former EADS Astrium SAS) of Toulouse is prime for the MSI instrument. The industrial core team also comprises Jena Optronik (Germany), Boostec (Bazet, France), Sener and GMV (Spain), and AMOS, Belgium. The VNIR detectors are built by Airbus DS-ISAE-e2v, while the French company Sofradir received a contract to provide the SWIR detectors for MSI.
Calibration: A combination of partial on-board calibration with a sun diffuser and vicarious calibration with ground targets is foreseen to guarantee a high quality radiometric performance. State-of-the-art lossy compression based on wavelet transform is applied to reduce the data volume. The compression ratio will be fine tuned for each spectral band to ensure that there is no significant impact on image quality.
The observation data are digitized on 12 bit. A shutter mechanism is implemented to prevent the instrument from direct viewing of the sun in orbit and from contamination during launch. The average observation time per orbit is 16.3 minutes, while the peak value is 31 minutes (duty cycle of about 16-31%).
Figure 68: MSI instrument architecture (image credit: ESA)
Table 6: MSI instrument parameters
Spectral bands: MSI features 13 spectral bands spanning from the VNIR (Visible and Near Infrared) to the SWIR (Short-Wave Infrared), featuring 4 spectral bands at 10 m, 6 bands at 20 m and 3 bands at 60 m spatial sampling distance (SSD), as shown in Figure 71.
Table 7: Specification of VNIR and SWIR FPAs 86)
Figure 69: The MSI instrument (left) and the associated VNIR focal plane (right), image credit: Airbus DS-ISAE-e2v
Figure 70: Left: VNIR FPA (image credit: Airbus DS-F, ev2); right: SWIR FPA (image credit: Airbus DS-F, Sofradir)
Figure 71: MSI spatial resolution versus waveleng: Sentinel-2’s span of 13 spectral bands, from the visible and the near-infrared to the shortwave infrared at different spatial resolutions ranging from 10 to 60 m on the ground, takes land monitoring to an unprecedented level(image credit: ESA)
Table 8: MSI spectral band specification
The filter-based pushbroom MSI instrument features a unique mirror silicon carbide off-axis telescope (TMA) with a 150 mm pupil feeding two focal planes spectrally separated by a dichroic filter. The telescope comprises three aspheric mirrors: M2 mirror is a simple conic surface, whereas the other mirrors need more aspherization terms. The spectral filtering onto the different VNIR and SWIR spectral bands is ensured by slit filters mounted on top of the detectors. These filters provide the required spectral isolation.
CMOS and hybrid HgCdTe (MCT) detectors are selected to cover the VNIR and SWIR bands. The MSI instrument includes a sun CSM (Calibration and Shutter Mechanism). The 1.4 Tbit image video stream, once acquired and digitized is compressed inside the instrument.
The instrument carries one external sensor assembly that provides the attitude and pointing reference (star tracker assembly) to ensure a 20 m pointing accuracy on the ground before image correction.
The detectors are built by Airbus Defence and Space-ISAE-e2v: they are made of a CMOS die, using 0.35µm CMOS process, integrated in a ceramic package (Figure 72). The VNIR detector has ten spectral bands, two of them featuring an adjacent physical line allowing TDI operating mode, with digital summation performed at VCU (Video and Compression Unit) level. On-chip analog CDS (Correlated Double Sampling) allows to reach a readout noise of the order of 130 µV rms. For each detector, the ten bands are read through 3 outputs at a sample rate of 4.8MHz. The detector sensitivity has been adjusted for each band through CVF (Charge to Voltage conversion Factor) in view of meeting SNR specifications for a reference flux, while avoiding saturation for maximum flux. A black coating deposition on the non-photosensitive area of the CMOS die is implemented to provide high straylight rejection.
Figure 72: Illustration of the MSI VNIR detector (image credit: Airbus DS, Ref. 83)
Figure 73: MSI electrical architecture (image credit: Astrium SAS, Ref. 82)
The filter assemblies are procured from Jena Optronik (JOP) in Germany. A filter assembly is made of filter stripes (one for each spectral band) mounted in a Titanium frame. The aims of the filter assembly are: i) to separate VNIR spectral domain into the ten bands B1 to B9, ii) to prevent stray light effects. This stray light limitation is very efficient since it is made very close to the focal plane. Each filter stripe, corresponding to each spectral band, is aligned and glued in a mechanical mount. A front face frame mechanically clamps the assembly together.
The FEE (Front End Electronics) are procured from CRISA in Spain. Each FEE unit provides electrical interfaces to 3 detectors (power supply, bias voltages, clock and video signals) plus video signal filtering and amplification.
Video and Compression Unit (VCU) is manufactured by JOP and aims i) at processing the video signals delivered by the FEEs : digitization on 12 bits, numerical processing, compression and image CCSDS packet generation, ii) interfacing with the platform (power supply, MIL-BUS, PPS), iii) providing the nominal thermal control of the MSI.
Figure 74: Internal configuration of MSI (image credit: EADS Astrium)
The mechanical structure of MSI instrument holds the 3 mirrors, the beam splitter device, the 2 focal planes and 3 stellar sensors. It is furthermore mounted on the satellite through 3 bolted bipods. This main structure (Figure 75) has a size of 1.47 m long x 0.93 m wide x 0.62 m high with a mass of only 44 kg.
The optical face of these mirror blanks have been grounded by Boostec before and after CVD coating (i.e. before polishing), with a shape defect of few tens of a µm. M1 and M2 are designed to be bolted directly on the main SiC structure. M3 is mounted on the same structure through glued bipods. 87)
Table 9: MSI mirror characteristics
Mirror manufacturing: The mirror optomechanical design was performed by EADS-Astrium on the basis of the SiC-100 sintered silicon carbide from Boostec who produced the mirror blanks and delivered them to AMOS (Advanced Mechanical and Optical Systems), Liege, Belgium. AMOS is in charge of the deposition of a small layer of CVD-SiC (Chemical Vapor Deposition-Silicon Carbide) on the mirror. The purpose is to generate a non-porous cladding on the mirror surface which allows the polishing process reaching a microroughness state, compatible with the system requirements regarding straylight. 88)
Figure 76: Optical elements and schematic layout of the MSI telescope (image credit: EADS Astrium)
VNIR and SWIR focal plane assemblies: Both focal planes accommodate 12 elementary detectors in two staggered rows to get the required swath. The SWIR focal plane operates at -80ºC whereas the VNIR focal plane operates at 20ºC. Both focal planes are passively cooled. A monolithic SiC structure provides support to the detectors, the filters and their adjustment devices and offers a direct thermal link to the radiator.
Figure 77: Focal plane configuration (image credit: EADS Astrium)
Filters and detectors: Dedicated strip filters,mounted on top of each VNIR or SWIR detector, provide the required spectral templates for each spectral band. The VNIR detector is made of a CMOS die, using the 0.35 µm CMOS technology, integrated in a ceramic package. The detector architecture enables “correlated double.”
The so-called VNIR Filter Assembly contains 10 VNIR bands (from 443 nm to 945 nm) and the so-called SWIR Filter Assembly includes 3 SWIR bands (from 1375 nm to 2190 nm). The sophisticated development of the filter assemblies is caused by the specified spectral performance parameters and the high stray light requirements due to the topology of the spectral bands. 89)
Sampling for the 10 VNIR spectral bands along with TDI (Time Delay IntegrationI) mode for the 10 m bands. Black coating on the die eliminates scattering.
Figure 78: Photo of the VNIR (top) and SWIR spectral filter assemblies (image credit: Jena Optronik)
Figure 79: Photo of a CMOS detector with black coating (image credit: EADS Astrium)
The SWIR detector is made of an HgCdTe photosensitive material hybridized to a silicon readout circuit (ROIC) and integrated into a dedicated hermetic package. The SWIR detector has three spectral bands for which the spectral efficiency has been optimized. The B11 and B12 bands are being operated in (TDI) mode.
Figure 80: Photo of the EM model of the SWIR detector at hybridization stage (image credit: Sofradir)
CSM (Calibration and Shutter Mechanism): In MSI, the two functions of calibration and shutter are gathered in one single mechanism to reduce mass, cost and quantity of mechanisms of the instrument, increasing its reliability at the same time. The CSM is located at the entrance of MSI, a rectangular device of ~ 80 cm x 30 cm, mounted on the frame of the secondary structure. The design and development of the CSM is provided by Sener Ingenieria y Sistemas, S.A., Spain. 90)
Figure 81: Photo of the CSM (Calibration and Shutter Mechanism) mechanical configuration (image credit: Sener)
Requirements and design drivers:
• During launch the CSM has to protect the instrument from sun illumination and contamination by covering the instrument entrance with a rectangular plate (named the door). This is the close position, which has to be maintained under the action of the launch loads.
• Once in orbit, the following functions are required from the CSM:
- To allow Earth observation to the instrument (MSI) the door needs to rotate from the close position 63º inwards the instrument and maintain it stable without power. This is the open position.
- From time to time, in calibration mode of the MSI, the CSM inserts a sun diffuser in front of the primary mirror and the sun diffuser is illuminated by direct solar flux. This mode corresponds to a door position located 55º from the close position outward the instrument. This position must be also stable without any power supply.
Figure 82: Sentinel-2A/MSI sun diffuser. Size: 700 x 250 mm2 ensuring calibration of each pixel into the FOV (image credit: Airbus DS-F)
- In case of emergency, the CSM has to rotate the door to the close position from any initial position to prevent the sun light to heat sensible components of the instrument. Similarly to the previous positions, the close position shall be stable without power supply.
Figure 83: View of the CSM in calibration position (image credit: Sener)
A face to face ball bearing as rotation axis hinge in the opposite side of the actuator is used supported by means of an axially flexible support. Apart from that the pinpuller mounted on a flexible support, holds the door during launch by means of a cylindrical contact with respect to the door bushing. This design is the result of the optimization made in order to reach a stiff and robust but light and hyper-statically low constrained mechanism to make it compatible under possible thermal environments.
The pinpuller provides a reliable launch locking device and allows after pin retraction the mechanism to rotate in both senses.
The MSI instrument design represents state-of-the-art technology on many levels that is being introduced for next generation European land-surface imagers. Obviously, its performance will set new standards for future spaceborne multispectral imagers.
Storage technology introduction:
MMFU (Mass Memory and Formatting Unit):
The introduction of MMFU by EADS Astrium GmbH and IDA (Institut für Datentechnik und Kommunikationsnetze) at TU Braunschweig represents a new spaceborne storage technology based on SLC (Single Level Cell) NAND-Flash memory devices.
Note: NAND (Not And) is a Boolean logic operation that is true if any single input is false. Two-input NAND gates are often used as the sole logic element on gate array chips, because all Boolean operations can be created from NAND gates.
The NAND storage technology is not only an established technology in commercial applications but represents also a real and effective alternative for mass memory systems in space. The main advantages of the NAND-Flash technology are: a) the non-volatile data storage capability and b) the substantially higher storage density.
In the commercial world the NAND technology has become the preferred solution for storing larger quantities of data on devices such as SSDs (Solid State Drives), USB (Universal Serial Bus) Flash memory sticks, digital cameras, mobile phones and MP3-Players. In the space business, this technology has been used in some experiments only, but not in the frame of large scale mass memory systems. This is now going to be changed. 91) 92) 93)
Astrium and IDA have continuously worked for over seven years on the subject “NAND-Flash Technology for Space”. In the frame of an ESA study dubbed SGDR (Safe Guard Data Recorder) this NAND-Flash technology has been introduced and intensively evaluated.
As a result of this extensive testing, the radiation effects of this technology are well known meanwhile and appropriate error handling mechanisms to cope with the observed effects have been developed. For the S2 (Sentinel-2) mission, a complete qualification program has been performed including radiation tests, assembly qualification, construction analysis, electrical characterization, reliability tests like burn-in, destructive physical analysis, stress and life tests.
All these investments led to the final conclusion that the selected SLC NAND-Flash is an adequate technology for high capacity memory systems for space, even for systems with very high data integrity requirements.
Table 10 lists some main requirements and provides in parallel the related figures of two Astrium MMFU implementations. The first implementation is based on SLC NAND-Flash devices and will be launched with the Sentinel 2 satellite. The second option uses SDR-SDRAM devices, which was the initially required baseline technology for this mission.
The related simplified architectural block diagram of the Astrium Sentinel-2 MMFU is shown in Figure 84. The MMFU receives two parallel data streams either from the nominal or redundant VCU (Video Compression Unit). The interfaces are cross-strapped with redundant PDICs (Payload Data Interface Controllers). After reception and adaptation to internal data formats of the received source packets, the data is stored in memory modules. FMM (Flash Memory Module) and respectively SMM for the SDR-SDRAM memory module. For replay, the data is read out from two parallel operated memory modules and routed via two active TFGs (Transfer Frame Generators) providing interfaces for downlink and test. The system is controlled by a Memory System Supervisor, which is based on an ERC32 processor. The required supply voltages are provided by a power converter.
Each function is implemented by nominal and redundant hardware components. The functions and boards are summarized in Table 11:
Storage capacity: Astrium uses for all boards a standard format. Therefore the maximum number of memory and other devices which can be assembled on one board is limited by this form factor. Both types of memory modules are nearly identical in form, fit and function and because they can be mutually replaced; this represents a good basis for comparison.
The selected NAND-Flash device provides a capacity of 32 Gbit plus some spare. It is realized by means of four 8 Gbit dies encapsulated in a standard TSOP1 package. In total, the FMM (Flash Memory Module) includes 76 devices. The devices are arranged in four partitions which can be independently powered. A partition represents also the lowest level for reconfiguration. Each partition contains sixteen devices to store user data and three devices that are used to store parity information. This configuration enables single symbol error correction and double symbol error detection.
The SDRAM based memory module has a similar organization. There are also four partitions and each devices for single symbol error correction. A device is represented by a stack which contains eight SDRAM chips with a capacity of 512 Mbit each. From this follows the user storage capacity per memory module and some other parameters as listed in Table 12.
The number of FMM modules is determined by the total data rate and the operational concept, which requires the operation of two independent data streams. Therefore there are two memory modules operated in parallel. The third one is provided for redundancy.
The number of SMM modules is mainly determined by the required capacity. Also here two modules are operated in parallel and one SMM is included for reliability reasons.
The much higher storage density of the NAND-Flash devices (factor of 8) leads to a massive reduction in the number of required memory modules. For a mass memory system this becomes especially evident, if there is a requirement for a large user capacity as in case of the Sentinel-2 MMFU. Further positive aspects evolve with reduction of the number of modules. The complete system design from electrical and mechanical point of view is greatly relaxed.
Mass and volume: With reduction of the number of memory modules, it is obvious that directly related physical budgets like mass and volume, decline accordingly. Mass is always a critical issue for space missions which can be reduced by using NAND-Flash technology; but also the complete system design of a satellite, in terms of mass, power, thermal and other aspects, can be positively influenced by applying NAND-Flash based memory systems. In case of the Sentinel-2 MMFU, indeed 14 Kg (about 50%) can be saved.
Power: The power consumption is also reduced by more than 50% (Table 10). This is mainly caused by the number of memory modules operated in parallel. In case of Flash, there are only two active memory modules. In case of the SDRAM technology, 10 memory modules are operated in parallel: up to four modules for data access, two modules for read, two modules for write, and all other modules in data retention mode. Data retention means that the modules store user data and the SDRAM chips have to be refreshed and scrubbed for error detection and correction.
In contrast, a Flash-based memory module can be completely switched off without loss of data in the data retention mode. For a minimum, the partitions can be switched off and the power consumption of the controller part of the module is reduced due to low activity.
It is not obvious, that, in all cases, NAND-Flash consumes less power than SDR-SDRAM based systems. The power consumption depends on several factors like required storage capacity, data rates and operations. Generally it can be said, that as long as the required storage capacity determines the number of memory devices, Flash might be the better choice. If the number of memory devices is determined by the required data rate, SDRAM based systems may have a better performance from a power consumption point of view.
Data rates: Table 13 shows that SDR-SDRAM devices provide a much better performance from data rate point of view. The overall performance of a memory module depends on further characteristics like type of interfaces, memory controller performance, and maximum power consumption and others. Generally an SDRAM based memory module has advantages in terms of access speed.
The lower performance of NAND-Flash is determined by three characteristics. During writing the NAND-Flash devices need to be programmed and this takes a time of about 700 µs per 4 kbyte data (one device page). Additionally the so-called blocks of a NAND-Flash device have to be erased before programming. This consumes another 2 ms per block (64 pages). Last but not least, the selected NAND-Flash devices use an eight bit interface for serial commanding, addressing and data transfer with a maximum operating frequency of 40 MHz.
This lack in performance can be mitigated by mainly two measures. The first straight forward measure is parallel operation of NAND-Flash devices. The second measure is interleaved access to several NAND-Flash devices. Interleaving uses the programming time of a NAND-Flash device to write in parallel the next device. These methods allow increasing the write access performance.
Life time and reliability: NAND-Flash devices provide a limited endurance. This is caused by an inherent wear out mechanism of the Flash memory cells which limits the number of erase and write cycles to about 105 cycles. To mitigate the endurance limitation, most Flash memory systems are equipped with an address management system, which distributes the write accesses rather uniformly over the address space. This technique is called Wear Leveling.
Furthermore the very high device capacity of NAND-Flash devices offers the opportunity to implement a physical address space, which exceeds the required logical user address space by a factor of n. This enhances the wear out limit of the logical addresses by the factor of n too. Hence there are two methods to keep the total count of write accesses to the same physical address below the wear out limit.
Radiation and error rates: In general, sensitivity of electronic devices to space radiation is a major topic and is also shortly discussed here through a comparison of NAND-Flash and SDR-SDRAM devices.
The mass memory system based on NAND-Flash shows clear advantages and fits well to the high storage capacity and moderate data rates of the Sentinel-2 application. The very high storage density of the NAND-Flash devices leads to a reduced number of memory modules with advantages in terms of power consumption, mass and volume. Furthermore this feature improves the reliability and eases the system design from mechanical and electrical points of view.
Figure 85: Photo of the EQM (Engineering Qualification Model), Sentinel-2 MMFU (image credit: Astrium)
Table 14: Parameters of the Sentinel-2 MMFU 94)
For Copernicus operations, ESA has defined the concept and architecture for the Copernicus Core ground segment, consisting of a Flight Operations System (FOS) and a Payload Data Ground Segment (PDGS). Whereas the flight operations and the mission control of Sentinel-1 and -2 is performed by ESOC (ESAs European Space Operations Center in Darmstadt, Germany), the operations of Sentinel-3 and the Sentinel-4/-5 attached payloads to meteorological satellites is performed by EUMETSAT.
The ground segment includes the following elements:
• Flight Operations Segment (FOS): The FOS is responsible for all flight operations of the Sentinel-2 spacecraft including monitoring and control, execution of all platform activities and commanding of the payload schedules. It is based at ESOC, Darmstadt in Germany and comprises the Ground Station and Communications Network, the Flight Operations Control Centre and the General Purpose Communication Network.
• Payload Data Ground Segment (PDGS): The PDGS is responsible for payload and downlink planning, data acquisition, processing, archiving and downstream distribution of the Sentinel-2 satellite data, while contributing to the overall monitoring of the payload and platform in coordination with the FOS.
The Service Segment, geographically decentralized, will utilize the satellite data in combination with other data to deliver customized information services to the final users.
The baseline ground station network will include four core X-band ground stations for payload observation data downlink and one S-band station for Telemetry, Tracking and Control (TT&C). To a limited extent, the system can also accommodate some direct receiving local user ground stations for Near-Real Time applications.
The systematic activities of the PDGS include the coordinated planning of the mission subsystems and all processes cascading from the data acquired from the Sentinel-2 constellation, mainly:
1) The automated and recurrent planning of the satellite observations and transmission to a network of distributed X-band ground stations
2) The systematic acquisition and safeguarding of all spacecraft acquired data, and its processing into higher level products ensuring quality and timeliness targets
3) The recurrent calibration of the instrument as triggered by the quality control processes
4) The automated product circulation across PDGS distributed archives to ensure the required availability and reliability of the data towards users
5) The long-term archiving of all mission data with embedded redundancy over the mission lifetime and beyond.
Figure 86: PGDS context in Sentinel-2 system (image credit: ESA)
Figure 87: The Sentinel-2 ground segment (image credit: ESA)
Figure 88: Physical layout of the PGDS ground stations (image credit: ESA) 95)
• CGS (Core Ground Stations: Matera (Italy), Maspalomas (Spain), Svalbard (Norway), Alaska (USA).
• PAC (Processing/Archiving Center): Farnborough (UK), Madrid (Spain)
• MPC (Mission Performance Center): TBD
• PDMC (Payload Data Management Center): ESA/ESRIN, Frascati, Italy.
Table 15: Sentinel-2 level-1 and level-2 products
Copernicus / Sentinels EDRS system operations:
EDRS (European Data Relay Satellite) will provide a data relay service to Sentinel-1 and -2 and initially is required to support 4 Sentinels simultaneously. Each Sentinel will communicate with a geostationary EDRS satellite via an optical laser link. The EDRS GEO satellite will relay the data to the ground via a Ka-band link. Optionally, the Ka-band downlink is planned to be encrypted, e.g. in support to security relevant applications. Two EDRS geo-stationary satellites are currently planned, providing in-orbit redundancy to the Sentinels. 96)
EDRS will provide the same data at the ground station interface as is available at the input to the OCP (Optical Communications Payload) on-board the satellites, using the same interface as the X-band downlink. The EDRS transparently adapts the Sentinels data rate and format to the internal EDRS rate and formats, e.g. EDRS operates at bit rates of 600 Mbit/s and higher.
With EDRS, instrument data is directly down-linked via data relay to processing and archiving centers, while other data continues to be received at X-band ground stations. The allocation of the data to downlink via X-band or EDRS is handled as part of the Sentinel mission planning system and will take into account the visibility zones of the X-band station network and requirements such as timeliness of data.
Figure 89: Sentinel missions - EDRS interfaces (image credit: ESA)
Copernicus / Sentinel data policy:
The principles of the Sentinel data policy, jointly established by EC and ESA, are based on a full and open access to the data:
• anybody can access acquired Sentinel data; in particular, no difference is made between public, commercial and scientific use and in between European or non-European users (on a best effort basis, taking into consideration technical and financial constraints);
• the licenses for the Sentinel data itself are free of charge;
• the Sentinel data will be made available to the users via a "generic" online access mode, free of charge. "Generic" online access is subject to a user registration process and to the acceptation of generic terms and conditions;
• additional access modes and the delivery of additional products will be tailored to specific user needs, and therefore subject to tailored conditions;
• in the event security restrictions apply to specific Sentinel data affecting data availability or timeliness, specific operational procedures will be activated.
Sen2Coral (SEOM S24Sci Land and Water: Coral Reefs)
The objective of ESA’s SEOM (Scientific Exploration of Operational Missions) Program Sen2Coral is the preparation of the exploitation of the Sentinel-2 mission for coral reefs by developing and validating appropriate, open source algorithm available for the community. The project objectives are the scientific exploitation and validation of the Sentinel-2 MSI (Multispectral Instrument) for mapping (habitat, bathymetry, and water quality) and detection change for coral reef health assessment and monitoring, and algorithm development dedicated to Sentinel-2 capabilities to satisfying these objectives. 102)
To address the extremely interesting and challenging questions posed by this project a consortium of contractors with appropriate background knowledge and skills has been assembled. The consortium comprises:
• ARGANS Limited, UK
• CNR-IREA, Italy
• CS-SI, France
The consortium is complimented by a science team of consultants and partners who are recognized international scientists in the field.
• A critical analysis of feedback from scientists and institutions collected through consultations in ESA and Third Party workshops, symposia and conferences.
• Proposal of potential observation scenarii for Sentinel-2 in terms of required spatial coverage and repeat cycle considering user requirements, existing observation initiatives and synergy with other sensors (Landsat, SPOT sensor families).
• Identifying scientific priority areas and providing guidance for future scientific data exploitation projects. 103)
Tropical coral reefs are globally important environments both in terms of preservation of biodiversity and for the substantial economic value their ecosystem services provide to human communities. Managing and monitoring reefs under current environmental threats requires information on their composition and condition, i.e. the spatial and temporal distribution of benthos and substrates within the reef area. Determining the relative abundance of biotic types such as coral and macroalgae is the key for detecting and monitoring important biotic changes such as phase or regime shifts due to changes in environmental conditions. Coral bleaching events, where stressed corals expel their symbiotic algae and turn white in color, can provide indications of anthropogenic stressors and climate change impacts, while subsequent coral mortality may be a key determinant of future reef state. In addition to monitoring of current status, maps of benthos have the potential to inform management decisions such as the placement of marine protected areas and could in the future be used to seed models to predict ecosystem dynamics.
Figure 90: Image of the North Palau Reef (Western Pacific), acquired with Sentinel-2A on Feb. 10, 2016 (image credit: ESA, Sen2Coral consortium)
Figure 91: Image of Fatu Huku (Pacific) acquired with Sentinel-2A on Feb. 11, 2016 (image credit: ESA, Sen2Coral consortium)
Figure 92: Image of Heron Island, Great Barrier Reef, acquired with Sentinel-2A on Jan. 31, 2016 (image credit: ESA, Sen2Coral consortium)
Background: The degradation of coral reefs is a fact, with 55% of reefs being affected by overfishing and destructive fishing methods, which as the most pervasive threats, whereas 25% of reefs are affected by coastal development and pollution from land, including nutrients from farming and sewage, while one tenth suffer from marine-based pollution (local pressures are most severe in South-East Asia, where nearly 95 per cent of coral reefs are threatened).
In addition the coral reefs’ ecosystems appear to be the first to respond to global climate changes, such as increased sea surface temperature (SST), ultraviolet radiation (UV) and acidification of seawater that results from higher levels of atmospheric CO2 concentration.
Sentinel-2 MSI Data Acquisition:
The MSI (Multispectral Instrument) of the Sentinel-2A mission offers several potential technical advantages in the remote sensing of coral reefs due to:
• 10 meter spatial resolution allowing improvement in visual interpretation of reef features, classification accuracy and bathymetry.
• Additional water penetrating optical band improving consistency under varying water conditions, reducing uncertainty in bottom type and bathymetric mapping, deeper bathymetric accuracy and ability to determine water optical properties.
• Additional NIR/SWIR bands enabling more consistent and accurate determination of atmospheric and surface glint correction.
• Short re-visit time enabling the use of image series to determine fundamental uncertainties for change detection.
• Addresses the current limited remote sensing acquisition plan covering the coast areas.
Figure 93: Overview of processing steps (image credit: Sen2Coral consortium)
Algorithm Development & Data Processing:
The objective “to develop and validate new algorithms relevant for coral reef monitoring based on Sentinel-2 observations” will be addressed by parameterizing existing models for processing hyper-spectral & multi-spectral data and developing pre-processors for these models to build Sentinel-2 data processing algorithms for the retrieval of coral reefs’ static and dynamic characteristics. The code developed will be made available open source.
Validation and uncertainty analysis will involve both comparing Sentinel MSI performance versus Landsat-8 on coral reef mapping objectives and comparing coral reef monitoring products against in situ data from reef sites representative of different composition and structure.
To design, verify and validate three coral reef monitoring products making the best use of Sentinel-2 MSI mission characteristics:
• Habitat mapping of coral reefs
• Coral reef change detection
• Bathymetry over coral reefs.
A 6 day field campaign around the South Pacific island of Fatu Huku was undertaken by French scientist Antoine Collin to collect in-situ data to test and validate the capabilities of the Sentinel-2 satellite to monitor coral reef bleaching.
Fatu Huku Island in French Polynesia was chosen as the survey site because of the presence of developed coral reefs and it is an area water temperatures are high as a result of the current El Niño event. During the survey, water temperature exceeding 30°C were recorded and coral bleaching, the expulsion of the symbiotic algae that provide energy from sunlight to the coral, was observed to be taking place.
Data collected from this field campaign complements archives of in-situ data collected over previous years from coral reef sites across the globe such as at Heron Island and Lizard Island, in Australia, and reefs around Palau, in the western Pacific Ocean.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).
The Sentinel series:
Provides data continuity for: