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.
Table 4: AOCS performance requirements in normal mode
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).
Figure 13: Twin observation configuration of the Sentinel-2 spacecraft constellation (image credit: ESA)
• 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 May 2019, the previously single large Sentinel-2 file has been split into two files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the Sentinel-2 mission and its imagery in the period 2019
Mission status and imagery of 2019
• June 14, 2019: The Copernicus Sentinel-2 mission takes us over the island of Bali, one of the 27 provinces of Indonesia. - Indonesia has more volcanoes than any other country in the world, owing to its position on the Pacific Ring of Fire. The islands of Java, Lombok, Sumbawa and Bali lie over a subduction zone where the Indo-Australian plate slides under the Eurasian plate, creating frequent seismic activity. 40)
- The central volcano, which is a predominant feature in this image, is called Mount Agung or Gunung Agung, meaning ‘Great Mountain'. The symmetrical and conical stratovolcano is the highest in Bali, standing at over 3000 m. When it erupted in 1964, it was one of the largest eruptions of the 20th century, claiming over 1000 lives and leaving more than 80,000 people homeless.
- After being dormant over the following 50 years, Agung reawakened in November 2017. Fortunately, small earthquakes warned authorities in time for 100,000 people to be evacuated to safety. Agung still remains very active, with frequent small eruptions spewing ash and lava, causing flights to be cancelled.
- In the image of Figure 17, a bright orange spot can be seen in the volcano's crater. Recent research provides evidence that Agung and its neighboring Batur volcano, visible northwest of Agung, may have a connected magma plumbing system. 41)
- Mount Batur, or Gunung Batur, has an unusual shape, with the volcanic cone visible in the center of two concentric calderas.
Figure 17: Dotted with clouds, Mount Seraya is visible on the peninsula that juts to the east. Its volcanic rock creates a rugged terrain, but is surrounded by lush vegetation. The area is well known for its many Hindu temples, including the famous Lempuyang Temple, known locally as Pura Luhur Lempuyang. This image of Sentinel-2, captured on 2 July 2018, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• June 7, 2019: The Copernicus Sentinel-2 mission takes us over Lake Valencia, in northern Venezuela. This false-color image (Figure 18) was processed in a way that makes vegetation of the Henri Pittier National Park, north of the lake, appear in fluorescent green. These bright colors contrast with the blackness of the lake. 42)
- Unfortunately, the inflow of untreated wastewater from the surrounding industrial and agricultural lands has led to the lake to become contaminated. The lake now suffers from algal blooms and between 1960 and 1990 it lost over 60% of its native fish species.
- It was at this very lake that the German naturalist and explorer, Alexander von Humboldt, witnessed how human behavior could cause harm to our natural ecosystem and climate. During his travels in the late 18th century, he noted the surrounding barren land which had been cleared for plantations and crops for sugar and tobacco. He attributed the decreasing water levels in the lake to climate change.
- "When forests are destroyed, the springs are entirely dried up," he wrote in his travel report, the Relation historique du voyage aux régions équinoxiales du nouveau continent (1814-17). "The beds of the rivers are converted into torrents whenever great rains fall on the heights.... Hence it results, that the destruction of forests, the want of permanent springs, and the existence of torrents, are three phenomena closely connected together."
- The now poor-quality waters of Lake Valencia prevent the development of tourism and recreational activities in the region.
Figure 18: With a surface area of 370 km2, Lake Valencia formed a few million years ago and is now a reservoir for the cities of Valencia on the west shores and Maracay on the east shores. This image, which was captured on 2 February 2019 with Sentinel-2, 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)
• May 31,2019: The Copernicus Sentinel-2 mission takes us over El Salvador, the smallest and most densely populated country in Central America. 43)
- Lake Guija, visible in the top left of the image (Figure 19), lies on the border between El Salvador and Guatemala. The lake once formed part of the Mayan Empire and legend says that it also hides an ancient city beneath its waters.
- El Salvador sits on the eastern edge of the Pacific Ring of Fire, and despite being a small country, it has 25 volcanoes. The volcano complex of the Cerro Verde National Park can be seen dotted with clouds in the lower left of the image.
Figure 19: Captured on 30 January 2019, this false-color image was processed in a way that makes vegetation appear red. 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 Cerro Verde National Park is over 2000 m above sea level. It is home to a cluster of three volcanoes surrounded by lush rainforest. Santa Ana, the highest volcano in the country, is clearly visible with its circular peak.
- Izalco, located directly below Santa Ana, was born in 1770 and has erupted more than 50 times since. Its odd color and shape is due to these frequent eruptions.
- The large body of water to the right of Izalco is Lake Coatepeque, one of the largest crater lakes in the country. It is home to a variety of aquatic life and has remnants of ancient volcanic activity such as hot springs and openings emitting steam known as fumaroles.
- The large volcano in the right of the image is named San Salvador. It is adjacent to the capital, with which it shares its name. The city sprawls close to the nearby Lake Ilopango, which occupies the crater of an extinct volcano.
• May 24, 2019: The image of Figure 20 depicts the fragmented coast of western Pakistan, part of the Indus River Delta. A river delta forms when sediment carried from the river enters a stagnant body of water, creating an alluvial fan, which in this case extends 150 km along the coastline. The Indus River, visible on the right, veers through the Sindh Province and is one of the longest rivers in the world, rising in Tibet and flowing around 3000 km before emptying into the Arabian Sea. 44)
- The Indus Delta consists of creeks, swamps, marshes and the seventh largest mangrove forest in the world.
- However, owing to major irrigation works and dams built on the river, as well as low rainfall, the amount of silt discharged into the sea has reduced, affecting the mangrove and local community significantly. A huge proportion of the delta has been lost and the survival of the delta freshwater species, including the Indus river dolphin, are at risk.
- Also responsible for pollution is the port city of Karachi, which is partially visible in the top left of the image.
- To the top right, there are two important bodies of water on the edge of the stony desert, both of which are also wildlife sanctuaries. The artificial, square-shaped Haleji Lake, was expanded in World War II, for the use of additional water for the troops. The freshwater lake supports an abundance of aquatic vegetation, and is home to a number of species of birds.
- To the far right, the freshwater Keenjhar Lake is a major source of drinking water for Karachi, as well as for Thatta, which is to the right of the yellow-beige patch of land.
- Both lakes, as well as the River Indus Delta, are sites of wetland designated to be of international importance under the Ramsar Convention – an international treaty for the conservation and sustainable use of wetlands.
Figure 20: Captured on 14 April 2018 by the Copernicus Sentinel-2A satellite, this image shows western Pakistan and an important wetland area. 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)
• May 17, 2019: The Copernicus Sentinel-2 satellite takes us over the Po Valley in northern Italy. The Po River, the longest river in Italy, flows over 650 km from west to east across the country, and ends at a delta projecting into the Adriatic Sea near Venice. The river flows through some of Italy's important cities of the north. 45)
Figure 21: Image of the Po Valley, the most densely populated area in Italy, accounting for nearly half of the national population. This composite image contains several images captured between June 2018 and February 2019, allowing us to see the area free from clouds and smog. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018–19), processed by ESA, CC BY-SA 3.0 IGO)
- On the very left of the image, next to the river, the city of Turin can be seen. A business and cultural center, Turin is the capital of the Piedmont region. Rich in history, the city is home of the Shroud of Turin, a famous religious relic, as well as the Residences of the Royal House of Savoy. Turning to modern day, several International Space Station modules, such as Harmony and Columbus, were manufactured in Turin.
- Moving east, the city of Milan can be seen nestling below the Alps. Although Milan is the second most populous city in Italy after Rome, the wider metropolitan area extends over Lombardy and eastern Piedmont, making it the largest metropolitan area in Italy.
- Further east, the blue body of Lake Garda can be seen to the left of Verona. With an area of 370 km2, Garda is the largest lake in Italy and the third largest in the Alpine region. East of the lake is the Adige River, flowing south before curving east toward Verona. The city of Verona has been awarded World Heritage Site status by UNESCO because of its urban structure and architecture such as the circular Roman amphitheater.
- Along the coast, the turquoise colors of the Venetian lagoon and the islands that make up the city of Venice are visible. Famous for its musical and artistic cultural heritage, millions of tourists flock to the archipelago every year.
- As the Po River nears the Adriatic Sea, its agricultural landscape dominated by fields can be seen. Agriculture is one of the main industries in the Po Basin because of the fertile soils. Cereals, including rice, and a variety of vegetables are commonly grown in this area.
- The main arms of the river push the delta into the sea. An important ecosystem, the area has been a regional park since 1988 and a biosphere reserve since 2015.
• May 10, 2019: ESA's Living Planet Symposium – the largest Earth observation conference in the world – is being held on 13–17 May in Milan, Italy. Held every three years, these symposia draw thousands of scientists and data users from around the world to discuss their latest findings on how satellites are taking the pulse of our planet. 46)
- Over 4000 participants will gather at the largest congress center in Europe: the MiCo Convention Center. With its iconic architecture, this modern building has become a landmark. The event will not only see scientists present their latest findings on Earth's environment and climate derived from satellite data, but will also focus on Earth observation's role in building a sustainable future and a resilient society.
- Milan is the second biggest city in Italy and, like most large urban environments, it suffers from air pollution. While there is an effort to reduce the emission of pollutants, the city is also incorporating more vegetation into its development plans. This not only makes the environment more pleasant, but the plants also help soak up greenhouse gases such as carbon dioxide.
- The Bosco Verticale, or the Vertical Forest, for example, aims to inspire the need for urban biodiversity. The two tower blocks have plants and trees planted on its façade, and are located just north of the historical center. The vegetation covering both towers is equivalent to 20,000 m2 of forest and home to a variety of birds and butterflies. This vegetation absorbs approximately 30 tons of carbon dioxide per year.
- Another example of the city's efforts to ‘go green', is the Biblioteca degli Alberi, or Library of Trees, visible next to the Bosco Verticale. With its geometric design and irregular patches of land, the gardens are home to over 100,000 plants and trees, interlinked with pedestrian and bike paths.
- But it doesn't stop there, the local government aims to plant another three million trees by 2030.
Figure 22: In this high-resolution image, captured by Copernicus Sentinel-2 orbiting around 800 km above, the center of Milan is clearly visible. The famous Milan Cathedral or Duomo di Milano with its surrounding square can be seen in the center of the image. Taking six centuries to complete, it is one of the largest gothic cathedrals in the world. This image, also featured on the Earth from Space video program, was captured on 24 September 2018 by the Copernicus Sentinel-2 mission. (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• May 03, 2019: The Copernicus Sentinel-2 mission takes us over an area in southern Germany, where approximately 15 million years ago an asteroid crashed through Earth's atmosphere. The high-speed impact formed what is now known as the Ries crater. Although difficult to spot at first in the image, the result of the impact is actually still visible today. 47)
- With a diameter of 26 km, the rim of the crater can be seen as a semi-circle in the image, delineated by dark green forest to the south. The flat ‘crater floor' is ideally suited for agricultural use and the corresponding fields mark the crater's extent.
- The medieval town of Nördlingen (in the Donau-Ries district of Bavaria) was built in its depression. The historical center, approximately 1 km wide, appears as a reddish circle, visible with its red rooftops surrounded by a wall.
- The asteroid was estimated to be travelling at 70,000 km per hour, and when it made impact with Earth, the high-speed force exposed the rock to intense pressure and heat, over 25,000°C. The impact led to the creation of over 70,000 tons of microscopic diamonds, each around 0.2 mm in size.
- Overlooked by the town's inhabitants, the stone buildings were constructed almost entirely with diamond-encrusted rock. Details on the impact can be found in the well-known Rieskrater Museum in Nördlingen.
- For centuries, Nördlingen locals believed the town was built in the crater of a volcano. But in the 1960s two American scientists (Gene Shoemaker and Edward Chao) proved that the depression was, in fact, caused by a meteorite impact. Today, visitors around the world gather to marvel at this glittering town, also known as the backdrop to the original Willy Wonka and the Chocolate Factory film.
Figure 23: The Sentinel-2 satellite of ESA captured this image of the Nördlinger Ries on 1 July 2018, it 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)
Figure 24: An aerial view of the town of Nördlingen inside the meteorite Ries crater
• April 26, 2019: The Copernicus Sentinel-2 mission takes us over Australia's northeast state of Queensland, where a large amount of sediment is visible gushing into the Coral Sea, close to the Great Barrier Reef lagoon. 48)
- In early 2019, many areas in Queensland received more than their annual rainfall in less than a week. The downpour led to millions of dollars' worth of damage, including homes being destroyed and the loss of almost 500,000 cattle.
- The Burdekin River rises on the northern slopes of Boulder Mountain and flows close to 900 km before emptying into the Coral Sea. The Burdekin River is one of Australia's larger rivers by discharge volume, and is a major contributor of sediment and freshwater to the Great Barrier Reef lagoon.
- The Great Barrier Reef, the world's largest coral reef, extends for 2000 km along the northeast coast of Australia and covers almost 350,000 km2. The reef is an interlinked system of about 3000 reefs and 900 coral islands, divided by narrow passages. An important area of biodiversity, the reef was made a UNESCO World Heritage Site in 1981.
- The sand-color sediment plume can be seen stretching over 35 km from the coast, dangerously close to the vivid turquoise reef. The blues of the coral contrast with the dark-colored waters of the Coral Sea.
- The coral reef suffers regular damage, more than half of the reef has disappeared over the last 30 years owing to climate change, coral bleaching and pollution. Large quantities of sediment that flow out from rivers carry chemicals and fertilizers from inland farms. The sediment blankets the coral, and reduces the amount of light, as well as potentially causing harmful algae blooms.
- Data from Copernicus Sentinel-2 plays a key role in providing information on pollution in lakes and coastal waters. Frequent coverage is also fundamental to monitoring floods.
Figure 25: This image was captured a few days after the torrential rain, and shows the muddy waters flowing from the Burdekin River into the Coral Sea. It was captured on 10 February 2019, it 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)
• April 19, 2019: The Copernicus Sentinel-2 mission takes us over one of the most remote islands in the world: Easter Island. Located in the Pacific Ocean, over 3500 km off the west coast of South America, this Chilean island is also known as Rapa Nui by its original inhabitants. The island was given its current name the day when the Dutch navigator Jacob Roggeveen arrived on 5 April 1722 – on Easter Sunday.
Figure 26: Easter Island, with a size of 163.6 km2 and a population of 7500, is a Chilean island in the southeastern Pacific Ocean, at the south-easternmost point of the Polynesian Triangle in Oceania. A Sentinel-2 acquired this image on 7 April 2019, it 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 island is famous for its monolithic stone statues, called Moai, said to honor the memory of the inhabitants' ancestors. There are nearly 1000 scattered around the island, usually positioned near freshwater. Many are located near the Rano Raraku volcano, on the southeast coast. The white edges along the southern coast show the harsh waves colliding with the shore.
- An interesting feature of the image is the ochre-orange color of the Poike – the peninsula on the eastern end of the island. In ancient times, it is said that there was a lot of vegetation on the island. However, land clearing for cultivation and the Polynesian rat played a role in deforestation, leading to the erosion of the soil, particularly in the east.
- Several reforestation projects have been attempted, including a eucalyptus plantation in the middle of the island, visible in dark green. The brown patch to the right of the plantation is likely to be a burn scar from a wildfire.
- The majority of the island's inhabitants live in Hanga Roa, the main town and harbor on the west coast, clearly visible in the image. Interestingly, the long runway of the island's only airport was once designated as an emergency landing site for the US space shuttle.
- At the very edge of the southwest tip of the island lies Ranu Kao, the largest volcano on the island. Its shape is distinctive owing to its crater lake, one of the island's only three natural bodies of water.
- Many tourists are drawn to the island for its mysterious history and isolated position. What is relatively unknown is the existence of two small beaches on the northeast coast. Anakena beach has white, coral sand, while the smaller Ovahe beach, surrounded by cliffs, has pink sand.
• April 5, 2019: This week, ESA is focusing on its core Basic Activities, which, for Earth observation, include preserving precious data. Long-time series of datasets are needed to determine changes in our planet's climate so it is vital that satellite data and other Earth science data are preserved for future generations and are still accessible and usable after many years. This example includes a series of satellite images going back to 1998. 49) 50) 51)
Figure 27: This long-time series of over 150 images, captured by the US Landsat series and the Copernicus Sentinel-2 missions, shows the development over 21 years of an important land reclamation project in the Western Desert of Egypt. This comparison highlights how this agricultural project has developed between January 1998 and March 2019. These images are also featured on the Earth from Space video program (image credit: USGS/contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
- Egypt is over 95% desert, making a very small proportion of its land suitable for agriculture. As the demand for food grows, the need for agricultural development in desert areas has intensified.
- This set of images shows an important land reclamation project in East Oweinat, in the Western Desert of Egypt.
- The circular shapes in the images, each approximately 800 meters wide, indicate the irrigation method used here, with water being supplied by a set of sprinklers rotating around a central pivot. Fossil water, stored underground for thousands of years, comes from the Nubian Sandstone Aquifer, the largest known fossil aquifer discovered.
- The water in the East Oweinat area is low in salt content, making it ideal for cultivation purposes. Crops such as wheat, potatoes and barley are grown here, and are exported through the Sharq El Owainat airport, visible in the right side of the image.
- Another interesting feature in this time series is the drifting sand dunes visible mainly in the upper left corner, which is a phenomena common in sandy deserts with constant winds.
- Changes over the last 21 years are clearly visible when more fields develop, but the data also show other subtle changes within the fields themselves. This data can be used to monitor changes in land-cover over time. Long-term preservation of the satellite data from different missions ensures that changes to the land can be monitored by analyzing data from the archives.
• March 22, 2019: Today is World Water Day, but with millions of people in Mozambique, Malawi and Zimbabwe struggling to cope in the aftermath of Cyclone Idai, the notion of water shortages may not be at the forefront of our minds right now. Even so, floods, like we see here, lead to real problems accessing clean water. Whether the problem is inundation or water scarcity, satellites can help monitor this precious resource. 52)
Figure 28: Water levels in the Theewaterskloof Dam in South Africa's Western Cape Province have dropped dramatically over recent years. The dam is the major source of water for domestic and agricultural uses in the region. Over the last year, this lack of water has caused the production of grain to drop by more than 36% and the production of wine grapes to drop by 20%, for example. It is estimated that it will need to receive at least three years of good winter rainfall for it to return to its earlier healthy level. Thanks to the TIGER initiative, the Stellenbosch University is applying machine-learning algorithms to data from the Copernicus Sentinel-1 and Sentinel-2 missions to carefully monitor the situation (video credit: ESA, the video contains modified Copernicus Sentinel data (2017–18), processed by ESA, CC BY-SA 3.0 IGO)
- With more than two billion people living without safe water and around four billion people suffering severe water scarcity for a least one month a year, achieving water for all is a huge challenge. And, coupled with a growing global population and climate change, it's likely to become even more challenging.
- Water allows life on Earth to thrive. The same water has existed for billions of years, cycling through the air, oceans, lakes, rocks, animals and plants and back again. The water we drink today may have once been inside a dinosaur!
- Our most precious resource is probably the strangest thing in the universe. Defying the laws of chemistry, it's the only known substance that can exist naturally as a gas, liquid and solid within a relatively small range of air temperatures and pressures found on the surface of Earth.
- Although there is no shortage of water on Earth, less than 3% is freshwater. Then the vast majority of this is locked up in icecaps and glaciers, leaving less than 1% available for drinking and other domestic needs, agriculture and industrial processes, and more.
- Freshwater is the single most important natural resource on the planet, but we are very rapidly running out of it – as illustrated by dwindling water bodies.
Figure 29: The Earth's water cycle. The total amount of water present on the Earth is fixed and does not change. Powered by the Sun, water is continually being circulated between the oceans, the atmosphere and the land. This circulation and conservation of the Earth's water, known as the water cycle, is a crucial component of our weather and climate (image credit: ESA/AOES Medialab)
Figure 30: Glacial decline (10 December 2018). 53) A paper published recently in Nature Geosciences describes how a multitude of satellite images have been used to reveal that there has actually been a slowdown in the rate at which glaciers slide down the high mountains of Asia. This animation simply shows how glaciers in Sikkim in northeast India have changed between 2000 and 2018. One of the images is from the NASA/USGS Landsat-7 mission captured on 26 December 2000 and the other is from Europe's Copernicus Sentinel-2A satellite captured on 6 December 2018 [image credit: NASA/USGS/University of Edinburgh/ETH Zurich/ the image contains modified Copernicus Sentinel data (2018)]
• March 22, 2019: The 22 March is World Water Day, which focuses on the importance of freshwater. The Sustainable Development Goals of the United Nations aim to achieve a better and more sustainable future. Goal number 6 focuses on ensuring the availability and sustainable management of water for all by 2030. This image takes us over Lake Chad at the southern edge of the Sahara, where water supplies are dwindling. 54)
- Once one of Africa's largest lakes, Lake Chad has shrunk by around 90% since the 1960s. This receding water is down to a reduction of precipitation, induced by climate change, as well as development of modern irrigation systems for agriculture and the increasing human demand for freshwater.
Figure 31: This comparison shows Lake Chad imaged on 6 November 1984 by the US Landsat-5 satellite and on 31 October 2018 by the Copernicus Sentinel-2A satellite. The rapid decline of the lake's waters in just 34 years is clearly to see. These images are also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA (For Landsat image: USGS/ESA), CC BY-SA 3.0 IGO)
- Straddling the border of Chad, Niger, Cameroon and Nigeria, the lake is a major source of freshwater for millions of people in the area. It is also a source for irrigation, fishing and it was once rich in biodiversity.
- As the lake continues to dry up, many farmers and herders move towards greener areas or move to larger cities to seek alternative work. Several attempts have been made to replenish these shrinking waters, however little progress has been achieved.
- The borders of the lake's body are only partly visible in the most-recent image – as the majority of the shoreline is swamp and marsh. The Chari River, visible snaking its way towards Lake Chad at the bottom of the image, provides over 90% of the lake's waters. It flows from the Central African Republic following the Cameroon border from N'Djamena, where it joins with its main tributary the Logone River.
- The demand for water is growing inexorably. Access to water is vital – not only for drinking, but also for agriculture, energy and sanitation. By providing measurements of water quality and detecting changes, the Copernicus Sentinel-2 mission can support the sustainable management of water resources.
• March 22, 2019: World Water Day! 55) The 66th United Nations General Assembly adopted a resolution declaring the Water Action Decade from 22 March 2018 to March 2028. The UN Water Action Decade is pursuing two goals:
- Spreading knowledge on the topic of water and water pollution control, including information on water-related Sustainable Development Goals (SDGs);
- more effective communication measures to implement water-related goals.
Figure 32: The UN Sustainable Goal 6 is crystal clear: Water for all by 2030. For World Water Day we take a look at ways that space can help this global challenge. While Earth-observing satellites monitor our precious water resources, technologies developed for human space missions also serve global needs in harsh environments here on Earth (video credit: ESA)
• March 21, 2019: The UN International Day of Forests is held annually on 21 March. It raises awareness of the importance of all types of forest and the vital role they play in some of the biggest challenges we face today, such as addressing climate change, eliminating hunger and keeping urban and rural communities sustainable. As the global population is expected to climb to 8.5 billion by 2030, forests are more important than ever. 56)
- This year, the International Day of Forests put a particular focus on education, but also on making cities a greener, healthier and happier place to live. In cities, trees can help many urban challenges. They act as air filters by removing pollutants, reduce noise pollution, offer shade and provide an oasis of calm in an otherwise busy urban environment, for example.
- While Bangkok, which is home to over eight million people, is an example of ongoing efforts being made to increase green spaces to improve city life, it also has a much-valued green haven, which can be seen in the center of the image.
- This horseshoe or lung-shaped, green oasis is Bang Kachao and is in the middle of the bustling city.
- Rich in gardens, mangroves and agricultural fields, the 2000 hectares of land is a significant contrast to the vastness of the city's urban sprawl. Fighting Bangkok's traffic and air pollution, Bang Kachao's lush green forest provides the dense city, and the surrounding Samutprakan province, with a flow of fresh air.
Figure 33: Captured on 22 January 2019 by the Copernicus Sentinel-2B satellite, this true-color image shows Thailand's most populous city Bangkok, and its ‘Green Lung' Bang Kachao. The government-protected oasis of green is wrapped around the Chao Phraya River, which is seen flowing through the city of Bangkok before emptying into the Gulf of Thailand (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
Legend to Figure 33: Bang Kachao is an artificial island formed by a bend in the Chao Phraya River and a canal at its western end. It lies south of the Thai capital Bangkok in the Phra Pradaeng District of Samut Prakan Province. The island, covering 16 km2, has been traditionally agricultural with only a relatively small population.
• March 21, 2019: Billions of image pixels recorded by the Copernicus Sentinel-2 mission have been used to generate a high-resolution map of land-cover dynamics across Earth's landmasses. This map also depicts the month of the peak of vegetation and gives new insight into land productivity. 57)
- Using three years' worth of optical data, the map can indicate the time of vegetation peak and variability of vegetation across seasons. Developed by GeoVille, an Austrian company specialized in the analysis of satellite data, this land-cover map dynamics map uses Copernicus Sentinel-2 archive data from 2015-18, and gives a complete picture of variations of vegetation. The map is displayed at a resolution of 20 m, however a 10 m version is available on request.
Figure 34: Data from the Copernicus Sentinel-2 mission has been used to generate a new high-resolution map of vegetation across Earth's entire landmass. The new map depicts global vegetation dynamics and gives insight into land productivity. The time of vegetation peak i.e. the month at which greenness maximum occurs is shown in red (spring) and green (summer) to blue tones (autumn and winter.) The variability of vegetation greenness is represented by light tones in low amplitude areas such as managed grasslands, while high amplitudes are represented by saturated color tones. Areas with low biomass such as urban areas and open bodies of water are shown in black, while areas with higher biomass appear in grey and white tones (image credit: ESA, the image contains modified Copernicus Sentinel data (2016–18), processed by GeoVille)
- It can, for example, support experts working with land-cover classification and can serve as input for services in areas such as agriculture, forestry and land-degradation assessments.
- "In particular, we use this as a basis to develop services for the agrofood industry and farmers growing potatoes and other crops, as well as information on how vegetation changes over the year," explains Eva Haas, Head of GeoVille's Agricultural Unit (Innsbruck, Austria).
Figure 35: The inland delta of the Niger River spreads across central Mali – a unique ecosystem in West Africa. A result of the Niger river flowing into the sandy Sahelian plains, this vast network of channels, swamps, and lakes mitigates the severity of the arid climate by supplying water during October and November (blue). In contrast the image shows the sparse rain fed vegetation in the surrounding region (dark green). This image is part of a new high-resolution map of vegetation across Earth's entire landmasses generated with Copernicus Sentinel-2 data (image credit: ESA, the image contains modified Copernicus Sentinel data (2016–18), processed by GeoVille)
- The land-cover dynamic layer was produced with GeoVille's processing engine LandMonitoring.Earth, a fully-automated land-monitoring system built on data streams from the Copernicus Sentinel-1 and Sentinel-2 missions, as well as ESA third party missions such as the US Landsat missions.
- "Using the system, we processed the complete Copernicus Sentinel-2 image archive along with artificial intelligence, machine learning and big data analytics," explains Michael Riffler, Head of Research and Development at GeoVille.
- "However, the key is the dense time-series of the Copernicus Sentinel-2 data which allows this information to be retrieved for the first time. To date, we have processed more than 23 billion pixels."
Figure 36: The image shows different crop types around Emmelrod in the Netherlands. Here, green shows summer crops, red is potatoes, orange is market crops, yellow is cereals and blue depicts grassland. The area is important for the agrofood sector and, in particular, has strong ties to the international potato industry. By integrating Copernicus Sentinel-2 based crop-type monitoring directly into existing industry workflows, the agrofood industry can gain information about the growth and potential yield of crops, potatoes in particular, including the impact of ongoing droughts (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by GeoVille)
- The development has been done through ESA's Earth observation innovation hub – Φ-lab, and has been implemented by GeoVille and its subsidiary in the Netherlands – GEO4A.
- "This map forms an excellent foundation for other – more specialized – land cover classifications, whose development and deployment can be further accelerated by applying machine learning and AI," says Iarla Kilbane-Dawe, the head of ESA's Φ-Lab in Frascati, Italy.
- The LandMonitoring.Earth system is designed to efficiently implement major client solutions such as the European Copernicus Land Monitoring Service products. Experts can specify desired land monitoring data for any place on the globe for any given time period, and receive a quality-controlled output, depending on the required geographic coverage and frequency.
- The idea is to make information available to non-experts along with the specific resources and tools that they need.
• March 15, 2019: The Copernicus Sentinel-2 mission takes us over Nairobi, one of the fastest growing cities in East Africa. 58)
- The population of Nairobi has increased significantly in the last 30 years, with rural residents flocking to the city in search of employment. The city, visible in the center of the image, now has a population of over three million, with the vast majority spread over 200 informal settlements.
- Kibera, which can be seen as a light-colored patch at the south-western edge of the city, is considered one of the largest urban slums in Nairobi. Most residents live in small mud shacks with poor sanitation, a lack of electricity and limited access to clean water.
- While migration provides economic benefits to the city, it also creates environmental challenges. Owing to its urbanization, the city has spread into green spaces such as the nearby parks and forests. In this image, the densely populated area is contrasted with the flat plains of Nairobi National Park, directly south of the city. The 117 km2 of wide-open grass plains is colored in light-brown. The park is home to lions, leopards, cheetahs and has a black rhino sanctuary.
- The dark patches in the image are forests. The Ngong Forest, to the west of the city, includes exotic and indigenous trees, and hosts a variety of wild animals including wild pigs, porcupines, and dik-diks.
- To the north of the city, the dark Karura Forest is visible. The 1000 hectare urban forest features a 15 m waterfall, and hosts a variety of animals including bush pigs, bushbucks, suni and harvey's duiker, as well as some 200 bird species.
- Although Africa is responsible for less than 5% of global greenhouse-gas emissions, the majority of the continent is directly impacted by climate change. Rapid population growth and urbanization also exposes residents to climate risks.
- On 14 March 2019, the first regional edition of the One Planet Summit took place at the UN Compound, which is in the north of the city. The One Planet Summit, part of the UN Environment Assembly, focuses on protecting biodiversity, promoting renewable energies and fostering resilience and adaptation to climate change.
- Data from Copernicus Sentinel-2 can help monitor changes in urban expansion and land-cover change. Copernicus Sentinel-2 is a two-satellite mission. Each satellite carries a high-resolution camera that images Earth's surface in 13 spectral bands.
- As delegates gather in Nairobi for the UN Environment Assembly, ESA is saddened by the news of the Ethiopian Airlines accident. Lives lost included those working for organizations also dedicated to achieving a better world for all and who were travelling to the assembly. — Our thoughts are with the families, colleagues and friends of those affected.
Figure 37: This image of the Sentinel-2 mission was captured on 3 February 2019, is also featured on the Earth from Space video program
- The Tiber River can be seen snaking its way southwards in the image. The third longest river in Italy, it rises in the Apennine Mountains and flows around 400 km before flowing through the city of Rome and draining into the sea near the town of Ostia. The Tiber River plays an important role in sediment transport, so coastal waters here are often discolored. However, the recent rains resulted in a large amount of sediment pouring into the Tyrrhenian Sea, as this image shows. The sediment plume can be seen stretching 28 km from the coast, carried northwest by currents.
Figure 38: The Copernicus Sentinel-2B satellite captured this true-color image on 5 February 2019, just three days after heavy rainfall in Rome and the surrounding area of Lazio, Italy. It shows sediment gushing into the Tyrrhenian Sea, part of the Mediterranean Sea. The downpour on 2 February led to flooded streets, the closing of the banks of the Tiber River and several roads (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• February 22, 2019: The Copernicus Sentinel-2A satellite takes us over western Sicily and the islands of Favignana and Levanzo in Italy. The image of Figure 39 shows a false-color image included the near-infrared channel and was processed in a way, that makes vegetation appear in bright red. 60)
- The bright turquoise colors, near the port city of Trapani, at the top of the image, and the Isola Grande in the middle of the image, depict salt marshes. Both the Saline di Trapani e Paceco Nature Reserve and the Stagnone Nature Reserve with their shallow sea waters, windy coast and abundant sunshine, make the area between Marsala, at the bottom of the image, and Trapani an ideal place for salt production.
- The reserve consists of more than 1000 hectares of landscape dotted with windmills, migratory birds such as flamingos and light-red lagoons visible in summer. This greenish-blue color is heavily contrasted with the black of the open Mediterranean Sea.
- The islands, off the coast, are rich in history, both boasting Paleolithic and Neolithic cave paintings. The most famous being the Grotta del Genovese on the picturesque island of Levanzo, at the top left of the image. The cave was discovered only in 1949 and is estimated to be between 6000 and 10 000 years old.
- Below, the butterfly-shaped island of Favignana, known for its tuna fisheries and a type of limestone known as tufa rock, is the largest of the Aegadian islands. In 241 BC, one of the Punic Wars' naval battles was fought at the Cala Rossa (Red Cove), named after the bloodshed.
Figure 39: Captured on 3 September 2018 by the Copernicus Sentinel-2A satellite, this false-color image shows part of western Sicily in Italy and two of the main Aegadian Islands: Favignana and Levanzo. 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)
• February 15, 2019: Copernicus Sentinel-2 brings you some of the jewels of the Maldives for Valentine's week. Arguably one of the most romantic destinations in the world, the Maldives lie in the Indian Ocean about 700 km southwest of Sri Lanka. The nation is made up of more than 1000 coral islands spread across more than 20 ring-shaped atolls. 61)
- Like many low-lying islands, the Maldives are particularly vulnerable to sea-level rise. In fact, the Maldives are reported to be the flattest country on Earth, with no ground higher than 3 m and 80% of the land lying below 1 m. With satellite records showing that over the past five years, the global ocean has risen, on average, 4.8 mm a year, rising seas are a real threat to these island jewels.
- With the promise of white sandy beaches, azure ocean waters and coral reefs, this romantic getaway draws more than 600,000 tourists every year. While tourism is extremely important for the national economy, development on these pristine islands create pressures, such as ensuring an adequate supply of freshwater, treating sewage and potential pollution entering the ocean. Other environmental issues facing the Maldives include the loss of habitats of endangered species and the damage to the coral reefs.
- The Maldives are undoubtedly fragile but one of the most beautiful places on the planet, and a place to be loved and cherished now and in the future. Valentine's Day reminds us of love and maybe this year and beyond it's good to remember to love our planet.
Figure 40: A number of these little islands can be seen in the image, with the turquoise colors depicting clear shallow waters dotted by coral reefs and the red colors highlighting vegetation on land. Different cloud formations can also be seen, the difference in appearance is likely to be due to the different height above the surface. This image, which was captured on 26 August 2015, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by ESA, CC BY-SA 3.0 IGO)
- The region tends to be very arid and this false-color image has been processed to highlight different types of rock, soil and sand in pinks, purples and yellows.
- Part of the ‘great north road' can also been seen running from the bottom-left to the top-right. The road is one of the best in the country, linking Nairobi in the south of the country to Ethiopia. The northern 500-km stretch from Isiolo to the Kenyan–Ethiopian border town of Moyale took about nine years to build and was completed recently, but has reduced travel time from Nairobi to Moyale from three days to about 12 hours and opened up new opportunities for trade and business. Moyale can be seen in the top-right of the image.
Figure 41: The bright green at the top of the image depicts vegetation, but the rest of the area appears relatively devoid of vegetation. Several dry river beds can also be seen etched into the landscape and the black shape in the middle-left appears to be an area of freshly burnt land. The lack of water has, at times, led to clashes between clans over access to water and pasture for cattle. When the rains do come, however, this dry dusty land can burst into life and turn a rich green. This Copernicus Sentinel-2A 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)
• February 04, 2019: Wildfires can cause devastation and are also to blame for more than a quarter of greenhouse gases being released into the atmosphere. Satellites play a key role in mapping landscape scarred by fire – but the Copernicus Sentinel-2 mission has revealed that there are more fires than previously thought. 63)
Figure 42: This Copernicus Sentinel-2 image from 26 January 2019 shows fire-scarred land near the Betty's Bay area of Cape Town in South Africa. This false-color image has been processed to show burned areas in dark greys and browns, and areas covered with vegetation are shown in red [image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO] 64)
- From the vantage of space, satellites can be used to detect fires and monitor how they spread and, in the first instance, this can often help relief efforts. However, satellites are also important for mapping the scars that fires leave in their wake, particularly in remote regions.
- It is currently estimated that fires contribute 25–35% of total annual greenhouse gas emissions to the atmosphere so more precise information gained from satellite-based scar-burn maps could help to better understand how they add to the greenhouse effect.
- Land disturbed by fire is an ‘essential climate variable', which are global datasets for the key components of Earth's climate.
- Fire-scar mapping is also used for managing natural resources, assessing fire risk and for adopting mitigating strategies, for example.
- Thanks to Copernicus Sentinel-2's ability to zoom in on our planet, researchers have discovered that there are more areas that are being affected by fire than previously thought.
- A paper published recently in Remote Sensing of the Environment describes how researcher used the high-resolution imaging capability of the Copernicus Sentinel-2 mission to produce the first detailed continental map of burns caused by wildfires. 65)
- Sentinel-2 is a two-satellite constellation built for the EU's Copernicus environmental monitoring program. Each identical satellite carries a high-resolution multispectral imager. The mission has a myriad of uses, particularly related to monitoring the health of world's vegetation and mapping how the surface of our land changes.
- The authors focussed on sub-Saharan Africa as the region that accounts for around 70% of burned area worldwide according to global satellite databases, making it the ideal testbed for evaluating the potential for improving the understanding of global impacts of fire.
Figure 43: Copernicus Sentinel-2 reveals more fires in Africa than thought. The authors of Ref. 65) focussed on sub-Saharan Africa and found that 4.9 million km2 of land had been burned in 2016 (left image), which is 80% more than reported with information from coarser-resolution satellite sensors (right image). These new-found areas comprised mainly burned areas smaller than 100 ha (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by the University of the Basque Country–E. Roteta)
• January 25, 2019: Zaragoza is the capital of the province of Zaragoza in the region of Aragon in northeast Spain. It is home to about half of Aragon's population, making it the fifth largest municipality in Spain. 66)
Figure 44: This Copernicus Sentinel-2B image features the city of Zaragoza nestling in the Ebro valley and flanked by mountains to the south. The image was captured on 25 February 2018, it is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
- In the top-right of the image, the Ebro River can be seen winding its way through the city. Between its source in the Cantabrian Mountains in the northwest and its delta on the Mediterranean coast, the Ebro River is fed by more than 200 tributaries as it flows across much of northern Spain. In fact, the Ebro River discharges more water into the sea than any other river in Spain.
- In an otherwise arid region, the river is used to irrigate crops in the valley – fields can be seen in the top-right of the image.
- To the south of the city and dominating the image, lie mountains, relatively devoid of vegetation. There are also mountains to the north that are beyond the frame of this image. These mountains, which effectively surround Zaragoza, form a barrier to moisture from the Atlantic Ocean and from the Mediterranean Sea, creating a semi-arid climate.
- On average, Zaragoza only has about 350 mm of precipitation a year, compared to Paris in France, for example, which has around 650 mm of precipitation a year. In recent years, efforts – from discounts on water-saving products to new watering systems for parks – have been in helping to reduce water consumption. Efforts such as these resulted in Zaragoza's per capita use of water dropping from 150 liters/day in 1997 to just 99 liters/day by 2012.
• January 18, 2019: The Copernicus Sentinel-2 mission takes us over Gangotri, one of the largest glaciers in the Himalayas and one of the main sources of water for the Ganges River. 67)
- The Gangotri Glacier is in the Indian Himalayan state of Uttarakhand. The head of the glacier can be seen in the lower-right of the image near the Chaukhamba Peak. From here, Gangotri flows around 30 km northwest, but like many of the world's glaciers it is in retreat. Studies suggest that Gangotri has been receding for well over 200 years. Measurements have shown, that it retreated by as much as 35 meters a year between the mid-1950s and mid-1970s. While this has now reduced to about 10 meters a year, observations show that the glacier is thinning.
- The glacier's terminus is called Gomukh, which means ‘mouth of a cow', presumed to describe what the snout of this huge glacier once resembled. Importantly, the headwaters of the Bhagirathi River form here. In Hindu culture and mythology, this is considered to be the source of the Ganges River and consequentially the destination for many spiritual pilgrimages and treks. Gomukh is a 20 km trek from the village of Gangotri, which is in the top left of the image of Figure 45. While Gomukh and Gangotri have much spiritual significance, the Bhagirathi River offers an important supply of freshwater as well as power as it passes through a number of power stations, including the Tehri hydroelectric complex 200 km downstream (not pictured).
- Gangotri is in an area also known as ‘the third pole', which encompasses the Himalaya-Hindu Kush mountain range and the Tibetan Plateau. The high-altitude ice fields in this region contain the largest reserve of freshwater outside the polar regions. With such a large portion of the world's population dependent on water from these cold heights, changes in the size and flow of these glaciers can bring serious consequences for society by affecting the amount of water arriving downstream.
- From the vantage point of space, satellites, such as the Copernicus Sentinels, provide essential information to monitor the changing face of Earth's glaciers, which are typically in remote regions and therefore difficult to monitor systematically from the ground.
Figure 45: Sentinel-2 captured this image on 7 January 2018, it is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
• January 11, 2019: The Copernicus Sentinel-2B satellite takes us along the lower reaches of the brown, sediment-rich Uruguay River. Here, the river forms the border between Argentina and Uruguay and is the site of the Esteros de Farrapos e Islas del Río Uruguay wetlands. 68)
- Composed of lagoons, swamps and 24 islets, the Esteros are a haven for wildlife, protected as a national park and included on the List of Wetlands of International Importance of the Ramsar Convention.
- This wetland system is home to 130 species of fish, 14 species of amphibian, 104 species of bird – a quarter of all birds found in Uruguay – and 15 species of mammal, including the maned wolf, the largest canid (meaning dog-like) species in South America.
- A tourist attraction and a waterway for transport, the Esteros also play an important role in regulating flood levels and maintaining water quality, as well as safeguarding the banks of the Uruguay River from erosion.
- Visible to the lower left – its built structures shown in grey-white – is the Argentinian town of Gualeguaychú. On the eastern shore of the Uruguay River is the Uruguayan city of Fray Bentos, an important national harbor, famous for a plant that once exported corned beef around the world. Now inactive, this sprawling industrial complex has become a World Heritage Site.
- The dark green area to the east of the Esteros is devoted to forestry, an important industry for the region. A pulp mill is located close to Fray Bentos.
Figure 46: Sentinel-2B acquired this image of the Uruguay River wetlands on 17 August 2018, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
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. 69) 70) 71) 72) 73) 74) 75)
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 47: 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 50.
Table 7: Specification of VNIR and SWIR FPAs 76)
Figure 48: The MSI instrument (left) and the associated VNIR focal plane (right), image credit: Airbus DS-ISAE-e2v
Figure 49: Left: VNIR FPA (image credit: Airbus DS-F, ev2); right: SWIR FPA (image credit: Airbus DS-F, Sofradir)
Figure 50: 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 51). 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 52: MSI electrical architecture (image credit: Astrium SAS, Ref. 72)
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 53: Internal configuration of MSI (image credit: EADS Astrium)
Figure 54: Mechanical configuration of the telescope (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 54) 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. 77)
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. 78)
Figure 55: 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 56: 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. 79)
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 57: Photo of the VNIR (top) and SWIR spectral filter assemblies (image credit: Jena Optronik)
Figure 58: 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 59: 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. 80)
Figure 60: 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 61: 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 62: 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. 81) 82) 83)
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.
Table 10: Sentinel-2 MMFU requirements and resulting implementations
The related simplified architectural block diagram of the Astrium Sentinel-2 MMFU is shown in Figure 63. 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.
Figure 63: Architecture of the MMFU system (image credit: Astrium)
Each function is implemented by nominal and redundant hardware components. The functions and boards are summarized in Table 11:
Table 11: Number of functions and boards
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.
Table 12: Performance characteristics of Astrium Sentinel 2 MMFU memory modules
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.
Table 13: Performance characteristics of the memory devices
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 64: Photo of the EQM (Engineering Qualification Model), Sentinel-2 MMFU (image credit: Astrium)
Table 14: Parameters of the Sentinel-2 MMFU 84)
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 65: PGDS context in Sentinel-2 system (image credit: ESA)
Figure 66: The Sentinel-2 ground segment (image credit: ESA)
Figure 67: Physical layout of the PGDS ground stations (image credit: ESA) 85)
• 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. 86)
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 68: 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. 92)
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. 93)
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 69: Image of the North Palau Reef (Western Pacific), acquired with Sentinel-2A on Feb. 10, 2016 (image credit: ESA, Sen2Coral consortium)
Figure 70: Image of Fatu Huku (Pacific) acquired with Sentinel-2A on Feb. 11, 2016 (image credit: ESA, Sen2Coral consortium)
Figure 71: 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 72: 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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40) "East Bali, Indonesia," ESA Earth observation image of the week, 14 June 2019, URL: http://www.esa.int/spaceinimages/Images/2019/06/East_Bali_Indonesia
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42) "Lake Valencia, Venezuela," ESA, 7 June 2019, URL: http://www.esa.int/spaceinimages/Images/2019/06/Lake_Valencia_Venezuela
43) "Earth from Space: El Salvador," ESA, 31 May 2019, URL: http://www.esa.int/spaceinimages/Images/2019/05/El_Salvador
44) "Western Pakistan," ESA Earth observation image of the week: the Copernicus Sentinel-2 mission takes us over western Pakistan and an important wetland area, 24 May 2019, URL: http://www.esa.int/spaceinimages/Images/2019/05/Western_Pakistan
45) "Po Valley, Italy," ESA, Earth observation image of the week, 17 May 2019, URL: http://www.esa.int/spaceinimages/Images/2019/05/Po_Valley_Italy
46) "Milan, Italy," ESA, Earth observation image of the week, 10 May 2019, URL: http://www.esa.int/spaceinimages/Images/2019/05/Milan_Italy
47) "Ries crater, Germany," ESA, 03 May 2019, URL: http://www.esa.int/spaceinimages/Images/2019/05/Ries_crater_Germany
48) "Queensland floods," ESA, 26 April 2019, URL: http://m.esa.int/spaceinimages/Images/2019/04/Queensland_floods
49) "Egyptian crop circles," ESA, Earth observation image of the week, 05 April 2019, URL:http://m.esa.int/spaceinimages/Images/2019/04/Egyptian_crop_circles
50) "Cultivating Egypt's Desert," NASA Earth Observatory, 10 March 2017, URL: https://earthobservatory.nasa.gov/images/89820/cultivating-egypts-desert
51) "Agriculture in Egypt's Western Desert," NASA Earth Observatory, 15 December 2018, URL: https://earthobservatory.nasa.gov/images/144383/agriculture-in-egypts-western-desert
52) "Satellites key to addressing water scarcity," ESA, 22 March 2019, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Satellites_key_to_addressing_water_scarcity
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54) "Lake Chad's shrinking waters," ESA, Earth observation image of the week, 22 March 2019, URL: http://m.esa.int/spaceinimages/Images/2019/03/Lake_Chad_s_shrinking_waters
55) "World Water Day: what's space got to do with it?," ESA, 22 March 2019, URL: http://m.esa.int/spaceinvideos/Videos/2019/03/World_
56) "Bangkok's green lung," ESA, 21 March 2019, URL: http://m.esa.int/spaceinimages/Images/2019/03/Bangkok_s_green_lung
57) "Land-cover dynamics unveiled," ESA, 21 March 2019; URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-2/Land-cover_dynamics_unveiled
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59) "Sediment plume at sea," ESA, 25 February 2019, URL: http://m.esa.int/spaceinimages/Images/2019/02/Sediment_plume_at_sea
60) Favignana, Levanzo and western Sicily," ESA, Earth observation image of the week, 22 February, 2019, URL: http://m.esa.int/spaceinimages/Images/2019/02/Favignana_Levanzo_and_western_Sicily
61) "Jewels of the Maldives," ESA, Earth observation image of the week, 15 February 2019, URL: http://m.esa.int/spaceinimages/Images/2019/02/Jewels_of_the_Maldives
62) "Northeast Kenya," ESA, Earth observation image of the week, 08 February 2019, URL: http://m.esa.int/spaceinimages/Images/2019/02/Northeast_Kenya
63) "More of Africa scarred by fires than thought," ESA, 04 February 2019, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus/
64) "Burn scars near Cape Town," ESA, 04 February 2019, URL: http://m.esa.int/spaceinimages/Images/2019/02/Burn_scars_near_Cape_Town
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83) Giuseppe Mandorlo, "Sentinel-2 Mass Memory and Formatting Unit and Future File Based Operations," Proceedings of ADCSS (Avionics Data, Control and Software Systems) Workshop, ESA/ESTEC, Noordwijk, The Netherlands, Oct.23-25, 2012, URL: http://congrexprojects.com/docs/12c25_2510/06mandorlo_mmfufileops.pdf?sfvrsn=2
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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 (email@example.com).
The Sentinel series:
Provides data continuity for: