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.
• 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. 21)
• 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. 22)
- 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. 23)
- 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. 24)
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. 25)
• 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. 26)
• 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. 27)
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. 28) 29)
Figure 11: Sentinel-2A solar array deployment test at IABG (Airbus Defence & Space), image credit: ESA 30)
- 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. 33)
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. 34)
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)
Launch: A launch of Sentinel-2B is scheduled for March 7, 2017 on a Vega vehicle of Arianespace from Kourou. 35)
Figure 14: Alternate schematic view of the Sentinel-2 spacecraft (image credit: ESA)
• February 10, 2017: The Italian island of Sicily experienced an unusual cold spell and snowfall across parts of southern Europe. As a consequence the mountains of Sicily are visible in white across the northern part of the island. While Italy's northern regions experienced little snowfall this winter, the central and southern areas have seen abnormally cold conditions and snowfall in mountainous areas. 36)
- Mount Etna, an active volcano, is visible at upper right of Figure 15. Positioned over the zone where the African plate collides with and slips under the Eurasian plate, Etna's frequent eruptions are often accompanied by large lava flows, smoke and ash.
- Sentinel-2 provides optical data for land and vegetation monitoring. Its main instrument has 13 spectral bands, and this false-color image was processed including the near-infrared channel – which explains why vegetation appears red. The varying shades of red and other colors across the entire image indicate how sensitive the instrument is to differences in chlorophyll content. This is used to provide key information on plant health; brighter reds indicate healthier vegetation.
Figure 15: Part of Sicily is pictured in this false-color image from the Sentinel-2A satellite, acquired on January 8, 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA)
• February 3, 2017: Iran's Musa Bay on the northern end of the Persian Gulf is pictured in this image from the Sentinel-2A satellite. Near the center of Figure 16, we can see the port city of Bandar Imam Khomeini, situated at the terminus of the Trans-Iranian Railway – a route that links the Persian Gulf with Iran's capital, Tehran. 37)
- The dark area to the right of the port is Musa Bay, a shallow estuary. The large geometric structures along the top appear to be evaporation ponds for extracting naturally occurring minerals from the ground. - The left side of the image is dominated by the marshes and mudflats of the Shadegan wildlife refuge. It is the largest wetland in Iran, and plays a significant role in the natural ecology of the area.
- The region provides a wintering habitat for a wide variety of migratory birds, and is the most important site in the world for a rare species of aquatic bird: the marbled duck. The northern part of the wetland is a vital freshwater habitat for many endangered species. This area is considered a wetland of international importance by the RAMSAR Convention, an intergovernmental treaty for the sustainable use of wetlands.
Figure 16: This Sentinel-2A image, acquired on January 13, 2017, shows Iran's Musa Bay (image credit: ESA, the image contains modified Copernicus Sentinel data (2017), processed by ESA)
• February 2, 2017: A river delta usually leads to the open sea, but the delta formed by the Okavango River is different. After rising in Angola and flowing through Namibia, the river meanders into Botswana, where it branches out to create an inland delta – one of the world's most important wetlands (Figure 17). 38)
- Wetlands, both coastal and inland, are important for people and the environment. Their many benefits include acting as natural safeguards against disasters, protecting communities most vulnerable to the devastating effects of floods, droughts and storm surges. They also provide a habitat for a multitude of animals and plants, and filter and store water.
- Every year, 2 February marks World Wetlands Day. It commemorates the Convention on Wetlands also known as the RAMSAR Convention, which was signed on 2 February 1971 to provide a framework for national and international cooperation for the conservation and use of wetlands and their resources. This year's theme is ‘Wetlands for Disaster Risk Reduction'.
- Well-managed wetlands provide resilience for communities against extreme weather and help to minimize the damage from these hazards. Coastal wetlands such as mangroves protect against flooding and serve as buffers against saltwater intrusion and erosion. Inland wetlands such as floodplains, lakes and peatlands and deltas like Okavango can reduce the risk of drought.
- The Okavango Delta, a World Heritage site, includes permanent swamps that cover about 15 000 km2 during the dry season but can swell to around three times this size, providing a home for some of the world's most endangered species of large mammals. In sharp contrast, the surrounding Kalahari Desert is a lifeline for local communities and wildlife alike – and therefore it is extremely important that it is well managed.
- Through the GlobWetland Africa project, ESA and the African team of the RAMSAR convention help to use satellite observations for the conservation, wise-use and effective management of wetlands in Africa. Through the project, African stakeholders are provided with methods and tools to fulfil their commitments to RAMSAR.
Figure 17: Marking World Wetlands Day, this Sentinel-2A image features the Okavango Delta in Botswana – a lifeline for local communities and wildlife alike. Sentinel-2A captured this image on Dec. 2, 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
• January 13, 2016: Sentinel-2A observed the region of Saint Petersburg in winter. While this image may appear to be in black and white, it is in true color – although the snow cover and lack of vegetation during the winter lend very little color to the scene. 39)
- One of the most prominent features is the large area of ice and snow covering the water. Looking closer to the lower-central part of the image, we can see where icebreakers have created a straight route to and from Saint Petersburg's port. The boats leaving the port continue west following a channel through the Saint Petersburg Dam south of Kotlin Island, and into the Gulf of Finland.
- There are five other breaks along the northern stretch of the dam without ice because the flowing water prevented freezing. - A 25 km-long dam complex protects the city from storm surges, and also acts as a bridge from the mainland to Kotlin Island.
- On the right, the Neva River flows through the center of Saint Petersburg – Russia's second largest city. Sometimes dubbed the ‘Venice of the North' for its numerous canals and more than 400 bridges, the city center dates back to 1703 and was built by Tsar Peter the Great. Today, Saint Petersburg is a UNESCO World Heritage Site.
Figure 18: The snow-covered Russian city of Saint Petersburg on the Neva Bay is pictured in this image from the Sentinel-2A satellite (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
• December 23, 2016: Sentinel-2A takes us over northwestern China near the border with Kazakhstan and Kyrgyzstan in this false-color image. The mountains pictured are part of the Tian Shan range, which stretches about 2800 km across this border region, making it one of the longest mountain ranges in Central Asia. 40)
- The glaciers of Tian Shan have lost about a quarter of their ice mass since the 1960s, and scientists estimate that half of the remaining glaciers will have melted by 2050. Glaciers are a key indicator of climate change, and their melting poses threats to communities living downstream.
- We know well that snow and clouds are both white – had this image (Figure 19) been in true color, we wouldn't be able to differentiate between the two. But Sentinel-2's imager can view the area in different parts of the spectrum, and can separate clouds from snow. In this image, clouds are white while snow appears blue. This is particularly important for mapping snow cover. A few clouds can been seen over the mountains near the center of the image, with thicker cloud cover in the valleys to the north.
- The orange area on the right side of the image is part of the Bayanbulak Basin, a large grassland area of about 24 000 km2. Although not pictured, the basin also hosts an important wetland and China's very own ‘Swan lake' – the highest-altitude breeding ground for swans in the world.
- This area of the Tian Shan mountains in China's Xinjiang Region became a UNESCO World Heritage Site in 2013.
Figure 19: This image of China's Tian Shan range, observed by the Sentinel-2A satellite, was captured on 18 November 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
• December 20, 2016: Images from the Sentinel-2A satellite from February to October 2016 (Figure 20) show the changing landscape in Spain's Brazo de Este natural park and around the city of Los Palacios y Villafranca. 41)
- The Copernicus Sentinel-2 mission is designed to provide images that can be used to distinguish between different crop types as well as data on numerous plant features, such as leaf area, chlorophyll content and water content – all essential for accurately monitoring plant growth.
Figure 20: Part of the Guadalquivir river basin, the area pictured has a rich agriculture with crops including rice, watermelon, pepper, cucumber, tomato and quinoa. In this animation we can clearly see changes in the fields as different crops grow at different rates, and are harvested in different seasons (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
• December 16, 2016: Seville, the capital of the Andalusian autonomous community and the province of Seville, Spain, is located on the Guadalquivir river (Figure 21). While the original course of the river is visible snaking through the city on the right, we can see where water has also been redirected in a straighter course on the left. 42)
- The fertile valley of the Guadalquivir is evident by the plethora of agricultural structures, particularly noticeable in the upper right. The Sierra Morena mountain range runs north of the Guadalquivir basin, and we can see the foothills in the upper-left corner.
- Another notable feature in the upper-central section of the image is the open pit copper mine, appearing white. This type of mining is often practised when deposits of minerals or rocks are found near the surface. To the west of this mine, two other open-pit mines are filled with water.
- South of these water-filled mines we see two circular structures reminiscent of clamshells. These are large solar power plants, where mirrored panels are positioned to face a solar power tower –sitting at the southernmost tip of the structures seen here – which receives the focused sunlight and acts as a furnace to produce energy.
- Seville has a municipal population of about 703,000 as of 2011, and a metropolitan population of about 1.5 million, making it the fourth-largest city in Spain. Its Old Town, with an area of 4 km2, contains three UNESCO World Heritage Sites: the Alcázar palace complex, the Cathedral and the General Archive of the Indies.
Figure 21: The western area of Spain's Province of Seville and its capital with the same name (right) is pictured in this image from the Sentinel-2A satellite. The image was acquired by the Sentinel-2A satellite on 26 July 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
- The southern part of the country is dominated by the Alps, some of which are snow-capped. One of the more obvious features in the lower central part of the image is the curved x-shape of the Aletsch Glacier, the largest in the Alps. Owing to climate change, the glaciers in this region are showing long-term retreat.
- North of the Alps, the landscape descends into the Central Plateau, which covers about a third of Switzerland and is home to major cities like Zurich and the de facto capital city, Bern. It is the most densely populated region and hosts the majority of the country's industry, manufacturing and farming.
- Along the northwestern edge of the country are the Jura mountains, consisting of a sequence of ‘folds' in the geology, visible in the image as linear ridges running roughly southwest to northeast.
- Switzerland has thousands of lakes shaped by glaciers during the last ice age, about 15,000 years ago. Lake Geneva in the west is shared with France, while Lake Constance in the east is shared with Germany and Austria, making Lake Neuchâtel in the northwest the largest entirely within Switzerland. The lakes appear in different colors owing to variations in algae content or to the presence of finely ground rock flowing in from the mountain glaciers.
- Near the center of the country we can see Lake Lucerne with its four ‘arms'. The city of Lucerne sits on the western end of the lake, and is the site of the latest ESA ministerial council.
Figure 22: Sentinel-2A image of Switzerland at 10 m resolution (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by GeoVille)
• November 25, 2016: A detailed land-cover map showing forest in Chiapas state in southern Mexico. The map (Figure 23) was produced using Copernicus Sentinel-2 optical data from 14 April 2016. It shows the kind of products that are possible through the new ESA-backed Forestry Thematic Exploitation Platform (F-TEP). Such products can support initiatives such as the UN's Reduced Emissions from Deforestation and Degradation (REDD+), which is a global agreement that developing countries should receive financial compensations for slowing the rates of deforestation and forest degradation in recognition of the role of forests as carbon sinks. 44)
- "F-TEP is a new ‘one-stop shop' online platform enabling the forestry sector to make easier use of satellite data," explains Tuomas Häme of VTT Technical Research Center of Finland, managing the development of the platform for ESA. "Users are able to map and explore their forests from the comfort of a web-based browser, within which they can rapidly access and process all available data, then disseminate the results."
- As part of a pilot project, the platform is being used to map the extensive Chiapas forest to assess its carbon stocks, with the Ministry of Environment and Natural History of the state government of Chiapas and several Mexican non-governmental organizations. Chiapas is the second most forested state in Mexico, and home to the Lacandon jungle – one of the last major tropical rainforests in the northern hemisphere. Covering 600,000 hectares, it is home to about 60% of Mexico's tropical tree species, 3500 species of plants and more than 1600 species of animals.
- The mapping is performed through an automated process with full 10 m-resolution Sentinel-2 images being run through ‘decision tree' software to pick out trees. Very high-resolution 1 m-class satellite imagery is used to cross-check the results, combined with cross-checks from the ground.
- Achieving a standardized space-based method of assessing forest carbon stocks could be key to implementing the REDD+ scheme. — While comparable forest mapping once took about three years to produce, use of the platform combined with Sentinel-2's frequent coverage allows new maps to be updated in a matter of weeks.
Figure 23: The Chiapas forest land-cover map (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by VTT Technical Research Center of Finland Ltd.)
• November 18, 2015: Figure 24 of Sentinel-2A shows the Gibson Desert in western Australia. Covering an area of over 150,000 km2, the desert sports gravel terrains covered by desert grasses, as well as red sandy plains and dunefields. A drought in the 1980s forced the indigenous Pintupi people to the central-eastern area of the desert, where they made contact with Australian society in what is believed to be one of the last first-contact events in Australia. 45)
- On the left side of this false-color image, we see many strange shapes in varying shades of blue. These are the remnants of areas purposefully burned by the Pintupi people to encourage plant growth or drive game animals into the open. — Many of the Pintupi people moved to settlements when the British military began testing missiles in the region in the 1950s. The areas that they had burned became overgrown, becoming even more susceptible to manmade or lightning-caused fires, which then burn out of control, leaving behind large burned scars.
- In the lower-right corner of the image we can make out a circular structure. This is the Connolly Basin impact crater, believed to have been formed around 60 million years ago. Some 9 km across, the rim rises 25–30 m above the crater's basin.
Figure 24: Sentinel-2A false color image of the Gibson Desert in Western Australia, captured on Dec. 25, 2015 (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by ESA)
• November 17, 2016: The image of Figure 25 shows the Frankfurt airport at upper center, the city itself, to the north-east of the airport, and the meeting of the Rhine and Main rivers, with the Rhine flowing from bottom center towards the upper left, and the much narrower Main flowing from top right through the city.
- It also shows the city of Darmstadt, 35 km south of Frankfurt, sitting on a gentle slope between the forested Odenwald mountains and the Rhine River. — Darmstadt is seen as the built-up area to the right of the ‘V' intersection between Autobahns 5 and 67, directly south of the airport. Darmstadt is an important center for scientific institutes, universities and high-tech companies – and, since 1967, it has hosted the center known today as ESA's European Space Operations Center (ESOC). It is home to Sentinel-1 and -2 mission control, from where the three satellites of the two dual missions are operated, 24 hours/day, year round. The fourth, Sentinel-2B, is set for launch in 2017. 46)
- There are about 900 ESA staff and contractors working at the center, with 11 missions comprising 17 spacecraft now flying and nine missions in preparation. — In September 2017, the center will mark its 50th anniversary.
Figure 25: This image spotlights the Rhine-Main area south of the city of Frankfurt, one of Europe's leading business, transport and innovation hubs. The image was acquired by the Sentinel-2A satellite on 29 August 2015 (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by ESA)
• October 28, 2016: Sentinel-2A brings us over the snowy landscape of the Putorana Plateau in northern Central Siberia (Figure 26). The area pictured shows part of the Putoransky State Nature Reserve, which is listed as a UNESCO World Heritage Site. Situated about 100 km north of the Arctic Circle, the site serves as a major reindeer migration route – an increasingly rare natural phenomenon – and is one of the very few centers of plant species richness in the Arctic. 47)
- Virtually untouched by human influence, this isolated mountain range includes pristine forests and cold-water lake and river systems. The lakes are characterized by elongated, fjord-like shapes, such as Lake Ayan in the upper-central part of the image. Zooming in on the lake we can see that it is mostly ice-covered, with small patches of water peeking through around its lower reaches.
- Another feature of this area are the flat-topped mountains, formed by a geological process called ‘plume volcanism': a large body of magma seeped through Earth's surface and formed a blanket of basalt kilometers thick. Over time, cracks in the rock filled with water and eroded into the rivers and lakes we see today.
Figure 26: This Sentinel-2A image of the Putorana Plateau in Siberia was acquired on March 2, 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
• October 21, 2016: Part of Nepal, including its capital city, Kathmandu, and the Himalayan foothills are pictured in this satellite image (Figure 27). Vegetation appears red in this false-color image, while waterways and buildings appear light green and blue. 48)
- Surrounded by four mountain ranges, Kathmandu valley at the top of the image is recognized as a UNESCO World Heritage Site for its temples and monuments. However, some of these sites collapsed during the April 2015 earthquake that struck the region, claiming thousands of lives and causing widespread damage throughout the valley.
- This image demonstrates just a slice of Nepal's varied terrain: from the mountains to the north to the plains in the south. We can see how water runs off of the mountains, forming large rivers that cut through the forested plain, with some areas of agriculture. The lower part of the image appears hazier than the mountainous areas because humidity is higher in the plains.
Figure 27: Sentinel-2A image of Kathmandu, Nepal's capital city, and its surroundings (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by ESA)
- The Anti-Atlas range was born from continental collision, and geologists believe it was once higher than the Himalayas, but was reduced through erosion. Here the land is mostly dry and barren as the mountains belong to the Saharan climate zone. But some stream channels created by occasional water runoff or from when the climate was much wetter than today, are visible.
- The circle at the center of the image (Figure 28) is the Ouarkziz crater. Some 3.5 km in diameter, the crater was created when a meteor hit Earth less than 70 million years ago, when dinosaurs still roamed the planet.
Figure 28: This image of the Ouarkziz crater (center of image) was captured by the Copernicus Sentinel-2A satellite on 9 March, 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA)
• Sept. 14, 2016: The Figures 29 and 30 from Sentinel-2A show the beautiful lush Portuguese main island of Madeira before it was devastated by wildfires in August 2016. Madeira is famous for its rugged green landscape and is home to unique endemic flora and fauna. In fact, two thirds of the island is given over to national park to protect this natural environment. These ‘false-color' images (Figure 29 and 30) show the vegetation in red. By contrast, the image from 17 August shows large black patches where the fires encroached on the capital Funchal in the southeast and also further to the west, leaving the land scarred. 50)
- The recent devastation brought by wildfires to the beautiful Portuguese island of Madeira is all too clear in these images from Sentinel-2A.
Figure 29: Sentinel-2A MSI image of Madeira acquired on 7 August 2016 (image credit: ESA)
Figure 30: Sentinel-2A MSI image of Madeira acquired on 17 August 2016 (image credit: ESA)
• September 9, 2016: Plankton, the most abundant type of life found in the ocean, are microscopic marine plants that drift on or near the surface of the sea (Figure 31). They are sometimes referred to as ‘the grass of the sea' because they are the basic food on which all other marine life depends. Since plankton contain photosynthetic chlorophyll pigments, these simple organisms play a similar role to terrestrial ‘green' plants in the photosynthetic process. Plankton are able to convert inorganic compounds such as water, nitrogen and carbon into complex organic materials. 51) 52)
- With their ability to ‘digest' these compounds, they are credited with removing as much carbon dioxide from the atmosphere as their counterparts on land. As a result, the oceans have a profound influence on climate. Since plankton are a major influence on the amount of carbon in the atmosphere and are sensitive to environmental changes, it is important to monitor and model them into calculations of future climate change.
- Although some types of plankton are individually microscopic, the chlorophyll they use for photosynthesis collectively tints the color of the surrounding ocean waters, providing a means of detecting these tiny organisms from space with dedicated sensors, such as Sentinel-2's MSI (Multispectral Imager) with 13 spectral bands.
- Some algae species are toxic or harmful. If they surge out of control during optimal blooming conditions they can exhaust the water of oxygen and suffocate larger fish. This phenomenon has dramatically increased in recent decades, and is particularly dangerous to fish farms because the fish cannot flee affected areas. Early warning of harmful blooms from satellites can help to prevent fish farmers from losing their stock, as it happened in Chile recently.
Figure 31: Although it may appear as a watercolor painting, this image is a natural-color capture of a plankton bloom in the Barents Sea by the Sentinel-2A satellite, acquired on June 30, 2016 (image credit: ESA, contains modified Copernicus Sentinel data (2016), processed by ESA)
• September 7, 2016: On July 17, 2016, a huge stream of ice and rock tumbled down a narrow valley in the Aru Range of Tibet. When the ice stopped moving, it had spread a pile of debris that was up to 30 meters thick across 10 km2. Nine people, 350 sheep, and 110 yaks in the remote village of Dungru were killed during the avalanche (Figure 32). 53) 54)
- The massive debris field makes this one of the largest ice avalanches ever recorded. The only event of a comparable size was a 2002 avalanche from Kolka Glacier in the Caucasus region, explained Andreas Kääb, a glaciologist at the University of Oslo. The cause of the avalanche is unclear. "This is new territory scientifically," said Kääb. "It is unknown why an entire glacier tongue would shear off like this. We would not have thought this was even possible before Kolka happened."
- The OLI (Operational Land Imager) instrument, a similar instrument on Landsat-8, acquired an image on June 24, 2016 (Figure 33), that shows the same area before the avalanche.
- Kääb's preliminary analysis of satellite imagery indicates that the glacier showed signs of change weeks before the avalanche happened. Normally, such signs would be clues the glacier might be in the process of surging, but surging glaciers typically flow at a fairly slow rate rather than collapsing violently in an avalanche.
- After inspecting the satellite imagery, University of Arizona glaciologist Jeffrey Kargel agreed that a surging glacier could not be the cause. "The form is completely wrong," he said. "It must be a high-energy mass flow. Maybe liquid water lubrication at the base played some role," he said.
- Tian Lide, a glaciologist at the Chinese Academy of Sciences, visited the site in August and described the avalanche as "baffling" because the area where the ice collapse began is rather flat. "We failed to reach the upper part of the glacier for safety reasons," he said in an email, "but we will go the upper part [later] to see if we can find some more hints about what caused the glacier disaster."
Figure 32: The MSI (Multispectral Imager) on the Sentinel-2A captured this image of the debris field on July 21, 2016 (image credit: ESA, NASA Earth Observatory)
Figure 33: OLI image of Landsat-8 acquired on June 24, 2016 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS)
• September 2, 2016: The Upsala Glacier in Argentina's Los Glaciares National Park is pictured in this Sentinel-2A image (Figure 34). The park was named a UNESCO World Heritage site in 1981 and is the largest in the country, covering an area of over 7000 km2. 55)
- Many glaciers in the national park and in the wider Patagonian Ice Field have been retreating during the last 50 years because of rising temperatures. The Upsala Glacier has retreated more than 3 km in the past 15 years.
- Glaciers are the largest reservoirs of freshwater on our planet, and their melting or growing is one of the best indicators of climate change. Satellite data can help to monitor changes in glacier mass and, subsequently, their contribution to rising sea levels.
- Taking a closer look at the terminus of the Upsala Glacier, we can see how icebergs have broken off and are floating in the water of the upper reaches of Lake Argentino. The lake's unique color is attributed to ‘glacier milk' – suspended fine sediment produced by the abrasion of glaciers rubbing against rock. The darker lines following the flow of the glacier are moraines: accumulations of rock, soil and other debris – including glacial milk – that have been deposited by the glacier.
Figure 34: The Upsala Glacier in Argentina's Los Glaciares National Park is pictured in this Sentinel-2A image from 22 January 2016 (image credit: ESA, contains modified Copernicus Sentinel data (2016), processed by ESA)
• May 27, 2016: The Sentinel-2A satellite takes us to the diverse landscape of the eastern Atacama desert in South America. The region pictured (Figure 35) lies around 200 km east of the Chilean city of Antofagasta on the Pacific coast (not pictured), and is virtually devoid of vegetation. 56)
- At the top of the image we can see part of Chile's largest salt flat, the Salar de Atacama. With an average elevation of some 2300 m above sea level, it is formed by waters flowing down from the Andes, which, having no drainage outlets, are forced to evaporate, leaving salt deposits.
- It is the world's largest and purest active source of lithium, containing some 30% of the world's lithium reserve base, and providing almost 30% of the world's lithium carbonate supply.
- The bright turquoise rectangles and squares visible along the top part of the image are evaporation ponds. Subsurface salt brines are pumped from beneath the saline crust in two different areas. In one of them, extracted salt brines have unrivalled concentration levels of potassium and lithium. In the other, the brines obtained contain high concentrations of sulphate and boron.
- In the lower right part of the image we can see the Socompa stratovolcano, known for its ‘debris avalanche deposit' where the land collapsed on its western rim some 7000 years ago. The area has since been partially filled by lava, and we can see dark lava flows around the volcano.
- The MSI (Multispectral Instrument) on Sentinel-2 uses parts of the infrared spectrum to analyze mineral composition where vegetation is sporadic. In this false-color image, the intense shades of brown and orange come from the use of an infrared part of the spectrum leading to an exaggeration of color intensity.
Figure 35: This Sentinel-2A image of Chile's salt flat was acquired on March 8, 2016 (image credit: ESA, the image contains modified Copernicus Sentinel data , processed by ESA)
• May 20, 2016: Rolling sand dunes in the expansive Rub' al Khali desert on the southern Arabian Peninsula are pictured in this image from the Sentinel-2A satellite (Figure 36). Also known at the ‘Empty Quarter', the Rub' al Khali is the largest contiguous sand desert in the world. Precipitation rarely exceeds 35 mm a year and regular high temperatures are around 50°C. 57)
- The yellow lines and dots in this false-color image are sand dunes. Looking closer at the dunes in the lower right, many have three or more ‘arms' shaped by changing wind directions and are known as ‘star dunes'. They tend to ‘grow' upwards rather than laterally, and reach up to 250 m in height in some parts of the Rub' al Khali.
- The dunes are interspersed with hardened flat plains – remnants of shallow lakes that existed thousands of years ago, formed by monsoon-like rains and runoff. The multispectral instrument on Sentinel-2 uses parts of the infrared spectrum to detect subtle changes in vegetation cover, but can also see changes in mineral composition where vegetation is sparse. In this image, shades of brown to bright purple show the mineral composition, possibly including salt or gypsum.
Figure 36: This image was captured by Sentinel-2A on 22 December 2015 (image credit: ESA, the image contains modified Copernicus Sentinel data , processed by ESA)
• May 19, 2016: Sentinel-2A is demonstrating how it can be used to help forecast ocean waves around our coasts: sunlight reflected from the water surface reveals complex waves as they encounter the coastline and seafloor off the tip of Dorre Island, Western Australia (Figure 37). 58)
- ESA's ocean scientist, Craig Donlon, explained, "The instrument images the same ocean scene from slightly different angles and at slightly different times. -Scientists at OceanDataLab processed the data to determine the distribution of ocean waves and the direction they are heading. This is extremely important for anyone working at sea."
- The fine resolution of Sentinel-2A's multispectral imager provides a view of the tilting facets of the waves, expressed as measurable intensity contrasts. The instrument images the same ocean scene from slightly different angles and at slightly different times. Scientists at OceanDataLab first transformed these radiances into estimates of sea-surface slope and then ran a cross-spectral analysis to determine the wave spectrum and wave velocity.
Figure 37: This image was taken by the Copernicus Sentinel-2 satellite on 1 October 2015. It shows how reflection of solar radiation by the sea surface reveals the complex patterns of waves as they interact with the coastline and seafloor off the tip Dorre Island, Western Australia. Several superimposed wave sets that have been reflected and bent by the coastal features and the shape of the seabed can be seen. Longer swell waves are also evident, with surf and breaking waves at the coastline itself (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by OceanDataLab)
• May 18, 2016: Using almost 7000 images captured by the Sentinel-2A satellite, this mosaic of Figure 38 offers a cloud-free view of the African continent – about 20% of the total land area in the world. The majority of these separate images were taken between December 2015 and April 2016, totalling 32 TB of data. Thanks to Sentinel-2A's 290 km-wide swath and 10-day revisit at the equator, the chance of imaging Earth's surface when the skies are clear is relatively high. Nevertheless, being able to capture the Tropics cloud-free over the five months is remarkable. 59)
- Sentinel-2A's identical twin, Sentinel-2B, is due to be launched in 2017. As a constellation, the two satellites will orbit 180° apart. Along with their wide swaths, this will allow Earth's main land surfaces, large islands, as well as inland and coastal waters to be covered every five days. This will further improve the probability of gaining a cloud-free look at a particular location.
Figure 38: This African mosaic, the first mosaic of Africa generated through ESA's Climate Change Initiative Land Cover project, was presented at the Living Planet Symposium in Prague, Czech Republic (image credit: this image contains modified Copernicus Sentinel data (2016), processed by Brockmann Consult/ Université catholique de Louvain, The Netherlands)
• May 9, 2016: Different types of crops growing east of the Czech capital, Prague (left), are distinguished in this land cover classification image (Figure 39). This image was produced in collaboration with the European Commission (lead by the Joint Research Centre), the State Agricultural Intervention Fund of the Czech Republic and ESA. 60)
- With its 13 spectral bands, the Sentinel-2 mission for Europe's Copernicus program is the first optical Earth observation mission of its kind to include three bands in the ‘red edge', which provide key information on vegetation state. Sentinel-2 is designed to provide images that can be used to distinguish between different crop types as well as data on numerous plant indices, such as leaf area, leaf chlorophyll and leaf water – all essential to monitor plant growth accurately.
Figure 39: This crop map was created by combining over 1000 scenes from the Sentinel-1, Sentinel-2 and Landsat-8 satellites taken over the course of 2015 (image credit: DUE Sentinel-2 for Agriculture project; contains modified Copernicus Sentinel data (2015))
• April 29, 2016: Figure 40 of Sentinel-2A is an image of central western Namibia, an area surrounding the Namib Naukluft Park. The National Park includes part of the Namib – the world's oldest desert – and the Naukluft Mountain range. It is the largest game park in Africa and the fourth largest in the world. 61)
- A typical west coast desert, moisture enters as fog, from the Atlantic Ocean, rather than receiving actual rainfall. A phenomenon also found along the west coasts of South and North America, the surface water of Namibia's coast is relatively cold, so that moist air moving in with westerly winds cools and falls as rain before it reaches the coast, allowing only fog to reach inland.
- The fog enables life in this extremely arid region, for snakes, geckos and particular insects like the fogstand beetle, which survives by collecting water on its bumpy back from early-morning fogs, as well as hyenas, gemsboks and jackals.
- The winds carrying the fog also create the imposing sand dunes, whose age is rendered by the burnt orange color. The iron in the sand is oxidized, developing this rusty-metal color over time. It becomes brighter as the dune ages, as is clearly visible along the middle of this natural-color image.
- Also visible along the top-left part of the image is the Kuiseb River bordered on one side by some of the tallest sand dunes in the world, and on the other by barren rock. The river blocks the movement of the dunes, which are blown northwards by the winds.
- A road cuts through the top-right corner of the image. It is part of the C14 Highway, which runs for some 600 km from Walvis Bay, through Helmeringhausen and ends in Goageb.
Figure 40: Sentinel-2A image of central western Namibia, an area surrounding the Namib Naukluft Park, acquired on January 28, 2016 (the image contains modified Copernicus Sentinel data , processed by ESA)
• March 31, 2016: ESA and Australia's national geological survey, Geoscience Australia, today agreed to cooperate to ensure data from the EU's Sentinel satellites are accessible in Southeast Asia and the South Pacific. The agreement supports the Australian government and European Commission's partnership to ensure the EU's Copernicus Earth observation program benefits their citizens and the broader international community. 62)
- A key component of the cooperation will be the establishment of a regional data access and analysis hub managed by GA (Geoscience Australia). This hub will greatly improve access to Copernicus data in a region which is densely populated and experiencing high rates of economic growth, but which faces significant challenges in areas where Earth observation can help. These challenges include the protection of environmental assets, promotion of sustainable natural resource development and risk reduction from natural disasters.
- ESA will supply GA with high-speed access to data from the Sentinel satellites through its Copernicus data access infrastructure. Through a consortium with Australia's CSIRO (Commonwealth Science and Industrial Research Organization), Canberra and Australian state governments, GA will make the data hub available to users in the Southeast Asia and the South Pacific region. The hub is projected to provide access to over 12 PB (Petabytes) of data by 2025, and is expected to go beyond simply providing users with the ability to download Copernicus data.
- "The regional data hub will also provide a high-performance environment in which all the data can be analyzed and applied at full scale to big regional challenges like the blue economy, sustainable livelihoods and climate change adaptation," said GA's head of Earth and Marine Observations, Dr Adam Lewis. "By enabling multiple user groups, from multiple countries, to come together and ‘work around' such a comprehensive set of data, we are helping to make sure the full potential of the EU's amazing program is realized and that regional partners can find regional solutions to regional challenges."
- The data access hub will be established at Australia's National Computational Infrastructure, the largest facility of its kind in the southern hemisphere, taking advantage of the Australian government's investments in science and research infrastructure to support the region. The cooperation will also make it easier for European and Australian experts to collaborate on the calibration and validation activities that are fundamental to ensuring that users have access to high-quality satellite data and value-added products they can trust.
- "Through GA, CSIRO and many other players, Australia has long made a valued contribution to our calibration and validation activities. Its technical expertise, world-class facilities and the diversity of geographies they have access to makes them a key player," said Pier Bargellini from ESA's Copernicus Space Component Mission Management and Ground Segment Division. "Through this arrangement, we expect to see this grow even further, with Australia making a particular contribution to ensuring Copernicus data satisfies local and regional requirements."
- Under the arrangement, GA will also act as a coordinating point for European partners to obtain access to Australian in-situ data, which is made available through the efforts of many Australian government agencies, research partnerships and universities.
- "The EU's Copernicus program is about applications and services, and these applications and services are most useful when satellite and in-situ data are integrated," said Andreas Veispak, the European Commission's Head of Unit for Space Data for Societal Challenges and Growth. "We welcome GA's commitment to act as a coordination point for access to in-situ data. Australia has a record of providing outstanding data, including through programs like the integrated marine observing system and terrestrial ecosystem research network. We are looking at linking Copernicus more closely to these efforts."
- The regional data hub will become operational on 1 July, 2016.
Figure 41: Sentinel-2A captured Lake Amadeus in Australia's Northern Territory on 19 December 2015 (image credit: Copernicus Sentinel data (2015)/ESA) 63)
• March 25, 2016: The Etosha salt pan is the most prominent feature, forming part of the Kalahari Basin in northern Namibia (Figure 42). It is believed that a lake was first formed tens of millions of years ago. More recently – mere thousands of years ago – the Kunene River would have flowed through this area, filling the large lake before tectonic movement changed the river course. The lake then dried up, leaving behind some 4800 km2 of exposed minerals. 64)
- Today only the Ekuma River, seen flowing down from the upper left, feeds water into the pan – but very little water actually flows in as it seeps into the riverbed.
- Part of the wider Etosha National Park, the pan is a designated Ramsar wetland of international importance. It is the only known mass breeding ground for flamingos in Namibia, seeing as many as one million flamingos at a time during the wet season when rain water forms pools in parts of the pan.
- Built-up mounds of clay and salt throughout the pan also draw animals who use them as salt licks. Animals including lions, elephants, leopards and even black rhinoceroses can be seen in the park. The name ‘Etosha' means ‘great white place' in the language of the local Ovambo tribe – and looking at the image we understand why.
Figure 42: This Sentinel-2A image of the Etosha salt pan in northern Namibia was acquired on September 18, 2015 (image credit: Copernicus Sentinel data (2016)/ESA)
• March 15, 2016: ESA has agreed with NASA, NOAA and the USGS to make data available to them from the European Sentinel satellites. With the third Copernicus satellite, Sentinel-3A, recently launched, ESA has signed technical arrangements with these US agencies for accessing Sentinel data. These arrangements coordinate the technical implementation covering the Sentinel data access to the US. 65) 66)
- ESA and its international partners are pursuing Earth observation activities in a number of areas of common interest, and are sharing each other's satellite data. All sides are committed to the principle of full, free and open access to the European Sentinel and the NASA, NOAA and USGS Earth observation satellite data and information.
- The signed arrangement will allow NASA, NOAA and USGS to systematically retrieve the Sentinel data from a dedicated International Data Hub operated by ESA. These agencies will then transfer the data to the US, absorbing them in their existing data access systems, such as EarthExplorer and GloVIS, and disseminating them to their own user communities.
- For over three decades, ESA has been acquiring, processing and disseminating data from a number of US missions such as Landsat to the European user communities as part of its Earthnet Third Party Mission Program.
- While the US agencies' objective is to serve the US user communities with priority, the Sentinel data will continue to be freely accessible for Copernicus Services, as well as to users worldwide, through the ESA operated data hubs.
• Feb. 26, 2016: Like most of Egypt's landscapes, the image of Figure 43 is dominated by arid desert – namely the Eastern Desert between the Nile River and the Red Sea. The distinctive pattern of water erosion from rivers and streams is clearly visible as they make their way towards the Nile, at which point the rolling sandy highlands drop abruptly at the Nile valley, visible along the bottom of the image. 67)
- Fields of intensive farming along the Nile appear red owing to this false-color image being processed to include the near-infrared. The varying shades of red indicate how sensitive the MSI (Multispectral Instrument) on Sentinel-2 is to differences in chlorophyll content, providing key information on plant health.
- The Nile valley is one of the world's most densely populated areas. The river is the primary source of water for both Egypt and Sudan's populations, supporting life in an otherwise uninhabitable environment, as evidenced by the stark contrast between the colors of this image.
- Zooming in along the bottom of Figure 43, one can see clusters of black dots where cities and towns are located, in addition to the fields. In the lower right, just above the red area, there is an interesting pattern of roads from the bird's-eye view – possibly a developing residential area.
Figure 43: Sentinel-2A image of central-eastern Egypt acquired on January 17, 2016 (image credit: Copernicus Sentinel data (2016)/ESA)
• Feb. 12, 2016: Figure 44 features the diverse landscapes of the autonomous Community of Madrid in the heart of Spain. The community and country's capital city is visible near the center of the image.68)
Figure 44: Sentinel-2A acquired this image of Madrid and its surroundings on November 16, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• January 26, 2016: ESA and Airbus DS signed a contract to deliver two further optical satellites for the European Copernicus program. As part of the Sentinel-2 Earth observation satellite system, these two new models, called "Sentinel-2C" and "Sentinel-2D", will observe the environment and land surfaces and continue from 2021 with the measurements carried out by the first two flight units as part of the European Copernicus program. As prime contractor, Airbus Defence and Space will lead an industrial consortium of more than 50 companies from 17 European countries and the USA. 69)
• January 22, 2016: The natural-color image of Sentinel-2A (Figure 45) features the small nation of Bahrain and parts of eastern Saudi Arabia. Located on the southwestern coast of the Persian Gulf, Bahrain is a small Arab state, made up of an archipelago consisting of Bahrain Island and some 30 smaller islands. The total area of Bahrain is about 780 km2. 70)
- In the middle of the image, on the Persian Gulf, the King Fahd Causeway is clearly visible. Built between 1981 and 1986, it consists of a series of bridges and stretches of road connecting Saudi Arabia and Bahrain. The Saudi and Bahraini passport control centers are also noticeable in the middle of the Causeway.
- On the right of the image is the island of Bahrain, home to some 1.5 million people, with its modern capital Manama featured at the top of the island. The greys represent the densely built city center and surrounding towns. Strikingly relaxed and cosmopolitan, Manama has been at the center of major trade routes since antiquity. On the top right part of the island, on a smaller island about 7 km northeast of the capital, Bahrain International Airport is visible.
- Most of Bahrain is a flat and arid desert plain, with recurrent droughts and dust storms the main natural dangers for its inhabitants. Famous for its pearl fisheries for centuries, today it is also known for its financial, commercial and communications sectors.
- Towards the central left part of the island, Bahrain University is observable. Also visible, the Al Areen Wildlife Reservation, both a nature reserve and zoo, one of the five protected areas of the country, and the only protected area on land.
- On the bottom-right tip of the island a series of horseshoe-shaped artificial atolls are clearly visible. Durrat Al Bahrain, one of the largest artificial islands in Bahrain, comprises six atolls and five fish-shaped islands.
- On the left side of the image, in Saudi Arabia, part of the Rub' al-Khali, the world's largest sand desert, is also visible.
- Distinct throughout the entire image, the striking variations of blue represent the shallow versus deep waters, with the presence of coral reefs.
Figure 45: This Sentinel-2A image, acquired on Sept. 18, 2015, is showing the colors of the Persian Gulf and the archipelago of the island state of Bahrain (image credit: Copernicus Sentinel data (2015)/ESA)
• December 18, 2015: The false-color image of Figure 46 features southern Mongolia, bordered by China to the south and Russia to the north. Known for its vast, harsh stretches of space and its nomadic people, Mongolia sits deep within eastern Asia, distant from any ocean. Home to the two-humped Bactrian camel, herds of horses and the Gobi Desert, Mongolia is predominantly a sandy and rocky plain, with an average elevation of some 1500 m above sea level. 71)
- The Gobi Desert covers parts of China and of southern Mongolia. It is a rain shadow desert, formed by the Himalayas blocking the Indian Ocean's rain from reaching the Gobi territory. Asia's largest desert and the fifth largest in the world, much of the Gobi is not sandy, but rocky. With long, cold winters and short, cool-to-hot summers, the climate of the Gobi Desert presents powerful extremes, with rapid temperature shifts of as much as 35ºC, not only seasonally but also within 24 hours. - At the bottom of the image, part of the Baga Bogd Mountain range is visible. Its highest peak has an elevation of 3600 m.
- Low vegetation is present during the warm months. This, along with some scattered trees, gives the red tones that can be seen in the image. Varying tones of red represent the various types of vegetation and the varying density and condition of the plants.
- The sharp image of the MSI (Multispectral Imager) on Sentinel-2A reveals spectacular erosion patterns where the eroded soil, with the help of rain, is carried from the mountain slopes to the lower regions.
- There is a very distinct body of water towards the top right part of the image, the Taatsiin Tsagaan Lake, one of the four saline lakes that make up the Valley of the Lakes. Mongolia joined the Ramsar Convention on 8 April 1998, which covers Wetlands of International Importance. The lake's depth and high concentration of salt give the water a vivid turquoise color.
Figure 46: False-color image of southern Mongolia, acquired by Sentinal-2A on August 15, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• December 11, 2015: The natural color image of Figure 47 features the area of Les Deux Alpes and surroundings, in France. A ski resort in the French Isère department, the village of Les Deux Alpes is located at an altitude of 1650 m with its ski lifts running up to 3600 m. Located near Western Europe's largest mountain, Mont Blanc, it accesses the greatest skiable glacier in Europe and is France's second oldest ski resort. 72)
- The relief differences in the area are clear thanks to Sentinel-2's high-resolution multispectral instrument. The brownish colors represent those parts of the mountains without vegetation or settlements. The village of Le Bourg-d'Oisans is clearly visible in the center of the image, with agricultural plots around it.
- The grey area on the top left corner is the city of Grenoble, in the Rhône-Alps region of southeastern France. It sits along the Isère River, at 214 m above sea level. Home to some 160 000 people, Grenoble's history goes back 2000 years. Today it is a leading scientific research center, renowned for research in nuclear physics and microelectronics.
- Among various bodies of water, the Lac Monteynard-Avignonet is clearly visible, snaking its way down the image. This is a 10 km-long and, in some places, 300 -wide artificial reservoir created in 1961. Often windy and rippled, the lake is considered to be one of the best places for wind and kite surfing in Europe.
Figure 47: Sentinel-2A portrait of the Les Deux Alpes and surroundings in France, acquired on August 29, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• December 3, 2015: ESA is pleased to announce the availability of Sentinel-2A orthorectified products in the Sentinel Data Hub. Any products acquired from 28 November onward are available to any user. Sentinel-2 products can be searched for by selecting Sentinel-2 in the search menu, or search bar. 73)
- Sentinel-2 is currently in its Ramp-up Phase, operating the following observation scenario: with an average of 10 minutes MSI sensing time per orbit, Sentinel-2A is acquiring Europe and Africa systematic on every orbit, while the rest of the sunlit world land masses between 56º South and 84º North will be mapped with a 30 day revisit time.
• November 27, 2015: This false-color image of south Khartoum in Sudan (Figure 48) was one of the first from Sentinel-2A, acquired on 28 June 2015, five days after the spacecraft arrived in orbit. The scene confirms that Sentinel-2A is doing the job it was designed for: monitoring vegetation. The mission tracks variability in land surface conditions, with its wide swath width and frequent revisits showing how vegetation changes during the growing season. The high-resolution multispectral instrument reveals the area's agricultural condition. 74)
- Part of the Blue Nile River is visible on the upper right corner. The scattered reds bordering the river denote the dense vegetation. In this arid part of the country, much of the agriculture is highly concentrated around the river. Along the Blue Nile, farming patterns recall French-style farms. Every agricultural plot is a distinctive rectangle, with some substantially longer than others. This geometric arrangement allows each plot to be irrigated. The main crops include sorghum, wheat, cotton, sunflower groundnuts, vegetables, fruit trees, and alfalfa.
Figure 48: The Sentinel-2A scene lies just south of the capital, Khartoum, the country's second largest city. It is located between the White Nile River on the left (not visible) and the Blue Nile River on the right, which flows west from Ethiopia (image credit: Copernicus Sentinel data (2015)/ESA)
• November 20, 2015: The image of Merida (Figure 49) was acquired by Sentinel-2A. Merida, with a population of 60,000, is the capital of the autonomous community of Extremadura, in western Spain. Owing to the satellite's high-resolution multispectral instrument, the color distinction of this arid area is obvious. The greys are the small towns of Montijo and Santa Amalia, on either side of Merida, while the scattered greens are fields of different crops and plants, crisscrossed with canals. The brown and reddish are the typical colors of fields without vegetation, which was the case when the image was captured in August 2015. 75)
- The Guadiana River is also visible, crossing through the centre of the image, along with various smaller bodies of water, all fundamental for irrigating the many fields in such a dry area. The land is divided into estates, where vineyards and olive groves are cultivated along with wheat. Dry farming predominates, with winter wheat and barley as major crops.
- In the lower central part of the image, the small town of Almendralejo is visible, situated in a brownish area. Here the local agriculture features extensive cereals, fruit and grapes, with many vineyards around the town, where a local red wine and brandy are produced.
- Sitting on the north bank of the Guadiana River, Merida was designated a UNESCO World Heritage site in 1993 because of its various archaeological remains. Founded by the Romans in 25 BC, the town still has many Roman remains. A granite bridge, the longest of all Roman bridges still used by pedestrians, is one of the major remains. North of Merida, the Proserpina Dam is visible, a large Roman reservoir that carried water to the town by a magnificent aqueduct, of which there are extensive remains.
Figure 49: True-color image of Merida in western Spain, acquired by Sentinel-2A on August 11, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• November 13, 2015: Figure 50 is a false-color image featuring the city of Qingdao and its surroundings, in China's eastern Shandong province. A major cultural center, Qingdao is home to the Ocean University of China and other higher education facilities. It is also one of China's main hubs for marine science and technology. Qingdao is located on the south coast of the Shandong Peninsula, at the eastern entrance to Jiaozhou Bay. Off the Yellow Sea, it is one of the best natural harbors in China. 76)
- Owing to the satellite's multispectral high-resolution instrument, one can clearly make out boats entering and exiting the bay, along with the impressive 26.7 km long Jiaozhou Bay Bridge running across the entire bay. As of 2012, the Guinness World Records lists the bridge as the world's longest bridge over water.
- Various aquacultures are visible along the coast of the bay, including the farming of fish, crustaceans, molluscs and aquatic plants.
- Towards the top of the image, one can make out a big body of water, the Jihongtan Reservoir, the biggest of the various reservoirs featured.
- Owing to the image processing, vegetation appears in reds scattered throughout the entire scene, showing how fertile and lush the region is.
Figure 50: This false-color image of Qingdao, China was captured by Sentinel-2A on August 21, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• November 6, 2015: The capital of Egypt, Cairo is one of the largest cities in Africa. It has existed for over 1000 years on the same spot on the Nile River banks. Located in the northeastern part of the country, Cairo is the passage to the Nile delta. The Nile River is the father of African rivers and the longest river in the world. With a length of some 6650 km, it rises south of the equator and flows northwards through northeastern Africa, draining into the Mediterranean Sea. 77)
- The river is the cause of the strong contrasts we see in the image. The river's fertility allowed the Egyptians to thrive despite the arid surrounding desert. It has always delivered the necessary water to transform the desert into a lush garden, where produce such as tomatoes, potatoes, sugar cane, rice and even cotton are grown. The Nile Delta, in fact, ranks among the world's most fertile farming areas. The sharp borderline between green fields and the yellow–brown desert is clear. Notice how the area is greener on the west side – the terrain is flatter, so more easily irrigated than the higher terrain to the east.
- The city of Cairo shows striking contrasts. Along the well-irrigated shoreline, the green reveals the thick vegetation, while the grey areas denote the dense city. In the older areas to the east, however, beneath the foothills of the Eastern Desert and the rocky Muqattam Hills, brown and ochre are the dominant colors.
- The city continuously mixes ancient and new. The Pyramids of Giza, erected on a rocky plateau on the west bank of the Nile, stand at the southwestern edge of the city, while the world's oldest surviving obelisk in the northeast marks the site of Heliopolis, a suburb of Cairo some 10 km from the city center.
Figure 51: This image from Sentinel-2A, acquired on August 13, 2015, features Cairo and portions of the Nile Delta in Egypt (image credit: Copernicus Sentinel data (2015)/ESA)
• October 23, 2015: Mexico City (Figure 52), the home of nearly nine million people, is the densely populated, high-altitude capital of Mexico.The optical camera of Sentinel-2A clearly shows the difference between the densely built city center and the vast surrounding vegetation. The brownish-grey patch in the right corner of the central part of the image is a flat area with some agriculture, crisscrossed by canals. Mexico International Airport is also visible, and further along the dark green rectangle is Lake Nabor Carrillo. This is a reservoir, encompassing more than 14,163 ha, which is 41 times larger than New York's Central Park. 78)
- Mexico City is located in the Valley of Mexico, also called the Valley of Anáhuac, a large valley in the high plateaus in the center of Mexico, at an altitude of 2240 m. This valley is in the Trans-Mexican Volcanic Belt, which is at least 2200 m above sea level. Mountains and volcanoes surround it, with elevations reaching beyond 5000 m.
- The city rests mainly on the heavily saturated clay of what used to be Lake Texcoco. This soft base is collapsing through the over-extraction of groundwater, and the city has sunk as much as nine meters in some areas since the beginning of the 20th century.
- Clouds are scattered throughout the image, under which lie various national parks and some of the still-active volcanoes, such as Popocatépetl at 5426 m.
Figure 52: This natural-color Sentinel-2A image features Mexico City and its surroundings, acquired on August 6, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• Figure 53 was released by ESA on October 16, 2015 showing the beautiful true-color image of the Red Sea coral reefs off the coast of Saudi Arabia. This vast, desolate area in the very northern corner of the Red Sea is bordered by the Hejaz Mountains to the east. The area was once crisscrossed by ancient trade routes that played a vital role in the development of many of the region's greatest civilizations. 79)
- The Red Sea separates the coasts of Egypt, Sudan and Eritrea to the west from those of Saudi Arabia and Yemen to the east. It contains some of the world's warmest and saltiest seawater. With hot sunny days and the lack of any significant rainfall; dust storms from the surrounding deserts frequently sweep across the sea. This hot dry climate causes high levels of evaporation from the sea, which leads to the Red Sea's high salinity.
- The Red Sea is just over 300 km across at its widest point, about 1900 km long and up to 2600 m deep. Much of the immediate shoreline is quite shallow, dotted with coral reefs along most of the coast — making excellent diving spots in many areas. The Red Sea lies in a fault separating two blocks of Earth's crust – the Arabian and African plates.
- Its name derives from the color changes in the waters. Normally, the Red Sea is an intense blue–green. Occasionally, however, extensive algae blooms form and when they die off they turn the sea a reddish-brown color.
- Navigation in the Red Sea is difficult. The shorelines in the northern half provide some natural harbors, but the growth of coral reefs has restricted navigable channels and blocked some harbor facilities. Shallow submarine shelves and extensive fringing reef systems rim most of the Red Sea, by far the dominant reef type found here. The lighter blue water depicted in the image means that the water is shallower than the surrounding darker blue water.
- Furthermore, water clarity is exceptional in the Red Sea because of the lack of river discharge and low rainfall. Therefore, fine sediment that typically plagues other tropical oceans, particularly after large storms, does not affect the Red Sea reefs.
Figure 53: Deep blue Red Sea reefs captured with Sentinel-2A on June 28, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• Sept. 18, 2015: The early Sentinel-2A ‘color vision' image of Figure 54 captures part of the Mississippi swamps on the east and west banks of the Mississippi River, south of New Orleans and north of the Mississippi Delta. 80)
- From agricultural monitoring to charting changing lands, images from Europe's Sentinel-2A ‘color vision' satellite can be used for many practical applications and to keep us, and our planet, safe. The red color scattered throughout the image shows the enormous amount of vegetation in the area, while the grey represents the various bodies of water.
- Close to the heart of the snake-like Mississippi River, the image clearly shows the typical French-style fields, with rows of sugar cane, around the towns of Lucy, Edgard and Wallace. On the east bank of the Mississippi lie the towns of LaPlace, Reserve, Lions, Garyville and Mount Airy, each with industries along the river, including a chemical plant, sugar refinery, grain elevators and an oil refinery.
- Bayous are scattered all over the image. A bayou is a Franco-English term for an extremely slow-moving stream or river, marshy lake or wetland. They are commonly found in the Mississippi River Delta, famous within the states of Louisiana and Texas. Though fauna varies by region, many bayous are home to crawfish, certain species of shrimp, other shellfish, catfish, frogs, toads, American alligators and crocodiles, and the alligator snapping turtle.
- Towards the upper left part of the image, under the many clouds, lies Baton Rouge, the capital of Louisiana and its second-largest city. On the eastern bank of the Mississippi River, Baton Rouge is a major industrial, petrochemical, medical, research, motion picture and growing technology center of the American south. The port of Baton Rouge is the ninth largest in the United States in terms of tonnage shipped.
Figure 54: This MSI image of Sentinel-2A was captured on July 15, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• Sept. 11, 2015: The varying shades of red and other colors across the entire image (Figure 55) indicate how sensitive the satellite's multispectral camera is to differences in vegetation cover and chlorophyll content. This is used to provide key information on plant health. The brighter reds indicate more photosynthetically active vegetation, as seen in many of the fields and along the Roveto Valley Abruzzi mountain range in the lower left. 81)
- In the very center of the image, a cloud and its shadow are clearly visible over the plain. On the central left side, one can make out an industrial area, whereas the town of Avezzano is just further north.
- The entire area in the center is where the Fucino Lake used to be. The Romans founded settlements on its banks as the lake provided fertile soil and a large quantity of fish. However, the lake was believed to harbor malaria, and, not having a natural outflow, it repeatedly flooded the surrounding arable land.
- In 1862 Prince Alessandro Torlonia commissioned a Swiss engineer to drain what was once Italy's third largest lakes. A 6.3 km long and 21 m wide canal was dredged. By 1875 the lake was completely drained, and the resulting plain is one of Italy's most fertile regions today.
- A canal is clearly visible running horizontally across the center of the image.
- In the lower-right section of the plain is a cluster of dots surrounded by fields: the Fucino Space Center, one of the largest civil space centers in the world, a node for missions operations. The dots are the 100 antennas sited on an extension of 370 ,000 m2. Fucino also hosts one of the control centers that will manage the 30 satellites and the operational activities of Galileo, the European satellite navigation system.
Figure 55: This Sentinel-2A false color image, captured on July 8, 2015, shows agricultural structures in the Abruzzo region of central Italy (Copernicus Sentinel data (2015)/ESA)
• Sept. 4, 2015: The Sentinel-2A satellite has been in orbit for only a matter of weeks, but new images of an algal bloom in the Baltic Sea show that it is already exceeding expectations. Built essentially as a land monitoring mission, Sentinel-2 will also certainly find its way into marine applications. 82)
- Warm weather and calm seas this August have increased the amount of biological activity in the central Baltic Sea, with the Finnish algae monitoring service Alg@line reporting a dominance of cyanobacteria in the region at this time.
- The Baltic Sea faces many serious challenges, including toxic pollutants, deep-water oxygen deficiencies, and toxic blooms of cyanobacteria affecting the ecosystem, aquaculture and tourism. The situation was so bad that in 1974 the Helsinki Convention for the Protection of the Marine Environment of the Baltic Sea Area was created to improve the state of the sea. Since then, the health of the Baltic Sea has improved dramatically.
- Blooms in the Baltic Sea usually appear as a green–yellow soup or a mass of blue–green threads along density gradients within the sea. The streaks and filaments, eddies and whirls of biological activity are clearly visible in these new images.
- Cyanobacteria have qualities similar to algae and thrive on phosphorus in the water. High water temperature and sunny, calm weather often lead to particularly large blooms that pose problems to the ecosystem and, therefore, aquaculture and tourism. Toxicity varies between different species, but can also vary within the same species. Because of this, several teams monitor the status of blooms in the region using ships.
Figure 56: Sentinel-2A captured this detailed image of an algal bloom in the middle of the Baltic Sea on 7 August 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
Legend to Figure 56: The image, which has a spatial resolution of 10 m, reveals the bloom in exquisite detail as well as a ship heading into the ‘eye of this algal storm'. The ship's wake can be seen as a straight dark line where the bloom has been disturbed by the ship's propellers.
• Sept. 4. 2015: Figure 57 features Lake Amadeus in Australia's desert. The image shows the variety of the sandy, rocky and salty formations within the lake. Around 180 km long and 10 km wide, Amadeus is the largest salt lake in the Northern Territory, just 50 km north of Uluru/ Ayers Rock. 83)
- Lake Amadeus contains up to 600 million tons of salt. However, harvesting is not feasible because of its remote location. Owing to the aridity of the area, the surface of Lake Amadeus is often a dry salt crust. When rainfall is sufficient, it becomes part of an east-flowing drainage system that eventually connects to the Finke River.
- A UNESCO World Heritage Site and one of Australia's most recognizable landmarks, Uluru/Ayers Rock is a large sandstone rock formation standing 348 m high, rising 863 m above sea level and with a circumference of 9.4 km.
- Also clearly visible in the lower-central part of the image are the Petermann Ranges. These mountains run 320 km across the border between Western Australia and the southwest corner of the Northern Territory. Their highest point is 1158 m above sea level. The range was formed about 550 million years ago as compression folded a section of Earth's crust.
Figure 57: Lake Amadeus in Australia's Northern Territory, captured on July 13, 2015 with the Sentinel-2A spacecraft (image credit: Copernicus Sentinel data (2015)/ESA)
• July 31, 2015: The largest lake in Figure 58 is the southern part of Lake Maggiore. Straddling the border of Italy's Lombardy and Piedmont regions – with its northern end in Switzerland (not visible) – the lake covers an area of over 210 km2. Its outlet, the Ticino river, snakes south past the Milan–Malpensa Airport at the bottom of the image. 84)
- Near the center of the image is the glacial Lake Varese, appearing in lighter blue when compared to the other lakes in the image. This demonstrates Sentinel-2's ability to measure differences in the conditions of inland water bodies – one of the mission's main applications along with land cover, agriculture and forestry.
Figure 58: Sentinel-2A image of lakes on the southern side of the Italian Alps, acquired on June 27, 2015 (image credit: Copernicus Sentinel data (2015)/ESA)
• July 27, 2015: From agricultural monitoring to charting changing lands, early images from Europe's new Sentinel-2A satellite show how the ‘color vision' mission's critical observations can be used to keep us and our planet safe. Only one example from several land-monitoring applications is shown here. 85)
- Sentinel-2's imager has 13 spectral bands, from the visible and the near-infrared to the shortwave infrared at different spatial resolutions, taking land monitoring to an unprecedented level. In fact, it is the first optical Earth observation mission of its kind to include three bands in the ‘red edge', which provide key information on the state of vegetation. - This was demonstrated by Pierre Defourny from the University of Louvain in Belgium, who showed how the satellite is even able to discriminate between different crops, showing an example of sunflowers and maize growing near Toulouse in France.
Figure 59: In this image from 6 July 2015 acquired near Toulouse, France, the satellite's multispectral instrument was able to discriminate between two types of crops: sunflower (in organge) and maize (in yellow), image credit: Copernicus Sentinel data (2015)/ESA/University of Louvain/CESBIO
• July 10, 2015: More than 90% of Algeria, which is the largest country in Africa (2,381,741 km2 ), is covered by the Sahara desert. Major oil and natural gas deposits lie beneath the Sahara, contributing to Algeria's position as one of the wealthiest African nations. 86)
- In its entirety, the Sahara stretches from the Atlantic Ocean to the Red Sea and is centered on the Tropic of Cancer. It is the world's largest hot desert, covering an area of about 9 million km2 over parts of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Tunisia and Sudan.
Figure 60: The sandy and rocky terrain of the Sahara desert in central Algeria was captured in this image by the Sentinel-2A satellite, also acquired on June 27, 2015 and delivered in the first scan of Earth with the MSI instrument (image credit: Copernicus Sentinel data (2015)/ESA)
Legend to Figure 60: The area pictured is about 90 km south of the El Ménia oasis – also known as El Goléa – in Algeria's Ghardaïa province. Running north to south just left of the large sand dune at the center, one can see a road that connects El Ménia to Ain Salah in the south, which was once an important link on the trans-Saharan trade route.
The heat and lack of water render vast desert areas highly unwelcoming, making satellites the best way to observe these environments on a large scale. In addition, optical imagery of deserts from space is arguably the most fascinating: the diversity and untouched state of these landscapes produce unique and striking scenes.
• June 29, 2015: Just four days after being lofted into orbit, Europe's Sentinel-2A satellite delivered its first images of Earth, offering a glimpse of the ‘color vision' that it will provide for the Copernicus environmental monitoring program. 87)
- With a swath width of 290 km, the satellite's first acquisition began in Sweden and made a strip-like observation through central Europe and the Mediterranean, ending in Algeria. The data were relayed in real time to Italy's Matera ground station, where teams eagerly awaited their arrival for processing.
- While northern and central Europe were mostly cloudy, Italy's typical sunny weather allowed the teams to get their first glimpse of the multispectral instrument's capabilities over the northwestern part of the country and the French Riviera — and they were excited by what they saw. With a ground resolution of 10 m per pixel, the images show individual buildings in Milan, agricultural plots along the Po River, and ports along the southern French coast.
- "This new satellite will be a game changer in Earth observation for Europe and for the European Copernicus program," said Philippe Brunet, Director for Space Policy, Copernicus and Defence at the European Commission. The Director of ESA's Earth Observation Programs, Volker Liebig, commented, "Sentinel-2 will enable us to provide data for the program's land monitoring services and will be the base for a wide spectrum of applications reaching from agriculture to forestry, environmental monitoring to urban planning."
- The MSI (Multispectral Imager) is being calibrated during the commissioning phase – which will take about three months to complete – but the quality of these first images already exceeds expectations. In addition to demonstrating the imager's high resolution, these initial data also foreshadow the mission's land-monitoring applications in areas such as agriculture, inland and coastal waters and land-cover mapping.
- The imager's 13 spectral bands, from the visible and the near infrared to the shortwave infrared at different spatial resolutions, take land monitoring to an unprecedented level. In fact, Sentinel-2A is the first optical Earth observation mission of its kind to include three bands in the ‘red edge', which provide key information on the state of vegetation.
- This weekend's activities also demonstrated that the operational processor works flawlessly, paving the way for the mission's systematic data generation to come.
Figure 61: First MSI image of Sentinel-2A, acquired on 27 June 2015, just four days after launch, covering the Po Valley, framed by the Alps in the north and the coastal mountains of France and Italy in the south (image credit: Copernicus data (2015)/ESA)
Figure 62: This close-up of Milan is a subset from the first image of Figure 61 of Sentinel-2A, acquired on 27 June 2015 (image credit: Copernicus data (2015)/ESA)
Figure 63: A close-up of an area in the Po Valley — showing Pavia (center) and the confluence of the Ticino and Po rivers — is a subset of Figure 61 from the Sentinel-2A, acquired on 27 June 2015. Processed using the high-resolution infrared spectral channel, the satellite's instrument will provide key information on crop type and health, assisting in food security activities (image credit: Copernicus data (2015)/ESA)
Figure 64: This close-up of France's southern coast from Nice airport (lower left) to Menton (upper right) is a subset of Figure 61 from the Sentinel-2A, acquired on June 27, 2015. This false color image was processed including the instrument's high-resolution infrared spectral channel (image credit: Copernicus data (2015)/ESA, Ref. 87)
Figure 65: This image of Sardinia, acquired on June 27, 2015, covers section of the island's northwestern Sassari province, with parts of the coast visible along the left side and bottom. Agricultural fields dominate the inland, with a large area of vineyards at the center of the image (image credit: Copernicus data (2015)/ESA)
Legend to Figure 65: The varying shades of red and other colors across the entire image indicate how sensitive the multispectral instrument is to differences in chlorophyll content. This is used to provide key information on plant health and, for this image, the brighter reds indicate healthier vegetation. In the lower left section, one can see a large hilly area with significant vegetation – indicated by the red coloring. However, a bright white/light-blue section of this area shows where the hills have been cut into for surface mining.
• LEOP (Launch and Early Orbit Phase) formally ended on June 26, 2015. The mission control team dealt with several typical problems seen in any launch, including issues with a sticky valve, a star tracker and a GPS unit. These have been resolved and the satellite is now in excellent health. "We conducted our first orbital maneuver using the Sentinel-2A thrusters yesterday, and this went exactly as planned," said Spacecraft Operations Manager Franco Marchese. "Overall, this LEOP has gone very smoothly and we are well en route to achieving our reference orbit within next week." 89)
- LEOP is being followed by the 3-month commissioning phase. The two main objectives now will be to assess and characterize the spacecraft performance. In parallel, calibration and validation activities will be conducted for the MSI (Multispectral Imager) payload, involving CNES and ESA. In addition, the new optical data communication capability will be commissioned by DLR and Tesat Space.
- The spacecraft will also be readied to start the routine acquisition of high-resolution images of Earth's land surfaces, large islands, inland and coastal waters on a ten-day revisit cycle, which will drop to five days when the constellation with the Sentinel-2B satellite is implemented in 2016.
• June 23, 2015: Just a few minutes after separation from its Vega launcher on 23 June, the Sentinel-2A satellite automatically activated its solar array and transmitter, oriented itself into an Earth-pointing mode, and started transmitting 'telemetry' – onboard status signals – to the ground. Receipt of these first crucial data from the new mission marked the start of an intensive phase in the ESOC MOC (Mission Control Center) in Darmstadt, Germany. 90)
- For the next several days, an extended team of spacecraft engineers, systems specialists, flight dynamics experts and ground station technicians will shepherd Sentinel-2A through LEOP Launch and Early Orbit Phase).
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. 91) 92) 93) 94) 95) 96) 97)
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 66: Illustration of the MSI instrument (image credit: ESA, Ref. 8)
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 69.
Table 7: Specification of VNIR and SWIR FPAs 98)
Figure 67: The MSI instrument (left) and the associated VNIR focal plane (right), image credit: Airbus DS-ISAE-e2v
Figure 68: Left: VNIR FPA (image credit: Airbus DS-F, ev2); right: SWIR FPA (image credit: Airbus DS-F, Sofradir)
Figure 69: 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 70). 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 71: MSI electrical architecture (image credit: Astrium SAS, Ref. 94)
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 72: Internal configuration of MSI (image credit: EADS Astrium)
Figure 73: 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 73) 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. 99)
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. 100)
Figure 74: 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 75: 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. 101)
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 76: Photo of the VNIR (top) and SWIR spectral filter assemblies (image credit: Jena Optronik)
Figure 77: 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 78: 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. 102)
Figure 79: 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 80: 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 81: 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. 103) 104) 105)
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 82. 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 82: 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 83: Photo of the EQM (Engineering Qualification Model), Sentinel-2 MMFU (image credit: Astrium)
Table 14: Parameters of the Sentinel-2 MMFU 106)
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 84: PGDS context in Sentinel-2 system (image credit: ESA)
Figure 85: The Sentinel-2 ground segment (image credit: ESA)
Figure 86: Physical layout of the PGDS ground stations (image credit: ESA) 107)
• 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. 108)
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 87: 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. 114)
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. 115)
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 88: Image of the North Palau Reef (Western Pacific), acquired with Sentinel-2A on Feb. 10, 2016 (image credit: ESA, Sen2Coral consortium)
Figure 89: Image of Fatu Huku (Pacific) acquired with Sentinel-2A on Feb. 11, 2016 (image credit: ESA, Sen2Coral consortium)
Figure 90: 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 91: 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.
1) P. Martimort, O. Arino, M. Berger, R. Biasutti, B. Carnicero, U. Del Bello, V. Fernandez, F. Gascon, B. Greco, P. Silvestrin, F. Spoto, O. Sy, "Sentinel-2 Optical High Resolution Mission for GMES Operational Services," Proceedings of IGARSS 2007 (International Geoscience and Remote Sensing Symposium), Barcelona, Spain, July 23-27, 2007
2) P. Martimort, F. Spoto, B. Koetz, O. Arino, M. Rast, "GMES Sentinel-2, The Optical High Resolution Mission for GMES Operational Services," July 16, 2007, URL: http://www.earthobservations.org/documents/cop/ag_gams/200707_01/gmes-sentinel2.pdf
3) ESA Sentinel-2 Team, "GMES Sentinel-2 Mission Requirements Document," Issue 2, Revision 1, 08.03.2010, URL: http://esamultimedia.esa.int/docs/GMES/Sentinel-2_MRD.pdf
4) F. Spoto, M. Berger, "Sentinel-2 Presentation," March 7-8, 2007, ESA/ESRIN, URL: http://esamultimedia.esa.int/docs/GMES/ESA/4_coloc_GMES_S2_GSC_day_7_8-March_2007.pdf
5) P. Martimort, M. Berger, B. Carnicero, U. Del Bello, V. Fernandez, F. Gascon, P. Silvestrin, F. Spoto, Omar Sy, O. Arino, R. Biasutti, B. Greco, "Sentinel-2 : The Optical High Resolution Mission for GMES Operational Services," ESA Bulletin, No 131, Aug. 2007, pp. 19-23, URL: http://www.esa.int/esapub/bulletin/bulletin131/bul131b_martimort.pdf
6) Philippe Martimort, "The Optical High Resolution Mission The for GMES Operational Services for Services," GMES Sentinel-2, AGRISAR Workshop, Noordwijk, The Netherlands, Oct. 15-16, 2007, URL: http://www.dlr.de/hr/Portaldata/32/Resources/dokumente/agrisar/(03)_GMES_S2-Presentation_AGRISAR.pdf
7) F. Spoto, P. Martimort, O. Sy, P. Bargellini, B. Greco, "Sentinel-2: the European operational fast revisit high resolution land observing mission," Sentinel-2: the European operational fast revisit high resolution land observing mission
8) François Spoto, Philippe Martimort, Omar Sy, Paolo Laberinti, Stefane Carlier, Umberto Del Bello, Valérie Fernandez, Volker Kirschner, Claudia Isola, Matthias Drusch, Pier Bargellini, Franco Marchese, Olivier Colin, Ferran Gascon, Bianca Hoersch, Aimé Meygret, "The GMES Sentinel-2 Operational Mission," Proceedings of the ESA Living Planet Symposium, SP-686, Bergen Norway, June 28-July 2, 2010
9) "Copernicus: new name for European Earth Observation Programme," European Commission Press Release, Dec. 12, 2012, URL: http://europa.eu/rapid/press-release_IP-12-1345_en.htm
10) ESA's Sentinel-2 team, "Color Vision for Copernicus, The story of Sentinel-2," ESA Bulletin No 161, May 11, 2015, pp. 2-9, URL: http://esamultimedia.esa.int/multimedia/publications/ESA-Bulletin-161/offline/download.pdf
12) GMES Sentinel-2 Industry Day, Nov. 26, 2007, URL: http://esamultimedia.esa.int/docs/industry/Sentinel/Nov07/Sentinel-2-Industry-Day-Nov-07-Astrium-VGs.pdf
14) Francois Spoto, Omar Sy, Paolo Laberinti, Philippe Martimort, Valerie Fernandez, Olivier Colin, Bianca Hoersch, Aime Meygret, "Overview of Sentinel-2," Proceedings of IGARSS (International Geoscience and Remote Sensing Symposium), Munich, Germany, July 22-27, 2012
15) "Astrium to build ESA's second Sentinel-2 satellite for GMES," March 31, 2010, URL: http://www.esa.int/esaLP/SEME2GIK97G_LPgmes_0.html
17) "Sentinel-2 — The Operational Copernicus Optical High Resolution Land Mission," ESA, URL: http://esamultimedia.esa.int/docs/S2-Data_Sheet.pdf
18) S. Winkler, G. Wiedermann, W. Gockel, "High-Accuracy On-Board Attitude Estimation for the GMES Sentinel-2 Satellite: Concept, Design, and First Results," AIAA Guidance, Navigation and Control Conference and Exhibit, August 18-21, 2008, Honolulu, Hawaii, USA, AIAA 2008-7482
19) "CORECI An integrated COmpression REcording and CIphering solution for earth observation satellites," 2014, Airbus DS, URL: http://www.space-airbusds.com/media/document/ens_4_coreci_2014_bd.pdf
20) "Compression Recording Ciphering Unit," Airbus DS, URL: http://www.space-airbusds.com/en/equipment/coreci-an-integrated-compression-recording-and-ciphering-solution-for-earth.html
21) "Revealing Sentinel-2B," ESA, Jan. 12, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/01/Revealing_Sentinel-2B
22) "Copernicus' Second Eye is ready to meet its Launcher," Airbus DS, Nov. 15, 2016, URL: https://airbusdefenceandspace.com/newsroom/news-and-features/copernicus-second-eye-is-ready-to-meet-its-launcher/
23) "Airbus Defence and Space completes second Copernicus "Eye","Airbus DS Press Release, June 15, 2016, URL: https://airbusdefenceandspace.com/newsroom/news-and-features/airbus-defence-and-space-completes-second-copernicus-eye/
24) "Processing begins with the Sentinel-2A payload for Arianespace's Vega launch in June," Arianespace, April 27, 2015, URL: http://www.arianespace.com/news-mission-update/2015/1287.asp
25) "Preparing to launch 'color vision' satellite," ESA, April 23, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-2
26) "Last stretch before being packed tight," ESA, April 8, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
27) "Last look at Sentinel-2A," ESA, Feb. 24, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
28) "Airbus Defence and Space delivers Sentinel-2A environmental monitoring satellite for testing," Airbus DS Press Release, Aug. 21, 2014, URL: http://www.space-airbusds.com/en/press_centre/airbus-defence-and-space-delivers-sentinel-2a-environmental-monitoring.html
29) "Bringing Sentinel-2 into focus," ESA, May 28, 2014, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus-Bringing_Sentinel-2_into_focus
30) "Sentinel-2," ESA Bulletin, No 160, November 2014, p. 76
31) "Second Copernicus environmental satellite safely in orbit," ESA, June 23, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
32) "Arianespace orbits second satellite in Copernicus system, Sentinel-2A, on fifth Vega launch," Arianespace Press Release, June 22, 2015, URL: http://www.arianespace.com/news-press-release/2015/6-22-2015-VV05-launch-success.asp
33) Robert Lange, Frank Heine, Hartmut Kämpfer, Rolf Meyer, "High Data Rate Optical Inter-Satellite Links," 35th ECOC (European Conference on Optical Communication) Sept. 20-24, 2009, Vienna, Austria
35) "Sentinel-2B launch preparations off to a flying start," ESA, January 12, 2017, URL: http://m.esa.int/Our_Activities/Observing_the_Earth/Copernicus
36) "Sicilian snow," ESA Earth observation image of the week, Feb. 10, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/02/Sicilian_snow
37) "Musa Bay, Iran," ESA Earth observation image of the week, Feb. 3, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/02/Musa_Bay_Iran
38) "Botswana wetlands," ESA, Feb. 2, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/02/Botswana_wetlands
39) Saint Petersburg," ESA Earth observation image of the week, Jan. 13, 2017, URL: http://m.esa.int/spaceinimages/Images/2017/01/Saint_Petersburg
40) "China's Tian Shan mountains," ESA, Earth observation image of the week, Dec. 23, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/12/China_s_Tian_Shan_mountains
41) "Agricultural monitoring in Spain," ESA, Dec. 20, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/12/Agricultural_monitoring_in_Spain
42) "Seville, Spain," ESA, Earth observation image of the week, Dec. 16, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/12/Seville_Spain
43) "Switzerland," ESA, Earth observation image of the week, Dec. 2, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/12/Switzerland
44) "Chiapas forest land-cover map," ESA, Nov. 25, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/11/Chiapas_forest_land-cover_map
45) "Gibson Desert," ESA, Earth observation image of the week, Nov. 18, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/11/Gibson_Desert
46) "Sentinel sees us," ESA, URL: http://m.esa.int/spaceinimages/Images/2016/11/Sentinel_sees_us
47) "Putorana Plateau, Siberia," ESA, Earth observation image of the week. Oct. 28, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/10/Putorana_Plateau-Siberia
48) "Kathmandu, Nepal," ESA, Earth observation image of the week, Oct. 21, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/10/Kathmandu_Nepal
49) "Ouarkziz crater," ESA, Sept. 30. 2016, URL: http://m.esa.int/spaceinimages/Images/2016/09/Ouarkziz_crater
50) "Fire-scarred Madeira," ESA, Earth observation image of the week, Sept. 14, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/09/Fire-scarred_Madeira2
51) "Barents bloom," ESA, Sept. 9, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/08/Barents_bloom
52) "Earth from Space: Barents bloom," ESA Earth from Space video program, Sept. 9, 2016, URL: http://m.esa.int/spaceinvideos/Videos/2016/09/Earth_from_Space_Barents_bloom
53) "Massive and Mysterious Ice Fall in Tibet," NASA Earth Observatory, Sept. 7, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=88677&src=eoa-iotd
54) "Nine killed by avalanche in Tibet," China Daily, July 18, 2016, URL: http://www.chinadaily.com.cn/china/2016-07/18/content_26128513.htm
55) "Upsala Glacier," ESA image of the week, Sept. 2, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/08/Upsala_Glacier
56) "Chile's salt flat," ESA, May 27, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/05/Chile_s_salt_flat
57) "Rub al Khali," ESA Earth observation image of the week, May 20, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/05/Rub_al_Khali
58) "Sun glitter reveals coastal waves," ESA, May 19, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
59) "African mosaic," ESA, May 18, 2015, URL: http://www.esa.int/spaceinimages/Images/2016/05/African_mosaic
60) "Czechered landscape," ESA, May 9, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/05/Czechered_landscape
61) "Colorful Naukluft," ESA, Earth observation image of the week, April 29, 12016, URL: http://www.esa.int/spaceinimages/Images/2016/04/Colourful_Naukluft
62) "Australia ensured access to Sentinel data," ESA, March 31, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
63) "Lake Amadeus," ESA, March 30, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/03/Lake_Amadeus
64) "Etosha," ESA Earth observation image of the week, March 25, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/03/Etosha
65) "Sentinel data wanted," ESA, March 15, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Sentinel_data_wanted
67) "Eastern Desert of Egypt," ESA Earth observation image of the week, Feb. 26, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/02/Eastern_Desert
68) "Madrid," ESA, Feb. 12, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/02/Madrid
69) "ESA selects Airbus Defence and Space for two new Sentinel-2 satellites," Airbus DS, January 26, 2016, URL: http://www.space-airbusds.com/en/press_centre/esa-selects-airbus-defence-and-space-for-two-new-sentinel-2-satellites.html
70) "Colors of the Persian Gulf," ESA, Jan. 22, 2016, URL: http://www.esa.int/spaceinimages/Images/2016/01/Colours_of_the_Persian_Gulf
71) "Mongolian marvel," ESA image of the week, release on Dec. 18, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/12/Mongolian_marvel
72) "French Portrait," ESA Image of the week released on Dec. 11, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/12/French_portrait
73) "Sentinel-2A products available in the Data Hub," ESA, Dec. 3, 2015, URL: https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/sentinel-2/news/-/article/sentinel-2a-products-available-in-the-data-hub
74) "Khartoum, Sudan," ESA Image of the week released on Nov. 27, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/11/Khartoum_Sudan
75) "Merida, Spain," ESAImage of the week , Nov. 20, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/11/Merida_Spain
76) "Qingdao, China," ESA Image of the week, released on Nov. 13, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/11/Qingdao_China
77) "Cairo, Egypt," ESA, Earth observation image of the week, Nov. 6, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/11/Cairo_Egypt
78) "Mexico City," ESA Earth observation image of the week, released on Oct. 23, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/10/Mexico_city
79) "Deep blue Red Sea reefs," ESA, Earth observation image of the week, October 16, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/10/Deep_blue_Red_Sea_reefs
80) "Mississippi swampland," ESA,'Earth observation image of the week,' released on Sept. 18, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/09/Mississippi_swampland
81) "Avezzano, Italy," ESA, Sept. 11, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/09/Avezzano_Italy
82) "Sentinel-2 catches the eye of algal storm," ESA, Sept. 4, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
83) "Australian desert," ESA, Sept. 4, 23015, URL: http://www.esa.int/spaceinimages/Images/2015/09/Australian_desert
84) "Northern Italy," ESA, Earth observation image of the week, July 31, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/07/Northern_Italy
85) "First applications from Sentinel-2A," ESA, July 22, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
86) "Central Algeria," ESA, Earth observation image of the week, July 10, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/07/Central_Algeria
87) "Sentinel-2 delivers first images," ESA, June 29, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-2-/Sentinel-2_delivers_first_images
88) "Northwest Sardinia," ESA, July 3, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/07/Northwest_Sardinia
89) "Sentinel-2A completes critical first days in space," ESA, June 26, 2015, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus
90) "Under control," ESA, June 23, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/06/Under_control
91) Vincent Cazaubiel, Vincent Chorvalli, Christophe Miesch, "The Multispectral Instrument of the Sentinel-2 Program," Proceedings of the 7th ICSO (International Conference on Space Optics) 2008, Toulouse, France, Oct. 14-17, 2008
92) Michel Bréart de Boisanger, Olivier Saint-Pé, Franck Larnaudie, Saiprasad Guiry, Pierre Magnan, Philippe Martin Gonthier, Franck Corbière, Nicolas Huger, Neil Guyatt, "COBRA, a CMOS Space Qualified Detector Family Covering the Need for many LEO and GEO Optical Instruments," Proceedings of the 7th ICSO (International Conference on Space Optics) 2008, Toulouse, France, Oct. 14-17, 2008
93) François Spoto , Philippe Martimort, Omar Sy, Paolo Laberinti, "Sentinel-2, Optical High Resolution Mission for GMES Operational services," Sentinel-2 Preparatory Symposium, ESA/ESRIN, Frascati, Italy, April 23-27, 2012, URL: http://www.s2symposium.org/
94) Vincent Chorvalli, Stéphane Espuche, Francis Delbru, Cornelius Haas, Philippe Martimort, Valérie Fernandez, Volker Kirchner, "The Multispectral Instrument of the Sentinel-2 Em Program Results," Proceedings of the ICSO (International Conference on Space Optics),Ajaccio, Corse, France, Oct. 9-12, 2012, paper: ICSO-023, URL: http://congrex.nl/icso/2012/papers/FP_ICSO-023.pdf
95) S. Espuche, V. Chorvalli, A. Laborie, F. Delbru, S. Thomas, J. Sagne, C. Haas, P. Martimort, V. Fernandez, V. Kirchner, "VNIR focal plane results from the multispectral instrument of the Sentinel-2 mission," Proceedings of the ICSO (International Conference on Space Optics), Tenerife, Canary Islands, Spain, Oct. 7-10, 2014, URL: http://congrexprojects.com/Custom/ICSO/2014/Papers/1.%20Tuesday%207-20October/Session%203A%20Detectors%20for%20Visible-20ROIC/2.74651_Espuche.pdf
96) "Sentinel-2 MSI Introduction," ESA User Guide, URL: https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi
97) "Sentinel-2 MSI Technical Introduction," ESA, URL: https://earth.esa.int/web/sentinel/sentinel-2-msi-wiki/-/wiki/Sentinel%20Two/What+is+Sentinel+Two
98) Jean-Loup Bezy, "Optical Instruments in ESA's Earth Observation Missions," Proceedings of the ICSO (International Conference on Space Optics), Tenerife, Canary Islands, Spain, Oct. 7-10, 2014, URL: http://congrexprojects.com/Custom/ICSO/2014/Presentations/01%20Plenary-20Room/Session%201/1.%20Optical%20Instruments%20in%20ESAs-20Earth%20Observations%20Missions,%20Jean-Loup%20Bezy.pdf
99) Michel Bougoin, Jerome Lavenac, "The SiC hardware of the Sentinel-2 Multi Spectral Instrument," Proceedings of the ICSO (International Conference on Space Optics), Ajaccio, Corse, France, Oct. 9-12, 2012, paper: ICSO-028, URL: http://congrex.nl/icso/2012/papers/FP_ICSO-028.pdf
100) P. Gloesener, F. Wolfs, F. Lemagne, C. Flebus, "Manufacturing, testing and alignment of Sentinel-2 MSI telescope mirrors," Proceedings of the ICSO (International Conference on Space Optics), Ajaccio, Corse, France, Oct. 9-12, 2012 , paper: ICSO-034, URL: http://congrex.nl/icso/2012/papers/FP_ICSO-034.pdf
101) Karin Schröter, Uwe Schallenberg, Matthias Mohaupt, "Technological Development of Spectral Filters for Sentinel-2," Proceedings of the 7th ICSO (International Conference on Space Optics) 2008, Toulouse, France, Oct. 14-17, 2008
102) J. A. Andion, X. Olaskoaga, "Sentinel-2 Multispectral Instrument Calibration and Shutter Mechanism," Proceedings of the 14th European Space Mechanisms & Tribology Symposium – ESMATS 2011, Constance, Germany, Sept. 28–30 2011 (ESA SP-698)
103) M. Staehle, M. Cassel, U. Lonsdorfer l, F. Gliem, D. Walter, T. Fichna, "Sentinel 2 MMFU: The first European Mass Memory System Based on NAND-Flash Storage Technology," Proceedings of the DASIA (DAta Systems In Aerospace) 2011 Conference, San Anton, Malta, May 17-20, 2011, ESA SP-694, August 2011
104) M. Staehle, M. Cassel, U. Lonsdorfer, F. Gliem, D. Walter, T. Fichna, "Sentinel-2 MMFU: The first European Mass Memory System based on NAND-Flash Storage Technology," Proceedings of ReSpace/MAPLD 2011, Aug. 22-25, 2011, Albuquerque, NM, USA, URL: https://nepp.nasa.gov/respace_mapld11/talks/thu/ReSpace_C/1030%20-%20Cassel.pdf
105) 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
106) Michael Stähle, Tim Pike, "ADCSS 2012 Astrium - Current and Future Mass Memory Products," 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_2510/09stahele_astriumfinal.pdf?sfvrsn=2
108) H. L. Moeller, S. Lokas, O. Sy, B. Seitz, P. Bargellini, "The GMES-Sentinels – System and Operations," Proceedings of the SpaceOps 2010 Conference, Huntsville, ALA, USA, April 25-30, 2010, paper: AIAA 2010-2189
109) Henri Laur, "SAR Interferometry opportunities with the European Space Agency: ERS-1, ERS-2, Envisat, Sentinel-1A, Sentinel-1B, ESA 3rd Party Missions (ALOS)," Fringe 2009 Workshop - Advances in the Science and Applications of SAR Interferometry, Frascati, Italy, Nov. 30-Dec. 4, 2009
110) "ESA Member States approve full and open Sentinel data policy principles," ESA, Nov. 27, 2009, URL: http://www.esa.int/esaEO/SEMXK570A2G_environment_0.html
111) Susanne Mecklenburg, "GMES Sentinel Data Policy - An overview," GENESI-DR (Ground European Network for Earth Science Interoperations - Digital Repositories) workshop, ESAC, Villafranca, Spain, December 4, 2009
112) Bianca Hoersch, "GMES Space Component & Sentinel(-2)," Landsat Science Team Meeting, Mountain View, CA, USA, Jan. 19-21, 2010, URL: http://landsat.usgs.gov/documents/Jan_2010_Landsat_Science
115) John Hedley, Chris Roelfsema, Benjamin Koetz, Stuart Phinn (2012), "Capability of the Sentinel 2 mission for tropical coral reef mapping and coral bleaching detection", Remote Sensing of the Environment, Vol. 120, pp: 145-155, 2012, URL : https://www.researchgate.net/publication/256850163_Capability_of_the-Sentinel_2_mission_for_tropical_coral_reef_mapping_and_coral_bleaching_detection
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).
The Sentinel series:
Provides data continuity for: