Sentinel-2 is a constellation of two optical imaging satellites, which are a part of Copernicus - the European Union’s Earth observation program.
|Mission status||Operational (nominal)|
|Launch date||23 June 2015|
|End of life date||2038|
|Measurement domain||Land, Atmosphere|
|Measurement category||Vegetation, Radiation budget, Albedo and reflectance, Multi-purpose imagery (land)|
|Instrument type||High resolution optical imagers|
|CEOS EO Handbook||See Copernicus: Sentinel-2 summary|
The Sentinel-2 satellites are used for monitoring inland and coastal water quality, and the management of crops and forests.
Both satellites are identical and have a Multispectral Instrument (MSI) onboard. This instrument comprises a three-mirror anastigmat (TMA) telescope to collect and focus light, a beam splitter to separate visible and near-infrared (VNIR) from short-wave infrared (SWIR), two focal planes with 12 detectors on each for the two different radiation types, a diffuser for radiometric calibration, and a calibration and shutter mechanism (CSM) to protect the instrument from sunlight at launch.
The MSI has 13 bands: three visible bands with a spatial resolution of 10 m, one visible band with a resolution of 60 m, three NIR (Near-Infrared) bands with a resolution of 20 m, and six SWIR (Short Wave Infrared) bands with a resolution of 60 m.
The Sentinel-2 satellites have a 5-day revisit time between them, each with a swath of 290 km. The two satellites follow the same sun-synchronous orbit with an inclination of 98.6° but are 180° out of phase. They orbit at an altitude of 786 km with a period of 101 minutes.
Space and Hardware Components
Sentinel-2 uses the AstroBus-L of EADS (European Aeronautic Defence and Space Company) Astrium. Onboard this bus in addition to the MSI is radio frequency communications. They provide X-band MSI data downlink at 560 Mbit/s, and telemetry, tracking, and command (TT&C) data link with 64 kbit/s uplink and 2 Mbit/s downlink.
Due to their design life of seven years, Sentinel-2A and 2B are set to be replaced by Sentinel-2C and 2D in 2024 and 2025 respectively.
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. It is 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)
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:
• 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 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 data source for the GMES Land Fast Track Monitoring Services and 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 the 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
Fast Track Service (Land Monitoring Core Services)
Compliance of the Sentinel-2 system geographic
All land areas/islands covered (except Antarctica)
5 days revisit cloud free fully in line with vegetation changes
Spectral sampling unique
Unique set of measurement/calibration bands
Sentinel-2A launch in 2014: the mission complements the SPOT and Landsat missions.
< 1 ha MMU (Minimum Mapping Unit) fully achievable with 10 m
Systematic push-broom acquisitions, plus lateral mode capability for emergency events monitoring
Fast Track Service (Emergency Response Core Service)
Compliance of the Sentinel-2 system
Spatial resolution down to 5 m
Reference/damage assessment maps limited to the 10m SSD (Spatial Sampling Distance)
Accessibility/timeliness down to 6 hrs offline & 24hrs in NRT
Fully compliant (retrieval of already archived reference data in < 6 hrs, and delivery of data after request in NRT in 3 hrs for L1c)
Table 1: 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 the ground as a backup.
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 which 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 to 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 it 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 the 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 and, timely and accurate satellite data 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 can 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 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 policymakers to detect early signs of food shortages in developing countries (Ref. 10).
June 23, 2015, by Vega from Kourou, French Guiana
March 2017, by Vega from Kourou, French Guiana
Sun-synchronous at altitude 786 km, Mean Local Solar Time at descending node: 10:30 (optimum Sun illumination for image acquisition)
Geometric revisit time
Five days from two-satellite constellation (at equator)
Seven years (carries consumable for 12 years: 123 kg of fuel including end of life deorbiting)
MSI (Multispectral Imager)
MSI covering 13 spectral bands (443–2190 nm), with a swath width of 290 km and a spatial resolution of 10 m (four visible and near-infrared bands), 20 m (six red edge and shortwave infrared bands) and 60 m (three atmospheric correction bands).
MSI data: transmitted via X-band to core Sentinel ground stations and via laser link through EDRS.
Agriculture, forests, land-use change, land-cover change. Mapping biophysical variables such as leaf chlorophyll content, leaf water content, leaf and area index; monitoring coastal and inland waters; risk and disaster mapping
Managed, developed, operated and exploited by various ESA establishments
ESA Member States and the European Union
Airbus Defence & Space Germany for the satellite, Airbus Defence & Space France for the instrument
CNES: Image quality optimization during in-orbit commissioning
Table 2: Facts and figures
Copernicus: the new name for the GMES Programme
Copernicus is the new name of the European Commission's Earth Observation Programme, previously known as GMES (Global Monitoring for Environment and Security). The new name was announced on December 11, 2012, by EC (European Commission) Vice-President Antonio Tajani during the Competitiveness Council.
In the words of Antonio Tajani: “By changing the name from GMES to Copernicus, we are paying homage to a great European scientist and observer: Nicolaus Copernicus (1473-1543). As he was the catalyst in the 16th century to better understand our world, so the European Earth Observation Programme gives us a thorough understanding of our changing planet, enabling concrete actions to improve the quality of life of the citizens. Copernicus has now reached maturity as a programme and all its services will enter soon into the operational phase. Thanks to greater data availability user take-up will increase, thus contributing to that growth that we so dearly need today.” Copernicus is the new name of the former GMES program 1)
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. It is a standard modular ECSS (European Cooperation for Space Standards) 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. The FDIR is hierarchically structured and can easily be adapted to specific mission needs.
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 by 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).
The geolocation accuracy requirements of < 20 m for the imagery translate into the following AOCS performance requirements as stated in Table 4.
Attitude determination error (onboard knowledge)
≤ 10 µrad (2σ) per axis
AOCS control error
≤ 1200 µrad (3σ) per axis
Relative pointing error
≤ 0.03 µrad/1.5 ms (3σ); and ≤ 0.06 µrad/3.0 ms (3σ)
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 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)
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 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. The total capacity of 102 Ah @ EOL. Mass = 51 kg.
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).
Spacecraft mass, power
~1200 kg, 1700 W
Hydrazine propulsion system
120 kg hydrazine (including provision for safe mode, debris avoidance and EOL orbit decrease for faster re-entry)
Spacecraft design life
7 years with propellant for 12 years of operations
AOCS (Attitude and Orbit Control Subsystem)
- 3-axis stabilized based on multi-head Star Tracker and fiber optic gyro
- Accurate geo-location (20 m without Ground Control Points)
X-band payload data downlink at 560 Mbit/s
Onboard data storage
2.4 Tbit, and data formatting unit (NAND-flash technology as baseline) that supplies the mission data frames to the communication subsystems.
LCT (Laser Communication Terminal) link is provided via EDRS (European Data Relay Satellite)
Table 5: Overview of some spacecraft parameters
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 (similar 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.
• 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. 31) 32) Sentinel-2A is scheduled to launch in June 2015; Sentinel-2B, which is identical in design, is set to follow in March 2017.
• 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. 30)
• 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 Sentinel 2 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. 29)
• 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. 28)
• 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. 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. 27)
• 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-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.
• 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. 25)
• 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. 24)
• February 27, 2017: The ninth Vega light-lift launcher is now complete at the Spaceport, with its Sentinel-2B Earth observation satellite installed atop the four-stage vehicle in preparation for a March 6 mission from French Guiana. 23)
• July 29, 2021: Airbus has finished the integration of the Copernicus Sentinel-2C satellite. It is the third of its kind and will now be shipped to Munich to undergo extensive environmental tests to prove its readiness for space. The test campaign will last until March 2022. 22)
From an altitude of 786 km, the 1.1 ton “C” satellite will enable the continuation of imaging in 13 spectral bands with a resolution of 10, 20 or 60 m and a uniquely large swath width of 290 km. Each Sentinel-2 satellite collects 1.5 TB/day, after onboard compression. The two identical satellites are flying in the same orbit but 180° apart for optimal coverage and revisit time. The satellites orbit the Earth every 100 minutes covering all of Earth’s land surfaces, large islands, and inland and coastal waters every five days.
• August 9, 2021: Engineers at Airbus Defence and Space in Friedrichshafen, Germany, have now transported the Sentinel-2C satellite to IABG’s facilities in Ottobrunn for a series of exhaustive tests that will run until the end of 2021. The program includes tests that simulate noise and vibrations of liftoff, as well as the extreme temperature swings it will experience in space. It also includes tests that check correct deployment of the solar wing and electromagnetic compatibility tests in this environment.
• January 21, 2022: Part of Mecklenburg–West Pomerania, also known as Mecklenburg-Vorpommern, a state in northeast Germany is featured in this image captured by the Copernicus Sentinel-2 mission. A portion of the northwest coast of Poland can be seen on the right of the image. 69) Given this image was captured in February, it is most likely an onset of a spring bloom. Agricultural and industrial run-off pours fertilisers into the sea, providing additional nutrients algae need to form large blooms.
• January 26, 2022: An unusual snowstorm has blanketed parts of Turkey and Greece, causing power cuts and chaos on the roads and flight cancellations. These two satellite images, from the Copernicus Sentinel-2 mission, show Athens: the image of Figure 16 was captured on 25 January and the image of Figure 17 is from 20 January. 68)
• January 28, 2022: The Copernicus Sentinel-2 mission takes us over northwest Lesotho – a small, land-locked country surrounded entirely by South Africa. 67) The country’s agricultural system faces a growing number of issues, including a small portion of the land deemed arable, as well as other climate-related vulnerabilities such as drought, floods and extreme temperatures occurring more frequently.
- All other colours visible in the image are different mixtures of red, green and blue, and vary according to the stage of vegetation growth. A distinct pattern emerges due to topographical differences in this mountainous landscape. The Copernicus Sentinel-2 mission’s revisit time of just five days, along with the mission’s range of spectral bands, means that changes in plant health and growth can be more easily monitored.
• February 4, 2022: The Copernicus Sentinel-2 mission takes us over Batura Glacier – one of the largest and longest glaciers in the world, outside of the polar regions. 66) Glacier shrinkage is a prominent sign of ongoing climate change. However, unlike many glaciers around the world, the glaciers residing in the mountain ranges in Karakoram are not responding to global warming. Their retreating is less than the global average, and in some cases, are either stable or growing. Satellites can help monitor changes in glacier mass, extents, trace area and length of glacier changes through time and derive surface velocity. Learn more about how Copernicus Sentinel-2 can help enhance glacier monitoring.
• February 4, 2022: New eruption at Krakatoa Volcano. 65)
• February 11, 2022: Hereford, which is the county seat of Deaf Smith County in Texas, is widely known for its agriculture industry. 64) Circular shapes in the image are an example of centre-pivot irrigation systems, where equipment rotates around a central pivot and crops are watered with sprinklers. This type of irrigation helps farmers manage their watering demands as well as help conserve their precious water sources.
- Shades of red, yellow and green depict changes in vegetation growth at the beginning of the season. Black patches of land indicate very low vegetation for the season, while white signifies a high level of vegetation during these dates. The Normalised Difference Vegetation Index is widely used in remote sensing as it gives scientists an accurate measure of health and status of plant growth.
• February 18, 2022: The Copernicus Sentinel-2 mission takes us over Tenerife – the largest of Spain’s Canary Islands. 63) Tenerife's weather and climate are heavily influenced by the trade winds blowing from the northeast for most of the year, bringing humidity and precipitation to the north of the island, as well as to the northern slopes of Mount Teide. This effect can be clearly seen in the dark green colours in the image showing vegetation cover.
• March 4, 2022: Today, the Copernicus Sentinel-2 mission takes us over the Pyrenees Mountains in southwest Europe. The mountain range forms a natural border between France and Spain with the small, landlocked country of Andorra sandwiched in between. 62) The Copernicus Sentinel-2 mission is designed to play a key role in mapping differences in land cover to understand the landscape, map how it is used and monitor changes over time.
• March 18, 2022: Lake Nasser, visible in the lower-right in black, is a vast lake and reservoir located in southern Egypt and northern Sudan. The lake was created as a result of the construction of the Aswan High Dam across the waters of the Nile in the late-1960s. This ambitious project was designed to provide irrigation to new agricultural developments and attract people to the region. 61)
• March 25, 2022: The Copernicus Sentinel-2 mission takes us over Carrara – an Italian city known especially for its world-famous marble, visiblejust above the centre of the image. 60) What appears as snow cover on the rugged mountains is actually bright white marble, contrasting with Tuscany’s lush green vegetation. Also featured in this summery image from Sentinel-2 are the towns of Forte dei Marmi, Pietrasanta, Lido di Camaiore and Viareggio.
• March 30, 2022: Spotted by the Copernicus Sentinel-2 mission, the Conger ice shelf collapsed in East Antarctica around 15 March. 59)
• April 01, 2022: Barranquilla, the capital of the Atlántico department in northwest Colombia, is featured in this image taken by the Copernicus Sentinel-2 mission. 58) The urban area of Barranquilla, with airport runways visible south of the city, contrasts with the Ciénaga Grande de Santa Marta swampy marshes to the east visible in dark green.
Other notable features in the image include the El Guajaro Reservoir, around 50 km southwest of Barranquilla. In addition to sewage discharges, the reservoir receives agricultural runoff, which leads to blooms of harmful microorganisms, otherwise known as cyanobacteria. These types of algae are most likely why the lake appears in emerald green in today’s image. Satellite data from the Copernicus Sentinel-2 mission can track the growth and spread of harmful algae blooms in order to alert and mitigate against damaging impacts for tourism and fishing industries.
• April 8, 2022: The Copernicus Sentinel-2 mission takes us over part of Sindh – the third-largest province of Pakistan. 57) The colourful image was created by combining three separate images from the near-infrared channel from the Copernicus Sentinel-2 mission. The Copernicus Sentinel-2 mission is specifically designed to provide images that can be used to distinguish between crop types as well as data on numerous plant indices, such as leaf area index, leaf chlorophyll content and leaf water content – all of which are essential to accurately monitor plant growth.
• April 11, 2022: After decades of drought, water levels in Lake Powell, the second-largest humanmade reservoir in the United States, have shrunk to its lowest level since it was created more than 50 years ago, threatening millions of people who rely on its water supply. 56) In mid-March 2022, Lake Powell’s elevation dropped to an astonishing 1074 m above sea level – the lowest the lake has been since it was filled in 1980. This drastic drop in water levels is documented in natural-colour images captured by the Copernicus Sentinel-2 mission.
• April 29, 2022: Mount Aso, the largest active volcano in Japan, is featured in this image captured by the Copernicus Sentinel-2 mission. 55) Satellite data can be used to detect the slight signs of change that may foretell an eruption. Once an eruption begins, optical and radar instruments can capture the various phenomena associated with it, including lava flows, mudslides, ground fissures and earthquakes. Atmospheric sensors on satellites can also identify the gases and aerosols released by the eruption, as well as quantify their wider environmental impact.
• May 05, 2022: The global trade in agricultural commodities provides food, fuel and fibre to consumers around the world. Commodity production, however, is also linked with negative environmental impacts, including the loss and degradation of forested land. 52)
In a new study published in Science Advances, a team of scientists from Europe and the US, combined detailed shipping data from Trase with corporate disclosures, farm-level production and remote sensing data to better understand how commodity traders source products on the ground, and how this affects the implementation of corporate zero-deforestation commitments. 53) Findings to support this article partially come from a recently published study in Science Direct, where the authors identified cocoa plantations in both Ivory Coast and Ghana using satellite data from the Copernicus programme. The team were able to detect cocoa plantations thanks to Sentinel-1’s radar data combined with Sentinel-2’s optical imagery in a big data cloud-computing environment. 54)
• May 6, 2022: The Rhine River, the longest river in Germany, is featured in this colourful image captured by the Copernicus Sentinel-2 mission. 51) Each colour in this week’s image represents the average NDVI value of an entire season between 2018 and 2021. Shades of red depict peak vegetation growth in April and May, green shows changes in June and July, while blue shows August and September. Colourful squares, particularly visible in the left of the image, show different crop types.
• May 20, 2022: Bonn, one of the oldest cities in Germany, can be seen straddling the Rhine River in the lower half of the image, around 24 km south of Cologne. 50) Along the river lies one of the most modern congress centres in Europe: the World Conference Center Bonn. It is here where ESA’s Living Planet Symposium 2022 will take place.
• May 24, 2022: Today, at ESA’s Living Planet Symposium, much of the focus was on furthering the uptake of Earth observation and advancing the digital transformation in Africa to address societal challenges. The free and open access to data and services has allowed African institutions to develop applications to monitor water quality in lakes, prepare adaptation measures for agriculture and to monitor biodiversity, for example.
Optical data from the Copernicus Sentinel-2 mission have shown that the area of land across the whole continent affected by fire is 80% bigger than previously thought. Satellite data showing burned ground not only reveal damage from wildfires, but also where slash and burn practices have taken place.
• June 3, 2022: Puglia (Apulia), the heel of the boot-shaped country, has the longest coastline of any Italian mainland region. Covering almost 20,000 km2, it is Italy’s seventh largest region and its coastline, dotted with some of Italy’s finest sandy beaches and azure seas, runs for around 800 km. 48) As well as providing detailed information about Earth’s vegetation, the Copernicus Sentinel-2 mission is designed to play a key role in mapping differences in land cover to understand the landscape, map how it is used and monitor changes over time.
• June 9, 2022: A team of scientists have used satellite data to detect methane plumes from an offshore platform in the Gulf of Mexico. This is the first time that individual methane plumes from offshore platforms are mapped from space. 47) Luis Guanter, from the Valencia Polytechnic University, commented, “The results here demonstrate how satellites can detect methane plumes from offshore infrastructure. This represents a breakthrough in the monitoring of industrial methane emissions from space, as it opens the door to systematic monitoring of emissions from individual offshore platforms.”
• June 17, 2022: Part of the Glacier Bay National Park and Preserve, which lies along the coast of southeast Alaska, is featured in this image captured by the Copernicus Sentinel-2 mission. 46) Muir Glacier, formerly the most famous of the tidewater glaciers, once rose around 80 m above water and was nearly 3 km wide but has now shrunk and receded and no longer reaches the sea. Glacier Bay is just one of the many areas suffering from the effects of global warming.
- The exhibition focuses on the world’s largest mountain glaciers with 90 photographic comparisons displayed alongside scientific data collected during the team’s expedition to the world’s largest mountain glaciers. More information on the exhibition, which is part of a scientific collaboration between ESA and is sponsored by UNESCO, can be found here.
• June 24, 2022: Lake Balkhash, the largest lake in Central Asia, is featured in this false-colour image captured by the Copernicus Sentinel-2 mission. 45) The two parts of the lake are united by a narrow strait, the Uzynaral visible in the centre of the image, with a depth of around 6 m. The sediment plume passing through the Uzynaral Strait is most likely due to waves stirring up sediments from the bottom of the lake. This has led to a higher reflection and thus a brighter water colour in this part of the lake.
• June 27, 2022: The Po River, the longest river in Italy, is hitting record low water levels after months without heavy rainfall. This Copernicus Sentinel-2 animation shows a part of the Po Valley, near Piacenza, and reveals how the river has significantly shrunk between June 2020 and June 2022. 44) The river is used for drinking water, nourishing vast swathes of agricultural land, as well as producing hydroelectric power across northern Italy.
• July 8, 2022: Fuerteventura and Lanzarote, part of the Canary Islands lying in the North Atlantic Ocean, are featured in this false-colour image captured by the Copernicus Sentinel-2 mission. 43) Lanzarote has a long history of eruptions and is often referred to as the ‘Island of the 1000 volcanoes’, yet it is actually the least mountainous Canarian Island. Fuerteventura is the oldest island in the Canary Archipelago, having risen between 12 and 20 million years ago owing largely to volcanic activity.
• July 25, 2022: Hundreds of residents and tourists have been evacuated from the east Aegean island of Lesbos (also known as Lesvos), Greece, after a wildfire broke out on the morning of 23 July. The fire, which has been raging near the coastal area of Vatera, a popular tourist destination, has burned pine forest, shrubland and cultivated fields. 42)
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. 36)
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. 37)
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 15).
• The first stage separated 1 min 55 seconds after liftoff, followed by the second stage and fairing at 3 min 39 seconds and 3 min 56 seconds, respectively, and the third stage at 6 min 32 seconds.
• After two more ignitions, Vega’s upper stage delivered Sentinel-2B into the targeted Sun-synchronous orbit. The satellite separated from the stage 57 min 57 seconds into the flight.
• Telemetry links and attitude control were then established by controllers at ESOC in Darmstadt, Germany, allowing activation of Sentinel’s systems to begin. The satellite’s solar panel has already been deployed.
• After this first ‘launch and early orbit’ phase, which typically lasts three days, controllers will begin checking and calibrating the instruments to commission the satellite. The mission is expected to begin operations in three to four months.
Sentinel-2B will join its sister satellite Sentinel-2A and the other Sentinels part of the Copernicus program, the most ambitious Earth observation program to date. Sentinel-2A and -2B will be supplying ‘color vision’ for Copernicus and together they can cover all land surfaces once every five days thus optimizing global coverage and the data delivery for numerous applications. The data provided by these Sentinel-2 satellites is particularly suited for agricultural purposes, such as managing administration and precision farming.
With two satellites in orbit it will take only five days to produce an image of the entire Earth between the latitudes of 56º south and 84º north, thereby optimizing the global coverage zone and data transmission for numerous applications.
To ensure data continuity two further optical satellites, Sentinel-2C and -2D, are being constructed in the cleanrooms of Airbus and will be ready for launch as of 2020/2021.
Note: As of 01 April 2021, the Sentinel-2 file has been split into a total of six files. — As of May 2019, the previously single large Sentinel-2 file has been split into two additional files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the Sentinel 2 images and mission development in 2022
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. 70) 71) 72) 73) 74) 75) 76)
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%).
Spectral range (total of 13 bands)
0.4-2.4 µm (VNIR + SWIR)
Spectral dispersion technique
Dichroic for VNIR and SWIR split
Mirror dimensions of telescope
M1 = 440 mm x 190 mm
SSD (Spatial Sampling Distance)
10 m: (VNIR) B2, B3, B4, B8 (4 bands)
290 km, FOV= 20.6º
Monolithic Si (VNIR); hybrid HgCdTe CMOS (SWIR)
Cooling of SWIR detector to < 210 K
Instrument mass, power
~290 kg, < 266 W
450 Mbit/s after compression
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 56.
VNIR (Visible and Near Infrared)
SWIR (Short-Wave Infrared)
Monolithic CMOS (Complementary Metal–Oxide–Semiconductor)
MCT, CTIA (Capacitive Feedback Transimpedance Amplifier) ROIC
7.5-15 µm pitch
15 µm pitch
1 TDI (Time Delay Integration) stage for 2 lines
1 TDI stage for 2 lines, 2 additional lines for pixel deselection
Table 7: Specification of VNIR and SWIR FPAs 77)
Spectral bands (center wavelength in nm/SSD in m)
Measurement or calibration
B1 (443/20/60), B2 (490/65/10) &
B8 (842/115/10), B8a (865/20/20),
Water vapor correction
B2 (490/65/10), B3 (560/35/10), B4 (665/30/10),
Land cover classification,
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 57). 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.
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.
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 60) 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. 78)
aspheric of-axis concave
central fixture at back side
442 x 190
aspheric on-axis convex
central fixture at back side
147 x 118
aspheric of-axis concave
glued bipods on outer edges
556 x 291
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. 79)
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.
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. 80)
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.
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.
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. 81)
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.
- 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.
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. 82) 83) 84)
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.
User storage capacity
2.4 Tbit (EoL)
6 Tbit (BoL)
2.8 Tbit (BoL)
No of memory modules
≤ 29 kg
< 15 kg
< 27 kg
Max volume (L x H x W)
710 mm x 260 mm x 310 mm
345 mm x 240 mm x 302 mm
598 mm x 240 mm x 302 mm
Power (record & replay)
≤ 130 W
< 54 W
< 126 W
Power (data retention)
< 29 W (0 W)
< 108 W
Instrument input data rate
490 Mbit/s + 80 kbit/s (housekeeping)
Output data rate (downlink)
2 x 280 Mbit/s
Life time in orbit
up to 12.5 years
Bit error rate (GCR) per day
≤ 9 x 10-13 / day
5.9 x 10-14 / day
< 9 x 10-13 / day
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 69. The MMFU receives two parallel data streams either from the nominal or redundant VCU (Video Compression Unit). The interfaces are cross-strapped with redundant PDICs (Payload Data Interface Controllers). After reception and adaptation to internal data formats of the received source packets, the data is stored in memory modules. FMM (Flash Memory Module) and respectively SMM for the SDR-SDRAM memory module. For replay, the data is read out from two parallel operated memory modules and routed via two active TFGs (Transfer Frame Generators) providing interfaces for downlink and test. The system is controlled by a Memory System Supervisor, which is based on an ERC32 processor. The required supply voltages are provided by a power converter.
Each function is implemented by nominal and redundant hardware components. The functions and boards are summarized in Table 11:
MMFU with NAND-Flash
MMFU with SDR-SDRAM
Boards (Physical Assembly)
Boards (Physical Assembly)
Memory System Supervisor
Payload Data Interface Controller
Transfer Frame Generators
Total Board Count
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.
SLC NAND-FMM (Flash Memory Module)
SDR-SMM (SDRAM Memory Module)
Quad Die Stack TSOP I
Eight Die Stack TSOP II
Data bus width
Partition net capacity
Count of partitions per module
Count of devices per module
Module net capacity
Accessible unit (read/write)
0.5 (by design)
Accessible unit (erase)
Type of module data interfaces
Max. Input data rate
Max. Output data rate
Module power (max data rate)
Module power (data retention)
mm x mm
200 x 243.5
200 x 243.5
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.
Die capacity (not stacked)
2.7 V – 3.6 V
3.0 V – 3.6 V
Data bus width
Temperature range (std. available)
- 40ºC to + 85ºC
0ºC to +70ºC
Maximum read performance @ IO clock
< 250 Mbit/s @ 40 MHz on page level (4 k x 8)
< 800 Mbit/s @ 100 MHz burst operation
2 ms on block level (256 k x 8)
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.
2400 Gbit (EOL) with Flash technology
Input data rate
2 x 540 Mbit/s
Instrument mass, size
14 kg, L: 302 x W: 345 x H: 240 mm
< 35 W
Simultaneous record and replay
Flexible real-time SW based embedded File Management System with PUS (Packet Utilization Standard) services
CCSDS conform output Data Formatting at a data rate of 2 x 280 Mbit/s
7.5 years lifetime in-orbit
Table 14: Parameters of the Sentinel-2 MMFU 85)
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.
• 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.
Level-1 image processing includes:
- a) Radiometric corrections: straylight/crosstalk correction and defective pixels exclusion, de-noising, de-convolution, relative and absolute calibration
Level 2 image processing includes:
- a) Cloud screening
Level 3 provides spatio-temporal synthesis
Simulation of cloud corrections within a Level 2 image
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. 87)
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.
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. 93)
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. 94)
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.
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.
Algorithm Development & Data Processing
The objective “to develop and validate new algorithms relevant for coral reef monitoring based on Sentinel-2 observations” will be addressed by parameterizing existing models for processing hyper-spectral & multi-spectral data and developing pre-processors for these models to build Sentinel-2 data processing algorithms for the retrieval of coral reefs’ static and dynamic characteristics. The code developed will be made available open source.
Validation and uncertainty analysis will involve both comparing Sentinel MSI performance versus Landsat-8 on coral reef mapping objectives and comparing coral reef monitoring products against in situ data from reef sites representative of different composition and structure.
To design, verify and validate three coral reef monitoring products making the best use of Sentinel-2 MSI mission characteristics:
• Habitat mapping of coral reefs
• Coral reef change detection
• Bathymetry over coral reefs.
A 6 day field campaign around the South Pacific island of Fatu Huku was undertaken by French scientist Antoine Collin to collect in-situ data to test and validate the capabilities of the Sentinel-2 satellite to monitor coral reef bleaching.
Fatu Huku Island in French Polynesia was chosen as the survey site because of the presence of developed coral reefs and it is an area water temperatures are high as a result of the current El Niño event. During the survey, water temperature exceeding 30°C were recorded and coral bleaching, the expulsion of the symbiotic algae that provide energy from sunlight to the coral, was observed to be taking place.
Data collected from this field campaign complements archives of in-situ data collected over previous years from coral reef sites across the globe such as at Heron Island and Lizard Island, in Australia, and reefs around Palau, in the western Pacific Ocean.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).