Minimize Copernicus: Sentinel-2

Copernicus: Sentinel-2 — The Optical Imaging Mission for Land Services

Space Segment   Launch   Mission Status   Sensor Complement   Ground Segment   References

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)

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."

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

Fast Track Service (Land Monitoring Core Services)

Compliance of the Sentinel-2 system

Geographic coverage

All land areas/islands covered (except Antarctica)

Geometrical revisit

5 days revisit cloud free fully in line with vegetation changes

Spectral sampling

Unique set of measurement/calibration bands

Service continuity

Sentinel-2A launch in 2014: the mission complements the SPOT and Landsat missions.

Spatial resolution

< 1 ha MMU (Minimum Mapping Unit) fully achievable with 10 m

Acquisition strategy

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 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).

Sentinel-2A launch

June 23, 2015, by Vega from Kourou, French Guiana

Sentinel-2B launch

March 2017, by Vega from Kourou, French Guiana

Orbit

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)

Design life

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).

Receiving stations

MSI data: transmitted via X-band to core Sentinel ground stations and via laser link through EDRS.
Telecommand and telemetry data: transmitted from and to Kiruna, Sweden

Main applications

Agriculture, forests, land-use change, land-cover change. Mapping biophysical variables such as leaf chlorophyll content, leaf water content, leaf area index; monitoring coastal and inland waters; risk and disaster mapping

Mission

Managed, developed, operated and exploited by various ESA establishments

Funding

ESA Member States and the European Union

Prime contractors

Airbus Defence & Space Germany for the satellite, Airbus Defence & Space France for the instrument

Cooperation

CNES: Image quality optimization during in-orbit commissioning
DLR: Optical Communication Payload (provided in kind)
NASA: cross calibrations with Landsat-8

Table 3: Facts and figures

 


 

Space segment:

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)

In March 2010, ESA and EADS-Astrium GmbH signed another contract to build the second Sentinel-2 (Sentinel-2B) satellite, marking another significant step in the GMES program. 15) 16) 17)

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.

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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).

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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.

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 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.

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Figure 3: Sentinel-2 spacecraft architecture (image credit: Astrium GmbH)

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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.

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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).

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
- A body pointing capability in cross-track is provided for event monitoring

- Accurate geo-location (20 m without Ground Control Points)

RF communications

X-band payload data downlink at 560 Mbit/s
S-band TT&C data link (64 kbit/s uplink, 2 Mbit/s downlink) with authenticated/encrypted commands

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.

Optical communications

LCT (Laser Communication Terminal) link is provided via EDRS (European Data Relay Satellite)

Table 5: Overview of some spacecraft parameters

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Figure 6: Schematic view of the deployed Sentinel-2 spacecraft (image credit: EADS Astrium)

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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.

 

Development status:

• February 27, 2017: The ninth Vega light-lift launcher is now complete at the Spaceport, with its Sentinel-2B Earth observation satellite installed atop the four-stage vehicle in preparation for a March 6 mission from French Guiana. 21)

• January 12, 2017: Sentinel-2B arrived at Europe's spaceport in Kourou, French Guiana on 6 January 2017 to be prepared for launch. After being moved to the cleanroom and left for a couple of days to acclimatise, cranes were used to open the container and unveil the satellite. Over the next seven weeks the satellite will be tested and prepared for liftoff on a Vega rocket. 22)

• November 15, 2016: Sentinel-2B has successfully finished its test program at ESA/ESTEC in Noordwijk, The Netherlands. The second Sentinel-2 Airbus built satellite will now be readied for shipment to the Kourou spaceport in French Guiana begin January 2017. It is scheduled for an early March 2017 lift-off on Vega. 23)

- Offering "color vision" for the Copernicus program, Sentinel-2B like its twin satellite Sentinel-2A will deliver optical images from the visible to short-wave infrared range of the electromagnetic spectrum. From an altitude of 786 km, the 1.1 ton satellite will deliver images in 13 spectral bands with a resolution of 10, 20 or 60 m and a uniquely large swath width of 290 km.

• June 15, 2016: Airbus DS completed the manufacture of the Sentinel-2B optical satellite; the spacecraft is ready for environmental testing at ESA/ESTEC. The Sentinel-2 mission, designed and built by a consortium of around 60 companies led by Airbus Defence and Space, is based on a constellation of two identical satellites flying in the same orbit, 180° apart for optimal coverage and data delivery. Together they image all Earth's land surfaces, large islands, inland and coastal waters every five days at the equator. Sentinel-2A was launched on 23 June 2015, its twin, Sentinel-2B, will follow early next year. 24)

- The Sentinel-1 and -2 satellites are equipped with the Tesat-Spacecom's LCT (Laser Communication Terminal). The SpaceDataHighway is being implemented within a Public-Private Partnership between ESA and Airbus Defence and Space.

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Figure 8: Sentinel-2B being loaded at Airbus Defence and Space's satellite integration center in Friedrichshafen, Germany (image credit: Airbus DS, A. Ruttloff)

• April 27, 2015: The Sentinel-2A satellite on Arianespace's next Vega mission is being readied for pre-launch checkout at the Spaceport, which will enable this European Earth observation platform to be orbited in June from French Guiana. — During activity in the Spaceport's S5 payload processing facility, Sentinel-2A was removed from the shipping container that protected this 1,140 kg class spacecraft during its airlift from Europe to the South American launch site. With Sentinel-2A now connected to its ground support equipment and successfully switched on, the satellite will undergo verifications and final preparations for a scheduled June 11 liftoff. 25)

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Figure 9: Sentinel-2A is positioned in the Spaceport's S5 payload processing facility for preparation ahead of its scheduled June launch on Vega (image credit: Arianespace)

• April 23, 2015: The Sentinel-2A satellite has arrived safe and sound in French Guiana for launch in June. The huge Antonov cargo aircraft that carried the Sentinel-2A from Germany, touched down at Cayenne airport in the early morning of 21 April. 26)

• April 8, 2015: The Sentinel-2A satellite is now being carefully packed away in a special container that will keep it safe during its journey to the launch site in French Guiana. The satellite will have one final test, a ‘leak test', in the container to ensure the propulsion system is tight. Bound for Europe's Spaceport in French Guiana, Sentinel-2A will leave Munich aboard an Antonov cargo plane on 20 April. Once unloaded and unpacked, it will spend the following weeks being prepared for liftoff on a Vega rocket. 27)

• February 24, 2015: Sentinel-2A is fully integrated at IABG's facilities in Ottobrunn, Germany before being packed up and shipped to French Guiana for a scheduled launch in June 2015. 28)

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Figure 10: Photo of the Sentinel-2A spacecraft in the thermal vacuum chamber testing at IAGB's facilities (image credit: ESA, IABG, 2015)

• In August 2014, Airbus Defence and Space delivered the Sentinel-2A environmental monitoring satellite for testing . In the coming months, the Sentinel-2A satellite will undergo a series of environmental tests at IABG, Ottobrunn, Germany, to determine its suitability for use in space. 29) 30)

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Figure 11: Sentinel-2A solar array deployment test at IABG (Airbus Defence & Space), image credit: ESA 31)

- Sentinel-2A is scheduled to launch in June 2015; Sentinel-2B, which is identical in design, is set to follow in March 2017. Together, these two satellites will be able to capture images of our planet's entire land surface in just five days in a systematic manner.

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Figure 12: Photo of the Sentinel-2A spacecraft at the satellite integration center in Friedrichshafen, Germany (image credit: Airbus DS, A. Ruttloff)

 

Launch: The Sentinel-2A spacecraft was launched on June 23, 2015 (1:51:58 UTC) on a Vega vehicle from Kourou. 32) 33)

RF communications: The payload data handling is based on a 2.4 Tbit solid state mass memory and the payload data downlink is performed at a data rate of 560 Mbit/s in X-band with 8 PSK modulation and an isoflux antenna, compliant with the spectrum bandwidth allocated by the ITU (international Telecommunication Union).

Command and control of the spacecraft (TT&C) is performed with omnidirectional S-band antenna coverage using a helix and a patch antenna. The TT&C S-band link provides 64 kbit/s in uplink (with authenticated/encrypted commands) and 2 Mbit/s in downlink..

The requirements call for 4 core X-band ground stations for full mission data recovery by the GMES PDS (Payload Data System).

In parallel to the RF communications, an optical LEO-GEO communications link using the LCT (Laser Communication Terminal) of Tesat-Spacecom (Backnang, Germany) will be provided on the Sentinel-2 spacecraft. The LCT is based on a heritage design (TerraSAR-X) with a transmit power of 2.2 W and a telescope of 135 mm aperture to meet the requirement of the larger link distance. The GEO LCT will be accommodated on AlphaSat of ESA/industry (launch 2012) and later on the EDRS (European Data Relay Satellite) system of ESA. The GEO relay consists of an optical 2.8 Gbit/s (1.8 Gbit/s user data) communication link from the LEO to the GEO satellite and of a 600 Mbit/s Ka-band communication link from the GEO satellite to the ground. 34)

To meet the user requirements of fast data delivery, DLR (German Aerospace Center) is funding the OCP (Optical Communication Payload), i.e. the LCT of Tesat, – a new capability to download large volumes of data from the Sentinel-2 and Sentinel-1 Earth observation satellites - via a data relay satellite directly to the ground. A contract to this effect was signed in October 2010 between ESA and DLR. 35)

Since the Ka-band downlink is the bottleneck for the whole GEO relay system, an optical ground station for a 5.625 Gbit/s LEO-to-ground and a 2.8 Gbit/s GEO-to-ground communication link is under development.

Orbit: Sun-synchronous orbit, altitude = 786 km, inclination = 98.5º, (14+3/10 revolutions/day) with 10:30 hours LTDN (Local Time at Descending Node). This local time has been selected as the best compromise between cloud cover minimization and sun illumination.

The orbit is fully consistent with SPOT and very close to the Landsat local time, allowing seamless combination of Sentinel-2 data with historical data from legacy missions to build long-term temporal series. The two Sentinel-2 satellites will be equally spaced (180º phasing) in the same orbital plane for a 5 day revisit cycle at the equator.

The Sentinel-2 satellites will systematically acquire observations over land and coastal areas from -56° to 84° latitude including islands larger 100 km2, EU islands, all other islands less than 20 km from the coastline, the whole Mediterranean Sea, all inland water bodies and closed seas. Over specific calibration sites, for example DOME-C in Antarctica, additional observations will be made. The two satellites will work on opposite sides of the orbit (Figure 13).

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Figure 13: Twin observation configuration of the Sentinel-2 spacecraft constellation (image credit: ESA)

 

Launch: The Sentinel-2B spacecraft was launched on March 7, 2017 (01:49:24UTC) on a Vega vehicle of Arianespace from Europe's Spaceport in Kourou, French Guiana. 36) 37) 38) 39)

• 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.

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Figure 14: Illustration of the Sentinel-2B spacecraft in orbit (image credit: Airbus DS, Ref. 38)

Figure 15: This technical view of the Sentinel-2 satellite shows all the inner components that make up this state-of-the-art high-resolution multispectral mission (video credit: ESA/ATG medialab)

Figure 16: As well as imaging in high resolution and in different wavelengths, the key to assessing change in vegetation is to image the same place frequently. The Sentinel-2 mission is based on a constellation of two satellites orbiting 180° apart, which along with their 290 km-wide swaths, allows Earth's main land surfaces, large islands, inland and coastal waters to be covered every five days. This is a significant improvement on earlier missions in the probability of gaining a cloud-free look at a particular location, making it easier to monitor changes in plant health and growth (video credit: ESA/ATG medialab)

 

Note: As of May 2019, the previously single large Sentinel-2 file has been split into two files, to make the file handling manageable for all parties concerned, in particular for the user community.

This article covers the Sentinel-2 mission and its imagery in the period 2019

Sentinel-2 imagery in the period 2018 to 2017

Sentinel-2 imagery in the period 2016 to 2015

 


 

Mission status and imagery of 2019

• June 14, 2019: The Copernicus Sentinel-2 mission takes us over the island of Bali, one of the 27 provinces of Indonesia. - Indonesia has more volcanoes than any other country in the world, owing to its position on the Pacific Ring of Fire. The islands of Java, Lombok, Sumbawa and Bali lie over a subduction zone where the Indo-Australian plate slides under the Eurasian plate, creating frequent seismic activity. 40)

- The central volcano, which is a predominant feature in this image, is called Mount Agung or Gunung Agung, meaning ‘Great Mountain'. The symmetrical and conical stratovolcano is the highest in Bali, standing at over 3000 m. When it erupted in 1964, it was one of the largest eruptions of the 20th century, claiming over 1000 lives and leaving more than 80,000 people homeless.

- After being dormant over the following 50 years, Agung reawakened in November 2017. Fortunately, small earthquakes warned authorities in time for 100,000 people to be evacuated to safety. Agung still remains very active, with frequent small eruptions spewing ash and lava, causing flights to be cancelled.

- In the image of Figure 17, a bright orange spot can be seen in the volcano's crater. Recent research provides evidence that Agung and its neighboring Batur volcano, visible northwest of Agung, may have a connected magma plumbing system. 41)

- Mount Batur, or Gunung Batur, has an unusual shape, with the volcanic cone visible in the center of two concentric calderas.

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Figure 17: Dotted with clouds, Mount Seraya is visible on the peninsula that juts to the east. Its volcanic rock creates a rugged terrain, but is surrounded by lush vegetation. The area is well known for its many Hindu temples, including the famous Lempuyang Temple, known locally as Pura Luhur Lempuyang. This image of Sentinel-2, captured on 2 July 2018, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

• June 7, 2019: The Copernicus Sentinel-2 mission takes us over Lake Valencia, in northern Venezuela. This false-color image (Figure 18) was processed in a way that makes vegetation of the Henri Pittier National Park, north of the lake, appear in fluorescent green. These bright colors contrast with the blackness of the lake. 42)

- Unfortunately, the inflow of untreated wastewater from the surrounding industrial and agricultural lands has led to the lake to become contaminated. The lake now suffers from algal blooms and between 1960 and 1990 it lost over 60% of its native fish species.

- It was at this very lake that the German naturalist and explorer, Alexander von Humboldt, witnessed how human behavior could cause harm to our natural ecosystem and climate. During his travels in the late 18th century, he noted the surrounding barren land which had been cleared for plantations and crops for sugar and tobacco. He attributed the decreasing water levels in the lake to climate change.

- "When forests are destroyed, the springs are entirely dried up," he wrote in his travel report, the Relation historique du voyage aux régions équinoxiales du nouveau continent (1814-17). "The beds of the rivers are converted into torrents whenever great rains fall on the heights.... Hence it results, that the destruction of forests, the want of permanent springs, and the existence of torrents, are three phenomena closely connected together."

- The now poor-quality waters of Lake Valencia prevent the development of tourism and recreational activities in the region.

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Figure 18: With a surface area of 370 km2, Lake Valencia formed a few million years ago and is now a reservoir for the cities of Valencia on the west shores and Maracay on the east shores. This image, which was captured on 2 February 2019 with Sentinel-2, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

• May 31,2019: The Copernicus Sentinel-2 mission takes us over El Salvador, the smallest and most densely populated country in Central America. 43)

- Lake Guija, visible in the top left of the image (Figure 19), lies on the border between El Salvador and Guatemala. The lake once formed part of the Mayan Empire and legend says that it also hides an ancient city beneath its waters.

- El Salvador sits on the eastern edge of the Pacific Ring of Fire, and despite being a small country, it has 25 volcanoes. The volcano complex of the Cerro Verde National Park can be seen dotted with clouds in the lower left of the image.

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Figure 19: Captured on 30 January 2019, this false-color image was processed in a way that makes vegetation appear red. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

- The Cerro Verde National Park is over 2000 m above sea level. It is home to a cluster of three volcanoes surrounded by lush rainforest. Santa Ana, the highest volcano in the country, is clearly visible with its circular peak.

- Izalco, located directly below Santa Ana, was born in 1770 and has erupted more than 50 times since. Its odd color and shape is due to these frequent eruptions.

- The large body of water to the right of Izalco is Lake Coatepeque, one of the largest crater lakes in the country. It is home to a variety of aquatic life and has remnants of ancient volcanic activity such as hot springs and openings emitting steam known as fumaroles.

- The large volcano in the right of the image is named San Salvador. It is adjacent to the capital, with which it shares its name. The city sprawls close to the nearby Lake Ilopango, which occupies the crater of an extinct volcano.

• May 24, 2019: The image of Figure 20 depicts the fragmented coast of western Pakistan, part of the Indus River Delta. A river delta forms when sediment carried from the river enters a stagnant body of water, creating an alluvial fan, which in this case extends 150 km along the coastline. The Indus River, visible on the right, veers through the Sindh Province and is one of the longest rivers in the world, rising in Tibet and flowing around 3000 km before emptying into the Arabian Sea. 44)

- The Indus Delta consists of creeks, swamps, marshes and the seventh largest mangrove forest in the world.

- However, owing to major irrigation works and dams built on the river, as well as low rainfall, the amount of silt discharged into the sea has reduced, affecting the mangrove and local community significantly. A huge proportion of the delta has been lost and the survival of the delta freshwater species, including the Indus river dolphin, are at risk.

- Also responsible for pollution is the port city of Karachi, which is partially visible in the top left of the image.

- To the top right, there are two important bodies of water on the edge of the stony desert, both of which are also wildlife sanctuaries. The artificial, square-shaped Haleji Lake, was expanded in World War II, for the use of additional water for the troops. The freshwater lake supports an abundance of aquatic vegetation, and is home to a number of species of birds.

- To the far right, the freshwater Keenjhar Lake is a major source of drinking water for Karachi, as well as for Thatta, which is to the right of the yellow-beige patch of land.

- Both lakes, as well as the River Indus Delta, are sites of wetland designated to be of international importance under the Ramsar Convention – an international treaty for the conservation and sustainable use of wetlands.

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Figure 20: Captured on 14 April 2018 by the Copernicus Sentinel-2A satellite, this image shows western Pakistan and an important wetland area. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

• May 17, 2019: The Copernicus Sentinel-2 satellite takes us over the Po Valley in northern Italy. The Po River, the longest river in Italy, flows over 650 km from west to east across the country, and ends at a delta projecting into the Adriatic Sea near Venice. The river flows through some of Italy's important cities of the north. 45)

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Figure 21: Image of the Po Valley, the most densely populated area in Italy, accounting for nearly half of the national population. This composite image contains several images captured between June 2018 and February 2019, allowing us to see the area free from clouds and smog. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018–19), processed by ESA, CC BY-SA 3.0 IGO)

- On the very left of the image, next to the river, the city of Turin can be seen. A business and cultural center, Turin is the capital of the Piedmont region. Rich in history, the city is home of the Shroud of Turin, a famous religious relic, as well as the Residences of the Royal House of Savoy. Turning to modern day, several International Space Station modules, such as Harmony and Columbus, were manufactured in Turin.

- Moving east, the city of Milan can be seen nestling below the Alps. Although Milan is the second most populous city in Italy after Rome, the wider metropolitan area extends over Lombardy and eastern Piedmont, making it the largest metropolitan area in Italy.

- Further east, the blue body of Lake Garda can be seen to the left of Verona. With an area of 370 km2, Garda is the largest lake in Italy and the third largest in the Alpine region. East of the lake is the Adige River, flowing south before curving east toward Verona. The city of Verona has been awarded World Heritage Site status by UNESCO because of its urban structure and architecture such as the circular Roman amphitheater.

- Along the coast, the turquoise colors of the Venetian lagoon and the islands that make up the city of Venice are visible. Famous for its musical and artistic cultural heritage, millions of tourists flock to the archipelago every year.

- As the Po River nears the Adriatic Sea, its agricultural landscape dominated by fields can be seen. Agriculture is one of the main industries in the Po Basin because of the fertile soils. Cereals, including rice, and a variety of vegetables are commonly grown in this area.

- The main arms of the river push the delta into the sea. An important ecosystem, the area has been a regional park since 1988 and a biosphere reserve since 2015.

• May 10, 2019: ESA's Living Planet Symposium – the largest Earth observation conference in the world – is being held on 13–17 May in Milan, Italy. Held every three years, these symposia draw thousands of scientists and data users from around the world to discuss their latest findings on how satellites are taking the pulse of our planet. 46)

- Over 4000 participants will gather at the largest congress center in Europe: the MiCo Convention Center. With its iconic architecture, this modern building has become a landmark. The event will not only see scientists present their latest findings on Earth's environment and climate derived from satellite data, but will also focus on Earth observation's role in building a sustainable future and a resilient society.

- Milan is the second biggest city in Italy and, like most large urban environments, it suffers from air pollution. While there is an effort to reduce the emission of pollutants, the city is also incorporating more vegetation into its development plans. This not only makes the environment more pleasant, but the plants also help soak up greenhouse gases such as carbon dioxide.

- The Bosco Verticale, or the Vertical Forest, for example, aims to inspire the need for urban biodiversity. The two tower blocks have plants and trees planted on its façade, and are located just north of the historical center. The vegetation covering both towers is equivalent to 20,000 m2 of forest and home to a variety of birds and butterflies. This vegetation absorbs approximately 30 tons of carbon dioxide per year.

- Another example of the city's efforts to ‘go green', is the Biblioteca degli Alberi, or Library of Trees, visible next to the Bosco Verticale. With its geometric design and irregular patches of land, the gardens are home to over 100,000 plants and trees, interlinked with pedestrian and bike paths.

- But it doesn't stop there, the local government aims to plant another three million trees by 2030.

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Figure 22: In this high-resolution image, captured by Copernicus Sentinel-2 orbiting around 800 km above, the center of Milan is clearly visible. The famous Milan Cathedral or Duomo di Milano with its surrounding square can be seen in the center of the image. Taking six centuries to complete, it is one of the largest gothic cathedrals in the world. This image, also featured on the Earth from Space video program, was captured on 24 September 2018 by the Copernicus Sentinel-2 mission. (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

• May 03, 2019: The Copernicus Sentinel-2 mission takes us over an area in southern Germany, where approximately 15 million years ago an asteroid crashed through Earth's atmosphere. The high-speed impact formed what is now known as the Ries crater. Although difficult to spot at first in the image, the result of the impact is actually still visible today. 47)

- With a diameter of 26 km, the rim of the crater can be seen as a semi-circle in the image, delineated by dark green forest to the south. The flat ‘crater floor' is ideally suited for agricultural use and the corresponding fields mark the crater's extent.

- The medieval town of Nördlingen (in the Donau-Ries district of Bavaria) was built in its depression. The historical center, approximately 1 km wide, appears as a reddish circle, visible with its red rooftops surrounded by a wall.

- The asteroid was estimated to be travelling at 70,000 km per hour, and when it made impact with Earth, the high-speed force exposed the rock to intense pressure and heat, over 25,000°C. The impact led to the creation of over 70,000 tons of microscopic diamonds, each around 0.2 mm in size.

- Overlooked by the town's inhabitants, the stone buildings were constructed almost entirely with diamond-encrusted rock. Details on the impact can be found in the well-known Rieskrater Museum in Nördlingen.

- For centuries, Nördlingen locals believed the town was built in the crater of a volcano. But in the 1960s two American scientists (Gene Shoemaker and Edward Chao) proved that the depression was, in fact, caused by a meteorite impact. Today, visitors around the world gather to marvel at this glittering town, also known as the backdrop to the original Willy Wonka and the Chocolate Factory film.

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Figure 23: The Sentinel-2 satellite of ESA captured this image of the Nördlinger Ries on 1 July 2018, it is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

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Figure 24: An aerial view of the town of Nördlingen inside the meteorite Ries crater

• April 26, 2019: The Copernicus Sentinel-2 mission takes us over Australia's northeast state of Queensland, where a large amount of sediment is visible gushing into the Coral Sea, close to the Great Barrier Reef lagoon. 48)

- In early 2019, many areas in Queensland received more than their annual rainfall in less than a week. The downpour led to millions of dollars' worth of damage, including homes being destroyed and the loss of almost 500,000 cattle.

- The Burdekin River rises on the northern slopes of Boulder Mountain and flows close to 900 km before emptying into the Coral Sea. The Burdekin River is one of Australia's larger rivers by discharge volume, and is a major contributor of sediment and freshwater to the Great Barrier Reef lagoon.

- The Great Barrier Reef, the world's largest coral reef, extends for 2000 km along the northeast coast of Australia and covers almost 350,000 km2. The reef is an interlinked system of about 3000 reefs and 900 coral islands, divided by narrow passages. An important area of biodiversity, the reef was made a UNESCO World Heritage Site in 1981.

- The sand-color sediment plume can be seen stretching over 35 km from the coast, dangerously close to the vivid turquoise reef. The blues of the coral contrast with the dark-colored waters of the Coral Sea.

- The coral reef suffers regular damage, more than half of the reef has disappeared over the last 30 years owing to climate change, coral bleaching and pollution. Large quantities of sediment that flow out from rivers carry chemicals and fertilizers from inland farms. The sediment blankets the coral, and reduces the amount of light, as well as potentially causing harmful algae blooms.

- Data from Copernicus Sentinel-2 plays a key role in providing information on pollution in lakes and coastal waters. Frequent coverage is also fundamental to monitoring floods.

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Figure 25: This image was captured a few days after the torrential rain, and shows the muddy waters flowing from the Burdekin River into the Coral Sea. It was captured on 10 February 2019, it is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

• April 19, 2019: The Copernicus Sentinel-2 mission takes us over one of the most remote islands in the world: Easter Island. Located in the Pacific Ocean, over 3500 km off the west coast of South America, this Chilean island is also known as Rapa Nui by its original inhabitants. The island was given its current name the day when the Dutch navigator Jacob Roggeveen arrived on 5 April 1722 – on Easter Sunday.

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Figure 26: Easter Island, with a size of 163.6 km2 and a population of 7500, is a Chilean island in the southeastern Pacific Ocean, at the south-easternmost point of the Polynesian Triangle in Oceania. A Sentinel-2 acquired this image on 7 April 2019, it is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

- The island is famous for its monolithic stone statues, called Moai, said to honor the memory of the inhabitants' ancestors. There are nearly 1000 scattered around the island, usually positioned near freshwater. Many are located near the Rano Raraku volcano, on the southeast coast. The white edges along the southern coast show the harsh waves colliding with the shore.

- An interesting feature of the image is the ochre-orange color of the Poike – the peninsula on the eastern end of the island. In ancient times, it is said that there was a lot of vegetation on the island. However, land clearing for cultivation and the Polynesian rat played a role in deforestation, leading to the erosion of the soil, particularly in the east.

- Several reforestation projects have been attempted, including a eucalyptus plantation in the middle of the island, visible in dark green. The brown patch to the right of the plantation is likely to be a burn scar from a wildfire.

- The majority of the island's inhabitants live in Hanga Roa, the main town and harbor on the west coast, clearly visible in the image. Interestingly, the long runway of the island's only airport was once designated as an emergency landing site for the US space shuttle.

- At the very edge of the southwest tip of the island lies Ranu Kao, the largest volcano on the island. Its shape is distinctive owing to its crater lake, one of the island's only three natural bodies of water.

- Many tourists are drawn to the island for its mysterious history and isolated position. What is relatively unknown is the existence of two small beaches on the northeast coast. Anakena beach has white, coral sand, while the smaller Ovahe beach, surrounded by cliffs, has pink sand.

• April 5, 2019: This week, ESA is focusing on its core Basic Activities, which, for Earth observation, include preserving precious data. Long-time series of datasets are needed to determine changes in our planet's climate so it is vital that satellite data and other Earth science data are preserved for future generations and are still accessible and usable after many years. This example includes a series of satellite images going back to 1998. 49) 50) 51)

Figure 27: This long-time series of over 150 images, captured by the US Landsat series and the Copernicus Sentinel-2 missions, shows the development over 21 years of an important land reclamation project in the Western Desert of Egypt. This comparison highlights how this agricultural project has developed between January 1998 and March 2019. These images are also featured on the Earth from Space video program (image credit: USGS/contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

- Egypt is over 95% desert, making a very small proportion of its land suitable for agriculture. As the demand for food grows, the need for agricultural development in desert areas has intensified.

- This set of images shows an important land reclamation project in East Oweinat, in the Western Desert of Egypt.

- The circular shapes in the images, each approximately 800 meters wide, indicate the irrigation method used here, with water being supplied by a set of sprinklers rotating around a central pivot. Fossil water, stored underground for thousands of years, comes from the Nubian Sandstone Aquifer, the largest known fossil aquifer discovered.

- The water in the East Oweinat area is low in salt content, making it ideal for cultivation purposes. Crops such as wheat, potatoes and barley are grown here, and are exported through the Sharq El Owainat airport, visible in the right side of the image.

- Another interesting feature in this time series is the drifting sand dunes visible mainly in the upper left corner, which is a phenomena common in sandy deserts with constant winds.

- Changes over the last 21 years are clearly visible when more fields develop, but the data also show other subtle changes within the fields themselves. This data can be used to monitor changes in land-cover over time. Long-term preservation of the satellite data from different missions ensures that changes to the land can be monitored by analyzing data from the archives.

• March 22, 2019: Today is World Water Day, but with millions of people in Mozambique, Malawi and Zimbabwe struggling to cope in the aftermath of Cyclone Idai, the notion of water shortages may not be at the forefront of our minds right now. Even so, floods, like we see here, lead to real problems accessing clean water. Whether the problem is inundation or water scarcity, satellites can help monitor this precious resource. 52)

Figure 28: Water levels in the Theewaterskloof Dam in South Africa's Western Cape Province have dropped dramatically over recent years. The dam is the major source of water for domestic and agricultural uses in the region. Over the last year, this lack of water has caused the production of grain to drop by more than 36% and the production of wine grapes to drop by 20%, for example. It is estimated that it will need to receive at least three years of good winter rainfall for it to return to its earlier healthy level. Thanks to the TIGER initiative, the Stellenbosch University is applying machine-learning algorithms to data from the Copernicus Sentinel-1 and Sentinel-2 missions to carefully monitor the situation (video credit: ESA, the video contains modified Copernicus Sentinel data (2017–18), processed by ESA, CC BY-SA 3.0 IGO)

- With more than two billion people living without safe water and around four billion people suffering severe water scarcity for a least one month a year, achieving water for all is a huge challenge. And, coupled with a growing global population and climate change, it's likely to become even more challenging.

- Water allows life on Earth to thrive. The same water has existed for billions of years, cycling through the air, oceans, lakes, rocks, animals and plants and back again. The water we drink today may have once been inside a dinosaur!

- Our most precious resource is probably the strangest thing in the universe. Defying the laws of chemistry, it's the only known substance that can exist naturally as a gas, liquid and solid within a relatively small range of air temperatures and pressures found on the surface of Earth.

- Although there is no shortage of water on Earth, less than 3% is freshwater. Then the vast majority of this is locked up in icecaps and glaciers, leaving less than 1% available for drinking and other domestic needs, agriculture and industrial processes, and more.

- Freshwater is the single most important natural resource on the planet, but we are very rapidly running out of it – as illustrated by dwindling water bodies.

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Figure 29: The Earth's water cycle. The total amount of water present on the Earth is fixed and does not change. Powered by the Sun, water is continually being circulated between the oceans, the atmosphere and the land. This circulation and conservation of the Earth's water, known as the water cycle, is a crucial component of our weather and climate (image credit: ESA/AOES Medialab)

Figure 30: Glacial decline (10 December 2018). 53) A paper published recently in Nature Geosciences describes how a multitude of satellite images have been used to reveal that there has actually been a slowdown in the rate at which glaciers slide down the high mountains of Asia. This animation simply shows how glaciers in Sikkim in northeast India have changed between 2000 and 2018. One of the images is from the NASA/USGS Landsat-7 mission captured on 26 December 2000 and the other is from Europe's Copernicus Sentinel-2A satellite captured on 6 December 2018 [image credit: NASA/USGS/University of Edinburgh/ETH Zurich/ the image contains modified Copernicus Sentinel data (2018)]

• March 22, 2019: The 22 March is World Water Day, which focuses on the importance of freshwater. The Sustainable Development Goals of the United Nations aim to achieve a better and more sustainable future. Goal number 6 focuses on ensuring the availability and sustainable management of water for all by 2030. This image takes us over Lake Chad at the southern edge of the Sahara, where water supplies are dwindling. 54)

- Once one of Africa's largest lakes, Lake Chad has shrunk by around 90% since the 1960s. This receding water is down to a reduction of precipitation, induced by climate change, as well as development of modern irrigation systems for agriculture and the increasing human demand for freshwater.

Figure 31: This comparison shows Lake Chad imaged on 6 November 1984 by the US Landsat-5 satellite and on 31 October 2018 by the Copernicus Sentinel-2A satellite. The rapid decline of the lake's waters in just 34 years is clearly to see. These images are also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA (For Landsat image: USGS/ESA), CC BY-SA 3.0 IGO)

- Straddling the border of Chad, Niger, Cameroon and Nigeria, the lake is a major source of freshwater for millions of people in the area. It is also a source for irrigation, fishing and it was once rich in biodiversity.

- As the lake continues to dry up, many farmers and herders move towards greener areas or move to larger cities to seek alternative work. Several attempts have been made to replenish these shrinking waters, however little progress has been achieved.

- The borders of the lake's body are only partly visible in the most-recent image – as the majority of the shoreline is swamp and marsh. The Chari River, visible snaking its way towards Lake Chad at the bottom of the image, provides over 90% of the lake's waters. It flows from the Central African Republic following the Cameroon border from N'Djamena, where it joins with its main tributary the Logone River.

- The demand for water is growing inexorably. Access to water is vital – not only for drinking, but also for agriculture, energy and sanitation. By providing measurements of water quality and detecting changes, the Copernicus Sentinel-2 mission can support the sustainable management of water resources.

March 22, 2019: World Water Day! 55) The 66th United Nations General Assembly adopted a resolution declaring the Water Action Decade from 22 March 2018 to March 2028. The UN Water Action Decade is pursuing two goals:

- Spreading knowledge on the topic of water and water pollution control, including information on water-related Sustainable Development Goals (SDGs);

- more effective communication measures to implement water-related goals.

Figure 32: The UN Sustainable Goal 6 is crystal clear: Water for all by 2030. For World Water Day we take a look at ways that space can help this global challenge. While Earth-observing satellites monitor our precious water resources, technologies developed for human space missions also serve global needs in harsh environments here on Earth (video credit: ESA)

• March 21, 2019: The UN International Day of Forests is held annually on 21 March. It raises awareness of the importance of all types of forest and the vital role they play in some of the biggest challenges we face today, such as addressing climate change, eliminating hunger and keeping urban and rural communities sustainable. As the global population is expected to climb to 8.5 billion by 2030, forests are more important than ever. 56)

- This year, the International Day of Forests put a particular focus on education, but also on making cities a greener, healthier and happier place to live. In cities, trees can help many urban challenges. They act as air filters by removing pollutants, reduce noise pollution, offer shade and provide an oasis of calm in an otherwise busy urban environment, for example.

- While Bangkok, which is home to over eight million people, is an example of ongoing efforts being made to increase green spaces to improve city life, it also has a much-valued green haven, which can be seen in the center of the image.

- This horseshoe or lung-shaped, green oasis is Bang Kachao and is in the middle of the bustling city.

- Rich in gardens, mangroves and agricultural fields, the 2000 hectares of land is a significant contrast to the vastness of the city's urban sprawl. Fighting Bangkok's traffic and air pollution, Bang Kachao's lush green forest provides the dense city, and the surrounding Samutprakan province, with a flow of fresh air.

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Figure 33: Captured on 22 January 2019 by the Copernicus Sentinel-2B satellite, this true-color image shows Thailand's most populous city Bangkok, and its ‘Green Lung' Bang Kachao. The government-protected oasis of green is wrapped around the Chao Phraya River, which is seen flowing through the city of Bangkok before emptying into the Gulf of Thailand (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

Legend to Figure 33: Bang Kachao is an artificial island formed by a bend in the Chao Phraya River and a canal at its western end. It lies south of the Thai capital Bangkok in the Phra Pradaeng District of Samut Prakan Province. The island, covering 16 km2, has been traditionally agricultural with only a relatively small population.

• March 21, 2019: Billions of image pixels recorded by the Copernicus Sentinel-2 mission have been used to generate a high-resolution map of land-cover dynamics across Earth's landmasses. This map also depicts the month of the peak of vegetation and gives new insight into land productivity. 57)

- Using three years' worth of optical data, the map can indicate the time of vegetation peak and variability of vegetation across seasons. Developed by GeoVille, an Austrian company specialized in the analysis of satellite data, this land-cover map dynamics map uses Copernicus Sentinel-2 archive data from 2015-18, and gives a complete picture of variations of vegetation. The map is displayed at a resolution of 20 m, however a 10 m version is available on request.

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Figure 34: Data from the Copernicus Sentinel-2 mission has been used to generate a new high-resolution map of vegetation across Earth's entire landmass. The new map depicts global vegetation dynamics and gives insight into land productivity. The time of vegetation peak i.e. the month at which greenness maximum occurs is shown in red (spring) and green (summer) to blue tones (autumn and winter.) The variability of vegetation greenness is represented by light tones in low amplitude areas such as managed grasslands, while high amplitudes are represented by saturated color tones. Areas with low biomass such as urban areas and open bodies of water are shown in black, while areas with higher biomass appear in grey and white tones (image credit: ESA, the image contains modified Copernicus Sentinel data (2016–18), processed by GeoVille)

- It can, for example, support experts working with land-cover classification and can serve as input for services in areas such as agriculture, forestry and land-degradation assessments.

- "In particular, we use this as a basis to develop services for the agrofood industry and farmers growing potatoes and other crops, as well as information on how vegetation changes over the year," explains Eva Haas, Head of GeoVille's Agricultural Unit (Innsbruck, Austria).

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Figure 35: The inland delta of the Niger River spreads across central Mali – a unique ecosystem in West Africa. A result of the Niger river flowing into the sandy Sahelian plains, this vast network of channels, swamps, and lakes mitigates the severity of the arid climate by supplying water during October and November (blue). In contrast the image shows the sparse rain fed vegetation in the surrounding region (dark green). This image is part of a new high-resolution map of vegetation across Earth's entire landmasses generated with Copernicus Sentinel-2 data (image credit: ESA, the image contains modified Copernicus Sentinel data (2016–18), processed by GeoVille)

- The land-cover dynamic layer was produced with GeoVille's processing engine LandMonitoring.Earth, a fully-automated land-monitoring system built on data streams from the Copernicus Sentinel-1 and Sentinel-2 missions, as well as ESA third party missions such as the US Landsat missions.

- "Using the system, we processed the complete Copernicus Sentinel-2 image archive along with artificial intelligence, machine learning and big data analytics," explains Michael Riffler, Head of Research and Development at GeoVille.

- "However, the key is the dense time-series of the Copernicus Sentinel-2 data which allows this information to be retrieved for the first time. To date, we have processed more than 23 billion pixels."

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Figure 36: The image shows different crop types around Emmelrod in the Netherlands. Here, green shows summer crops, red is potatoes, orange is market crops, yellow is cereals and blue depicts grassland. The area is important for the agrofood sector and, in particular, has strong ties to the international potato industry. By integrating Copernicus Sentinel-2 based crop-type monitoring directly into existing industry workflows, the agrofood industry can gain information about the growth and potential yield of crops, potatoes in particular, including the impact of ongoing droughts (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by GeoVille)

- The development has been done through ESA's Earth observation innovation hub – Φ-lab, and has been implemented by GeoVille and its subsidiary in the Netherlands – GEO4A.

- "This map forms an excellent foundation for other – more specialized – land cover classifications, whose development and deployment can be further accelerated by applying machine learning and AI," says Iarla Kilbane-Dawe, the head of ESA's Φ-Lab in Frascati, Italy.

- The LandMonitoring.Earth system is designed to efficiently implement major client solutions such as the European Copernicus Land Monitoring Service products. Experts can specify desired land monitoring data for any place on the globe for any given time period, and receive a quality-controlled output, depending on the required geographic coverage and frequency.

- The idea is to make information available to non-experts along with the specific resources and tools that they need.

• March 15, 2019: The Copernicus Sentinel-2 mission takes us over Nairobi, one of the fastest growing cities in East Africa. 58)

- The population of Nairobi has increased significantly in the last 30 years, with rural residents flocking to the city in search of employment. The city, visible in the center of the image, now has a population of over three million, with the vast majority spread over 200 informal settlements.

- Kibera, which can be seen as a light-colored patch at the south-western edge of the city, is considered one of the largest urban slums in Nairobi. Most residents live in small mud shacks with poor sanitation, a lack of electricity and limited access to clean water.

- While migration provides economic benefits to the city, it also creates environmental challenges. Owing to its urbanization, the city has spread into green spaces such as the nearby parks and forests. In this image, the densely populated area is contrasted with the flat plains of Nairobi National Park, directly south of the city. The 117 km2 of wide-open grass plains is colored in light-brown. The park is home to lions, leopards, cheetahs and has a black rhino sanctuary.

- The dark patches in the image are forests. The Ngong Forest, to the west of the city, includes exotic and indigenous trees, and hosts a variety of wild animals including wild pigs, porcupines, and dik-diks.

- To the north of the city, the dark Karura Forest is visible. The 1000 hectare urban forest features a 15 m waterfall, and hosts a variety of animals including bush pigs, bushbucks, suni and harvey's duiker, as well as some 200 bird species.

- Although Africa is responsible for less than 5% of global greenhouse-gas emissions, the majority of the continent is directly impacted by climate change. Rapid population growth and urbanization also exposes residents to climate risks.

- On 14 March 2019, the first regional edition of the One Planet Summit took place at the UN Compound, which is in the north of the city. The One Planet Summit, part of the UN Environment Assembly, focuses on protecting biodiversity, promoting renewable energies and fostering resilience and adaptation to climate change.

- Data from Copernicus Sentinel-2 can help monitor changes in urban expansion and land-cover change. Copernicus Sentinel-2 is a two-satellite mission. Each satellite carries a high-resolution camera that images Earth's surface in 13 spectral bands.

- As delegates gather in Nairobi for the UN Environment Assembly, ESA is saddened by the news of the Ethiopian Airlines accident. Lives lost included those working for organizations also dedicated to achieving a better world for all and who were travelling to the assembly. — Our thoughts are with the families, colleagues and friends of those affected.

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Figure 37: This image of the Sentinel-2 mission was captured on 3 February 2019, is also featured on the Earth from Space video program

• February 25, 2019: This Copernicus Sentinel-2 image of Figure38 shows a huge plume of sediment gushing into the sea following heavy rainfall in the Rome area. 59)

- The Tiber River can be seen snaking its way southwards in the image. The third longest river in Italy, it rises in the Apennine Mountains and flows around 400 km before flowing through the city of Rome and draining into the sea near the town of Ostia. The Tiber River plays an important role in sediment transport, so coastal waters here are often discolored. However, the recent rains resulted in a large amount of sediment pouring into the Tyrrhenian Sea, as this image shows. The sediment plume can be seen stretching 28 km from the coast, carried northwest by currents.

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Figure 38: The Copernicus Sentinel-2B satellite captured this true-color image on 5 February 2019, just three days after heavy rainfall in Rome and the surrounding area of Lazio, Italy. It shows sediment gushing into the Tyrrhenian Sea, part of the Mediterranean Sea. The downpour on 2 February led to flooded streets, the closing of the banks of the Tiber River and several roads (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)

• February 22, 2019: The Copernicus Sentinel-2A satellite takes us over western Sicily and the islands of Favignana and Levanzo in Italy. The image of Figure 39 shows a false-color image included the near-infrared channel and was processed in a way, that makes vegetation appear in bright red. 60)

- The bright turquoise colors, near the port city of Trapani, at the top of the image, and the Isola Grande in the middle of the image, depict salt marshes. Both the Saline di Trapani e Paceco Nature Reserve and the Stagnone Nature Reserve with their shallow sea waters, windy coast and abundant sunshine, make the area between Marsala, at the bottom of the image, and Trapani an ideal place for salt production.

- The reserve consists of more than 1000 hectares of landscape dotted with windmills, migratory birds such as flamingos and light-red lagoons visible in summer. This greenish-blue color is heavily contrasted with the black of the open Mediterranean Sea.

- The islands, off the coast, are rich in history, both boasting Paleolithic and Neolithic cave paintings. The most famous being the Grotta del Genovese on the picturesque island of Levanzo, at the top left of the image. The cave was discovered only in 1949 and is estimated to be between 6000 and 10 000 years old.

- Below, the butterfly-shaped island of Favignana, known for its tuna fisheries and a type of limestone known as tufa rock, is the largest of the Aegadian islands. In 241 BC, one of the Punic Wars' naval battles was fought at the Cala Rossa (Red Cove), named after the bloodshed.

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Figure 39: Captured on 3 September 2018 by the Copernicus Sentinel-2A satellite, this false-color image shows part of western Sicily in Italy and two of the main Aegadian Islands: Favignana and Levanzo. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)

• February 15, 2019: Copernicus Sentinel-2 brings you some of the jewels of the Maldives for Valentine's week. Arguably one of the most romantic destinations in the world, the Maldives lie in the Indian Ocean about 700 km southwest of Sri Lanka. The nation is made up of more than 1000 coral islands spread across more than 20 ring-shaped atolls. 61)

- Like many low-lying islands, the Maldives are particularly vulnerable to sea-level rise. In fact, the Maldives are reported to be the flattest country on Earth, with no ground higher than 3 m and 80% of the land lying below 1 m. With satellite records showing that over the past five years, the global ocean has risen, on average, 4.8 mm a year, rising seas are a real threat to these island jewels.

- With the promise of white sandy beaches, azure ocean waters and coral reefs, this romantic getaway draws more than 600,000 tourists every year. While tourism is extremely important for the national economy, development on these pristine islands create pressures, such as ensuring an adequate supply of freshwater, treating sewage and potential pollution entering the ocean. Other environmental issues facing the Maldives include the loss of habitats of endangered species and the damage to the coral reefs.

- The Maldives are undoubtedly fragile but one of the most beautiful places on the planet, and a place to be loved and cherished now and in the future. Valentine's Day reminds us of love and maybe this year and beyond it's good to remember to love our planet.

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Figure 40: A number of these little islands can be seen in the image, with the turquoise colors depicting clear shallow waters dotted by coral reefs and the red colors highlighting vegetation on land. Different cloud formations can also be seen, the difference in appearance is likely to be due to the different height above the surface. This image, which was captured on 26 August 2015, is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2015), processed by ESA, CC BY-SA 3.0 IGO)