Copernicus: Sentinel-2 — The Optical Imaging Mission for Land Services
Sentinel-2 is a multispectral operational imaging mission within the GMES (Global Monitoring for Environment and Security) program, jointly implemented by the EC (European Commission) and ESA (European Space Agency) for global land observation (data on vegetation, soil and water cover for land, inland waterways and coastal areas, and also provide atmospheric absorption and distortion data corrections) at high resolution with high revisit capability to provide enhanced continuity of data so far provided by SPOT-5 and Landsat-7. 1) 2) 3) 4) 5) 6) 7) 8)
Table 1: Copernicus is the new name of the former GMES program 9)
The overall GMES user requirements of the EU member states call for optical observation services in the areas of Global Climate Change (Kyoto Protocol and ensuing regulations), sustainable development, European environmental policies (e.g. spatial planning for Soil Thematic Strategy, Natura 2000 and Ramsar Convention, Water Framework Directive), European civil protection, common agricultural policy, development and humanitarian aid, and EU Common Foreign & Security Policy.
To meet the user needs, the Sentinel-2 satellite data will support the operational generation of the following high level products like:
• Generic land cover, land use and change detection maps (e.g. CORINE land cover maps update, soil sealing maps, forest area maps)
• Maps of geophysical variables (e.g. leaf area index, leaf chlorophyll content, leaf water content).
The mission is dedicated to the full and systematic coverage of land surface (including major islands) globally with the objective to provide cloud-free products typically every 15 to 30 days over Europe and Africa. To achieve this objective and to provide high mission availability, a constellation of two operational satellites is required, allowing to reach a 5-day geometric revisit time. The revisit time with only one operational satellite as it will be the case at the beginning of the deployment of the system is 10 days. - In comparison, Landsat-7 provides a 16-day geometric revisit time, while SPOT provides a 26-day revisit, and neither of them provides systematic coverage of the overall land surface.
The following list summarizes the top-level system design specifications derived from the user requirements:
• Sentinel-2 will provide continuity of data for services initiated within the GSE (GMES Service Element) projects. It will establish a key European source of data for the GMES Land Fast Track Monitoring Services and will also contribute to the GMES Risk Fast Track Services.
• The frequent revisit and high mission availability goals call for 2 satellites in orbit at a time, each with a 290 km wide swath using a single imaging instrument
• Continuous land + islands carpet mapping imaging within the latitude range of -56º to +83º (the selected orbit excludes imagery from Antarctica)
• 10 m, 20 m, and 60 m spatial resolution (in the VNIR to SWIR spectral range) to identify spatial details consistent with 1 ha MMU (Minimum Mapping Unit)
• An accurate geolocation (< 20 m) of the data is required (without GCPs) and shall be produced automatically to meet the timeliness requirements. The geolocation accuracy of Level 1 b imagery data w.r.t. WGS-84 (World Geodetic System - 1984) reference Earth ellipsoid of better than 20 m at 2σ confidence level without need of any ground control points is required.
• Very good radiometric image quality (combination of onboard absolute and on ground vicarious calibration).
• The mission lifetime is specified as 7.25 years and propellant is to be sized for 12 years, including provision for de-orbiting maneuvers at end-of-life.
• 2 weeks of satellite autonomy and maximum decoupling between flight operations and mission exploitation
Table 2: Sentinel-2 fast track service compliance to land user requirements
To provide operational services over a long period (at least 15 years following the launch of the first satellites), it is foreseen to develop a series of four satellites, with nominally two satellites in operation in orbit and a third one stored on ground as back-up.
In partnership: The Sentinel-2 mission has been made possible thanks to the close collaboration between ESA, the European Commission, industry, service providers and data users. Demonstrating Europe's technological excellence, its development has involved around 60 companies, led by Airbus Defence and Space in Germany for the satellites and Airbus Defence and Space in France for the multispectral instruments. 10)
The mission has been supported in kind by the French space agency CNES to provide expertise in image processing and calibration, and by the German Aerospace Center DLR that provides the optical communication payload, developed by Tesat Spacecom GmbH.
This piece of technology allows the Sentinel-2 satellites to transmit data via laser to satellites in geostationary orbit carrying the European Data Relay System (EDRS). This new space data highway allows large volumes of data to be relayed very quickly so that information can be even more readily available for users.
Seven years in the making, this novel mission has been built to operate for more than 20 years. Ensuring that it will meet users' exacting requirements has been a challenging task. Developing Sentinel-2 has involved a number of technical challenges, from early specification in 2007 to qualification and acceptance in 2015.
The satellite requires excellent pointing accuracy and stability and, therefore, high-end orbit and attitude control sensors and actuators. The multispectral imager is the most advanced of its kind, integrating two large visible near-infrared and shortwave infrared focal planes, each equipped with 12 detectors and integrating 450,000 pixels.
Pixels that may fail in the course of the mission can be replaced by redundant pixels. Two kinds of detectors integrate high-quality filters to isolate the spectral bands perfectly. The instrument's optomechanical stability must be extremely high, which has meant the use of silicon carbide ceramic for its three mirrors and focal plane, and for the telescope structure itself.
The geometric performance requires strong uniformity across the focal planes to avoid image distortion. The radiometric performance excluded any compromise regarding stray light, dictating a tight geometry and arrangement of all the optical and mechanical elements. The instrument is equipped with a calibration and shutter mechanism that integrates a large spectralon sunlight diffuser.
Each satellite has a high level of autonomy, so that they can operate without any intervention from the ground for periods of up to 15 days. This requires sophisticated autonomous failure analysis, detection and correction on board.
The ‘carpet mapping' imaging plan requires acquisition, storage and transmission of 1.6 TB per orbit. This massive data blast results from the combination of the 290 km swath with 13 spectral channels at a spatial resolution as high as 10 m.
In addition, the optical communication payload using the EDRS data link is a new technology that will improve the amount and speed of data delivery to the users. This was very recently demonstrated by Sentinel-1A, which also carries an optical communication payload.
Land in focus: Ensuring that land is used sustainably, while meeting the food and wood demands of a growing global population – a projected eight billion by 2020 – is one of today's biggest challenges. The Copernicus land service provides information to help respond to global issues such as this as well as focusing on local matters, or ‘hotspots', that are prone to specific challenges.
However, this service relies on very fast revisit times, timely and accurate satellite data in order to make meaningful information available to users – hence, the role of Sentinel-2. Through the service, users will have access to information about the health of our vegetation so that informed decisions can be made – whether about addressing climate change or how much water and fertilizer are needed for a maximum harvest.
Sentinel-2 is able to distinguish between different crop types and will deliver timely data on numerous plant indices, such as leaf area index, leaf chlorophyll content and leaf water content – all of which are essential to accurately monitor plant growth. This kind of information is essential for precision farming: helping farmers decide how best to nurture their crops and predict their yield.
While this has obvious economic benefits, this kind of information is also important for developing countries where food security is an issue. The mission's fast geometric revisit of just five days, when both satellites are operational, and only 10 days with Sentinel-2A alone, along with the mission's range of spectral bands means that changes in plant health and growth status can be easily monitored.
Sentinel-2 will also provide information about changes in land cover so that areas that have been damaged or destroyed by fire, for example, or affected by deforestation, can be monitored. Urban growth also can be tracked.
The Copernicus services are managed by the European Commission. The five ‘pan-European' themes covering 39 countries are addressed by the land service, including sealed soil (imperviousness), tree cover density, forest type, and grasslands. There is currently insufficient cloud-free satellite data in high resolution with all the necessary spectral bands that cover Europe fast enough to monitor vegetation when it is growing rapidly in the summer. Sentinel-2 will fill this gap.
This multi-talented mission will also provide information on pollution in lakes and coastal waters at high spatial resolution and with frequent coverage. Frequent coverage is also key to monitoring floods, volcanic eruptions and landslides. This means that Sentinel-2 can contribute to disaster mapping and support humanitarian aid work.
Leading edge: The span of 13 spectral bands, from the visible and the near-infrared to the shortwave infrared at different spatial resolutions ranging from 10 to 60 m on the ground, takes global land monitoring to an unprecedented level.
The four bands at 10 m resolution ensure continuity with missions such as SPOT-5 or Landsat-8 and address user requirements, in particular, for basic land-cover classification. The six bands at 20 m resolution satisfy requirements for enhanced land-cover classification and for the retrieval of geophysical parameters. Bands at 60 m are dedicated mainly to atmospheric corrections and cirrus-cloud screening.
In addition, Sentinel-2 is the first civil optical Earth observation mission of its kind to include three bands in the ‘red edge', which provide key information on the vegetation state.
Thanks to its high temporal and spatial resolution and to its three red edge bands, Sentinel-2 will be able to see very early changes in plant health. This is particularly useful for the end users and policy makers to detect early signs of food shortages in developing countries (Ref. 10).
Table 3: Facts and figures
In April 2008, ESA awarded the prime contract to Airbus Defence and Space (former EADS-Astrium GmbH) of Friedrichshafen, Germany to provide the first Sentinel-2A Earth observation satellite. In the Sentinel-2 mission program, Astrium is responsible for the satellite's system design and platform, as well as for satellite integration and testing. Astrium Toulouse will supply the MSI (MultiSpectral Instrument), and Astrium Spain is in charge of the satellite's structure pre-integrated with its thermal equipment and harness. The industrial core team also comprises Jena Optronik (Germany), Boostec (France), Sener and GMV (Spain). 11) 12) 13) 14)
Sentinel-2 uses the AstroBus-L of EADS Astrium, a standard modular ECSS (European Cooperation for Space Standards) compatible satellite platform compatible with an in-orbit lifetime of up to 10 years, with consumables sizeable according to the mission needs. The platform design is one-failure tolerant and the standard equipment selection is based on minimum Class 2 EEE parts, with compatibility to Class 1 in most cases. The AstroBus-L platform is designed for direct injection into LEO (Low Earth Orbit). Depending on the selection of standard design options, AstroBus-L can operate in a variety of LEOs at different heights and with different inclinations. An essential feature of AstroBus-L is the robust standard FDIR (Failure Detection, Isolation and Recovery) concept, which is hierarchically structured and can easily be adapted to specific mission needs.
Figure 1: Artist's rendition of the Sentinel-2 spacecraft (image credit: ESA, Airbus DS)
The satellite is controlled in 3-axes via high-rate multi-head star trackers, mounted on the camera structure for better pointing accuracy and stability, and gyroscopes and a GNSS receiver assembly. The AOCS (Attitude and Orbit Control Subsystem) comprises the following elements: 18)
• A dual frequency GPS receiver (L1/L2 code) for position and time information
• A STR (Star Tracker) assembly for precise attitude information (use of 3 STRs)
• A RMU (Rate Measurement Unit) for rate damping and yaw acquisition purposes
• A redundant precision IMU (Inertial Measurement Unit) for high-accuracy attitude determination
• Magnetometers (MAG) for Earth magnetic field information
• CESS (Coarse Earth Sun Sensors) for coarse Earth and Sun direction determination
• 4 RW (Reaction Wheels) and 3 MTQ (Magnetic Torquers)
• RCS (Reaction Control System) a monopropellant propulsion system for orbit maintenance with 1 N thrusters
The different tasks of the AOCS are defined the following modes:
• Initial Acquisition and Save Mode (rate damping, Earth acquisition, yaw acquisition, steady-state)
• Normal Mode (nominal and extended observation)
• Orbit Control Mode (in- and out-of-plane ΔV maneuvers).
Figure 2: Overview of the AOCS architecture (image credit: EADS Astrium)
The geolocation accuracy requirements of < 20 m for the imagery translate into the following AOCS performance requirements as stated in Table 4.
Table 4: AOCS performance requirements in normal mode
For Sentinel-2 it was decided to mount both the IMU and the star trackers on the thermally controlled sensor plate on the MSI. So the impact of time-variant IMU/STR misalignment on the attitude performance can be decreased to an absolute minimum. Furthermore, the consideration of the time-correlated star tracker noises by covariance tuning was decided.
Figure 3: Sentinel-2 spacecraft architecture (image credit: Astrium GmbH)
Figure 4: Block diagram of the Sentinel-2 spacecraft (image credit: EADS Astrium)
The EPS (Electric Power Subsystem) consists of:
• Solar Array (one deployable and rotatable single wing with three panels). Total array area of 7.1 m2. Use of 2016 triple junction GaAs solar cells with integrated diode. Total power of 2300 W (BOL) and 1730 W (EOL). The mass is < 40 kg.
• SADM (Solar Array Drive Mechanism) for array articulation. Use of a two phase stepper motor with µ-stepping to minimize parasitic distortions during MSI operation, motor step angle 1.5º. Mass of < 3.2 kg.
• PCDU (Power Control and Distribution Unit). PCDU with one unregulated 28 V ±4 V main power bus. Mass of < 21.6 kg; the in-orbit life is 12.25 years.
• Li-ion batteries with 8 cells in series. Total capacity of 102 Ah @ EOL. Mass = 51 kg.
Figure 5: Block diagram of the electrical power subsystem (image credit: EADS Astrium)
The OBC is based on the ERC32 PM (Processor Module) architecture. The PLDHS (Payload Data Handling System) provides source data compression from 1.3 Gbit/s to 450 Mbit/s [state-of-the-art lossy compression (wavelet transform)].
The spacecraft mass is ~ 1200 kg, including 275 kg for the MSI instrument, 35 kg for the IR payload (optional) and 80 kg propellant (hydrazine). The S/C power is 1250 W max, including 170 W for the MSI and < 100 W for the IR payload. The spacecraft is designed for a design life of 7.25 years with propellant for 12 years of operations, including deorbiting at EOL (End of Life).
Table 5: Overview of some spacecraft parameters
Figure 6: Schematic view of the deployed Sentinel-2 spacecraft (image credit: EADS Astrium)
Figure 7: The Sentinel-2 spacecraft in launch configuration (image credit: ESA)
Payload data are being stored in NAND flash memory technology SSR (Solid State Recorder) based on integrated CoReCi (Compression Recording and Ciphering) units of Airbus DS, available at various capacities. The CoReCi is an integrated image compressor, mass memory and data ciphering unit designed to process, store and format multi-spectral video instrument data for the satellite downlink. The mass memory utilizes high performance commercial Flash components, ESA qualified and up-screened for their use in space equipment. This new Flash technology allows mass and surface area used in the memory to be reduced by a factor of nearly 20 when compared with the former SD-RAM (Synchronous Dynamic Random Access Memory) based equipment. The first CoReCi unit has been successfully operating on SPOT-6 since September 2012. Sentinel-2A is carrying a CoReCi unit. 19) 20)
The MRCPB (Multi-Résolution par Codage de Plans Binaires) compression algorithm used is a wavelet transform with bit plane coding (similiar to JPEG 2000). This complex algorithm is implemented in a dedicated ASIC, with speeds of up to 25 Mpixel/s. Alternatively this unit can be supplied with a CCSDS compression algorithm using a new ASIC developed with ESA support. The ciphering is based on the AES algorithm with 128 bit keys. The modularity of the design allows the memory capacity and data rate to be adapted by adjusting the number of compressor and memory boards used.
• February 27, 2017: The ninth Vega light-lift launcher is now complete at the Spaceport, with its Sentinel-2B Earth observation satellite installed atop the four-stage vehicle in preparation for a March 6 mission from French Guiana. 21)
• January 12, 2017: Sentinel-2B arrived at Europe's spaceport in Kourou, French Guiana on 6 January 2017 to be prepared for launch. After being moved to the cleanroom and left for a couple of days to acclimatise, cranes were used to open the container and unveil the satellite. Over the next seven weeks the satellite will be tested and prepared for liftoff on a Vega rocket. 22)
• November 15, 2016: Sentinel-2B has successfully finished its test program at ESA/ESTEC in Noordwijk, The Netherlands. The second Sentinel-2 Airbus built satellite will now be readied for shipment to the Kourou spaceport in French Guiana begin January 2017. It is scheduled for an early March 2017 lift-off on Vega. 23)
- Offering "color vision" for the Copernicus program, Sentinel-2B like its twin satellite Sentinel-2A will deliver optical images from the visible to short-wave infrared range of the electromagnetic spectrum. From an altitude of 786 km, the 1.1 ton satellite will deliver images in 13 spectral bands with a resolution of 10, 20 or 60 m and a uniquely large swath width of 290 km.
• June 15, 2016: Airbus DS completed the manufacture of the Sentinel-2B optical satellite; the spacecraft is ready for environmental testing at ESA/ESTEC. The Sentinel-2 mission, designed and built by a consortium of around 60 companies led by Airbus Defence and Space, is based on a constellation of two identical satellites flying in the same orbit, 180° apart for optimal coverage and data delivery. Together they image all Earth's land surfaces, large islands, inland and coastal waters every five days at the equator. Sentinel-2A was launched on 23 June 2015, its twin, Sentinel-2B, will follow early next year. 24)
- The Sentinel-1 and -2 satellites are equipped with the Tesat-Spacecom's LCT (Laser Communication Terminal). The SpaceDataHighway is being implemented within a Public-Private Partnership between ESA and Airbus Defence and Space.
Figure 8: Sentinel-2B being loaded at Airbus Defence and Space's satellite integration center in Friedrichshafen, Germany (image credit: Airbus DS, A. Ruttloff)
• April 27, 2015: The Sentinel-2A satellite on Arianespace's next Vega mission is being readied for pre-launch checkout at the Spaceport, which will enable this European Earth observation platform to be orbited in June from French Guiana. — During activity in the Spaceport's S5 payload processing facility, Sentinel-2A was removed from the shipping container that protected this 1,140 kg class spacecraft during its airlift from Europe to the South American launch site. With Sentinel-2A now connected to its ground support equipment and successfully switched on, the satellite will undergo verifications and final preparations for a scheduled June 11 liftoff. 25)
Figure 9: Sentinel-2A is positioned in the Spaceport's S5 payload processing facility for preparation ahead of its scheduled June launch on Vega (image credit: Arianespace)
• April 23, 2015: The Sentinel-2A satellite has arrived safe and sound in French Guiana for launch in June. The huge Antonov cargo aircraft that carried the Sentinel-2A from Germany, touched down at Cayenne airport in the early morning of 21 April. 26)
• April 8, 2015: The Sentinel-2A satellite is now being carefully packed away in a special container that will keep it safe during its journey to the launch site in French Guiana. The satellite will have one final test, a ‘leak test', in the container to ensure the propulsion system is tight. Bound for Europe's Spaceport in French Guiana, Sentinel-2A will leave Munich aboard an Antonov cargo plane on 20 April. Once unloaded and unpacked, it will spend the following weeks being prepared for liftoff on a Vega rocket. 27)
• February 24, 2015: Sentinel-2A is fully integrated at IABG's facilities in Ottobrunn, Germany before being packed up and shipped to French Guiana for a scheduled launch in June 2015. 28)
Figure 10: Photo of the Sentinel-2A spacecraft in the thermal vacuum chamber testing at IAGB's facilities (image credit: ESA, IABG, 2015)
• In August 2014, Airbus Defence and Space delivered the Sentinel-2A environmental monitoring satellite for testing . In the coming months, the Sentinel-2A satellite will undergo a series of environmental tests at IABG, Ottobrunn, Germany, to determine its suitability for use in space. 29) 30)
Figure 11: Sentinel-2A solar array deployment test at IABG (Airbus Defence & Space), image credit: ESA 31)
- Sentinel-2A is scheduled to launch in June 2015; Sentinel-2B, which is identical in design, is set to follow in March 2017. Together, these two satellites will be able to capture images of our planet's entire land surface in just five days in a systematic manner.
Figure 12: Photo of the Sentinel-2A spacecraft at the satellite integration center in Friedrichshafen, Germany (image credit: Airbus DS, A. Ruttloff)
RF communications: The payload data handling is based on a 2.4 Tbit solid state mass memory and the payload data downlink is performed at a data rate of 560 Mbit/s in X-band with 8 PSK modulation and an isoflux antenna, compliant with the spectrum bandwidth allocated by the ITU (international Telecommunication Union).
Command and control of the spacecraft (TT&C) is performed with omnidirectional S-band antenna coverage using a helix and a patch antenna. The TT&C S-band link provides 64 kbit/s in uplink (with authenticated/encrypted commands) and 2 Mbit/s in downlink..
The requirements call for 4 core X-band ground stations for full mission data recovery by the GMES PDS (Payload Data System).
In parallel to the RF communications, an optical LEO-GEO communications link using the LCT (Laser Communication Terminal) of Tesat-Spacecom (Backnang, Germany) will be provided on the Sentinel-2 spacecraft. The LCT is based on a heritage design (TerraSAR-X) with a transmit power of 2.2 W and a telescope of 135 mm aperture to meet the requirement of the larger link distance. The GEO LCT will be accommodated on AlphaSat of ESA/industry (launch 2012) and later on the EDRS (European Data Relay Satellite) system of ESA. The GEO relay consists of an optical 2.8 Gbit/s (1.8 Gbit/s user data) communication link from the LEO to the GEO satellite and of a 600 Mbit/s Ka-band communication link from the GEO satellite to the ground. 34)
To meet the user requirements of fast data delivery, DLR (German Aerospace Center) is funding the OCP (Optical Communication Payload), i.e. the LCT of Tesat, – a new capability to download large volumes of data from the Sentinel-2 and Sentinel-1 Earth observation satellites - via a data relay satellite directly to the ground. A contract to this effect was signed in October 2010 between ESA and DLR. 35)
Since the Ka-band downlink is the bottleneck for the whole GEO relay system, an optical ground station for a 5.625 Gbit/s LEO-to-ground and a 2.8 Gbit/s GEO-to-ground communication link is under development.
Orbit: Sun-synchronous orbit, altitude = 786 km, inclination = 98.5º, (14+3/10 revolutions/day) with 10:30 hours LTDN (Local Time at Descending Node). This local time has been selected as the best compromise between cloud cover minimization and sun illumination.
The orbit is fully consistent with SPOT and very close to the Landsat local time, allowing seamless combination of Sentinel-2 data with historical data from legacy missions to build long-term temporal series. The two Sentinel-2 satellites will be equally spaced (180º phasing) in the same orbital plane for a 5 day revisit cycle at the equator.
The Sentinel-2 satellites will systematically acquire observations over land and coastal areas from -56° to 84° latitude including islands larger 100 km2, EU islands, all other islands less than 20 km from the coastline, the whole Mediterranean Sea, all inland water bodies and closed seas. Over specific calibration sites, for example DOME-C in Antarctica, additional observations will be made. The two satellites will work on opposite sides of the orbit (Figure 13).
Figure 13: Twin observation configuration of the Sentinel-2 spacecraft constellation (image credit: ESA)
• The first stage separated 1 min 55 seconds after liftoff, followed by the second stage and fairing at 3 min 39 seconds and 3 min 56 seconds, respectively, and the third stage at 6 min 32 seconds.
• After two more ignitions, Vega's upper stage delivered Sentinel-2B into the targeted Sun-synchronous orbit. The satellite separated from the stage 57 min 57 seconds into the flight.
• Telemetry links and attitude control were then established by controllers at ESOC in Darmstadt, Germany, allowing activation of Sentinel's systems to begin. The satellite's solar panel has already been deployed.
• After this first ‘launch and early orbit' phase, which typically lasts three days, controllers will begin checking and calibrating the instruments to commission the satellite. The mission is expected to begin operations in three to four months.
Sentinel-2B will join its sister satellite Sentinel-2A and the other Sentinels part of the Copernicus program, the most ambitious Earth observation program to date. Sentinel-2A and -2B will be supplying ‘color vision' for Copernicus and together they can cover all land surfaces once every five days thus optimizing global coverage and the data delivery for numerous applications. The data provided by these Sentinel-2 satellites is particularly suited for agricultural purposes, such as managing administration and precision farming.
With two satellites in orbit it will take only five days to produce an image of the entire Earth between the latitudes of 56º south and 84º north, thereby optimizing the global coverage zone and data transmission for numerous applications.
To ensure data continuity two further optical satellites, Sentinel-2C and -2D, are being constructed in the cleanrooms of Airbus and will be ready for launch as of 2020/2021.
Figure 14: Illustration of the Sentinel-2B spacecraft in orbit (image credit: Airbus DS, Ref. 38)
Figure 15: This technical view of the Sentinel-2 satellite shows all the inner components that make up this state-of-the-art high-resolution multispectral mission (video credit: ESA/ATG medialab)
Figure 16: As well as imaging in high resolution and in different wavelengths, the key to assessing change in vegetation is to image the same place frequently. The Sentinel-2 mission is based on a constellation of two satellites orbiting 180° apart, which along with their 290 km-wide swaths, allows Earth's main land surfaces, large islands, inland and coastal waters to be covered every five days. This is a significant improvement on earlier missions in the probability of gaining a cloud-free look at a particular location, making it easier to monitor changes in plant health and growth (video credit: ESA/ATG medialab)
Note: As of May 2019, the previously single large Sentinel-2 file has been split into two files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the Sentinel-2 mission and its imagery in the period 2019
Mission status and imagery of 2019
• October 11, 2019: The Copernicus Sentinel-2 mission takes us over two saline lakes in East Africa: the larger Lake Natron in northern Tanzania and the smaller Lake Magadi, just over the border in Kenya. 40)
- The saline waters make the lake inhospitable for many plants and animals, yet the surrounding salt water marshes are a surprising habitat for flamingos. In fact, the lake is home to the highest concentrations of lesser and greater flamingos in East Africa, where they feed on spirulina – a green algae with red pigments.
- The extinct Gelai Volcano, standing at 2942 m tall, is visible southeast of the lake.
- The pink-colored waters of Lake Magadi can also be seen at the top of the image. The lake is over 30 km long and has a notably high salt content, and in some places the salt is up to 40 m thick. The mineral trona can also be found in the lake's waters. This mineral is collected and used for glass manufacturing, fabric dyeing and paper production.
Figure 17: Lake Natron is around 60 km long and is fed mainly by the Ewaso Ng'iro River. Despite its dark color in this image, Lake Natron is often bright red owing to the presence of microorganisms that feed on the salts of the water. Sentinel-2 acquired this image on 3 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)
• October 4, 2019: The Netherlands is featured in this false-color image captured by the Copernicus Sentinel-2 mission. This image was processed in a way that included the near-infrared channel, which makes vegetation appear bright red. 41)
- Amsterdam, the capital city of the country, is visible towards the top of the image, on the edge of the IJmeer lake. The city's complex network of canals can be seen in the image, and the city is said to have over 1000 bridges.
- Rotterdam is the second largest city in the Netherlands and is visible in the lower left, along the banks of the New Meuse River, which divides the municipality into its northern and southern parts. Rotterdam's port is the largest port in Europe, stretching over 40 km in length and covering over 10,000 hectares.
- The Hague is north of the port, visible along the North Sea coast. The Hague is home to the Dutch seat of government, and the city also hosts the International Court of Justice and the International Criminal Court.
- To the north of The Hague is the coastal town of Noordwijk, home to ESA's European Space Technology Research Centre (ESTEC). ESTEC is ESA's technical centre where new missions are designed, their industrial development is managed and, in some cases, the spacecraft and instruments are tested.
- On Sunday 6 October, ESTEC is hosting its annual Open Day, where it will open its doors and give general public the chance to meet astronauts, space experts and get a behind-the-scenes glimpse of ESA's largest establishment. The Open Day is now fully booked.
- The theme of this year's event is ESA to the Moon – where Dutch ESA astronaut André Kuipers will be joined by pioneering Apollo astronauts Walt Cunningham, who flew on the first crewed Apollo mission, and Rusty Schweickart, who was the first person to fly the Lunar Module and use an Apollo lunar spacesuit for a spacewalk.
Figure 18: ESA's Earth from Space image of the Netherlands was acquired with the Sentinel-2 satellite. The image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2016), processed by ESA, CC BY-SA 3.0 IGO)
- The Rio Negro, visible in black, is the largest tributary of the Amazon and the world's largest black-water river. It flows 2300 km from Colombia, and it gets its dark coloring from leaf and plant matter that has decayed and dissolved in its waters.
- The Rio Negro contrasts significantly with the Solimões River – visible directly below - which owes its brown-coloring to its rich sediment content, including sand, mud and silt. After flowing for around 1600 km, the Solimões River meets the Rio Negro and together form this important junction.
- Owing to differences in temperature, speed and water density, the two rivers, after converging, flow side-by-side for a few kilometers , before eventually mixing.
- Manaus, the largest city in the Amazon Basin, is visible on the north bank of the Rio Negro. Despite being 1500 km from the ocean, Manaus is a major inland port. The Adolfo Ducke Forest Reserve is visible northeast of the city. The almost square-shaped block of land is a protected area named after the botanist Adolfo Ducke, and is used for the research of biodiversity.
Figure 19: This image of Sentinel-2, captured on 7 February 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)
- The strait ties the Beagle Gulf in the west with the Van Diemen Gulf to the east and separates Australia's mainland from Melville Island, part of the Tiwi Islands. The southernmost tip of Melville is visible in the upper part of the image.
- The three islands in the southern part of the strait, are the Vernon Islands, which host navigation aids to assist vessels passing through the strait.
- Australia's Northern Territory is a sparsely-populated region. With a population of around 140,000, Darwin is the territory's capital and largest city, and is visible in grey in the center of the image.
- In 1839, the HMS Beagle sailed into the waters of what is now known as Darwin Harbor. The harbor was named after the British evolutionist Charles Darwin, but, contrary to popular belief, Darwin himself never visited the area.
- With a strong Aboriginal culture, art and tropical summers, Darwin is a popular tourist destination. The Crocosaurus Cove in the heart of the city houses the world's largest display of Australian reptiles.
- The waters that surround Darwin are riddled with saltwater crocodiles and deadly box jellyfish, which inhabit the waters from October to May. The Adelaide River, known for its high concentration of saltwater crocodiles, can be seen to the right of Darwin, snaking its way northwards, flowing 180 km before emptying into the Timor Sea.
- The Djukbinj National Park, visible east of Adelaide River, is a protected area and consists mostly of wetlands. The close vicinity to the water makes the park a major breeding ground for a variety of water birds, including magpie geese, herons and egrets.
Figure 20: Sentinel-2 captured this image of the Clarence Strait on 24 June 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)
• September 10, 2019: Australia is tackling multiple bushfires that have broken out across New South Wales and Queensland over the past few days. 44)
- The flames, which were said to have been whipped up by strong winds, have now been contained. More than 600 firefighters have been deployed to tackle the fires, and multiple homes and outbuildings have been damaged.
Figure 21: In this image captured by the Copernicus Sentinel-2 mission on 8 September, fires burning in the Yuraygir National Park and Shark Creek area are visible. Fires are also burning to the north and south of the villages of Angourie and Wooloweyah (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• September 6, 2019: The Copernicus Sentinel-2 mission takes us over a set of small towns in the Colli Albani hills known collectively as Castelli Romani. 45)
- Located around 20 km southeast of Rome, the Castelli Romani area is of volcanic nature, originating from the collapsing of the Latium volcano hundreds of thousands of years ago. The outlines of the inner and outer crater rims are clearly visible in the image.
- Two lakes now occupy the craters, the small Lake Nemi and the larger, oval-shaped Lake Albano. The town of Castel Gandolfo overlooks Lake Albano and is known for its papal summer residence where many popes have spent their summers since the 17th century.
- Owing to cooler temperatures during summer, the hills and small towns are a popular destination for city dwellers trying to escape the heat.
- Each town has its own attraction, for example Ariccia is famous for its porchetta or roast pork, and Frascati is predominantly known for its wine.
- Frascati, which is just north of Lake Albano, is known for a number of scientific research institutes. These include ENEA, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development; CNR, the Italian Research Council; INFN, the National Institute for Nuclear Physics; as well as ESA's Earth observation center.
- From 9–13 September, ESA is holding the φ-week event, focusing on Earth observation and FutureEO — to review the latest developments in Open Science trends. The week will include a variety of inspiring talks, workshops on how Earth observation can benefit from the latest digital technologies and help shape future missions.
Figure 22: This Sentinel-2 image was acquired on 13 October 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)
• August 21, 2019: An unprecedented wildfire has ripped through the island of Gran Canaria, one of Spain's Canary Islands off the northwest coast of Africa. The wildfire, which started on Saturday 17 August, has now started to subside after engulfing around 10,000 hectares of land, leading to the evacuation of over 9000 people. 46)
- The Copernicus Emergency Mapping Service was activated to help respond to the fire. The service uses satellite observations to help civil protection authorities and, in cases of disaster, the international humanitarian community, respond to emergencies.
- The fire started near the town of Tejeda and spread to Tamadaba Natural Park, driven by a combination of high temperatures, strong winds and low humidity. According to authorities, over 700 firefighters on the ground and 16 aircraft helped tackle the blaze, with some flames reaching over 50 meters in height.
Figure 23: This false color image, captured on 19 August, was created using the shortwave infrared bands from the Copernicus Sentinel-2's instrument, and allows us to clearly see the fires on the ground in bright orange. Burned scars are visible in dark brown. These bands also allow us to see through smoke – but not through clouds (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• July 26, 2019: The Copernicus Sentinel-2 mission takes us over Lake Balaton in western Hungary. With a surface area of around 600 km2 and a length of around 78 km, this freshwater lake is the largest in central Europe (Figure 24). 47)
- The lake is mainly fed by the Zala River at its western end. The lakewater flows out near the eastern end via an artificial channel called the Sió, which eventually feeds into the Danube River.
- Originally five separate water bodies, the barriers between have been eroded away to create the lake it is today. Remnants of the dividing ridges can be seen in Balaton's shape – with the Tihany Peninsula on the northern shore narrowing the width of the lake to approximately 1.5 km.
- Lake Balaton's striking emerald-green color in this image is most likely due to its shallow waters and chemical composition. It is heavy in carbonates and sulphates, and there are also around 2000 species of algae that grow in its waters.
- The lake supports a large population of plant and animal species. During migration and wintering sessions, the site is an important staging area for thousands of ducks and geese.
- Owing to its pleasant climate and fresh water, the Lake Balaton area is a popular tourist destination. The mountainous northern region is known for its wine, while popular tourist towns lie on the flatter southern shore.
Figure 24: This image of Lake Balaton, captured on 27 February 2019, 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)
• July 19, 2019: The Copernicus Sentinel-2 mission takes us over palm oil plantations in East Kalimantan - the Indonesian part of the island Borneo. 48)
- Palm oil is the most widely-produced tropical edible oil. It's used in a vast array of products – from ice cream and chocolates, to cosmetics such as make up and soap, to biofuel. Not only is it versatile, palm oil is also a uniquely productive crop. Harvested all year-round, oil palm trees produce up to nine times more oil per unit area than other major oil crops.
- To meet global demand, palm oil trees are grown on vast industrial plantations – leading to acres of rainforest being cut down. Between 1980 and 2014, global palm oil production increased from 4.5 million tons to 70 million tons, and is expected to increase.
- Indonesia is the largest producer of palm oil, followed by Malaysia. Together they account for 84% of the world's palm oil production.
- To produce palm oil in large enough quantities to meet growing demand, farmers clear large areas of tropical rainforest to make room for palm plantations. This leads to a loss of habitat for species such as the orangutan – declared as critically endangered by the WWF. In general, burning forests to make room for the crop is also a major source of greenhouse gas emissions.
Figure 25: In this image, captured on 15 February 2019, the various stages of the deforestation process are clearly visible – the green patches in the plantations are the well-established palm oil farms, while the light brown patches show the newly-harvested land. The surrounding lush rainforest is visible in dark green. 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)
• July 16, 2019: Celebrating 50 years since Apollo 11 blasted off with the first humans that would walk on the Moon, Copernicus Sentinel-2 captures the historic launch site at Kennedy Space Center, Cape Canaveral, Florida, US. 49)
- The crew – Neil Armstrong, mission commander, Michael Collins, command module pilot and Edwin ‘Buzz' Aldrin, lunar module pilot – were embarking on a milestone in human history.
- Just four days later on 20 July 1969, the lunar module, the Eagle, touched down. Watched on television by millions around the world, Neil Armstrong was the first to set foot on the Moon, famously saying, "That's one small step for man, one giant leap for mankind."
- A few minutes later, he was joined by Buzz Aldrin. They took photographs, planted the US flag, spoke to President Richard Nixon via radio transmission and spent a couple of hours walking and collecting dust and rocks. The two men returned to the lunar module, slept that night on the surface of the moon, and then the Eagle began its ascent back to re-join the command module, which had been orbiting the Moon with Michael Collins. Apollo splashed back down safely in the Pacific Ocean on 24 July 1969.
- The Moon has again captured the attention of space agencies. ESA and international partners are now looking forward to the next era of human exploration, and to better understand the resources available on the Moon to support human missions longer-term. While Apollo 11 touched down for the first time on the near side of the Moon 50 years ago, it is time to explore the far side, examine different types of lunar rocks there to probe deeper into the Moon's geological history and to find resources like water-ice that are thought to be locked up in permanently shadowed craters near the Moon's south pole.
Figure 26: On 16 July 1969, the Saturn V rocket carrying Apollo 11 began its momentous voyage to the Moon. It lifted off from launch pad 39A – which can be seen in this Copernicus Sentinel-2 image from 29 January 2019. Launch pad 39A is the second pad down from the top (the launch pad at the far top is 39B), image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO
• July 12, 2019: The Copernicus Sentinel-2 mission takes us over Mount Fuji, Japan's highest mountain standing at 3776 m tall. In this spring image, the mountain can be seen coated in pure white snow. 50)
- Mount Fuji is near the Pacific coast of central Honshu, straddling the prefectures of Yamanashi and Shizuoka. On a clear day, the mountain can be seen from Yokohama and Tokyo - both over 120 km drive away.
- The majestic stratovolcano is a composite of three successive volcanoes. Generations of volcanic activity have turned it into the Mount Fuji as we know it today. This volcanic activity is a result of the geological process of plate tectonics. Mount Fuji is a product of the subduction zone that straddles Japan, with the Pacific Plate and the Philippine Plate being subducted under the Eurasian plate.
- The last explosive activity occurred in 1707, creating the Hoei crater – a vent visible on the mountain's southeast flank, as well as the volcanic ash field which can be seen on the east side.
- Mount Fuji is a symbol of Japan, and a popular tourist destination. Around 300,000 people climb the mountain every year – and in the image several hiking trails can be seen leading to the base of the mountain. The city of Fujinomiya, visible in the bottom left of the image, is the traditional starting point for hikers.
- Many golf courses, a popular sport in Japan, can be seen dotted around the image.
- Worshipped as a sacred mountain, Mount Fuji is of great cultural importance for the Shinto religion. Pilgrims have climbed the mountain for centuries and many shrines and temples dot the landscape surrounding the volcano.
Figure 27: This snow-capped mountain is often shrouded in cloud and fog, but this image was captured on a clear day, by the Copernicus Sentinel-2A satellite - flying 800 km above. This image, captured on 8 May 2019, 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)
• July 5, 2019: The Copernicus Sentinel-2 mission takes us over a swirl of sea ice off the east coast of Greenland in the Irminger Sea, which is just south of the Denmark Strait between Greenland and Iceland. 51)
- The ice (Figure 28), which formed by freezing of the sea surface further north in the Arctic Ocean, has drifted southwards along the coast of Greenland before arriving at this location. The ice swirl is considered a typical eddy or vortex, commonly found in the summer marginal ice zone off the east coast of Greenland.
- The marginal ice zone is the transition region from the open ocean, visible in dark blue, to the white sea ice. Depending on wind direction, waves and ocean currents, it can consist of small, isolated ice floes drifting over a large area to smaller ice floes pressed together in bright white bands.
- Strong mesoscale air—ice—ocean interactive processes drive the advance and retreat of the sea ice edge, and result in the meanders or eddies visible in this region.
- Investigations of such ocean eddies and meanders began in the 1970s and 1980s in the Greenland Sea to gain a better understanding of the interactions between the ocean, ice and atmosphere.
Figure 28: In this image captured on 9 June 2019, small pieces of sea ice, known as ice floes, trace out the ocean currents beneath, resulting in a large swirl-like feature of approximately 120 km in diameter. 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)
• July 4, 2019: Mount Michael is an active stratovolcano on the remote Saunders Island, one of the South Sandwich Islands in the southern Atlantic Ocean. In situ observations of the volcano prove difficult owing to its remote location and the fact that it is almost 1000 m high and difficult to climb. However, modern satellite imagery can help survey isolated locations such as these. 52)
Figure 29: In these images captured by the Copernicus Sentinel-2 mission on 29 March 2018, a distinct hotspot can be seen in orange in the crater of the volcano. The true-color image shows volcanic ash over the snow and smoke plumes coming from its crater, drifting south-eastwards (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA)
- The assessment of Mount Michael's lava lake is presented in a recent report in the Journal of Volcanology and Geothermal Research. By using modern satellites, including the US Landsat, Copernicus Sentinel-2 and the US Terra missions, monitoring activity and thermal anomalies within the crater is now possible.
- The paper confirms that the rare lava lake is a continuous feature inside Mount Michael's crater, with a temperature of approximately 1000 °C.
- Only a handful of other volcanoes in the world are currently hosting persistent lava lakes – Masaya volcano, Mount Nyiragongo, Kīlauea, Mount Erebus, Mount Yasur, Ambrym and Erta Ale.
• On 30 June 2019, a wildfire broke out at a military training site in Lübtheen, in northern Germany. Authorities claim it is the largest blaze in the history of the Mecklenburg-Western Pomerania state. 53)
Figure 30: This animation was captured by the Copernicus Sentinel-2 mission, with a resolution of up to 10 m, on 1 July at 10:20 GMT (12:20 CEST). The true-color image shows the smoke emerging from the training site, while the other image was processed using the shortwave infrared which allows for a better view of the blaze under the smoke – which can be seen in bright orange (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
- Emergency services had difficulties containing the site, owing to unexploded munitions from military activities going back as far as World War II. Water has been diverted from the Elbe river to tackle the blaze. According to local firefighters, the fire swept through 400 hectares of forest, and hundreds of people were evacuated from their homes.
• June 28, 2019: The Copernicus Sentinel-2 mission takes us over the Gulf of Taranto, located on the inner heel of southern Italy. 54)
Figure 31: Taranto, an important coastal city, is visible on the bottom right of the image. Founded by a Greek colony in the 8th century, the city is now an important commercial port. The islets of San Pietro and San Paolo, known as the Cheradi Islands, protect the Mar Grande, the main commercial port of the city. It is separated from the Mar Piccolo, an inland lagoon, by a cape which closes the gulf. The industrial district, which is visible northwest of the city, has a high number of factories, oil refineries, steelworks and iron foundries. This image, captured on 6 March 2019, 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)
- Along the coast, the Aleppo pine forest of the Stornara Nature Reserve is clearly visible in dark green. It takes its name from the many starlings that migrate there during winter. The reserve was founded in 1977 and covers an area of approximately 1500 hectares.
- Directly above the forest, many various patches of agricultural fields can be seen. Favored by the Mediterranean climate, the food sector has been one of the strongest areas of the Apulian economy. Fruit, vegetables and cereals are grown in a range of crop types throughout the region, depending on the time of year. The blue patches visible are greenhouses.
- Considered as the 2019 European Capital of Culture along with Plovdiv, in Bulgaria, Matera can be seen in the top left of the image, in the Basilicata region.
- Matera hosts an important space hub. The Giuseppe Colombo Center for Space Geodesy, founded by the Italian Space Agency, is located here. It sends regular laser beams to the moon, where they reach reflectors that were placed there during the original Apollo missions and the Lunokhod Soviet robotic missions. These lasers measure the distance from the Earth to the moon, expanding our knowledge of the moon's internal structure.
- Located next door, the Matera Space Center is one of the ground stations for the reception and processing of data acquired by the Copernicus Sentinel satellites for ESA.
• June 27, 2019: One of the largest wildfires recorded in Arizona, US, has been burning since 8 June, destroying vast swathes of vegetation across the Superstition Mountains east of Phoenix. Efforts to contain the fire include spraying flame retardant from aircraft. Colored red so that firefighters can see it, the retardant is dropped ahead of the path of the fire to act as a break – and remarkably these red lines can be seen from space. 55)
Figure 32: This Copernicus Sentinel-2 image from 24 June not only captures the extent of the Woodbury fire and burn scars in Arizona, but also the red lines of the retardant (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• June 17, 2019: Today marks the 25th anniversary of World Day to Combat Desertification and Drought (WDCD). Under its theme ‘Let's grow the future together,' the initiative celebrates the 25 years of progress made in sustainable land management. 56)
- One ambitious project – the Great Green Wall – aims to improve life in Africa's desert regions by planting a belt of trees across the entire width of the continent. Once completed, the wall will be the largest living structure on the planet stretching across 20 countries - from Senegal in the west to Djibouti in the east.
- By 2030, the initiative aims to have restored 100 million hectares of degraded land, sequestered 250 million tons of carbon and created 10 million green jobs.
- Since the Green Wall started in 2007, progress has been made in restoring the Sahelian lands. In Senegal alone, almost 12 million trees have been planted, and 25,000 hectares of degraded land restored.
- Desertification is the degradation of dry land ecosystems, owing to overexploitation through human activities and climate change. According to the UN, 12 million hectares of land is lost yearly because of desertification and drought, and 75 billion tons of fertile soil is lost due to land degradation.
Figure 33: Captured by the Copernicus Sentinel-2 mission in 2019, this image shows the edge of the dry desert in west Africa contrasted with vegetated land. Signs of land degradation can be seen as brighter "islands" around villages and to a lesser extent along roads and rivers showing bare soil and degraded vegetation. The image shows parts of three African countries: Senegal, The Gambia and Guinea-Bissau (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• 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. 57)
- 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 34, 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. 58)
- Mount Batur, or Gunung Batur, has an unusual shape, with the volcanic cone visible in the center of two concentric calderas.
Figure 34: 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 35) 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. 59)
- Unfortunately, the inflow of untreated wastewater from the surrounding industrial and agricultural lands has led to the lake to become contaminated. The lake now suffers from algal blooms and between 1960 and 1990 it lost over 60% of its native fish species.
- It was at this very lake that the German naturalist and explorer, Alexander von Humboldt, witnessed how human behavior could cause harm to our natural ecosystem and climate. During his travels in the late 18th century, he noted the surrounding barren land which had been cleared for plantations and crops for sugar and tobacco. He attributed the decreasing water levels in the lake to climate change.
- "When forests are destroyed, the springs are entirely dried up," he wrote in his travel report, the Relation historique du voyage aux régions équinoxiales du nouveau continent (1814-17). "The beds of the rivers are converted into torrents whenever great rains fall on the heights.... Hence it results, that the destruction of forests, the want of permanent springs, and the existence of torrents, are three phenomena closely connected together."
- The now poor-quality waters of Lake Valencia prevent the development of tourism and recreational activities in the region.
Figure 35: 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. 60)
- Lake Guija, visible in the top left of the image (Figure 36), lies on the border between El Salvador and Guatemala. The lake once formed part of the Mayan Empire and legend says that it also hides an ancient city beneath its waters.
- El Salvador sits on the eastern edge of the Pacific Ring of Fire, and despite being a small country, it has 25 volcanoes. The volcano complex of the Cerro Verde National Park can be seen dotted with clouds in the lower left of the image.
Figure 36: 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 37 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. 61)
- The Indus Delta consists of creeks, swamps, marshes and the seventh largest mangrove forest in the world.
- However, owing to major irrigation works and dams built on the river, as well as low rainfall, the amount of silt discharged into the sea has reduced, affecting the mangrove and local community significantly. A huge proportion of the delta has been lost and the survival of the delta freshwater species, including the Indus river dolphin, are at risk.
- Also responsible for pollution is the port city of Karachi, which is partially visible in the top left of the image.
- To the top right, there are two important bodies of water on the edge of the stony desert, both of which are also wildlife sanctuaries. The artificial, square-shaped Haleji Lake, was expanded in World War II, for the use of additional water for the troops. The freshwater lake supports an abundance of aquatic vegetation, and is home to a number of species of birds.
- To the far right, the freshwater Keenjhar Lake is a major source of drinking water for Karachi, as well as for Thatta, which is to the right of the yellow-beige patch of land.
- Both lakes, as well as the River Indus Delta, are sites of wetland designated to be of international importance under the Ramsar Convention – an international treaty for the conservation and sustainable use of wetlands.
Figure 37: 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. 62)
Figure 38: 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. 63)
- Over 4000 participants will gather at the largest congress center in Europe: the MiCo Convention Center. With its iconic architecture, this modern building has become a landmark. The event will not only see scientists present their latest findings on Earth's environment and climate derived from satellite data, but will also focus on Earth observation's role in building a sustainable future and a resilient society.
- Milan is the second biggest city in Italy and, like most large urban environments, it suffers from air pollution. While there is an effort to reduce the emission of pollutants, the city is also incorporating more vegetation into its development plans. This not only makes the environment more pleasant, but the plants also help soak up greenhouse gases such as carbon dioxide.
- The Bosco Verticale, or the Vertical Forest, for example, aims to inspire the need for urban biodiversity. The two tower blocks have plants and trees planted on its façade, and are located just north of the historical center. The vegetation covering both towers is equivalent to 20,000 m2 of forest and home to a variety of birds and butterflies. This vegetation absorbs approximately 30 tons of carbon dioxide per year.
- Another example of the city's efforts to ‘go green', is the Biblioteca degli Alberi, or Library of Trees, visible next to the Bosco Verticale. With its geometric design and irregular patches of land, the gardens are home to over 100,000 plants and trees, interlinked with pedestrian and bike paths.
- But it doesn't stop there, the local government aims to plant another three million trees by 2030.
Figure 39: 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. 64)
- With a diameter of 26 km, the rim of the crater can be seen as a semi-circle in the image, delineated by dark green forest to the south. The flat ‘crater floor' is ideally suited for agricultural use and the corresponding fields mark the crater's extent.
- The medieval town of Nördlingen (in the Donau-Ries district of Bavaria) was built in its depression. The historical center, approximately 1 km wide, appears as a reddish circle, visible with its red rooftops surrounded by a wall.
- The asteroid was estimated to be travelling at 70,000 km per hour, and when it made impact with Earth, the high-speed force exposed the rock to intense pressure and heat, over 25,000°C. The impact led to the creation of over 70,000 tons of microscopic diamonds, each around 0.2 mm in size.
- Overlooked by the town's inhabitants, the stone buildings were constructed almost entirely with diamond-encrusted rock. Details on the impact can be found in the well-known Rieskrater Museum in Nördlingen.
- For centuries, Nördlingen locals believed the town was built in the crater of a volcano. But in the 1960s two American scientists (Gene Shoemaker and Edward Chao) proved that the depression was, in fact, caused by a meteorite impact. Today, visitors around the world gather to marvel at this glittering town, also known as the backdrop to the original Willy Wonka and the Chocolate Factory film.
Figure 40: The Sentinel-2 satellite of ESA captured this image of the Nördlinger Ries on 1 July 2018, it is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO)
Figure 41: 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. 65)
- In early 2019, many areas in Queensland received more than their annual rainfall in less than a week. The downpour led to millions of dollars' worth of damage, including homes being destroyed and the loss of almost 500,000 cattle.
- The Burdekin River rises on the northern slopes of Boulder Mountain and flows close to 900 km before emptying into the Coral Sea. The Burdekin River is one of Australia's larger rivers by discharge volume, and is a major contributor of sediment and freshwater to the Great Barrier Reef lagoon.
- The Great Barrier Reef, the world's largest coral reef, extends for 2000 km along the northeast coast of Australia and covers almost 350,000 km2. The reef is an interlinked system of about 3000 reefs and 900 coral islands, divided by narrow passages. An important area of biodiversity, the reef was made a UNESCO World Heritage Site in 1981.
- The sand-color sediment plume can be seen stretching over 35 km from the coast, dangerously close to the vivid turquoise reef. The blues of the coral contrast with the dark-colored waters of the Coral Sea.
- The coral reef suffers regular damage, more than half of the reef has disappeared over the last 30 years owing to climate change, coral bleaching and pollution. Large quantities of sediment that flow out from rivers carry chemicals and fertilizers from inland farms. The sediment blankets the coral, and reduces the amount of light, as well as potentially causing harmful algae blooms.
- Data from Copernicus Sentinel-2 plays a key role in providing information on pollution in lakes and coastal waters. Frequent coverage is also fundamental to monitoring floods.
Figure 42: This image was captured a few days after the torrential rain, and shows the muddy waters flowing from the Burdekin River into the Coral Sea. It was captured on 10 February 2019, it is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019), processed by ESA, CC BY-SA 3.0 IGO)
• April 19, 2019: The Copernicus Sentinel-2 mission takes us over one of the most remote islands in the world: Easter Island. Located in the Pacific Ocean, over 3500 km off the west coast of South America, this Chilean island is also known as Rapa Nui by its original inhabitants. The island was given its current name the day when the Dutch navigator Jacob Roggeveen arrived on 5 April 1722 – on Easter Sunday.
Figure 43: 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. 66) 67) 68)
Figure 44: 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. 69)
Figure 45: Water levels in the Theewaterskloof Dam in South Africa's Western Cape Province have dropped dramatically over recent years. The dam is the major source of water for domestic and agricultural uses in the region. Over the last year, this lack of water has caused the production of grain to drop by more than 36% and the production of wine grapes to drop by 20%, for example. It is estimated that it will need to receive at least three years of good winter rainfall for it to return to its earlier healthy level. Thanks to the TIGER initiative, the Stellenbosch University is applying machine-learning algorithms to data from the Copernicus Sentinel-1 and Sentinel-2 missions to carefully monitor the situation (video credit: ESA, the video contains modified Copernicus Sentinel data (2017–18), processed by ESA, CC BY-SA 3.0 IGO)
- With more than two billion people living without safe water and around four billion people suffering severe water scarcity for a least one month a year, achieving water for all is a huge challenge. And, coupled with a growing global population and climate change, it's likely to become even more challenging.
- Water allows life on Earth to thrive. The same water has existed for billions of years, cycling through the air, oceans, lakes, rocks, animals and plants and back again. The water we drink today may have once been inside a dinosaur!
- Our most precious resource is probably the strangest thing in the universe. Defying the laws of chemistry, it's the only known substance that can exist naturally as a gas, liquid and solid within a relatively small range of air temperatures and pressures found on the surface of Earth.
- Although there is no shortage of water on Earth, less than 3% is freshwater. Then the vast majority of this is locked up in icecaps and glaciers, leaving less than 1% available for drinking and other domestic needs, agriculture and industrial processes, and more.
- Freshwater is the single most important natural resource on the planet, but we are very rapidly running out of it – as illustrated by dwindling water bodies.
Figure 46: 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 47: Glacial decline (10 December 2018). 70) 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)]