PROBA-V (Project for On-Board Autonomy - Vegetation)
PROBA-V (Project for On-Board Autonomy - Vegetation)
The PROBA-V (Vegetation) mission definition is an attempt, spearheaded by ESA and CNES, to accommodate an improved smaller version of the large VGT (Vegetation) optical instrument of SPOT-4 and SPOT-5 mission heritage on a small satellite bus, such as the one of PROBA-2.
As of 2008, small satellite technologies have reached a level of maturity and reliability to be used as a platform for an operational Earth observation mission. Furthermore, advancements in the techniques of detectors, optics fabrication and metrology are considered sufficiently mature to permit the design of a compact multispectral optical instrument. 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16)
The C/D Phase started in July 2010. The system CDR (Critical Design Review) took place in the spring of 2011. The project is currently (summer 2012) in its Phase D, with a Final Acceptance Review planned for December 2012. ESA is responsible for the overall mission, the technological payloads and for the launcher selection.
Background: The VGT instruments (VGT1 & VGT2), each with a mass of ~140 kg and fairly large size, have provided the user community with almost daily global observations of continental surfaces at a resolution of 1.15 km on a swath of ~2200 km. The instruments VGT1 on SPOT-4 (launch March 24, 1998) and VGT2 on SPOT-5 (launch May 4, 2002) are quasi similar optical instruments operating in the VNIR (3 bands) and SWIR (1 band) range.
The Vegetation instruments were jointly developed and funded by France, Belgium, Italy, Sweden, and the EC (European Commission). The consortium of CNES, BelSPO (Federal Public Planning Service Science Policy), SNSB (Swedish National Space Board) and VITO (Flemish Institute for Technological Research) is providing the user segment services (data processing, archiving, distribution). Vegetation principally addresses key observations in the following application domains:
• General land use in relation to vegetation cover and its changes
• Vegetation behavior to strong meteorological events (severe droughts) and climate changes (long-term behavior of the vegetation cover)
• Disaster management (detection of fires and surface water bodies)
• Biophysical parameters for model input devoted to water budgets and primary productivity (agriculture, ecosystem vulnerability, etc.).
As of 2008, a Vegetation archive of 10 years of consistent global data sets has been established permitting researchers access on a long-term basis. The SPOT-5 operational lifetime is estimated to expire in 2012. Pleiades, the next French satellite for Earth Observation, is solely dedicated to high-resolution imaging (on a fairly narrow swath) and will not embark any instrument providing vegetation data.
Since the SPOT series spacecraft will not be continued and the SPOT-5 spacecraft will eventually fail — there is of course a great interest in the EO user community to the Vegetation observation in the context of a smaller mission, affordable to all concerned. 17)
PROBA-V will continue the production of Vegetation products exploiting advanced small satellite technology. However, this implies in particular a redesign of the Vegetation payload into a much smaller unit to be able to accommodate it onto the PROBA bus.
Overview of key requirements of the PROBA-V mission - and some improvements compared to SPOT/Vegetation:
- Data and service continuity: filling the gap between SPOT-VGT and the Sentinel-3 mission
- Spectral and radiometric performance identical to VGT
- GSD: 1 km mandatory, improved GSD is highly disirable: 300 m (VNIR bands), 600 m (SWIR band). Image quality and geometric accuracy, equal to or better than SPOT-VGT
- Provision of daily global coverage of the land masses in the latitudes 35º and 75º North and in the latitudes between 35° and 56° South, with a 90% daily coverage of equatorial zones - and 100% two-daily imaging, during day time, of the land masses in the latitudes between 35º North and 35º South..
Figure 1: Scenario of the PROBA-V gap-filler mission between SPOT-5 and Sentinel-3 (image credit: ESA) 18)
Figure 2: Illustration of the PROBA-V spacecraft in orbit (image credit: ESA)
An extensive feasibility study and trade-off work was undertaken to identify a solution that could meet not only the technical challenges, but that could also be developed and tested within a tight budget of a small satellite mission. 19) 20)
The PROBA-V project of ESA includes the Space Segment (platform contract award to QinetiQ Space NV of Kruibeke, Belgium - formerly Verhaert), the Mission Control Center (Redu, Belgium) and the User Segment (data processing facility) at VITO NV. VITO (Vlaamse instelling voor technologisch onderzoek - Flemish Institute for Technological Research) is located in northern Belgium. VITO's processing center of VGT1 and 2 data (SPOT-4 and SPOT-5) is operational since 1999. VITO is also the prime investigator and data service provider of PROBA-V for the user community including product quality control. 21)
• The Phase B of the project started in January 2009
• SRR (System Requirements Review) is in Q4 of 2009
• PDR (Preliminary Design Review) in Q2 of 2010
• HMA (Heterogeneous Mission Access) and QA4EO (Quality Assurance for Earth Observation) implementation for user data. Planned interoperability with GSCDA V2 (GMES Space Component Data Access Version 2).
Figure 3: PROBA-V project organization (image credit: ESA, Ref. 9)
An industrial team, led by QinetiQ Space NV (Belgium), is supported by several European subcontractors and suppliers, and is responsible for the development of the flight satellite platform, the vegetation payload and the Ground Segment.
The spacecraft bus (fully redundant) is of heritage from the PROBA-1 and PROBA-2 missions (structure, avionics, AOCS, OBS with minor modifications). The PROBA-V spacecraft has a total mass of 138 kg, and a volume of 80 cm x 80 cm x 100 cm. The three-axis stabilized platform is designed for a nominal mission lifetime of 2.5 years (Ref. 7). 22) 23) 24) 25)
The spacecraft resources management is built around ADPMS (Advanced Data and Power Management System), which is currently flying on PROBA-2. The data handling part of ADPMS is partitioned using compact PCI modules. A cold redundant mass memory module of 16 Gbit is foreseen for PROBA-V. The newly developed mass memory will use NAND flash technology.
The avionics architecture can be divided in several sections:
• The AOCS block, containing all AOCS equipment and the required additional electronics in order to adapt or convert interfaces and supply voltages.
• The ADPMS, featuring the two redundant data handling lanes and its power section. It is the center of all data handling, communications and power conditioning and distribution.
• The main payload (Vegetation Instrument).
• The technology demonstrators. Four technology demonstrator payloads have been incorporated in the design.
• The communication section, featuring full redundancy for all modules. It comprises the S-band TT&C subsystem and the X-band data downlink subsystem.
• The power distribution and conditioning part of ADPMS supplies an unregulated bus, with each equipment having its internal DC/DC converter. The power conditioning system is designed around a Li-ion battery and a dump resistor ((to dissipate excess current).
The data handling part of ADPMS is built up from several modules, each based on the compact PCI standard. The ADPMS design is fully redundant. The PROBA-V configuration of ADPMS comprises:
• MPM (Main Processor Module), based on a LEON2 processor (ASIC), providing the processing power, memory and physical interfaces to control all other peripheral boards
• TTM (Telecommand and Telemetry Module), providing the bidirectional interface between the spacecraft and the ground stations
• SIM (Spacecraft Interface Module), providing the bidirectional communication interfaces between the ADPMS and the other spacecraft units
• DAM (Data Acquisition Module), providing the data acquisition of analog, digital and temperature signals
• MMM (Mass Memory Module), providing a data storage capability of 16 GByte EDAC protected and based on NAND flash technology
• REM (Reconfiguration and Emergency Module (REM), providing hardware functions to allow an easy reconfiguration and recovery of ADPMS directly from ground in case of problems.
The Power Management System of ADPMS supplies a battery-regulated bus, designed around a Li-ion battery. The power management system is built-up from the following modules:
• PCM (Power Conditioning Module), managing and regulating the incoming and outgoing power
• PDM (Power Distribution Module), managing the power distribution and over current protections.
The power management system can manage a total power of 300 W. Each power output line can handle a current of 2 A.
Figure 4: The ADPMS avionics architecture (image credit: QinetiQ Space, ESA)
Table 1: Overview of PROBA-V subsystems
Figure 5: PROBA-V spacecraft accommodation, outer platform views on left, inner platform views on right (image credit: QinetiQ Space)
AOCS (Attitude and Orbit Control Subsystem) provides three-axis attitude control including high accuracy pointing and maneuvering in different spacecraft attitude modes. The AOCS SW is an extension of the one of PROBA-2, including the following algorithms required by the on-board autonomous mission and payload management: 26) 27)
- Prediction of land/sea transitions using a land sea mask to reduce the amount of data generated
- Optimization of attitude in Sun Bathing mode to enhance incoming power while avoiding star tracker blinding
- Momentum dumping without zero wheel speed crossings during imaging
- Estimations of remaining spacecraft magnetic dipole to reduce pointing error
- Autonomous avoidance of star tracker Earth/Sun blinding
- Inertial mode with fixed scanning rate for moon calibration.
The AOCS hardware selection for PROBA-V consists of a high accuracy double star tracker head, a set of reaction wheels, magnetotorquers, magnetometers and a GPS receiver.
The main AOCS modes are: Safe, Geodetic, Sun Bathing and Inertial mode.
- The satellite Safe mode is used to detumble the spacecraft after separation from the launcher and it will be used to recover from spacecraft anomalies.
- The Geodetic mode is used during nominal observation of the Earth's vegetation. In this mode the payload is pointed towards the geodetic normal to the Earth's surface. An extra steering compensation, yaw-steering, is added in this mode, to minimize the image distortion caused by the rotation of the Earth. This yaw-steering maneuver ensures that the spectral imagers are oriented such that the lines of pixels are perpendicular to the ground-trace at each moment. In this mode the star trackers and the GPS receiver are used as sensors and the reaction wheels as actuators.
- On each orbit, the spacecraft enters the Sun Bathing mode from -56º latitude until entry of eclipse. This is to enhance the incoming power.
- The Inertial mode coupled with an inertial scanning of the Moon at a fixed rate is used for monthly radiometric full moon instrument calibration purposes. The pointing towards the moon takes 2.5 min, 9 min for scanning the moon and 2.5 min to return to nominal observation mode. It is sufficient to have the moon in the FOV of the SI (Spectral Imager) for a number of pixels.
NGC Aerospace of Canada was responsible for the design, implementation and validation of the autonomous GNC (Guidance, Navigation and Control) algorithms implemented as part of the PROBA-1 and PROBA-2 AOCS software and has the same responsibilities for the PROBA-V mission.
Figure 6: Functional breakdown of the AOCS software (NGC Aerospace, ESA, QinetiQ Space)
Beyond the technology demonstration through the PROBA program, it is also noted that the AOCS software technology developed in the course of this program is now the baseline of the AOCS of a major operational mission of the GMES (Global Monitoring for Environment and Security) program: Sentinel-3. NGC Aerospace Ltd (NGC) of Sherbrooke, (Québec), Canada was responsible for the design, implementation and validation of the autonomous GNC (Guidance, Navigation and Control) algorithms implemented as part of the AOCS software of PROBA-1 and PROBA-2. NGC has the same responsibilities for the PROBA-V mission (Ref. 26).
Operational modes of AOCS:
The PROBA-V operational modes are illustrated in Figure 7 (critical modes in blue) and briefly described in Table 2. Transitions between any of the modes are possible and can be commanded by the ground station or, autonomously, by the on-board mission manager. The Magnetic mode is represented in a dotted rectangle in Figure 7 because it was not part of the launch configuration. The addition of the Magnetic mode was decided and implemented after the launch. It was decided to include it as an added safety feature for PROBA-V. The Magnetic mode replaces the Bdot mode as the spacecraft Safe mode. However, the Bdot mode remains available upon ground request or as an autonomous fallback mode in case of an anomaly with the Magnetic mode. 28)
Figure 7: Operational modes of the PROBA-V AOCS (image credit: PROBA-V consortium)
Table 2: PROBA-V AOCS software operational modes
The requirements for the PROBA-V AOCS software were first defined by QinetiQ Space. Then, NGC (NGC Aerospace Ltd.) completed the software design and the related validation tests. Finally, NGC and QinetiQ Space conducted, in close collaboration, the AOCS Software Acceptance Tests (SAT). In addition to this on-ground validation, prior to the addition of the Magnetic mode, the AOCS software was validated in flight. For this purpose, the various AOCS software functions and operational modes were activated and validated one at a time in an incremental manner in the weeks following the launch. This validation successfully demonstrated that the AOCS software meets the stringent PROBA-V requirements.
With the addition of the Magnetic mode, the validation process had to be followed again not only for the Magnetic mode, but to ensure non-regression of the already fully validated operational modes. The validation approach followed for the addition of the Magnetic mode is described in the next section after an overview of the Magnetic mode algorithm and of its implementation.
Magnetic mode design: The reader is referred to Ref. 28) , since this is a too lengthy discussion. However, from the in-flight results, it can be stated that the Magnetic mode meets its requirements both in terms of functionality and robustness. Indeed, it has been demonstrated that the spacecraft attitude is controlled as required and that maneuvers can be performed.
Since its successful in-flight validation, the Magnetic mode is the baseline Safe mode for PROBA-V. With its successful operation on-board PROBA-V, the Magnetic mode provides an alternative to the traditional B-dot algorithm for safe modes of missions where it might be desired to maintain three-axis pointing in order to point one of the spacecraft axis (e.g. antenna) towards the Earth.
The PROBA-V design was successful in meeting the challenges as can be seen by the pointing performance achieved in flight (Table 3).
EPS (Electric Power Subsystem): The PVA (Photo-Voltaic Array) uses GaAs triple junction cells with an of efficiency of 28%. To obtain the operating voltage of 31.5 V, 18 cells are included in each string in series with a blocking diode. The PVA consists of a total of 25 solar strings taken into account the loss of one string on the most contributing PVA panel. The average solar string power under EOL conditions (summer solstice and T = 40°C) yields 12.8 W. The maximal incoming power at EOL during an orbit is 144 W. The energy budget for PROBA-V is derived for a bus power consumption of 140 W assuming a worst case day in the summer and while not taken into account the effect of albedo. A worst case power budget analysis indicated a maximum capacity discharge of 1.66 Ah. Use of a Li-ion battery. The battery cells provide a capacity of 1.5 Ah per string. The PROBA-V battery is sized to 12 Ah taking into account capacity fading and loss of a string.
RF communications (PROBA-V): S-band for TT&C transmissions and low-gain antennas with omni-directional up- and downlink capability. The uplink symbol rate will be fixed at 64 ks/s, while the downlink can be set to a high rate (< 2 Ms/s) for nominal imaging or to a low rate at 329 ks/s for off-nominal conditions. The CCSDS protocol is used for the TT&C transmissions.
X-band downlink of the payload data is in X-band at a data rate of 35 Mbit/s. The onboard mass memory is 88 Gbit. The Redu station (Belgium) is being used for TT&C communication services. The X-band uses two cold redundant high-rate X-band transmitters (developed by Syrlinks, France) and two nadir pointing isoflux antennas, both RHCP.
The S-band transceivers will be connected to RS422 outputs (cross strapped) of ADPMS while the X-band transmitters (8090 MHz) will be connected to the LVDS outputs not cross-strapped. The X-band link budget results in a link margin of 6 dB which will allow a reduction of the RF output power. Therefore the X-band transmitter will be designed (customer furnished item) to support various output power settings such that after commissioning, a lower output power might be selected.
Data compression: The massive amount of data produced by the instrument is beyond the capabilities of the bandwidth available on board of a small satellite. Data are reduced by using a lossless data compression algorithm implemented in a specific electronics. The data compression ratio obtained using standard CCSDS compression algorithms (CCSDS 133.0 B-1) is shown in Table 4.
Table 4: Overview of compression rates
The CCSDS image data compression standard turned out to meet all the requirements in terms of image quality and reachable compression ratio, accordingly reaching the required target data rate. This compression algorithm has been implemented in specific electronics (FPGA) on the satellite. Among many other notable firsts, PROBA-V has therefore become the first European mission to fly the CCSDS image data compression standard.
The selection of an S-band transceiver and the development of an innovative and generic X-band transmitter for small satellites has been initiated in a collaborative program between CNES and ESA and is funded under GSTP-5 (General Support Technology Program-5). The X-band transmitter is a high-performance device optimized for the needs and constraints of small platforms for which small volume, low mass, low power consumption, and low cost cost are important parameters. Moreover, some key features such as modulation (filtered Offset-QSK), coding scheme (convolutional 7 ½), data and clock interfaces (LVDS packet wire serial interface) have been selected in compliance with CCSDS recommendations, but also to ease the interoperability with most of the existing on-board computers and ground station demodulators. 29)
Following CNES studies under ESA contract, two low-cost X-band transmitters compatible with data rates up to 100 Mbit/s were designed and manufactured by Syrlinks of Bruz, France. One transmitter uses a GaAs RF power amplifier and one X-band transmitter uses a new GaN (Gallium Nitride) RF power amplifier, part of ESA's developed GREAT2 (GaN Reliability Enhancement and Technology Transfer Initiative). 30) 31)
The development of the new X-band transmitter is based almost exclusively on COTS components to achieve at the same time high performances and low recurrent cost. The transmitter also features an innovative functionality with an on-board programmable RF output power from 1-10 W which allows to match finely with the chosen bit rate, and to reduce as much as possible the margins of the link budget and therefore the consumption power. PROBA-V is the first mission to use this newly developed transmitter. The transmitter has a mass of 1 kg, a size of 160 mm x 115 mm x 46 mm, an in-orbit life time of 5 years, and a radiation hardness of 10 krad. Data rates from 10-100 Mbit/s are available.
Table 5: Typical specification of the X-band transmitter
Figure 8: Overview of the X-band transmitter architecture (Syrlinks, CNES)
Incoming telemetry data is coded in a programmable device (CPLD) at the clock rate. I and Q baseband signals are filtered (7th order Butterworth filter) and then applied to the RF I/Q modulator. This modulator works in S-band. The S-to-X converter translates the modulated signal from S-band to X-band. X-Band signal is then amplified. The microcontroller manages the serial link with the OBC (On-Board Computer) of the platform. It decodes the commands and executes the actions. The microcontroller reads the different internal indicators (temperature, currents, ...) and controls the functions such as the RF synthesizer or the power supplies. The power supply is a galvanic isolated Dc/Dc converter followed by non-isolated Dc/Dc converters and linear regulators. Internal supplies are protected against over-current consumption, in case of latch-up.
The GaAs and GaN transmitter measured performances are similar. Table 6 gives the main typical results.
Figure 9: Photo of the X-band transmitter (image credit: Syrlinks, CNES, ESA)
• June 25, 2015: Europe's first item of high-performance gallium nitride technology to fly in space has completed its second year of operations. Hosted on ESA's Earth-observing PROBA-V minisatellite in 2013 as a test prototype, the transmitter is today used routinely to return mission imagery to the ground. "The X-band transmitter in question incorporates an experimental gallium nitride (GaN) amplifier," explains Andrew Barnes, overseeing ESA's work in GaN. "It is still working seamlessly today after two years in orbit, showing no drift in performance" (Ref. 31).
- The GaN-based transmitter is used to downlink data to PROBA-V's Kiruna ground station – in the Swedish Arctic – once per orbit for a week at a time, alternating with a second transmitter using a conventional gallium arsenide amplifier.
- With its data coming down at a standard rate of 42.22 Mbit/s during each roughly 12 minute pass, the m3-sized PROBA-V builds up a complete picture of all Earth's vegetation cover every two days.
- Access to the GaN-based transmitter also increases the operational flexibility of the satellite – in principle its data rate can be boosted to 100 Mbit/s , while its programmable radio frequency output power can also be increased as needed, while operating at a lower voltage than its conventional equivalent.
- Gallium nitride has been described as the most promising semiconductor since silicon, capable of operating at much higher voltages and temperatures than comparable materials. As an additional advantage, GaN also possesses inherent resistance against the radiation encountered in space.
- "In terms of communications for space, GaN offers a five- to ten-fold increase in communications power, while requiring no additional cooling systems," adds Andrew.
- "Its promise is such that back in 2008 ESA launched the ‘GaN Reliability Enhancement and Technology Transfer Initiative' (GREAT2), bringing together leading universities, research institutes and industry to develop space-compatible production processes for making GaN microwave power transistors and integrated circuits.
- With GREAT2 , ESA has come in at an early stage of industrialization to ensure that the resulting products meet the demanding requirements of space use, such as resistance to shock and temperature extremes, as well as continuous operations for years at a time."
- The GREAT2 partners include UMS (United Monolithic Semiconductors) based in Germany and France, responsible for the industrial foundry used for manufacturing GaN products.
Figure 10: GaN amplifier supply chain for PROBA-V (image credit: ESA)
- Since then, while the transmitter has been proving its worth in space, the first industrial prototypes have successfully completed their testing for reliability and robustness.
- "As a result of GREAT2 we were able to place the UMS GaN manufacturing process onto the European Preferred Parts List of the European Space Components Coordination – a list of recommended parts for space missions – in 2012," adds Andrew. "This was two years earlier than originally planned.
Figure 11: GaN on SiC wafers (image credit: ESA)
Figure 12: Photo of a PROBA-V integration test at QinetiQ Space (image credit: ESA) 32)
Figure 13: Photo of PROBA-V on top of the VESPA system on April 15, 2013 (image credit: ESA-Karim Mellab)
Table 7: PROBA-V key features
Launch: The PROBA-V spacecraft (primary payload) was launched on May 7, 2013 (02:06:31 UTC). The launch vehicle was Vega (with Arianespace as launch provider); the launch site was the Guiana Space Center, Kourou. This marks the first VERTA (Vega Research, Technology and Accompaniment) flight of VEGA (designated as VERTA-1). The mission is designated Flight VV02 in Arianespace's numbering system. 34) 35) 36)
The secondary payloads on this flight were:
• VNREDSat-1A (Vietnam Natural Resources, Environment and Disaster-monitoring Satellite) of STI-VAST (Space Technology Institute-Vietnam Academy of Science and Technology). The microsatellite VNREDSat-1A (115.3 kg) has been built by EADS Astrium, Toulouse, France. 37) 38)
• ESTCube-1 (Estonian Student Satellite-1), a 1U CubeSat (1.3 kg) technology demonstration mission of the University of Tartu.
PROBA-V will ride in the upper position of the VESPA (Vega Secondary Payload Adapter), while VNREDSat-1A and ESTCube-1 will sit in the lower position in the structure. The upper stage of the Vega vehicle is a liquid propulsion module with multiple re-ignition capability. The secondary payloads will be deployed last after re-ignition of the Vega upper stage.
Orbit of PROBA-V: Sun-synchronous orbit, altitude = 820 km, inclination = 98.8º, LTDN (Local Time on Descending Node) = 10:30 hours (with a drift limited between 10:30 and 11:30 AM during the mission lifetime). Note: In contrast to the SPOT-4 and SPOT-5 missions, PROBA-V will not have the capability to maintain its orbit.
Orbit of VNREDSat-1 and ESTCube-1: Sun-synchronous orbit, altitude =704 km, inclination = 98.7º. VNREDSat-1A was released 1 hour 57 minutes into flight. ESTCube-1 was ejected from its dispenser three minutes later. A last burn will now place the spent upper stage on a trajectory that ensures a safe reentry that complies with new debris mitigation regulations.
Figure 14: Artist's view of the PROBA-V minisatellite in orbit (image credit: ESA)
Figure 15: Aboard the second VEGA flight from Kourou, PROBA-V, V for Vegetation, is part of a series of small satellites made by ESA to demonstrate new technologies on orbit. But this satellite - of only one cubic meter - will be an operational tool to monitor vegetation on Earth. This video explains the mission of this innovative satellite mostly made in Belgium. It includes interviews of PROBA-V managers in English, French and Dutch (video credit: ESA PROBA-V, Published on Apr 19, 2017)
• May 15, 2019: The snow-capped peaks of the Southern Alps stretch more than 500 km northeast to southwest across New Zealand's South Island, imaged here in the southern hemisphere's winter by ESA's PROBA-V minisatellite – now completing its sixth year on orbit. 39)
Figure 16: New Zealand's South Island imaged by PROBA-V. This 100 m spatial resolution image was acquired on 1 May 2018 (image credit: ESA/Belspo – produced by VITO)
- Comprising 23 peaks above 3 000 m altitude, the glacier-lined Southern Alps are visited by more than half a million tourists annually. The mountains are located within a continuous tract of protected lands along the entire length of the island, made up of five national parks.
- Mount Cook, otherwise known by the Maori name Aoraki, is the tallest of the Southern Alps at 3,724 m. It is visible here in the middle of the mountain chain, with the long glacial Lake Pukaki below it.
- Launched on 7 May 2013, PROBA-V is a miniaturized ESA satellite tasked with a full-scale mission: to map land cover and vegetation growth across the entire planet every two days.
- Its main camera's continent-spanning 2250 km swath width collects light in the blue, red, near-infrared and mid-infrared wavebands at a 300 m pixel size, down to 100 m in its central field of view.
- VITO Remote Sensing in Belgium processes and then distributes PROBA-V data to users worldwide. An online image gallery highlights some of the mission's most striking images so far, including views of storms, fires and deforestation.
• March 27, 2019: A PROBA-V view of the internationally protected, volcanic archipelago of the Galápagos and its surrounding marine reserve. This island chain is renowned for its many endemic species that were studied by Charles Darwin, directly contributing to his famous theory of evolution by means of natural selection. 40)
- In 1535, the Spaniard Tomás de Berlanga, fourth bishop of Panama, first visited these islands by chance when he was sailing to Peru. On the maps of Mercator and Ortelius, famous geographers, the islands were named Insulae de los Galopegos or Islands of the Tortoises after the giant tortoises found there.
Figure 17: This false color composition highlights vegetation in red on the flanks of several volcanoes, in particular Wolf, Darwin, Alcedo, Santo Tomás and Cerro Azul volcanoes on Isla Isabella, the largest island. Its main camera's continent-spanning 2250 km swath width collects light in the blue, red, near-infrared and mid-infrared wavebands at a 300 m pixel size, down to 100 m in its central field of view (image credit: ESA/Belspo – produced by VITO)
• February 15, 2019: The rapid evolution of Egypt's Nile Delta over the last four years, as viewed from ESA's PROBA-V microsatellite. Think of it as a small token of our love for planet Earth: just a cubic meter in size, PROBA-V maps land cover and vegetation growth across the entire world every two days. 41)
Figure 18: Changing Nile Delta seen by PROBA-V: The Nile Delta in Egypt has already been a very dynamic area for ages. Between 2014 and 2018 the area has changed quite significantly, which was nicely captured by PROBA-V. The animation shows 100 m Proba-V images of 30 December 2014 and 19 May 2018. A large anthropogenic change that occurred in these 3.5 years and is clearly visible to the very right is the construction of the second Suez canal, which was completed in 2015. Further changes are pivot irrigation fields replaced the dry desert in the eastern part of the Nile Delta, while in the western part the opposite occurred. The numerous cities and villages within the delta contrast with the green vegetation background as grey splotches (image credit: ESA/Belspo – produced by VITO)
- Launched on 7 May 2013, the mission's continent-spanning 2250 km field of view collects light in the blue, red, near-infrared and mid-infrared wavebands, ideal for monitoring plant and forest growth as well as inland water bodies. Its imager has 300 m spatial resolution, increasing to 100 m within its central view.
- VITO Remote Sensing in Belgium processes and then distributes PROBA-V data to users worldwide. With more than five years of PROBA-V imagery now collected, VITO has created a new 2019 image calendar with a set of before-and-after comparisons to highlight the dynamic nature of our home planet.
- PROBA-V data is freely available to everyone. The new Mission Exploitation Platform offers on-demand processing power allowing users to create time-series comparisons and animations.
Figure 19: Vegetation swath: released on 11 February 2013. Image swath from Spot's Vegetation instrument stretching from West Africa to Norway (image credit: CNES/VITO)
• January 9, 2019: This PROBA-V view (Figure 20) shows all that is left of the Aral Sea, once one of the four largest lakes in the world and now one of the world's major ecological disaster areas. It has shrunk into separate lakes, surrounded by Earth's youngest desert. The Aral Sea was once a large land-locked lake between Kazakhstan in the North and Uzbekistan in the South, possessing an area of 68,000 km2 – twice that of Belgium. 42)
Figure 20: This 100 m-resolution image of PROBA-V was acquired on 15 June 2018 (image credit: ESA/Belspo – produced by VITO)
- However, the Aral Sea has dramatically shrunk since the 1960s when Soviet irrigation projects diverted water from the rivers supplying it. By the 2000s, the lake had shrunk to about 10% of its original size and by 2014 the horseshoe-shaped Southern Lake had virtually dried up.
- Groundwater levels also fell, vegetation was laid waste and a once-thriving fishing industry collapsed. The exposed lakebed formed the newly-christened Aralkum Desert, spawning pesticide-laced sandstorms that can reach as far as the Himalayas.
- Efforts to stabilize the situation are ongoing, including the replanting of hardy vegetation to reduce sandstorms. In 2005, the Kok-Aral Dam was completed to restore water levels in the Northern Lake –located at its bottom-east side. In addition, a sluice is periodically opened to replenish the Southern Lake.
- VITO Remote Sensing in Belgium processes and then distributes PROBA-V data to users worldwide. An online image gallery highlights some of the mission's most striking images so far, including views of storms, fires and deforestation.
- PROBA-V is currently the subject of ESA's latest ‘citizen science' competition, requesting teams to produce ‘super-resolution' images equivalent to its 100 m mode from sets of 300 m imagery.
• November 7, 2018: ESA's PROBA-V minisatellite images the verdant Yucatán peninsula, once home to the Maya civilization and the site of the impact believed to have doomed the dinosaurs. 43)
- As part of the Atlantic Hurricane Belt – placed between the Gulf of Mexico to the west and the Caribbean Sea to the east – the largely flat peninsula is vulnerable to storms from the east. Yet, its easternmost side is the site of popular beach resorts and tourist hotspots such as the city of Cancún. Moving further south towards Belize, the state of Quintana Roo is home to the biosphere reserve of Sian Ka'an, home to jaguars and archaeological sites of the Maya.
- On the western side, the large orange-brown spot is the city of Mérida, near the center of the buried Chicxulub crater. This was formed by the impact of a 10- to 15- km large asteroid or comet, triggering a major climate disruption and extinction event, just under 66 million years ago.
- VITO Remote Sensing in Belgium processes and then distributes PROBA-V data to users worldwide. An online image gallery highlights some of the mission's most striking images so far, including views of storms, fires and deforestation.
- PROBA-V is currently the subject of ESA's latest ‘citizen science' competition, requesting teams to produce ‘super-resolution' images equivalent to its 100 m mode from sets of 300 m imagery.
Figure 21: This 100 m resolution image of the Yucatán peninsula was acquired with PROBA-V on 23 July 2018 (image credit: ESA/Belspo – produced by VITO)
• May 04, 2018: ESA's Proba-V minisatellite has imaged all of the Antarctic after users asked for a survey of the icy southern continent. Proba-V collected the data between November 2017 and February 2018. 44)
- Imagery is available at 1 km, 300 m and 100 m resolution. For information on how to access it, click here. VITO Remote Sensing in Belgium processes and then distributes Proba-V data to users worldwide.
- On 7 May, 2018, PROBA-V will be 5 years on orbit. A PROBA-V symposium will be held in Ostend, Belgium (29-31 May, 2018) to bring researchers together to discuss the work being performed using the minisatellite.
Figure 22: Antarctic survey image of PROBA-V, collected between Nov. 2017 and Feb. 2018 (image credit: ESA/Belspo – produced by VITO)
• February 14, 2018: Figure 23 is a false-color image of Pyeongchang county and surrounding territory in South Korea – currently hosting the 2018 Winter Olympics. This is a view of the northern part of the country, with vegetation in red and built-up areas seen in grey, including capital city Seoul, astride the banks of the Hangang River, seen left. Pyeongchang county is located towards the east coast. Mountainous regions are seen dusted with snow. 45)
- The Winter Olympics run from 8 to 25 February. By adding four new disciplines, this international event is the first Winter Games to extend over 100 medals, spread across 15 sports.
- PROBA-V's main camera's continent-spanning 2250 km swath width collects light in the blue, red, near-infrared and mid-infrared wavebands at 300 m resolution and down to 100 m resolution in its central field of view.
Figure 23: PROBA-V false-color image of a portion of the Korean Peninsula with 300 m resolution, acquired on 21 January 2018 (image credit: ESA/Belspo – produced by VITO)
- Located just north of the border with Kazakhstan, Lake Chany is a large but shallow freshwater lake surrounded by wetlands, salt marshes and birch and aspen forests, making it an important stop for birds migrating southwards from colder Siberia.
Figure 24: This 100 m resolution image was acquired by PROBA-V on 1 December 2016 (image credit: ESA/Belspo – produced by VITO)
Figure 25: PROBA-V's Image of the Week - Overview 2017 (video credit: ESA PROBA-V, Published on Dec 16, 2017)
- The mountains – an extension of Europe's Alpine system – stretch some 2400 km through Morocco, seen here, into Algeria and Tunisia. The Atlas mountains are actually a set of five ranges dividing the northern Mediterranean climate from the arid Sahara to the south. A second, darker, range, the Anti-Atlas mountains, are seen to the south, with the the Draa River valley cutting through them – seen as a reddish line. The Draa, Morocco's longest river, flows south from the city of Ouarzazate city into the Sahara.
- The Berber-speaking Ouarzazate is a popular location for filmmakers, with productions such as Lawrence of Arabia (1962), The Mummy (1999) and Game of Thrones (2011–present) having been shot here.
Figure 26: In the summer of 2017, ESA's PROBA-V minisatellite surveyed North Africa's Atlas mountains, bordering the Sahara (image credit: ESA/Belspo – produced by VITO)
• September 20, 2017: PROBA-V captures Bolivia's Salar de Uyuni, the world's largest salt plain – its 10,500 km2 make it larger than some countries. Located in the highlands of southwestern Bolivia at an altitude of 3650 m, Salar de Uyuni is also extremely flat, varying less than 1 m across its expanse (Figure 27). It is so flat that it is often used to calibrate laser and radar altimeters on satellites. 48)
- The salt plains were formed 42 000–30 000 years ago as a result of transformations between several prehistoric lakes. The crusty top layer, several meters thick in places, lies on a brine rich in lithium (containing 50–70% of the world's reserves), potassium and magnesium.
Figure 27: The false-color PROBA-V image was acquired on 5 April 2017. On the western side of the Salar de Uyuni, some wavy patterns are visible, while blue shades on the northern and eastern edges indicate flooded areas. The small rectangular patches to the south of the salt flat indicate a large lithium mining area (image credit: ESA/Belspo – produced by VITO)
• July 27, 2017: ESA's Proba-V minisatellite reveals the seasonal changes in Africa's sub-Saharan Sahel, with the rainy season allowing vegetation to blossom between February (Figure 28 top) and September (bottom). 49)
- The semi-arid Sahel stretches more than 5000 km across Africa, from the Atlantic Ocean (Senegal, Mauritania) to the Red Sea (Sudan). The few months of the rainy season in the Sahel are much needed in these hot and sunny parts of Africa, and are critical for the food security and livelihood of their inhabitants.
- The name Sahel can be translated from Arabic as coast or shore, considered as the ever-shifting landward ‘coastline' of the arid Sahara Desert.
Figure 28: Technology image of the week: ESA's Proba-V minisatellite shows vegetation bloom across the African Sahel with the coming of the rainy season (image credit: ESA/Belspo – produced by VITO)
• June 21, 2017: ESA's PROBA-V minisatellite has captured the forest fire raging in central Portugal, revealing blackened scars and columns of smoke as well as pinpointing active fire hotspots. More than a thousand firefighters are tackling the forest fire in the Pedrógão Grande region, north east of Lisbon, which has been aflame since Saturday. Some 64 people have been reported dead and more than 130 injured. 50)
Figure 29: A forest fire in Portugal's Pedrógão Grande region, showing burnt scars, smoke plumes and hotspots (seen in red). This 100 m-resolution image was acquired on Tuesday 20 June 2017 by ESA's PROBA-V satellite (image credit: ESA/BELSPO produced by VITO)
- PROBA-V has a 2250 km-wide field of view with an overall 300 m resolution, narrowing to 100 m at the center. The satellite contributes to Europe's world-monitoring Copernicus program, which makes imagery and data freely available to authorities. The V stands for Vegetation – a lighter but fully functional redesign of the camera previously flown on France's full-sized Spot-4 and Spot-5 satellites.
- Launched on 7 May 2013, PROBA-V continues the supply of this much-needed information for applications such as assessing climate impact, managing water resources and monitoring crops.
- PROBA-V's wide view and polar orbit means it revisits every spot on Earth's land every two days, building up a new global composite for researchers every 10 days.
Figure 30: Before the blaze: Portugal's Pedrógão Grande region. This 100 m-resolution image was acquired on 19 May 2017 by PROBA-V, showing the region before the forest fire that started on 17 June (image credit: ESA/BELSPO produced by VITO)
- The dammed Zêzere river is seen in the center of the main image, with burnt scars and fires burning to its north. The village of Nodeirinho – home of many of the casualties – is situated amid the scars.
- The forest fire is believed to have been started by a lightning strike during an intense heatwave. Aircraft have been used to drop water over the Pedrógão Grande region.
Figure 31: Regional view of fire: A forest fire in Portugal's Pedrógão Grande region, showing burnt scars, smoke plumes and hotspots (seen in red). This 330 m-resolution image was acquired on 18 June 2017 by ESA's PROBA-V satellite (image credit: ESA/BELSPO produced by VITO)
• May 19, 2017: The Korean the mid-sized city of Mokpo (~250,000 inhabitants) is a historic naval base and gateway to the country's Honam Plain. Mokpo is visible in this false-color image as a blue–grey area on the estuary of the Yeonsang River (Figure 32). The port city is surrounded by more than 1,400 islands, which provide fishing grounds while safeguarding Mokpo from the effects of large typhoons and tsunamis. An extensive region of high sediment concentrations is also visible, extending into the Yellow Sea in a bow shape. 51)
Figure 32: South Korea's island-studded Mokpo port region was captured by ESA's Earth-observing PROBA-V minisatellite on October 6, 2016 at a nadir resolution of 100 m on a swath of 2250 km (image credit: ESA/Belspo – produced by VITO)
• March 29, 2017: Snow-dusted Norwegian fjords imaged by ESA's Earth-observing PROBA-V minisatellite. Norway's coastline is one of the world's longest – with a total length recently calculated at 80 000–100 000 km – owing to its famous fjords, narrow inlets bordered by steep cliffs created by glacial erosion during previous Ice Ages. 52)
- After these glaciers melted and Earth's crust rebounded, seawater flooded the valleys, leading to some fjords becoming very deep: the Sognefjord fjord (visible to the upper left) has a depth of 1300 m. From bottom to top the Bokna and Hardanger fjords are also seen. The white region in the middle is the Hardangervidda National Park, an extensive plateau at around 1200 m altitude, inhabited by wild reindeer.
Figure 33: Norwegian fjords imaged by PROBA-V, the image was acquired on 14 February 2017 (image credit: ESA/BELSPO – produced by VITO)
• The PROBA-V minisatellite of ESA with the vegetation instrument on board is fully operational in February 2017. — The VITO processing center in Belgium provided the image of the week (Figure 34) with the Flinders Ranges in Australia. 53)
- The high plateau of the Gammon Ranges on the eastern side and the alternating hills and ridges, often with a gentle slope on one side and steep slope on the other (cuesta landforms), make for a dramatic and beautiful landscape.
- The region has a semi-arid climate with hot dry summers and cool winters. It's a place rich in Aboriginal history and home to a vast array of wildlife such as kangaroos, parrots, emus and snakes. The flora is well adapted to this environment, with species such as cypress-pine, black oak and mallee, a low-growing, bush-like eucalyptus that is common in Australia.
Figure 34: PROBA-V false-color image of Flinders Range, Australia, showing the northern part of the rugged, weathered peaks and rocky gorges of the Flinders Ranges, the largest mountain range in the South Australian Outback (image credit: ESA-BELSPO 2017, produced by VITO)
• December 15, 2016: In honor of the UN "World Mountain Day" on 11 December, the image of Figure 35 depicts the snow-capped Himalayas, with Nepal to the south (with vegetation shown in red) and the bleaker Tibetan Plateau to the north. 54)
- Mount Everest, the tallest mountain of the world at 8848 m, is shown in white along with a few of its 8000 m-plus neighbors, including Kangchenjunga (8586 m), the third tallest mountain of the world, to the east of Everest. The Himalayas, which can be translated from Sanskrit as ‘abode of snow', are the source of many major Asian rivers.
Figure 35: PROBA-V – ESA's smallest Earth-observing mission – overflies Mount Everest, the highest mountain in the world, its peak seen left of center in this false-color image. This 100 m-resolution image was acquired by PROBA-V on 27 October 2016 (image credit: ESA/BELSPO – produced by VITO)
• October 19, 2016: ESA's PROBA-V minisatellite gives a false-color view of circular fields fed by underground water resource in the mist of the desert. This 100 m resolution image Figure 36) shows the Wadi As Sirhan basin of Saudi Arabia, with agricultural fields fed water by circular-pivot irrigation systems, amid the yellowish desert sands and surrounding low hills and rocks. 55)
- The VGT-P (Vegetation Instrument - PROBA) camera has a swath width of 2250 km, collecting light in the blue, red, near-infrared and mid-infrared wavebands at 300 m resolution and down to 100 m resolution in its central field of view.
Figure 36: False-color crops bloom in the Saudi Arabian desert, imaged by ESA's PROBA-V minisatellite (image credit: ESA/BELSPO, provided by VITO)
• August 2016: The compact SATRAM (Space Application of Timepix-based Radiation Monitor) is operating nominally in LEO orbit since 2013 on board the PROBA-V satellite and provides high-resolution wide-range radiation monitoring of the satellite environment. Equipped with the pixel detector Timepix, the technology demonstration payload determines the composition (particle types) and spectral characterization (stopping power) of the mixed radiation field with quantum imaging sensitivity, charged particle tracking, energy loss and directionality capability. The space radiation field is continuously sampled over the entire planet every few days. Results are given in the form of spatial- and time-correlated maps of dose rate and particle flux. 56)
- Preliminary exploitation of data from the SATRAM/Timepix payload serves for detailed radiation effects studies but also for physics research and space weather studies.
• August 26, 2016: ESA released a PROBA-V image of the Great Salt Lake in Utah, USA (Figure 37). The VGT-P instrumentation of the minisatellite provides a swath width of 2250 km in the blue, red, near-infrared and mid-infrared wavebands at 300 m resolution and down to 100 m resolution in its central field of view. 57)
Figure 37: Great Salt Lake, the largest salt lake in the western hemisphere, captured by ESA's PROBA-V satellite in June 2016 (image credit: ESA/BELSPO, provided by VITO)
• April 6, 2016: ESA's PROBA-V minisatellite gazes down at Earth's largest volcano – Mauna Loa, or ‘long mountain' which covers half of the island of Hawaii (Figure 38). Mauna Loa remains active, having last erupted in 1984. To the north of its distinctive blackened ridges is the still-higher Mauna Kea volcano – an extinct volcano whose crests are home to some of the world's leading astronomical observatories. 58)
- To its east is the very active Kilauea volcano, which has been erupting for more than three decades, the Hawaii Island being formed of five volcanoes altogether. The island's forest reserves are shown in green.
- Mauna Loa stands 4169 m above sea level, and extends another 5 km beneath the sea. Its 75,000 km3 volume depresses the adjacent sea bed another 6 km or so. This PROBA-V image was acquired on 19 February, 2016 with a resolution of 100 m. - VITO Remote Sensing in Belgium processes and then distributes PROBA-V data to users worldwide.
Figure 38: Hawaii, home to Earth's largest volcano, as imaged by PROBA-V, among ESA's smallest Earth-observing satellites (image credit: ESA/BELSPO, provided by VITO)
• February 8, 2016: Monitoring Earth's surface every day, ESA's PROBA-V minisatellite has had a ringside seat as the second largest lake in Bolivia, Lake Poopó, gradually dried up. Lake Poopó has now been declared fully evaporated. Occupying a depression in the Altiplano mountains, the saline Lake Poopó has in the past spanned an area of 3000 km2 — greater than France's Réunion Island. 59)
- But the lake's shallow nature, with an average depth of just 3 m, coupled with its arid highland surroundings, means that it is very sensitive to fluctuations in climate. Its official evaporation was declared last December. This is not the first time Lake Poopó has evaporated – the last time was in 1994 – but the fear is that any refilling might take many years, if it occurs at all.
- In the meantime local fishermen are left without livelihoods and the lake ecosystem is extremely vulnerable – Lake Poopó being recognized as a conservation wetland through the international Ramsar Convention.
- The evaporation has been variously linked to diversions of the lake's water sources for mining and agriculture, a persistent drought linked to El Niño warming in the Pacific Ocean and climate change.
Figure 39: PROBA-V tracks Lake Poopó evaporation in Bolivia. The three 100-m resolution PROBA-V images shown here were acquired on 27 April 2014, 20 July 2015 and 22 January 2016 respectively (image credit: ESA, BELSPO, VITO) 60)
• January 25, 2016: The PROBA-V minisatellite collected imagery in early 2016 of a large smoke plume from a bushfire south of Perth in Western Australia. Bushfires are frequent events during the long, dry Australian summer. In this fire, several hundred houses and an area exceeding 700 km2 have burned. Bushfires in the area are responsible for two deaths so far in 2016. Particularly hard hit was the town of Yarloop, which lost factories, a fire station, part of a local school and the heritage-listed Yarloop Timber Mill Workshops, which had been the most-intact example of a historical railway workshop in Australia. 61)
Figure 40: This 300 m resolution false-color image from ESA's PROBA-V satellite was acquired on Jan. 7, 2016, showing blue-gray smoke over Geographe Bay south of Perth in Western Australia (image credit: ESA/BELSPO, produced by VITO)
• January 2016: The PROBA-V mission has a nominal lifetime of 2.5 years; in 2015 the mission life was extended to 5 years. 62)
- Platform availability 99.9%; No safe mode in the last 12 months, all platform subsystems are nominal; Thermal situation very stable
- LTDN well within 10:30 – 11:30 hours; LTDN reaches 10:30 around Sept 2017; Stays well above 10:00 after 5 years.
- X-band data downlink DRS status: reliable!
1) Contract with SSC for the acquisition of PROBA-V X-band data at 3 stations: Kiruna (Sweden), North Pole (USA - Alaska) and Inuvik (Canada), allowing the PROBA-V reception of 10-11 passes per day
2) Acquisition performances are very good (in December over 315 passes acquired, only 4 had small data gaps = 99%); however rare delays in the data transfer from Inuvik
3) The Inuvik station will be upgraded with a fiber connection to the Canadian backbone during 2016, in order to improve the data transfer performances.
- PROBA-V Archive + Dissemination Status: Current PROBA-V Archive: 465 TB, with Disaster recovery: 930 TB; Total size of downloaded products: 252 TB.
• Dec. 15, 2015: ESA is pleased to announce that accessing PROBA-V data is easier than ever (and always free): 63)
- All level 1C (NRT), all 1 km products (NRT), and all 333 m and 100 m products (older than 1 month) can be downloaded immediately after registration to the PROBA-V portal.
- All 333 m and 100 m in NRT (Near Real Time) are also offered to ESA PIs by ESA (free of charge). Access is granted after ESA project proposal acceptance (proposal submission), see the PROBA-V Information Area on Earth
• October 21, 2015: Figure 41 presents a view of the glacier atop Africa's highest peak, as observed by ESA's PROBA-V minisatellite. The dormant volcano known as Mount Kilimanjaro is Africa's highest mountain, at 5895 m above sea level. It is also the tallest free-standing mountain in the world, rising about 4900 m above its surrounding plain. 64)
- Located close to the equator at 3ºS in Tanzania, only its summit is covered with snow and ice. The ascent towards the top is a journey through most of the world's climate zones, from the tropical to the Arctic. On the way the landscape shifts from tropical rain forest to moorland, alpine heather to desert and finally snow and ice. - The mountain is part of the Kilimanjaro National Park and is a major climbing destination. The mountain has been the subject of many scientific studies because of its shrinking glaciers.
Figure 41: This 100 m resolution false-color image from PROBA-V's main Vegetation camera, acquired on 14 June 2015, shows Kilimanjaro enveloped by clouds to the south and north. The gradual decrease of vegetation with altitude can be seen by the colors changing from green to brown and finally light blue, representing the summit's glacier (image credit: ESA, BelSPO, VITO)
• August 2015: PROBA-V provides continuation of SPOT-Vegetation (SPOT-VGT) products in its 4 bands: Blue, Red, NIR and SWIR. Aside from the global daily 1 km time series available from SPOT-VGT since 1998, PROBA-V brings new assets with a global daily 300 m time series for the same set of bands. In addition, 100 m products are available from March 16 2014, delivering a global coverage every 5 days. 65)
- The VGT-P (Vegetation-PROBA) instrument has several specific properties influencing its products : 1) VNIR and SWIR detectors mounted on different locations; 2) VNIR and SWIR with different GSD; 3) mechanically staggered SWIR detector composed by three overlapping detectors with an overlap area.
- Like SPOT-VGT, PROBA-V's spectral bands allow to discriminate between different types of land cover and land use, in particular plant species and crops, often measured by derived products such as the NDVI (Normalized Difference Vegetation Index). Vital uses of these data include day-by-day tracking of vegetation growth, early warnings to authorities of crop failures, monitoring of inland water resources and tracing trends of soil erosion and deforestation.
Table 8: Available products for PROBA-V
- Operational status: After more than a year of calibration monitoring, PROBA-V is able to show impressive results, showing a stable radiometric and geometric performance, and a consistency with missions such as SPOT-VGT, MERIS and Landsat-8. All performance requirements for the 1 km and 1/3 km products have been successfully achieved (Tables 9 and 10).
Table 9: PROBA-V geometric accuracy requirements
Table 10: PROBA-V radiometric accuracy requirements
• On May 7, 2015, PROBA-V was two years on orbit, operating nominally. - As ESA's PROBA-V works quietly on its main task of monitoring vegetation growth across Earth, the minisatellite is also picking up something from a little higher: signals from thousands of aircraft.
- During its operational life, the PROBA-V minisatellite has picked up aircraft positions, using an experimental ADS-B (Automatic Dependent Surveillance – Broadcast) receiver (Figure 42). The ADS-B receiver was built by DLR. These signals are regularly broadcast from aircraft, giving flight information such as speed, position and altitude. All aircraft entering European airspace are envisaged to carry ADS-B in the coming years. 66)
- The ADS-B signals include GPS data on the aircraft's position, speed and altitude, and the signals are designed to be detected by ground stations and nearby airplanes. The 1500 x 750 km footprint of the single satellite is relatively small and a fully world-wide operational system would require a constellation of satellites. Several commercial operators have indicated interest in establishing such a system.
Figure 42: As of May 2015, PROBA-V has picked up upwards of 25 million positions from more than 15 000 separate aircraft (image credit: ESA, DLR, SES Techcom)
Legend to Figure 42: There are roughly 20 000 aircraft worldwide from which the DLR (German Aerospace Center) and the SES Techcom team has captured more than 25 million positions. The team has identified more than 22,000 unique callsigns, identifying more than 15,000 aircraft by their unique ICAO (International Civil Aviation Organization) addresses (one aircraft can share a callsign with others, depending on the flight route).
• May 6, 2015: The Drakensberg mountain range – Afrikaans for ‘Dragon mountains' – is located in southern Africa and extends from northeast to southwest for about 1125 km. This 100 m resolution image (Figure 43) centers on uKhahlamba–Drakensberg Park, located at Lesotho's northeastern border with the South African province of Kwazulu-Natal, covering roughly 240,000 hectares. Lesotho's Malibamats'o River is visible to the upper left. 67)
- Rich in its diversity of habitats, the park is home to various populations of endemic birds, mammals and reptiles. It is also home to the largest collection of rock paintings in Africa, south of the Sahara. The paintings reflect the way of life of the San people, who lived in the area for more than four millennia. In 2000, UNESCO named the park as a World Heritage Site.
Figure 43: The Drakensberg mountain range in southern Africa, viewed by ESA's PROBA-V minisatellite (image credit: ESA, VITO)
• March 6, 2015: A high-speed camera for monitoring vegetation from space and combating famine in Africa is being adapted to spot changes in human skin cells, invisible to the naked eye, to help diagnose skin diseases like cancer. 68)
- In fact, the extraordinary digital infrared sensor from ESA's PROBA-V vegetation-scanning satellite is being adapted for several non-space applications. Mounted on a standard medical scanner, the space sensor can help doctors to look deeper into human tissues for detecting skin diseases earlier. It also has a bright future in industry: it has already been shown to improve solar cell production as well as spotting defective items on production lines.
- Leading-edge space technology: The PROBA-V camera has such a unique wide field of view that it allows the small satellite to build a fresh picture of our entire planet's flora every two days. Developed for ESA by the Belgian company Xenics, the camera sees light we cannot by looking in the shortwave infrared range.
- PROBA-V's ability to ‘see the unseeable' as Earth revolves beneath made the commercialization of the camera a natural step. With support from ESA and the Belgian Space Technology Transfer Program, the Xenics team created ‘Machine Vision', integrating cameras on inspection systems to replace humans in looking for imperfections. The high-speed resolution of our ‘line-scan' cameras makes them ideal for detecting hidden defects on fast-moving production lines, such as bottle manufacturing or sorting different types of plastics for recycling – all of which look similar to the human eye.
Figure 44: An OCT (Optical Coherence Tomography) scan for skin diseases, in particular to detect melanomas (image credit: Xenics)
• On March 4, 2015, ESA released Figure 45 in which the PROBA-V minisatellite captured the rare sight of standing water in the arid south Australian outback. Lake Frome, one of the whitest salt lakes in the southern hemisphere is visible to the right. Unusually, this 12 February image shows it filled with brackish water from the surrounding creeks in the area, which are typically dry. - Covering most of this 100 m spatial resolution image are the ranges and gorges of Vulkathunha-Gammon Ranges National Park, haven to many rare and endangered plants and animals. 69)
Figure 45: Lake Frome in South Australia as acquired by PROBA-V on Feb. 12, 2015 (image credit: ESA, VITO)
• Fall 2014: Study for PROBA-V Successor Mission: PROBA-V has been successfully launched on May 7,2013 and is providing a global monitoring in the continuity of the SPOT-VEGETATION mission. The progress in terms of ground resolution between Spot VGT and PROBA-V is a factor 3 (1 km to 300 m ground resolution product). The User Community requirements for the next generation of global monitoring call for a 100 m ground resolution product. This means an additional factor 3 improvement, but in a short time frame (5 years). After the success of the PROBA-V mission, the Belgian Science Policy (BELSPO) initiated a PROBA-V Successor feasibility study. This study was undertaken by VITO and CSL to identify potential tracks to achieve a follow-on mission which is expected to be relevant for the User Community. The mission analyses for each of these tracks was evaluated. Today the PROBA-V mission lifetime is expected to expire by mid of 2018. 70)
Since the interest for global land monitoring is expected to continue in the future, this study proposes mission requirements and a shortlist of optimal mission scenarios for a follow-on mission in this short time frame. The goal of such a new PROBA-V mission is clear: it should ensure the data continuity of global vegetation monitoring, while taking the opportunity to further improve the data quality. Data continuity is essential for understanding long term trends of land use that may affect the global equilibrium of the planet (in the context of scarcity for land or food, natural disasters, climate change). As for added value, a fine example is the improvement of spatial resolution when comparing PROBA-V with the spatial resolution in SPOT-VEGETATION products. An improvement in spatial resolution towards a full 100 m product is considered by the user community as the main target for a PROBA-V follow-on mission.
Figure 46: Comparison of coverage frequency and spatial resolution (image credit: VITO, CSL)
• Dec. 4, 2014: ESA released Figure 47 as 'image of the week': PROBA-V catches the Sangeang Api volcano on the island of Sangeang in Indonesia as a thick column of ash and sulphur dioxide pumps into the atmosphere. The dense ash grounded flights across much of the archipelago nation. 71)
Figure 47: PROBA-V images an Indonesian volcano, acquired on May 31, 2014 at a resolution of 300 m (image credit: ESA, VITO)
• The PROBA-V image (Figure 48) of western Brazil was released on October 16, 2014. This 300 m resolution image reveals the human impact on the world's largest tropical rainforest. The brownish colors indicate deforested areas – note the distinctive ‘fishbone' pattern as main roads are cut through an area, followed by secondary roads for further clearing. 72)
- INPE, the Brazilian Institute for Space Research, uses satellites to monitor Brazil's rainforests. Its results show the annual rate of deforestation has fallen from some 3900 km2 in 2004 to 900 km2 in 2013, although substantial amounts of precious forest are still disappearing every day.
- PROBA-V's images are processed and distributed to hundreds of scientific users by VITO, Belgium's Flemish Institute for Technological Research, extending the coverage of previous generations of the Vegetation camera flown on the SPOT-4 and SPOT-5 satellites.
Figure 48: Deforestation in the state of Rondônia in western Brazil, as imaged by ESA's PROBA-V minisatellite (image credit: ESA, VITO)
• The PROBA-V mission is operating nominally in August 2014. — For the annual Small Satellite Conference of AIAA/USU, Logan, UT, the PROBA-V project published a paper with the title: "PROBA-V: The example of onboard and onground autonomy," virtually the entire paper is presented in the last chapter of this file. It demonstrates vividly many autonomy concepts and aspects implemented successively for the PROBA series. The content might be of interest and value to the entire EO community.
• June 6, 2014: The SPOT Vegetation mission, flown on SPOT-4 and SPOT-5 for 16 years, marked 16 years of service in May, and has now passed the torch to its European counterpart. As of June 1, 2014, PROBA-V is the official successor mission — mapping land cover and vegetation growth across the entire planet every two days. The data can also be used for day-by-day tracking of extreme weather, alerting authorities to crop failures, monitoring inland water resources and tracing the steady spread of deserts and deforestation. 73)
- PROBA-V has demonstrated the benefit of the utilization of small satellites for an operational mission, as well as for the in-orbit demonstration of new technologies and technological payloads that can benefit from an early flight opportunity and quick implementation from decision to flight (Ref. 25). All embarked technological payloads are working properly and continuously on-board thanks to the allocation of the system resources that became available along with the project implementation. The flexibility of the PROBA platform and the integration process of the satellite has allowed to manifest even late flight opportunities for new technological payloads.- Due to the autonomous character of the flight and the ground segments, virtually all operational activities don't require human intervention, while keeping the availability of the system very high.
Figure 49: This image of Europe is a composite of PROBA-V images from 1–10 May 2014 (image credit: ESA, VITO)
• Status of ADS-B in late May 2014: General aspects of the results. 74)
The ADS-B receiver on board the satellite was the first experiment of its kind, receiving 1090ES ADS-B squitter signals transmitted from aircraft. Therefore the experimenter could not build on experiences or any evaluation results. The assessment of the achieved results should take into account the constraints under which this experiment was realized, as there were limitations in cost and time but in particular available resources on the satellite in terms of available power and geometry.
The reception of 1090 Extended Squitter ADS-B messages on board of the PROBA-V satellite is mainly affected by the following issues, which may lead to a loss of ADS-B information:
- RF signal loss due to the low signal level resulting from the distance between the receiving satellite at an altitude of approximately 820 km and the transmitting aircraft at an altitude of 0 to 12 km.
- RF signal loss due to the shapes of the satellite antenna vertical radiation pattern and the aircraft antenna vertical radiation pattern.
- Corruption of messages by garbling, when several messages arriving at the ADS-B antenna onboard of the satellite at the same time overlap and thus cannot be decoded by the ADS-B receiver.
- Speed of the satellite of about 27000 km/h, which leads to a limited time of observation for each detected aircraft of about 3 minutes maximum (Ref. 74).
A separate file of ADS-B was added to the eoPortal in June 2014, providing more information of ADS-B (Automatic Dependent Surveillance-Broadcast) over Satellite.
• On May 31, 2014, the SPOT-Vegetation program will hand over the torch to the PROBA-V mission. 75)
Legend to Figure 50: The Aral Sea is a striking example of the kind of changes the satellite series (SPOT-4, -5 and PROBA-V) with the Vegetation instrument has been tracking. Once the world's fourth-largest inland water body, it has lost around 90% of its water volume since 1960 because of Soviet-era irrigation schemes. The image depicts the white salt terrain left behind by the southern Aral Sea receding, now called the Aral Karakum Desert. The greenery to the south is cultivated land irrigated by the Amu Darya river.
Table 11: Some background on the SPOT Vegetation program (Ref. 75)
• On May 7, 2014, the PROBA-V minisatellite was 1 year on orbit. For this occasion, ESA and VITO provided some recent imagery of the PROBA-V spacecraft (Figures 51, 52 and 53). — PROBA-V is set to make a giant leap for a minisatellite: formally taking over the task of continuously charting our planet's global vegetation. 77)
Figure 51: An unusual view of South America and the Andes mountains, acquired by PROBA-V on April 23, 2014 (image credit: ESA, VITO)
Figure 52: The Nile Delta in Egypt, acquired by PROBA-V on March 24, 2014 (image credit: ESA, VITO)
Figure 53: India - from Sri Lanka to the Himalayas, PROBA-V acquired this image on March 14, 2014, (image credit: ESA, VITO)
• February 2014: In its first two months of work, the vegetation-monitoring PROBA-V minisatellite has yielded a valuable harvest for around a hundred scientific teams around the globe: more than 5000 images, 65 daily global maps and six 10-day global syntheses, plus a quick peek at the Olympics. ESA released the PROBA-V image of Figure 54 (333 m resolution) on February 17, 2014. Cloud covers much of the Black Sea itself. The city of Sochi is a sea port on the coast of the Black Sea (right next to the border of Georgia), while the snow events are taking place in the resort settlement of Krasnaya Polyana in the Caucasus Mountains. 78)
Figure 54: PROBA-V image of the Black Sea acquired on Feb. 7, 2014, including the Winter Olympics host city of Sochi (center of image), image credit: ESA, VITO
• January 2014: After the commissioning phase, the PROBA-V mission operations has been transferred within ESA to D/EOP (Directorate of Earth Observation Programs) as an ESA Earthwatch mission. The Vegetation images are online from the VITO/Copernicus user segment. 79)
• December 03, 2013: Less than seven months after launch, Earth-watcher PROBA-V is ready to provide global vegetation data for operational and scientific use. The crucial commissioning phase is now complete and the satellite has been declared ready for operations. 80)
It is anticipated, that with the data from PROBA-V, the user community, ranging from operational Copernicus services to scientific users, will be able to answer questions related to the state of global vegetation and its dynamic changes in a seasonal context. Furthermore, PROBA-V will extend the valuable time series that was started by the SPOT-4/5 Vegetation instruments 15 years ago.
Figure 55: PROBA-V image acquired on Oct. 26, 2013, showing Sicily, Italy with the twin volcanic plumes – one ash, one gas – from Mt. Etna (image credit: ESA, BELSPO)
• On July 10, 2013, the first global VGT map of PROBA-V was provided, demonstrating that the minisatellite is on track to continue a 15-year legacy of global vegetation monitoring from space. 81)
Figure 56: First uncalibrated global mosaic of vegetation from PROBA-V, June 2013 (image credit: ESA)
• July 02, 2013: The satellite is currently in its commissioning phase, which includes a careful cross-calibration of the Vegetation imager with its predecessor on France's Spot-5 satellite, to ensure data compatibility. 82)
Figure 57: PROBA-V image of the border region of northern Syria, southeastern Turkey and northern Iraq observed on June 28, 2013 (image credit: ESA)
Legend to Figure 57: The area pictured is about 500 km across, with large reservoir lakes along the Euphrates River visible on the left, and another along the Tigris River on the right. Reservoirs and rivers secure water supply in the very dry region. They also form the basis for what is visible in different shades of green along the river water's edges and irrigated agricultural plots to provide food and income to the population.
• June 13, 2013: An A320 Airbus overflying Scotland was the first aircraft 'seen' from space by a new receiver, the ADS-B (Automatic Dependant Surveillance-Broadcast) device of DLR. This verifies that tracking aircraft from space is possible. On May 23, 2013, the experiment was switched on for the first time, recording over 12,000 ADS-B messages within two hours, at an altitude of 820 km. The project team detected over 100 aircraft during the first pass over the British Isles, East Asia and Australia when the receiver was switched on. 83) 84)
ADS-B signals are broadcast by aircraft every second; they include aircraft position and velocity information. ADS-B equipment is being introduced on aircraft as a supplementary data source to the ground-based radar currently used to monitor air traffic. The problem with radar is that its coverage is restricted. Once out of the range of terrestrial radar stations, the continuous air traffic surveillance stops.
Figure 58: Tracking aircraft with the ADS-B receiver on board PROBA-V over Great Britain and the Atlantic Ocean (image credit: DLR)
• May 17, 2013: The PROBA-V spacecraft is in good health following its launch on May 7, 2013. The Vegetation imager has been switched on and the first image has been captured over western France. 85)
- PROBA-V reached its orbit of 820 km altitude just 55 minutes after launch. The first LEOP (Launch and Early Operations Phase) milestone was to check the first signs of life from the satellite as it flew over the ESA ground station in Kourou 40 minutes after separation. Then a full telemetry session confirmed the stabilization of the satellite's attitude. The onboard computer used its magnetorquers to control the satellite's attitude and compensate for the spin imparted by the separation.
- Since then, the project has been checking the various subsystems one by one, confirming that they have made it through the stress of launch in working order. These initial checks are now being followed by a diligent commissioning of every single detail of the overall system platform, instrument and technology demonstration payloads, which will take the next few months.
Figure 59: PROBA-V's first raw image acquired over France's west coast on May 15, 2013 (image credit: ESA)
Legend to Figure 59: The image was generated using the three VNIR bands, blue, red and near-infrared (NIR) superposed, the green being replaced by the NIR. It has not yet been radiometrically or geometrically corrected. Less than a cubic meter in volume, the miniaturized ESA satellite is tasked to map land cover and vegetation growth across the entire planet every two days.