SPOT-5 is the fifth satellite in the SPOT series of CNES (Space Agency of France), placed into orbit by an Ariane launcher. Since the first SPOT satellite was launched in 1986, the SPOT system has sought to provide continuity of service and constantly improved the quality of its products for the global user community.
Background: In 1994 the SPOT-5 program was approved by the French government, consisting initially of two identical S/C in orbit and two new optical imagers for these S/C, called HRG (High Resolution Geometric) and HRS (High Resolution Stereoscopic) to provide a ground resolution of 5m. In 1996, the SPOT-5 program was downsized (to one orbiting S/C) and redefined to improve the spatial resolution of the imagery below 5 m. As a result, an innovative image acquisition and processing scheme has been developed by CNES to obtain spatial resolutions of about 3 m from two 5 m images. In January 1999, a further functional improvement was introduced giving the HRS (High Resolution Stereoscopic) instrument a full stereoscopic capability. It was also decided to continue to fly the Vegetation instrument. The SPOT-5 satellite program continues the partnerships of France (CNES), Belgium (OSTC) and Sweden (SNSB) as established at the beginning of the SPOT program. 1)
• To provide image acquisition and service continuity consistent with previous SPOT satellites to satisfy the user investments. Hence, the same sun-synchronous orbit is used providing the existing functional instrument capabilities with a 26 day repeat cycle, the same off-track viewing capability of ± 27º about nadir, the same spectral band selection, and the same 60 km double swath.
• To improve the spatial resolution of the imagery to < 3 m in the panchromatic band and to 10 m in the multispectral mode. The SWIR band imagery remains at 20 m.
• To offer in parallel a stereoscopic along-track observation capability (instead of the previously provided cross-track capability). The intend is to offer high-resolution imagery to be used for DEM (Digital Elevation Model) generation with an accuracy of 10 m.
Figure 1: View of SPOT-5 spacecraft and its instruments (image credit: CNES)
The SPOT-5 satellite configuration takes advantage of the SPOT-4 bus design, using the extended platform design (SPOT MK2, provided by MMS) and service module accommodates twice the payload of the SPOT 3 bus. The ACS (Attitude Control Subsystem) provides a pointing accuracy of 0.05º and an attitude restitution of 6 x 10-5 radians. This excellent location accuracy [autonomous star tracker SED16 manufactured by EADS- Sodern, France] corresponds to < 50 m without ground control points (instead of 350 m on SPOT 1 to 4). The S/C structure has dimensions of: 3.4 m x 3.1 m x 6 m (excluding the solar array). The OBC (Onboard Processor) consists of a Marconi MDC 31750 processor. The S/C mass is 3030 kg at launch, power = 2400 W (EOL), batteries = 4 x 40 Ah, design life = 5-7 years. Note: In 2000 MMS became part of EADS Astrium. 5) 6) 7)
Figure 2: Schematic view of the SPOT-5 architecture (image credit: CNES)
Figure 3: Illustration of the deployed SPOT-5 spacecraft (image credit: CNES)
Launch: A launch of SPOT-5 on an Ariane-4 vehicle took place May 4, 2002. The secondary payload on this flight consisted of two nanosatellites with the name of IDEFIX. Both nanosatellites were designed, built and funded by AMSAT-France. Each nanosatellite has a mass of 6 kg. They remain attached to the third stage of Ariane-4.
RF communications: Onboard solid-state recording capacity of 90 Gbit (EOL). The onboard memory can store 550 images, compared to 400 on SPOT 4. Although the magnetic recorders provided more capacity (120 Gbit), the file management system allocates available storage capacity more efficiently. Onboard data compression of source data is provided with DCT (Direct Cosine Transform) of HRG and HRS data streams. Compression ratios of 2.28-2.8 are achieved depending on imaging mode.
The downlink is in X-band (QPSK modulation) at a data rate of 2 x 50 Mbit/s. The image transmission assembly consists of: a) Two QPSK modulators, b) two X-band solid-state power amplifiers (SSPAs) capable of delivering 20 watts, c) an output multiplexer (OMUX) filter that filters and combines signals before directing them to the antenna.
The data compression algorithm used is DCT (Discrete Cosine Transform), employing 8 x 8, non-overlapping blocks, derived from the JPEG standard with variable length coding and bit rate control. Compression ratios of 2.8 are used. 8)
Orbit: Sun-synchronous circular orbit (identical to those of SPOT-1 to -4), altitude = 832 km, inclination = 98.7º, period = 101.4 min, equator crossing on descending node at 10:30 AM, repeat cycle = 26 days, revolutions/day = 14 5/26.
• May 2016: In analogy to the previous SPOT-4 Take 5 experiment, within this timeframe a new experimental phase should allow placing SPOT-5 in a 5 days cycle orbit. Thanks to this orbit, it will be possible to acquire data over selected sites every 5 days under constant angles for duration of around 5 months over the majority of the vegetation phase.
The TAKE5 experiment benefits from the earth observation SPOT-5 satellite after the end of its commercial mission and before its de-orbiting, using SPOT-5 as a simulator for time series optical images from ESA's Sentinel-2 constellation. Sentinel-2A was launched on 23 June 2015, the second satellite Sentinel-2B should follow by the end of 2016. These 2 satellites will supply high resolution images with a large coverage (systematic acquisition of all lands, 290km swath) and high repetivity (5 days with 2 satellites). 9)
This huge volume of data will be a revolution for vegetation monitoring by satellite and needs to be prepared, in order to use the data: getting methods ready, developing new algorithms and new applications, automation of treatments .... To prepare Sentinel-2 applications, simulated images were available from aircraft or satellites such as FormoSat-2 and Landsat but none of these attempts combined the wide coverage, high resolution and frequent revisit of the Sentinel-2 constellation. So, when CNES offered to run short-term experiments with SPOT-4 before de-orbiting, CESBIO proposed the TAKE5 mission which consisted in moving SPOT-4 to a 5-day cycled orbit in order to simulate Sentinel-2 images.
This first TAKE5 experiment on SPOT-4, conducted by CNES, supplied time series images over 42 sites for 4 months, from February to mid-June 2013 and was very fruitful. The great success of TAKE5 with SPOT-4 was confirmed by ESA's decision to largely contribute to the renewal of TAKE5 experiment using SPOT5.
SPOT-5/TAKE5 supplies data every 5 days, with a resolution closer to Sentinel-2's (10 m) and over a more convenient period for summer crop monitoring in temperate zones (April to September 2015). TAKE5 was a new challenging mission for SPOT-5 as the TAKE5 orbit was outside the SPOT5's qualified flight dynamics. Moreover, the SPOT-5 system designed for its commercial mission had to be reconfigured to this new mission, involving different needs, within a short time. A 5 month feasibility study was required to verify that the SPOT-5 orbit could be modified and that the SPOT-5 system could be adapted to this new mission for which it had not been designed. Significant changes were needed with regard to the system fitted to SPOT-5's commercial mission. The experience acquired from SPOT-4/TAKE5 was only partially useful as the SPOT-4 and SPOT-5 systems are quite different and the constraints were not the same with SPOT-5. SPOT-5 reached its new orbit on 2 April 2015 and CNES took over the SPOT-5/TAKE5 mission on 8 April, for 5 months. During this period, the TAKE5 experiment has been providing images every 5 days over 150 sites selected after an international call for sites.
When CNES issued a call for ideas at the end of the SPOT-5 commercial mission, CESBIO proposed to renew the TAKE5 experiment using the satellite SPOT-5 for the same purpose.
The Sentinel-2 satellites and mission: ESA (European Space Agency) is developing and operating Sentinel-2, a next-generation Earth observation mission, within the Earth observation and monitoring program Copernicus of the European Commission. The Sentinel-2 mission focuses on global land monitoring at high resolution with high revisit capability. It is designed as a constellation of twin polar-orbiting satellites in the same orbit to fulfil revisit and coverage requirements. Vegetation, land cover and coastal areas are among the monitoring objectives. The first Sentinel-2A was launched on 23 June 2015, the second satellite Sentinel-2B should follow at the end of 2016. They are planned to have a 7-year lifespan, the mission duration is expected to be 20 years with the follow-on Sentinel-2 constellation.
The Sentinel-2 mission provides global coverage of the Earth's land surface every 10 days with one satellite and
- High resolution: 10, 20 or 60 m, the spatial resolution depending on spectral bands
- Large coverage: 290 km swath
- Multispectral optical imagery: 13 spectral bands, from the visible to the short-wave infrared portion of the spectrum
- Frequent revisit with constant viewing angles: 5 days with two-satellite constellation. The constant viewing angles will minimize the directional effects, allowing for high quality image time series.
Need for Sentinel-2 data: At the end of 2016 when the Sentinel-2 constellation is complete, and for many years after, users will have access to high resolution series of images acquired every 5 days, anywhere over the Earth's land surfaces. This huge volume of data will be a revolution for vegetation monitoring by satellite: it will change and enhance the way land surfaces are monitored using remote sensing and such an evolution needs to be prepared.
The SPOT-5/TAKE5 mission: For the SPOT5/TAKE5 experiment, sites of interest are provided by different sources:
- Sites selected by CNES/TOSCA (Terre solide, Océan, Surfaces Continentales, Atmosphère)
- ESA "internal" sites selected by ESA in response to exploitation projects to prepare the Sentinel-2 mission
- Scientific "external" sites selected by ESA, as a result of an international call for proposals to the worldwide users' community.
Figure 4: The SPOT-5/TAKE5 sites of interest (image credit: CNES)
• April 10, 2015: The SPOT-1 to -5 mission archive, the SPOT-6 and -7 mission archive and new acquisitions, the Pleiades mission archive and new acquisitions, and the SPOTMAPS 2.5 complete dataset are now available to the scientific user community. 10)
- The products are available in level 1 and level 3 (levels 1A/1B and orthorectified level 3 for SPOT-1 to -7, primary and orthorectified levels for Pleiades). Stereo and Tri-Stereo modes available on SPOT-6 and -7 and Pleiades are also available.
- The products can be made available for free through a project proposal submission via the SPOT information area and Pleiades information area on ESA's Earth Online Portal.
ESA is offering free of charge for scientific research and application development access to the following SPOT collections: 11)
- ESA SPOT archive collections (ESA online archive)
- Archived SPOT-1 to -5 all production levels (on demand)
- Archived and new SPOT-6 & -7 (acquisition modes: single ,stereo or tri-stereo) all production levels (on demand and standard service for tasking)
- SPOTMaps 2.5 m complete dataset (on demand).
• April 9, 2015: On 2 April 2015, the SPOT-5 satellite was successfully maneuvered into a new orbit (orbit lowered by 2.5 km) as part of the mission's final phase. This experimental phase for the mission, SPOT-5 (TAKE5), involves the satellite being tasked to observe selected sites before the satellite is deorbited later this year in autumn. 12)
- The end of SPOT-5 nominal mission was on March 31, 2015, deorbitation is planned in autumn 2015. In analogy to the previous SPOT-4 Take 5 experiment, within this timeframe a new experimental phase should allow placing SPOT-5 in a 5 days cycle orbit. Thanks to this orbit, it will be possible to acquire data over selected sites every 5 days under constant angles for duration of around 5 months over the majority of the vegetation phase (current assumed schedule 08/04/15-31/08/15). The experiment has been approved on 19 November 2014. 13)
- In December 2014, ESA launched a call for proposals of sites in order to choose the areas for which the observation data processing cost will be funded by ESA's Earthnet program. ESA PIs submitted 60 scientific projects of different thematic areas, proposing around 100 sites. ESA has carefully evaluated these proposals and selected more than 60 sites for the acquisition plan.
Figure 5: SPOT5 tracks during Take 5 experiment. In blue, the tracks from day 1 (every 5th day, starting from the 5th of April), day 2 is in green, day free in yellow, day 4 in orange and day five in red (image credit: CESBIO, ESA) 14)
Figure 6: On April 8, 2015, the first image of the SPOT-5 Take 5 campaign was acquired over Uganda at Lake Victoria. In this color composite 60 m resolution image, one can see part of Uganda's coast along the African Great Lake (image credit: ESA, CNES, Airbus DS)
Legend to Figure 6: There is nothing special of the SPOT-5 Take 5 image; it simply represents proof that everything went well at all stages, from programming to acquisition and processing, despite the fact that SPOT-5 is not on its nominal orbit anymore. To limit download time, it is only provided here at 60 m resolution. The color composite is : (red : SWIR, green : NIR, blue : Red). 15)
• The SPOT-5 commercial mission was ended on March 27, 2015 — after nearly 13 years of good services. But SPOT-5 isn't dead yet: following the success of the Take 5 experiment on SPOT-4, a new edition, co-funded by ESA, was decided for SPOT- 5. 16)
- The objective of this end of life experiment, as the previous one, is to prepare the arrival of ESA's Sentinel-2 satellites (launches scheduled for June 2015 and 2016). It's objective is to put SPOT- 5 on a high revisit orbit (5 days) and to acquire about 150 predefined sites every 5 days during 5 months, meaning 30 acquisitions of each site, in order to monitor the evolution of the vegetation and summer crops.
- On April 2, 2015, the SPOT-5 orbit was lowered by 2.5 km in order to reach an orbit at 820 km with a 5 day revisit cycle for the Take 5 mission and will remain on this orbit during 5 months. 17).
Table 1: Some statistics of the SPOT-5 mission 18)
Figure 7: In Red: Elevation30 (Reference 3D), In Pink: + 37 Mkm2 block adjusted datasets, ready for additional Elevation30 production (image credit: Airbus DS, Ref. 18)
Figure 8: This false-color image from the Spot-5 satellite was acquired on 28 September 2011 over central Belgium, capturing the capital city of Brussels (left), image credit: Airbus Defence and Space
Legend to Figure 8: Zooming in on the city, one can see a number of large parks, such as the Parc du Cinquantenaire or "Park of the fiftieth anniversary," a large public, urban park (30 hectares) in the easternmost part of the European Quarter in Brussels — home to the institutions of the European Union. Brussels is the de facto capital of the EU, and is a major center for international politics.
- Further west, one can see the Parc de Bruxelles or Warandepark, where the Royal Palace of Brussels and the Belgium Parliament are located.
- The yellow airfield in the northeast of the city is the Airport of Brussels , with the runways on the outside of the airfield.
- Darker blue areas throughout the image depict thick vegetation cover, such as the city parks and the large Sonian Forest south of Brussels. Stretching over 4400 hectares, the forest is home to animals such as deer, red squirrel and wild boar. Brown bear and wolf also once roamed this area, but have disappeared through human influence and changes in the ecosystem over hundreds of years.
- The city of Leuven (Dutch), or Louvain (French) in the Flemish region of Belgium can be seen in the upper right corner of the image.
• Jan. 15, 2015 - Flood in Madagascar : Several weeks of heavy rainfall have resulted in widespread flooding in Madagascar. It is believed that 14 people have died, almost 10,000 have been left homeless and over 80,000 are affected by the disaster. Many of those killed fell victim to landslides and damage to buildings caused by the heavy rain and wind. 20)
- The excessive rainfall is the result of two storms which have affected Madagascar over the past few weeks. First was Tropical Cyclone Bansi on 09 January. Then Tropical Cyclone Chedza struck the south-western part of the island on 16 and 17 January. Among the locations affected by the flooding are Antananarivo (the capital city), Manakara and Vangaindrano.
Figure 9: Flood extent in Vangaindrano, Madagascar, following Tropical Storm Chedza; the image was acquired on Jan. 19, 2015 by SPOT-5 (image credit: CNES, distribution: Airbus Defence and Space / Spot Image S.A.)
• On Nov. 26, 2014, ESA is inviting proposals for the SPOT-5 Take 5 call, which aims to select potential sites of observation for a new phase in the SPOT-5 mission. The end of SPOT-5's nominal mission is foreseen at the end of March 2015, with deorbiting expected in autumn of 2015. In analogy to the previous SPOT-4 Take 5 experiment, within this timeframe a new experimental phase should allow placing SPOT-5 in a 5 days cycle orbit. Thanks to this orbit, it will be possible to acquire data over selected sites every 5 days under constant angles for duration of around 5 months over the majority of the vegetation phase (current assumed schedule is 08/04/15-31/08/15). 21) 22)
- The observation data processing of the selected sites will be funded by ESA's Earthnet program, and the experiment is co-funded by CNES. Additionally, this call shall support the preparations for the upcoming Sentinel-2 mission, which shall provide data continuity for the SPOT missions.
• May 12, 2014: The current status of the SPOT-5 mission is nominal and the mission is going to be extended until the end of the month of March 2015 (Ref. 26).
• April 30, 2014: The SPOT-Vegetation mission, flown on SPOT-5 and SPOT-4, has been delivering images on the global vegetation status to more than 10,000 users worldwide on a daily basis. Now, 16 years later, it is time for SPOT-Vegetation to hand over the torch to its successor, the minisatellite PROBA- V(Vegetation) of ESA. 23)
- The SPOT-Vegetation mission is a collaboration between France, Belgium, Italy, Sweden and the EC that has been monitoring the global vegetation status for more than 16 years. The Vegetation instruments (VGT-1 and VGT-2) were incorporated in the SPOT program, a program that was founded in 1978.
- SPOT-4, with VGT-1 on board, was launched on March 24,1998. The VGT-2 instrument, incorporated onto the SPOT-5 satellite, was sent into orbit on May 4, 2002. SPOT-4 has been deactivated a couple of years ago, but SPOT-5 will still be delivering images of the Earth until the end of May 2014. Every day a new image of the global vegetation status is being processed, archived and distributed at the Image Processing Center of VITO in Belgium.
- On May 31, 2014, the SPOT-Vegetation program will hand over the torch to PROBA-V. PROBA-V is an ESA minisatellite mission designed and built by a Belgian consortium (QinetiQ Space NV, Belgium). VITO developed the user segment and is responsible for the operations, calibration and distribution of all imagery.
- As PROBA-V was launched one year before the end of Vegetation (on May 7, 2013), both missions had a nice and clean overlap of one year. This overlap is highly important to ensure cross-calibration between both missions which is necessary to guarantee a consistent time series.
- In addition to this intent of continuation, there is also an important upgrade in spatial resolution from 1 km (SPOT-Vegetation) to 300 m (PROBA-V), allowing extraction of more detailed information on crop yields, droughts, desertification, changes in the type of vegetation, deforestation, etc. This higher spatial resolution is also in line with the upcoming Sentinel-3 mission, hereby offering users the prospect of an uninterrupted times series of 25 years or more.
• April 25, 2014: The theme for Earth Day 2014 is ‘green cities' (Figure 10). As more and more people move to cities in search of jobs – and the reality of climate change becomes increasingly clear – the need to create sustainable communities is more important than ever. Recognized this year as the European Green Capital, Copenhagen (Capital of Denmark) has set a prime example with investments in sustainable technology, forward-thinking public policy and an educated and active public. The Danish city is a good model in terms of urban planning and design, and is working towards becoming carbon-neutral by the year 2025. 24)
Figure 10: This SPOT-5 image of Copenhagen (Denmark) was acquired 21 April 2011, with a resolution of 2.5 m and released on April 25, 2014 (image credit: Airbus Defence and Space)
• 2014: Throughout the Vegetation program, VITO (Flemish Institute for Technological Research) uninterruptedly hosted the prime user segment of both Vegetation-1 and Vegetation-2 multispectral instruments on board the SPOT-4 and SPOT-5 satellites. Operational since the launch of SPOT-4 in March 1998, and foreseen to continue at least until the end of the SPOT-5 mission, this user segment comprises a processing facility (PF), actively receiving, processing, correcting, archiving, and distributing the Vegetation data and derived added-value products. 25)
- First and foremost, the Vegetation program has been serving the needs of operational users – both institutional and commercial – requesting data in near-real time. However, scientific and educational users too benefited significantly, in particular from Vegetation's unique time series of the Earth's land cover, and more specifically the vegetation cover. Over the years, the centralized archive houses processed data covering the equivalent of 11,000 times the Earth's surface, and delivered more than 50 terapixels to around 10.000 users.
• 2014: The SPOT-5 spacecraft and its payload are still operational in early 2014 in its 12th year on orbit (design life of 5 years). However, the SPOT-5 local hour is drifting since maneuvers for inclination correction are no more performed (the hydrazine is saved for end of life operations). The end-of-life of SPOT-5 has been adjusted to the beginning of 2015 (nominally, during Q1 of 2015). 26)
• The SPOT-6 mission will complement the SPOT-5 mission by the end of 2012. 27)
Figure 11: Projected service profile of the SPOT family (image credit: )
• The SPOT-5 spacecraft and its payload are operating nominally in 2012 (10th year of on-orbit operations). The SPOT-5 local hour is slowly drifting since maneuvers for inclination correction are no more performed (hydrazine is saved for end of life operations). The end-of-life of SPOT-5 has been adjusted to: end of 2014/beginning of 2015. 28)
The SPOT-4 local hour is drifting since maneuvers for inclination correction are no more performed (hydrazine is saved for end of life operations). SPOT4 should be de-orbited when the local hour will be too low to maintain the main and VEGETATION missions -estimated to be sometime between December 2012 and March 2013 (Ref. 28).
• The SPOT-5 spacecraft and its payload are operating nominally in 2011.
- On April 1, 2011, a refocusing has been performed on the HRG-2 sensor. The result of this action is to recover the instrument's beginning-of-life performances (for relative and absolute FTM, and auto-test calibration).- The operational life expectancy of SPOT-5 remains unchanged, the estimate is for mid-2015. 29)
- After the devastating Japanese earthquake of March 11, 2011, SPOT-5 was tasked by the International Charter on Space and Major Disasters to cover the coast that took the full force of the subsequent tsunami. 30)
The situation regarding Japan's nuclear power plants recently prompted Astrium GEO-Information Services to activate its "SPOTMonitoring" service over the area. Daily change detection reports were delivered to subscribers free of charge March 17-25. The stricken Fukushima Dai-ichi nuclear power plant and its surroundings are still under surveillance and periodic reports will still be delivered over the next few months.
- 25 Years of SPOT Satellites: Since February 22, 1986, SPOT satellites have been keeping a watchful eye on the Earth. For over 25 years, this series of optical observation satellites has been providing images of our planet for an extensive range of applications, such as cartography, crop forecasts, geological exploration, and disaster management. 31)
All five of the SPOT satellites were developed and built by Astrium as prime contractor, responsible for the platform and high-resolution imaging system. Currently, the SPOT satellites are operated by Astrium GEO-Information Services, formerly Spot Image.
- On 8 January 2011, the SPOT-5 satellite acquired a series of images of the Darling River system in Australia south of St George, a town near the border between Queensland and New South Wales. SIS, an Astrium subsidiary in Australia, re-tasked the SPOT constellation to monitor the floods, in response to requests from Queensland's civil defence services and Geoscience Australia.
• On Dec. 1, 2010, Astrium Services created a single operational management structure bringing together the imagery and services experts Spot Image and Infoterra to form the new GEO-Information division of Astrium Services. The new unit of GEO-Information division of Astrium Services started business in January 2011 - operating the SPOT-4 and SPOT-5 satellites and providing the data to its customer base. 32)
• The SPOT-5 spacecraft and its payload are operating nominally in 2010. Currently, an operational life to mid-2015 is expected (Ref. 34).
• In January 2010, hours after the devastating January 12 earthquake struck Haiti, Spot Image personnel were in nearly constant communications with key customers and other organizations that needed access to imagery to assist in disaster response efforts. SPOT-5 captured its first image of Port-au-Prince on Jan. 14 and several more over the surrounding parts of Haiti in subsequent days.
The 2.5 m images were used by the U.S. government for logistics planning prior to deploying personnel to Haiti and later to manage resources on the ground. In accordance with the International Charter, which is an agreement by multiple nations to provide access to remote sensing data during natural disasters, Spot Image routed image scenes captured by the SPOT ground receiving stations to the Spot Image headquarters in France. There the data was used to generate maps of the stricken area for distribution to Non-Governmental Organizations aiding in the response. 33)
• The spacecraft and its instruments are operating nominally in 2009. Operational analysis studies conducted by CNES project a life expectancy at least to 2014 of the SPOT-5 mission. Chances are that the mission might continue its services until 2015 without serious anomalies. 34)
• In early 2008 some power problems of the power subsystem occurred. However, the exact cause could not be properly identified. The available power decreased slightly which is still quite sufficient to provide full service to all subsystems for mission operations. The situation became very stable in February 2008 and is continuously monitored - with no indication of any deterioration.
Figure 12: SPOT-5 sample image of Naples (Italy) in 2002 (image credit: CNES)
• The commissioning phase of the spacecraft and its instruments was completed on July 12, 2002. At this point, CNES handed over the responsibility for commercial operation of the SPOT-5 system to Spot Image (Ref. 35).
• July 10, 2002: The SPOT-5 in-orbit checkout review was held on July, 10, 2002. Tests performed during in-orbit checkout have shown that: 35)
- the satellite, ground telemetry and command systems, and passenger instruments are functioning perfectly and system availability is excellent
- geometric and radiometric quality of images from the two HRG (High-Resolution Geometric) instruments and the HRS (High-Resolution Stereoscopic) instrument is excellent, exceeding specifications; indeed, ways of further enhancing performance have already been identified.
• SPOT-5 was launched on May 4, 2015, the first image was received after 3 days on May 7, 2015.
Figure 13: First image of SPOT-5 showing the Eleusis Harbor, Greece, acquired on May 7, 2002 (image credit: Airbus DS, Ref.
• In April 2002, the French arms procurement agency, DGA (Délégation Générale pour l'Armement), signed a broad agreement guaranteeing French military access to the civilian SPOT-5 satellite's high-resolution imagery.
Sensor complement: (2 x HRG, HRS, Vegetation, DORIS)
HRG (High Resolution Geometric)
HRG was built by Astrium SAS of Vélizy, France to continue to improve the HRVIR service of SPOT-4. Two HRG instruments are provided in the conventional SPOT-series double-observation configuration, each with a FOV of 4.13º and the same cross-track pointing capabilities of ±27 º as the HRVIR imager on SPOT-4. The observation coverage of each HRG is 60 km in the nadir direction and >80 km in the oblique configuration (same two-swath coverage as before). The main components of the HRG instrument are:
• Stable structure supporting its mechanisms
• Optical subassembly
• Detection electronics
• Ancillary electronics.
HRG features a new linear detector array configuration geometry for the panchromatic band using two parallel rows (i.e., a dual array) of 12000 silicon CCD detectors (6.5 µm in size) for each instrument. The two PAN detector lines are offset in the focal plane in such as way as to provide coincident imagery of the same instantaneous cross-track area, each at a spatial resolution of 5 m. [Note: The dual array in the focal plane (offset by one half pixel in one direction and 3.5 pixels in the other to avoid overlapping) is sufficient to improve the sampling grid without doubling each array's acquisition rate. The new sampling concept is based on Shannon's theory of information which states that "the sampling frequency must be equal to or greater than twice the maximum signal frequency" to obtain clean images using interpolation.] The CCD integration time is within 0.75 ms for a dual-array observation in cross-track of 60 km in which the S/C is moving 5 m in the along-track direction.
Figure 14: View of the integrated HRG instrument (image credit: CNES)
Table 2: Specification of the HRG instrument
The detection unit, mounted in the instrument's focal plane, converts the light signal from the optical subassembly into electric signals for processing by the video electronics units.
Figure 15: Illustration of the detection unit (image credit: CNES)
Figure 16: Schematic view of HRG observation capabilities (image credit: CNES)
Supermode: The term refers to an acquisition process, specific to the HRG instrument of SPOT-5, through which an image sampled at 2.5 m may be obtained from two 5 m resolution panchromatic images acquired simultaneously, keeping within the same borders as the two 5 m resolution images. It is possible to combine the two 5 m pixel image samples into four new slightly overlapping image samples of about 3 m pixel size.
A specific image processing software, developed by CNES is used to reconstruct the final image after three processing steps: interleaving, interpolation and restoration. This new type of image, simulated with all its geometric and radiometric characteristics, has been compared by several users to other types of digital images at different ground resolutions. These users (cartographers, urban planners, environmental experts, foresters, agronomists,) have concluded that the supermode resolution is about 3 m (between 2.5 m and 3.5 m depending on applications and analyzed features). A new quincunx sampling mode was adopted referred to as THR (Très Haute Résolution) or very high resolution mode. 36) 37) 38)
Figure 17: Supermode processing scheme
Figure 18: Alternate view of the supermode scheme (image credit: SPOT Image)
HRS (High Resolution Stereoscopic)
The HRS instrument was developed and built by EADS Astrium SAS, sponsored by CNES and SPOT IMAGE.
The objective is to provide large-area along-track stereoscopic panchromatic imagery with good altimetric accuracy (5-10 m relative and 10-15 m absolute). Applications of the stereo imagery are seen in various fields such as map making and in the generation of DTMs (Digital Terrain Model) The panchromatic band (0.51-0.73 µm) of SPOT-1, -2, -3 is being reintroduced. The HRS instrument features two telescopes allowing a 20º fore view and a 20º aft view over a 120 km swath, respectively (Figure 20). A spatial resolution of 10 m is provided in cross-track and 5 m (parallax direction) in along-track. The stereo acquisition mode can be sustained for scene lengths of up to 600 km. HRS uses the same CCD line detector design as for the HRG instrument. 39)
Figure 19: Schematic illustration of the HRS instrument (image credit: CNES)
Table 3: Specification of HRS instrument
The HRS instrument consists of:
• A carbon-skin sandwich/aluminium honeycomb instrument panel supporting the mechanical interface with the SPOT 5 satellite and the instrument systems
• A stereo video module (MVS), which handles and processes data from the detection units. MVS actively controls the instrument's temperature and provides the ancillary systems required to operate it (chiefly power and TM/TC)
• A thermal cocoon encloses the temperature-sensitive components vital to achieve the instrument's required performance.
A few months after the commissioning phase of the HRS instrument in 2002, CNES proposed to ISPRS a joint initiative for a photogrammetric assessment the new HRS instrument, in particular with regard to the quality and accuracy of DEM (Digital Elevation Model) generation derived from HRS stereo pairs. This proposal was agreed to by ISPRS and given the name of HRS-SAP (High Resolution Stereoscopic-Scientific Assessment Program). An international study team was set up. As of mid-2004, preliminary results have already confirmed the high quality of the HRS instrument on board of Spot 5. Nevertheless, the DEM/DSM (Digital Elevation Model/Digital Surface Model) accuracy derived from HRS data has been assessed around 5 m (relative) and 10/15 m (absolute). 40) 41) 42) 43)
Figure 20: Illustration of the HRS viewing capability (image credit: CNES)
With some minor improvements regarding instrument operations, the Vegetation-2 instrument (VTG-2) is identical in its technical specification to Vegetation flown on SPOT-4. 44)
DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite)
See description of instrument under SPOT-4 and under TOPEX/Poseidon.
Summary of CNES SPOT series:
Table 4: Overview of SPOT series missions
Table 5: Overview of SPOT series spectral continuity and resolution improvement
Table 6: Overview of performance parameters of the SPOT family
Figure 21: Comparison of spacecraft bus sizes of the SPOT series
Improved attitude restitution for SPOT-5 (commissioning phase issues)
An extra attitude restitution process has been developed in order to provide an accurate attitude for the imagery location model. It uses enhanced SPOT-5 gyroscope readings, combined with absolute attitude angle measurements given by a stellar sensor. This stellar sensor, SED16 (built by SODERN, Limeil-Brivannes, France), is having its first in-flight experience on SPOT-5; it is designed around a CCD matrix observing numerous stars on each data take. SED16 has a wide FOV and is autonomous (i.e. it has its own built-in star catalog). SED16 can track up to ten stars simultaneously. The measurements are used by an onboard Kalman filter. 45) 46)
Figure 22: The star tracker on the space-facing side of the satellite between the two HRG instruments (image credit: CNES)
The SPOT-5 location model calibration addresses five main issues:
• The first issue is to get best relative and absolute location performances. It consists of relative orientation calibration for HRG, HRS and stellar location unit reference frames.
• The second issue is to get a model of THR (Très Haute Résolution) pairs relative shifts good enough to deliver the best 2.5 m sampled image. The first ever, true HRG images have been acquired during satellite design, a few months prior to launch. Such images contributed to THR processing validation and allowed ground calibration of THR detection lines relative shifts, way before launch. In-flight measures confirmed that such ground measures are reliable.
• The third item is to turn HRS stereo pairs parallax into a precise enough altitude estimate. It implies that HRS location models have to include an accurate model of objective distortions.
• A fourth issue deals with an evaluation of HRG's steering mirror mechanism calibration. The same location performance is required, regardless of HRG mirror viewing angles.
• The final issue deals with optimization of time delay between two HRG off-nadir image acquisitions. Such time delay depends on mirror damping speed. For a given viewing angle, called "Autotest", one can acquire HRG images of a designed pattern located in the focal plane. A straightforward processing of this image type indicates if the mirror command can be improved.
1) A. Ammar, A. Baudoin, D. Assemat, M. Arnaud, "The SPOT Programme, An Operational Earth Observation System," Proceedings 45th Congress of the International Astronautical Federation, October 9-14, 1994, Israel
2) A. Baudoin, "The Current and Future SPOT Program," Proceedings of the ISPRS Joint Workshop `Sensors and Mapping from Space 1999,' Sept. 27-30, 1999, Hannover, Germany
4) J.-P. Gleyzes, A. Meygret, C. Fratter, C. Panem, S. Ballarin, C. Valorge, "SPOT5 : System overview and image ground segment," Proceedings of IGARSS 2003, Toulouse, France, Juky 21-25, 2003
5) L. Barre, S. Thomas, P. Jacob, T. Foisneau, D. Vilaire, M. Pochard, "Night Sky Tests and In-Flight Results of SED16 Autonomous Star Sensor," Proceedings of the 26th AAS Conference on Guidance and Control, Breckenridge, CO, Feb. 5-9, 2003, Vol. 113 Advances in the Astronautical Sciences, Edited by I. J. Gravseth and R. D. Culp, AAS 03-042, pp. 389-398
6) L. Blarre, S. Thomas, et al., "Night Sky Tests and In-Flight Results of SED16 Autonomous Star Tracker," 5th International Conference on Spacecraft Guidance, Navigation and Control Systems, Frascati, Italy, Oct. 22-25, 2002, ESA SP-516
8) P. Lier, G. Moury, C. Latry, F. Cabot, "Selection of the SPOT-5 Image Compression Algorithm," Proceedings of SPIE, Vol. 3439,70, 1998
9) Martine Béhague, Olivier Hagolle, Sylvia Sylvander, Jean-Marc Walter, Florian Delmas, Laurence Houpert, Frédéric Daniaud, "TAKE5 experiment jazzes up SPOT5's end of operational life, using it to simulate the new Sentinel-2 mission," Proceedings of the 14th International Conference on Space Operations (SpaceOps 2016), Daejeon, Korea, May 16-20, 2016, paper: AIAA 2016 2408, URL: http://arc.aiaa.org/doi/pdf/10.2514/6.2016-2408
10) "SPOT and Pleiades data available for research and application development," ESA, April 10, 2015, URL: https://earth.esa.int/web/guest/missions/3rd-party-missions/current-missions/spot/news/-/article/spot-and-pleiades-data-available-for-research-and-application-development
12) "SPOT-5 Take 5 - First image released from campaign," ESA, April 9, 2015, URL: https://earth.esa.int/web/guest/missions/3rd-party-missions/current-missions/spot/news/-/article/spot-5-take-5-first-image-released-from-campaign
17) Ferrage Pascale, March 31, 2015, URL: ftp://ftp.ids-doris.org/pub/ids/dorismail/dorismail.0965
18) "Farewell SPOT-5," Airbus Defence and Space, April 28, 2015, URL: http://www.geo-airbusds.com/en/6371-farewell-spot5-thank-youits-been-amazing
19) "Brussels, the capital of Belgium," ESA, Feb. 27, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/02/Brussels
21) "SPOT-5 Take 5 announcement of opportunity," ESA, Nov. 26, 2014, URL: https://sentinel.esa.int/web/sentinel/missions/sentinel-2/news/-/article/spot-5-take-5-announcement-of-opportunity
22) Frank Martin Seifert, "SPOT-5 Take 5," GFOI (Global Forest Observation Initiative), Oct. 1, 2014, URL: http://gfoi.org/sites/default/files/GFOI-DEGRAD_Day1-07_Spot5Take5_Seifert.pdf
23) "After 16 years of successful operations, SPOT-VEGETATION ready to hand over the torch to PROBA-V," VITO, April 30, 2014, URL: https://www.vito.be/EN/HomepageAdmin/Home/Nieuws/Nieuwsberichten/Pages-news_spotvegetation_proba-v_apr2014.aspx
24) "Week in Images," ESA, April 25, 2014, URL: http://www.esa.int/Highlights/Week_In_Images_21_25_April_2014
25) Bart Deronde, Walter Debruyn, Eric Gontier, Erwin Goor, Tim Jacobs, Sara Verbeiren, Johan Vereecken, "15 years of processing and dissemination of SPOT-VEGETATION products," International Journal of Remote Sensing, Volume 35, Issue 7, 2014, pp. 2402-2420, DOI: 10.1080/01431161.2014.883102
26) Information provided by Alain Lapeyre of CNES, Chef de Service Exploitation des Satellites de Télédétection.
27) J. N. Hourcastagnou, P. Cales, "GSCB Workshop Presentation SPOT / AstroTerra," 3rd GSCB (Ground Segment Coordination Body) Workshop, 2012, ESA/ESRIN, Frascati, Italy, June 6-7, 2012, URL: http://earth.esa.int/gscb/papers/2012/16b-ASTRIUM_SPOT-AstoTerra.pdf
28) Information provided by Laurence Houpert of CNES (for the SPOT mission team), Toulouse, France
29) Information provided by Laurence Houpert of CNES, Toulouse, France
30) "SPOT-5 watches over Japan's coastline after earthquake and tsunami," Astrium Geo-Information Services, http://www.spotimage.co.jp/web/en/988-spot-5-watches-over-japans-coastline-after-earthquake-and-tsunami.php
31) "25 years of Spot satellites," Feb. 21, 2011, URL: http://www.interspacenews.com/FeatureArticle/tabid/130/Default.aspx?id=6158
32) "Astrium fully integrates Spot Image and Infoterra into new GEO-Information business division," Astrium, Dec. 1, 2010, URL: http://www.astrium.eads.net/node.php?articleid=6209
33) "Spot Provides Immediate Response to Haiti Earthquake," Spot Image, URL: http://archive.constantcontact.com/fs013/1102324034386/archive/1102902578471.html
34) Information provided by Frédéric Tavera, SPOT Mission Exploitation Manager of CNES, Toulouse, France
36) SPOT 5 brochure, "Supermode," of CNES and SPOT Image, May 1999
37) C. Latry, B. Rougé, "In Flight Commissioning of SPOT5 THR Quincunx Sampling Mode," Proceedings of SPIE, Vol. 4881, 9th International Symposium on Remote Sensing, Aghia Pelagia, Crete, Greece, Sept. 23-27, 2002
39) G. Planche, C. Masso, L. Maggiori, "HRS Camera: A Development and In-Orbit Success," Proceedings of the 5th International Conference on Space Optics, March 30-April 2, 2004, Toulouse, France, ESA SP-554
40) A. Baudoin, M. Schroeder, C. Valorge, M. Bernard, V. Rudowski, "The HRS-SAP initiative: A scientific assessment of the High Resolution Stereoscopic instrument on board of SPOT 5 by ISPRS investigators," Proceedings of ISPRS 2004, Istanbul, Turkey, July 12-23, 2004
41) Z. Li, A. Gruen, "Automatic DSM Generation from Linear Array Imagery Data," Proceedings of ISPRS 2004, Istanbul, Turkey, July 12-23, 2004
42) P. Reinartz, M. Lehner, R. Müller, M. Schroeder, "Accuracy Analysis from DEM and Orthoimages Derived from SPOT HRS Stereo Data without using GCP," Proceedings of ISPRS 2004, Istanbul, Turkey, July 12-23, 2004
43) S. Massera , P. Favé, R. Gachet, A. Orsoni, "Toward a Global Bundle Adjustment of SPOT-5 HRS Images," Proceedings of the 22nd Congress of ISPRS (International Society of Photogrammetry and Remote Sensing), Melbourne, Australia, Aug. 25 - Sept. 1, 2012, International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B1, 2012
45) E. Breton, A. Bouillon, R. Gachet, F. Delussy, "Pre-Flight and In-Flight Geometric Calibration of SPOT-5 HRG and HRS Images," Pecora 15/Land Satellite Information IV Conference, ISPRS Commission I Mid-term Symposium/FIEOS (Future Intelligent Earth Observing Satellites), Nov. 10-14, 2002, Denver, CO
46) J. F. Salaün, E. Chamontin, G. Moreau, O. Hameury, "The SPOT-5 AOCS in Orbit Performances," 5th International ESA Conference on Guidance Navigation and Control Systems, Frascati, Italy, Oct. 22-25, 2002
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).
The SPOT series: