Vegetation
Programming Centre
Vegetation Image Ground Segment
The Vegetation system is operated through centres located in France, Belgium and Sweden.
Part of the CNES control and command facilities in the SPOT 4 operations control centre, the Vegetation programming centre (CPV) is responsible for programming the Vegetation instrument.
In tandem with the Vegetation system operator, the CPV programs the instrument in line
with mission requirements (systematic imaging of exposed land whenever there is sufficient
illumination), requests for technological programming for the image quality centre and
system capability purposes (for instance, whether recorded imagery is suitable and the
possibility of dumping the onboard memory to the main imagery receiving station in
Kiruna).
Prepared programs are uploaded daily to the satellite at the same time as programming of
the main payload (HRVIR).
The image ground segment is a set of four facilities which receive and process Vegetation data to produce image products for system users:
The Kiruna-Esrange receiving station is located in northern Sweden to be able to
"see" SPOT 4 and its Vegetation passenger more often. Three to four times
daily, the station receives global imagery recorded by the satellite. A large 9-metre
antenna receives the X-band imagery data during SPOT 4 passes.
After inventory of the imagery the station forwards it to the processing centre. Formatted
computer files are then sent on a cartridge or via a telecommunications link over
international public networks. About one gigabyte of data, representing 200 million
pixels, are sent each day to the processing centre.
Since Vegetation also transmits imagery directly, several independant stations
distributed around the globe will be able to receive "L-band" data directly when
Vegetation is over their acquisition circle.
To check that the direct channel is operating as it should, a "small" reference
station with a 1.8 m diameter antenna, was installed at Aussaguel, near Toulouse,
close to the main SPOT imagery receiving station. It has been programmed for regular
reception of L-band Vegetation data and also to check the quality of the link and transmit
imagery data to the image quality centre for analysis.
The Vegetation imagery processing centre was built at Mol, in Belgium, 40 kilometres from Antwerp, on the grounds of the Flanders research centre VITO.
The CTIV receives all data from the Kiruna station and immediately archives them to ensure their long-term availability: the Vegetation archives are stored on automatically controlled cartridges. This will facilitate data transfer to the next generation of archive media, in five to ten years time.
Users of Vegetation imagery can order "specially made" products by choosing the imaging date, the target area, the type of projection and the image processing level: these might require imagery from a single acquisition (VGT-P product) or imagery extracted from a synthesis of several images compiled to eliminate clouds (VGT-S product). The processing parameters are defined by the user via an interface on Internet. When the user's order is deemed to be commercially and technically feasible, the centre generates the image products on computer media (CD-ROM or cartridge), or makes them available via Internet.
The centre is designed to make products available less than 48 hours after imagery
acquisition, on condition that the user has already "subscribed" to imagery
covering the target area.
All processing is done as soon as the necessary data are available, with as little human
intervention as possible.
Geometric processing compensates for instrument shortcomings and satellite motion,
while radiometric processing transforms data from each of the 1728 detectors into physical
values (radiance or reflectance).
Processing also includes a separate facility known as the GCP workshop which uses
predefined ground control points to adjust images that have already been precision
converted. This process is also known as georeferencing. This ensures the excellent
geometric quality of all image products produced by the centre.
The quality of satellite imagery depends on several parameters: the
quality of the imaging instrument of course, but also many parameters in the image
processing algorithms.
All of these parameters have to be precisely calibrated at the beginning of satellite
operations, by analysing the first images in depth. Subsequently, due to ageing of the
instrument and the satellite, some of the parameters will have to be recalculated from
time to time.
These calculations are done by algorithms used for processing the particular referency
imagery: night scenes, imagery generated using the instrument calibration lamp, images of
test sites (deserts) or scenes of sea, snow or clouds, etc.) They also process images of
areas which have already been accurately located (georeferencing).
The image quality centre also provides experts with tools enabling them to detect and
analyse the slightest defects in raw or processed imagery.
page updated on the 00-06-06