The VEGETATION products have been defined by the International Users' Committee. They are adapted to the particular missions described above and coherent as much as possible with the needs of existing projects. Two general categories of users could be identified :
research teams which are developing methodologies for the use of VEGETATION data or scientific biosphere studies : they generally have a study site (about 500 x 500 km2) and need long time series (one year of daily or weekly data ),
projects which are based on the use of both VEGETATION and other data sets, for which the data delivery has to be fully operational and for long periods, for comparison or historical studies (one continent every day). Typically, these projects are : MARS, TREES, IGBP...
overall organization of the different levels is shown in the following figure
(Fig. 2.1). To illustrate the special characteristics of the instrument, high
priority is given to design products that allows direct multitemporal registration
as well as simple superposition with simultaneously acquired high resolution
Fig. 2.1: VEGETATION products characteristics.
Four main functions are provided in order to satisfy the general definition of the mission. These functions are the following:
the generation and maintenance of a Core Archive which contains all the data received from the instrument system as well as the minimum ancillary data which are necessary to preprocess the raw data,
the generation of enhanced products at different levels, both as basic products that should be made widely available (P products) and as particular products or information data sets that should be adapted to important projects (S products),
the maintenance of a catalogue of existing data, accessed through easy communication means to the users, to provide timely information on data availability and quality,
the contacts with the users and projects to facilitate the use of VEGETATION products and the development of enhanced or new products, taking into account both the evolution of the needs of the community and the increasing capability to correct raw data for system or observational effects and extract new informations.
Two levels of enhanced products are defined corresponding to the existing needs of potential users:
P products correspond to data which be mostly used by physicists for methodological development that could be embedded into applications using VEGETATION data.
S products where some synthesis is applied on the "Core Archive" data to provide ground reflectances as well as some simply derived parameters. S products are composed by 2 products:
- The daily synthesis (S1)
- The ten-day synthesis (S10) and derived 2 degraded resolution products (S10.4 and S10.8).
- World Cover : Plate Carrée, Goode Homolosine, Equatorial Mercator, Equivalent Sinusoidal
- Continental projections : North America/ Albers, Africa/ Mercator or Plate Carrée, Western Europe/ Conic, Lambert, Asia, South America, Australia (TBD)
- Arctic/ Antarctic : polar stereo
Both P and S products families rely on a set of corrections that are summarized in the following table :
- spectral band registration
- satellite location and attitude correction
- terrain elevation to take into account parallax distortion and provide orthoimages.
pixels are resampled onto a regular grid, taking into account :
|Radiometric corrections||Calibration of all the detectors along the line-array detectors for each spectral bands to correct detector normalization and absolute calibration.|
to geographic projections for multitemporal analysis as well as for comparison
with high resolution data.
The set of projections chosen for the P products is compatible with the set of projections available for SPOT high resolution images to ensure direct registration between VEGETATION and HRVIR data.
|Status map||Provided with the images, indicating for each pixel one of the following cover classes at the time of acquisition: land, water, snow, ice and cloud.|
|Atmospheric corrections||Not applied. "Top of the Atmosphere" reflectances||Based on SMAC: water vapour, ozone & aerosols effects|
|Output product||Viewing segment or full segment necessary to overlap the geographical area requested by the user||Geocoded
mosaïc product over user selected rectangle, up to Global product
daily synthesis (S1)
ten-day synthesis (S10)