A requirement of the SENTINEL-3 mission is to provide surface vegetation products derived from synergistic and co-located measurements of OLCI and SLSTR optical instruments, similar to those obtained from the VEGETATION instrument on SPOT, and with complete Earth coverage in 1-2 days.
For 10 years, the SPOT VEGETATION mission has played an important role in meeting this need for information by offering high quality global data of the entire terrestrial surface on a daily basis to operational users.
The VEGETATION system relies on two observation instruments in orbit. The first of the two instruments (VEGETATION1) is aboard the SPOT 4 satellite, launched on March 24th 1998. The second (VEGETATION2) is aboard SPOT 5, which was placed into orbit on May 4th 2002. Having exceeded its planned life of 5 years it shall be replaced by the follow-on PROBA-V mission. PROBA-V has a ground resolution of 300 m and a swath width of 2 250 km. This small satellite also offers higher accuracy with respect to the instruments on the SPOT satellites. PROBA-V shall fill the gap between SPOT VEGETATION and the Sentinel-3 satellite that will supply operational information on the state of the world's vegetation as well as numerous other products from 2013 onwards.
Figure 1: Vegetation Product (Credit: SPOT-VEGETATION project)
The series of SPOT VGT products to be replicated within the SYN branch of SENTINEL-3 processing (synergy of OLCI and SLSTR) consists of the physical (VGT P), daily synthesis (VGT S1) and 10 day synthesis (VGT S10)
The product names P, S1 and S10 correspond to the standard SPOT VGT product names.
The VGP products (corresponding to VGT-P SPOT products) are adapted for scientific applications requiring highly accurate physical measurements. The data is corrected for systematic errors (error registration of the different channels, calibration of all the detectors along the line-array detectors for each spectral band) and re-sampled to predefined geographic projections. The pixel brightness count is the ground area's apparent reflectance as seen at the top of atmosphere for all spectral bands.
The VG1 and V10 products (respectively VGT-S1 and VGT-S10 SPOT products) are a maximum NDVI value composite of ground reflectance measurements of all segments received during 1 day and 10 days, respectively, for the entire surface of the Earth. These products provide surface reflectance for all spectral bands, the NDVI and ancillary data on image acquisition parameters.
Note that the composite method of VGT-S product will be evaluated and updated in the frame of coming evolutions. It is not specified yet but the "max NDVI" composite method could be replaced by a different one, following the resulting recommendations.