The aim of VGT continuity processing is to produce data from OLCI and SLSTR that replicates the SPOT-VGT P and S data for continuity of supply to the existing SPOT-VGT user community.
With respect to SPOT VGT, OLCI and SLSTR have an increased spectral and spatial resolution and a greater number of spectral bands. The success of VGT continuity products will essentially rely on the similarity to the SPOT VGT baseline products. A seamless transition is needed for a consistent time series, which is the main issue for this type of data.
An intermediate VGT Level-2 data structure is derived, which contains synthesized VGT TOA reflectance. Pixel flags and surface reflectance are calculated and added. This product, called VGK, will be used as input to generate the VGT S1/S10 products. To handle selection of the appropriate pixel for the VGT-S product, a final step computing the Normalised Difference Vegetation Index (NDVI), has been added at the end of the VGT continuity algorithm.