Validation of spectral continuity between PROBA-V and SPOT-VEGETATION global daily datasets

Spectral consistency with SPOT-VEGETATION is an important mission objective for PROBA-V, in particular for its 1 km products. This must allow service providers such as the Copernicus Global Land Service to extend the 16-year long timeseries of SPOTVEGETATION global 1km data with similar PROBA-V products. To evaluate the extent of spectral consistency, an evaluation of spectral response differences is performed by applying the spectral response of PROBA-V and SPOT-VEGETATION 2 to a spectral library of representative global land cover conditions. Datasets for surface reflectance values and Normalized Difference Vegetation Index (NDVI) are thus established for both missions. Through linear regression between the two datasets, spectral correction functions are defined, which can be used to improve the spectral consistency between PROBA-V and SPOT-VEGETATION products. The correspondence between PROBA-V and SPOT-VEGETATION products is then evaluated for the overlapping period when products from both missions were available. The effect of the spectral correction functions is assessed by comparing the correspondence obtained with and without this spectral correction applied. For the NDVI product, an additional offset correction is defined based on a limited sample of the overlapping period. The final spectral correction functions are then evaluated over the full overlapping period between PROBA-V and SPOT-VEGETATION. Discrepancies are observed which indicate a temporal behavior with respect to the correspondence of the mission products. Such temporal behavior can’t be explained by spectral response differences, and therefore other causes are investigated.