NDVI overstates vegetation cover over bare and sparsely vegetated soil.
As the vegetation cover over Sahel (and Sahara) is low the
NDVI values needed to be adjusted before comparison with rainfall.
In this study a linear NDVI correction process (*NDVI) was used:
*NDVI = (NDVI-NDVIo)/(NDVIs-NDVIo)
NDVIs is the value of NDVI at 100 % vegetation
cover and NDVIo is the value for bare soil.
The small figure shows both raw and adjusted NDVI in a S to N
transect across the map (left).
