Satellite-derived green vegetation fraction for the use in numerical weather prediction models

A simple procedure to derive areal fraction of green vegetation, f(g), from normalized difference vegetation index (ND VT) data was used to produce global monthly f(g) (0.15 degrees)(2)-resolution maps, which are now being incorporated in the National Centers for Environmental Prediction (NCEP) regional and global models. Assuming that the vegetated part of the pixel is covered by dense vegetation (i.e., its leaf area index is high), we calculate f(g)=(NDVI-NDVI0)/(NDVIinfinity-NDVI0), where NDVI0 and NDVIinfinity are specified as the lower and upper 5% of the global NDVI distribution for the whole year and in this study are assumed independent of vegetation/soil type. Preliminary tests indicate that the incorporation of the NDVI-derived green vegetation fraction, instead of the previously prescribed values, leads to improvement in modeling surface fluxes. (C) 1997 COSPAR.