Derivation and evaluation of global 1-km fractional vegetation cover data for land modeling

Fractional vegetation cover (sigma(nu)) is needed in the modeling of the la nd-atmosphere exchanges of momentum, energy, water, and trace gases. From g lobal 1-km, 10-day composite Advanced Very High Resolution Radiometer norma lized difference vegetation index (NDVI) data from April 1992 to March 1993 , global 1-km sigma(nu) is derived based on the annual maximum NDVI value f or each pixel in comparison with the NDVI value that corresponds to 100% ve getation cover for each International Geosphere-Biosphere Program land cove r type. This dataset is pixel dependent but season independent, with the se asonal variation of vegetation greenness in a pixel accounted for by the le af area index. The authors' algorithm is found to be insensitive to the use of a specific land cover classification. In comparison with an independent dataset derived by DeFries ct al. by using a more sophisticated statistica l approach, the current dataset has a similar spatial distribution but syst ematically smaller sigma(nu) (particularly over shrublands and barren land cover). It also gives sigma(nu) values that overall are consistent with tho se derived from higher-resolution aircraft and satellite data over Arizona and field-survey data over Germany.