A MODIFIED SOIL ADJUSTED VEGETATION INDEX

There is currently a great deal of interest in the quantitative charac terization of temporal and spatial vegetation patterns with remotely s ensed data for the study of earth system science and global change. Sp ectral models and indices are being developed to improve vegetation se nsitivity by accounting for atmosphere and soil effects. The soil-adju sted vegetation index (SAVI) was developed to minimize soil influences on canopy spectra by incorporating a soil adjustment factor L into th e denominator of the normalized difference vegetation index (NDVI) equ ation. For optimal adjustment of the soil effect, however, the L facto r should vary inversely with the amount of vegetation present. A modif ied SAVI (MSAVI) that replaces the constant L in the SAVI equation wit h a variable L function is presented in this article. The L function m ay be derived by induction or by using the product of the NDVI and wei ghted difference vegetation index (WDVI). Results based on ground and aircraft-measured cotton canopies are presented. The MSAVI is shown to increase the dynamic range of the vegetation signal while further min imizing the soil background influences, resulting in greater vegetatio n sensitivity as defined by a ''vegetation signal'' to ''soil noise'' ratio.