Sensor view angle and solar zenith angle effects on grassland canopy spectra

The experiment was conducted at the Kendall Site of the Walnut Gulch Experiment Watershed in southeastern Arizona during the 1990 growing season. A special apparatus for mounting a spectroradiometer and acquiring bidirectional reflectance data was constructed and used over a semi-desert grassland plot. For purposes of analyzing multidirectional vegetation spectral behavior, the Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) were calculated as a function of view angle and solar zenith angle throughout the growing season. The results have shown that the SAVI considerably minimized anisotropic behavior whereas the NDVI was very sensitive to both solar zenith and view angles. With further refinement the SAVI offers a technique whereby satellite measurements of vegetation activity could be further understood.