THE INTERPRETATION OF SPECTRAL VEGETATION INDEXES

Empirical studies report several plausible correlations between transf orms of spectral reflectance, called vegetation indexes, and parameter s descriptive of vegetation leaf area, biomass and physiological funct ioning. However, most indexes can be generalized to show a derivative of surface reflectance with respect to wavelength. This derivative is a function of the optical properties of leaves and soil particles. In the case of optically dense vegetation, the spectral derivative, and t hus the indexes, can be rigorously shown to be indicative of the abund ance and activity of the absorbers in the leaves. Therefore, the widel y used broad-band red/near-infrared vegetation indexes are a measure o f chlorophyll abundance and energy absorption.