A STUDY OF REFLECTANCE ANISOTROPY AND CANOPY STRUCTURE USING A SIMPLEEMPIRICAL-MODEL

The coefficients of a simple three-term model describing the bidirecti onal reflectance of vegetation canopies as a function of leaf area ind ex (LAI) were examined for potential information retrievable from bidi rectional reflectance measurements. Simulations of principal plane spe ctral reflectances (0.5-0.6 mu m, 0.06-0.7 mu, 0.7-0.8 mu m, and 0.8-1 .1 mu m), for vegetated canopies with LAI values ranging from 0.1 to 5 .0 under solar zenith angles of 20, 30, and 45 degrees, were generated with the use of a one-dimensional radiative transfer model. The simul ated reflectances were then fit with a simple model by using a least s quares procedure. Plots of the resulting coefficients with LAI showed that the degree of curvature of the simulated principal plane reflecta nces, as represented by one of the coefficients, and the coefficient e xpressing interaction of view zenith angle and view azimuth angle were both related to LAI. This relation holds in all four spectral bands, including the 0.7-0.8 mu m band, despite a lack of relation between th e constant coefficient (which is closely related to the nadir value) a nd LAI. Examination of the coefficients relating to solar zenith angle revealed a dependence on LAI. The coefficient for view zenith angle, or a related quantity, is suggested as a candidate for a bidirectional index that may be useful within the context of satellite-based vegeta tion classification and characterization schemes. Published by Elsevie r Science Inc.