The influence of leaf orientation and the specular component of leaf reflectance on the canopy bidirectional reflectance

Abstract

To calculate the plant canopy bidirectional reflectance distribution function (BDRF), the Monte Carlo method is used. The Ross - Marshak canopy model (Ross and Marshak, 1985; 1987a, b; 1988) is generalized to the case of the arbitrary leaf angle distribution (LAD). The contribution of the specular component of leaf reflectance given by the Fresnel law, resulting from the presence of the wax layer of a leaf, is taken into account. The influence of the LAD on the BRDF is estimated in the principal plane. The differences of the BRDF are shown between the canopies with equal first moments of the LAD and unequal second ones. The mathematical technique of the Monte Carlo method which allows estimation of the contribution of the specular component of the BRDF is derived. With the help of this technique a series of numerical experiments, showing the influence of the LAD on the contribution of the specular component of leaf reflectance, has been carried out. These results can be used for the interpretation of the remote sensing data of vegetation and for the inversion of canopy reflectance models, for estimating the LAD, and the size of the leaf wax layer.