AN ANALYTICAL MODEL FOR BIDIRECTIONAL REFLECTANCE FACTOR OF MULTICOMPONENT VEGETATION CANOPIES

Based on radiative transfer theory in vegetation and geometric-optical principles, an analytical physical model for calculating multiangular , multispectral reflectance over a non-random, multiple component vege tation canopy is developed. This model is derived by taking advantages of the previous leaf canopy and multicomponent canopy BRF models. It quantitatively accounts for both the impact of foliage elements' orien tation on the canopy hotspot through an innovative algorithm to estima te the hotspot function for any arbitrarily oriented foliage element a nd contributions of all foliage elements to the reflectance by multipl e scattering. Thus, it is characterized by more completely considering the integrative influence of spatial variations in optical and struct ural properties of all foliage elements on canopy reflectance than any previous analytical BRF models. Simulation results from this model de monstrate that canopy hotspot becomes strongest when the mean inclinat ion angle of foliage elements is around 20 degrees, and then it rapidl y decreases with an increase in that angle. Comparison with field meas ured BRF data shows that this model can reproduce the angular asymmetr ical distribution of canopy BRF, a feature of natural vegetation's ref lectance which all leaf canopy models cannot reproduce.