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 vegetation 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' orientation on the canopy hotspot through an innovative algorithm to estimate the hotspot function for any arbitrarily oriented foliage element and contributions of all foliage elements to the reflectance by multiple scattering. Thus, it is characterized by more completely considering the integrative influence of spatial variations in optical and structural properties of all foliage elements on canopy reflectance than any previous analytical BRF models. Simulation results from this model demonstrate that canopy hotspot becomes strongest when the mean inclination angle of foliage elements is around 20 degrees , and then it rapidly decreases with an increase in that angle. Comparison with field measured BRF data shows that this model can reproduce the angular asymmetrical distribution of canopy BRF, a feature of natural vegetation's reflectance which all leaf canopy models cannot reproduce.