An analytical hybrid GORT model for bidirectional reflectance over discontinuous plant canopies

Abstract—The geometric optical (GO) bidirectional reflectance model, combined with a new component spectral signature sub-model, can be used to estimate the bidirectional reflectance distribution function (BRDF) of discontinuous canopies. This approach retains the GO approach of incorporating the ef-fect of shadows cast by crowns on the background. The newly developed submodel uses an analytical approximation of the radiative transfer (RT) within the plant canopies to model the spectral properties of each scene component. A multiple scale-hotspot function that incorporates effects for smaller canopy objects like branches, stems and leaves was also well modeled. Comparison of model results with field measurements (ASAS, POLDER and PARABOLA) over an old black spruce forest in central Canada demonstrated that the model can predict the basic features of the BRDF, i.e., bowl shape and the hotspot. The benefits of the model presented are simplicity, improved treatment of multiple scattering and a new method of estimating the component signatures. Index Terms—Analytical GORT-BRDF model, discontinuous plant canopies