A simple hybrid BRDF model for discontinuous plant canopies

The geometric optical (GO) bidirectional reflectance model, combined with a component spectral signature submodel based on radiative transfer, can be used to estimate the bidirectional reflectance over discontinuous canopies. An analytical approximation of radiative transfer within a homogeneous medium derived from two stream method is adopted. A multiple scale-hotspot function that incorporates shadowing effects for smaller canopy objects like branches, stems and leaves was also well-modeled. Comparison of model results with field measurements (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.