The unified model of BRDF for the vegetation canopy

Abstract

The canopy bidirectional reflectance function (BRDF) characterizes the radiometric interface among vegetation, solar and the sensor, a stable, accurate and operational canopy BRDF model is the basis of retrieving canopy structure and biophysical parameters such as leaf area index and albedo by remote sensing method. The canopy reflectance can be divided into single scattering reflectance and multiple scattering reflectance. After the bidirectional gap fraction was derived by Poisson distribution, a new single scattering reflectance model was developed with Geometrical Optic model at leaf scale. The continuous canopy and discrete vegetation were unified by clumping index. So the area ratio of four components (sunlit crown, sunlit background, shadow crown and sunlit background) is parameterized. In order to simplify the expression of multiple scattering, a recollision probability based scattering model was used instead of the Radiative Transfer model. The validation using ground measurements has proved the reliability of the model.