An explicit canopy BRDF model and inversion

Abstract

Based on a rigorous canopy radiative transfer equation, the multiple scattering radiance is approximated by the asymptotic theory, and the single scattering radiance calculation, which requires an numerical integration due to considering the hotspot effect, is also simplified. A new formulation is presented to obtain more exact angular dependence of the sky radiance distribution. The unscattered solar radiance and single scattering radiance are calculated exactly, and the multiple scattering is approximated by the delta Two-Stream atmospheric radiative transfer model. The numerical algorithms prove that the paxametric canopy model is very accurate, especially when the viewing angles are smaller than 55°. Powell algorithm is then used to retrieve biospheric parameters from the ground measured multiangle observations.