AN ANALYTIC RADIATIVE-TRANSFER MODEL FOR A COUPLED ATMOSPHERE AND LEAF CANOPY

A new analytical radiative transfer model of a leaf canopy is develope d that approximates multiple-scattering radiance by a four-stream form ulation. The canopy model is coupled to a homogeneous atmospheric mode l as well as a non-Lambertian lower boundary soil surface. The same fo ur-stream formulation is also used for the calculation of multiple sca ttering in the atmosphere. Comparisons of radiance derived from the fo ur-stream model with those calculated by an iterative numerical soluti on of the radiative transfer equation show that the analytic model has a very high accuracy, even with a turbid atmosphere and a very dense canopy in which multiple scattering dominates. Because the coupling of canopy and atmospheric models fully accommodates anisotropic surface reflectance and atmospheric scattering and its effect on directional r adiance, the model is especially useful for application to directional radiance and measurements obtained by remote sensing. Retrieval of bi ophysical parameters using this model is under investigation.