Improvement of the DART model for simulating radiative transfer in heterogeneous 3-D vegetation

The DART model simulates radiative transfer in 3D canopies (leaves, grass, soil, water, trunks) using the discrete ordinate approach. It predicts bi-directional reflectance distribution functions (BRDF), 3D radiation regime for further determination of 3D photosynthesis rates and primary production, for any Sun and atmospheric (possibly anisotropic) configuration. Recent improvements are presented. Radiation terms associated with leaf volume and polarization mechanisms are now distinguished. Moreover three accelerating techniques are introduced: (1) Seidel method; i.e. simulation of scattering with radiation already scattered at the iteration stage, (2) decrease of the spherical harmonics expansion order with iteration orders, and (3) convergence with an exponential extrapolation. Comparison of simulations with remotely acquired spectral images of a forest cover stressed the usefulness of the DART model for conducting studies with remotely acquired information.