A modelling study of BRDF canopy and radiation regime for Boreal forests

This paper presents a new radiative transfer modelling approach, for retrieving information on forest structural characteristics and photosynthetic activity, both directly through an accurate computation of 3-D Photosynthetically Active Radiation (PAR) regime, and indirectly with the simulation of remote sensing measurements. DART model was used for investigating spectral behavior and PAR environment of boreal forest in Canada. Main features of BRDF (Bidirectional Reflectance Factor Distribution) anisotropy are clearly verified. Comparison between simulated and measured (PARABOLA, CASI, POLDER) BRDFs stresses the potential of DART, but also the importance and difficulty to use accurate field data. Differences in forest architectures induce distinct PAR transmission and 3-D absorbed PAR (APAR), and their influence on canopy photosynthesis is illustrated with the coupling of the DART model with a leaf model.