Incorporation of azimuthal dependence into the LCM2 coupled leaf/canopy reflectance model

Recently, a coupled leaf/canopy radiative transfer model, called LCM2, has been developed with NASA and AFRL (Air Force Research Laboratory) funding to investigate the feasibility of detecting spectral signatures from within and under a vegetation canopy. The model is unique in that it features a direct radiative transfer coupling between the leaf scattering elements and the canopy reflectance. The coupling is through the within-leaf radiative transfer model LEAFMOD. The leaf radiative transfer model characterizes photon scattering within a participating homogeneous leaf taking into account both biochemical composition and leaf thickness. The leaf model is incorporated as the scattering element in a canopy reflectance model (CANMOD) assuming a bi-Lambertian leaf scattering phase function. The primary distinction between conventional and canopy radiative transfer is canopy architecture which is introduced through leaf angle distributions. A Lambertian partially reflecting background is assumed to lie beneath the canopy. The influences of biochemical composition, average leaf thickness, reflecting background and canopy architecture on canopy reflectance can therefore be investigated. The model is extended here to include azimuthal dependence by considering the uncollided and first collided radiances separately. The LCM2 model with the new azimuthal correction will be coupled to an atmospheric radiative transfer code MODTRAN4 to simulate a satellite imager response at orbital altitude.