Applications of the 4-scale radiative-transfer model in the remote sensing of boreal forests

Remote sensing of forested regions depends greatly on the Sun and view geometries under which images are taken. A forest canopy radiative-transfer model based on detailed tree architecture named "4-scale" has been used in recent years to study the influence of boreal forest properties such as leaf area index (LAI), crown size, branches architecture, tree grouping, etc, on the bidirectional reflectance of different canopies. This paper presents updated results using the latest version of the model that contains a new multiple-scattering scheme that depends on the crown architecture as well as the spatial distribution of the trees. New simulations of ground-based PARABOLA and airborne POLDER reflectances in the red and near-infrared bands are shown, and the mechanisms controlling NDVI directionality are discussed The use of 4-Scale for directional corrections of airborne CASI data will also be shown. These results have implications on inversion techniques based on the shadow and sunlit proportions for the retrieval of LAI.