Tree Shape Description for Backscattering Modelling of Lai
نویسنده
چکیده
Several radiative techniques have been developed for inverse estimation of the leaf area indes (LAI) using optical data measured below the canopy (e.g. hemispherical photography) or above the canopy (remote sensing). In the inversion, a model of the three-dimensional distribution of leaves in the canopy is used to define the required relation between LAI and canopy transmittance and reflectance. However, due to limited information (data), rather simplified models (e.g. uniform leaf area distribution) have commonly been used, which has lead to erroneous estimates of LAI especially in structurally heterogeneous forests. The 3D distribution of leaf area in a forest stand is formed by the spatial distribution of trees, and the amount and distribution of leaf area within individual trees. For a realistic description of forest canopy structure, therefore, we need information (submodels) of the LAI and crown size and shape, at the tree level. The leaf area index of a tree is related with the size and shape of the tree, but the relationship is rather complicated. On the other hand the backscattering of a tree is also related to its shape. Since ENVISAT has the dual polarization capability, it is of interest to search for a relationship between the backscattering properties of a forest and the LAI values. This research is carried out in the ENVISAT AO-project ENVISAT in boreal forest mapping and LAI estimation (=ENBOR FORMAL). The first results of the three years long project concern the tree shape characterisation.
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