Measurements and modeling of vertical backscatter distribution in forest canopy

Abstract
This paper presents the results of analysis ,and modeling ,of the ,airborne ranging scatterometer HUTSCAT data obtained over an Austrian pine forest in Southern France. The objective is to use high vertical resolution backscatter profiles to validate a model ,which ,is subsequently ,used to determine,the scattering sources within a canopy ,and to understand ,the wave/tree interaction mechanisms. The backscatter coefficients derived from HUTSCAT measurements ,at X band at near ,normal incidence, and polarizations HH, VV, VH are analyzed. The tree crown backscatter separated from the ground ,backscattering shows ,a sensitivity of about ,3 dB between ,0 and ,200 m ,/ha.The estimation of tree height using HUTSCAT profiles gives very good results, with a mean precision of 1 meter. The vertical backscatter profiles are compared ,with the output from the MIT/CESBIO radiative transfer (RT) model coupled with a tree growth architectural model, AMAP, which recreates tree architecture using botanical bases. An a posteriori modification to the RT model is introduced, taking into account the vertical and horizontal variability of the scattering area, in order to estimate