Measurements and modeling of vertical backscatter distribution in forest canopy

This paper presents the results of analysis and modeling of the airborne ra nging Helsinki University of Technology Scatterometer (HUTSCAT) data obtain ed over an Austrian pine forest in southern France, The objective is to use high vertical resolution backscatter profiles to validate a model that is subsequently used to determine the scattering sources within a canopy and t o understand the wave/tree interaction mechanisms, The backscatter coefficients derived from HUTSCAT measurements at X-band at near-normal incidence and polarizations HH, VV, and VH are analyzed, The t ree crown backscatter separated from the ground backscattering shows a sens itivity of about 3 dB between 0 and 200 m(3)/ha.The estimation of tree heig ht using HUTSCAT profiles gives very good results, with a mean precision of 1 m, The vertical backscatter profiles are compared with the output from the MIT /CESBIO radiative transfer (RT) model coupled with a tree growth architectu ral model, AMAP, which recreates tree architecture using botanical bases. A n a posteriori modification to the RT model is introduced, taking into acco unt the vertical and horizontal variability of the scattering area in order to correctly estimate the backscatter attenuation. The results show good a greement between both simulated and HUTSCAT-derived vertical backscatter di stribution within the canopy The penetration depth at near normal incidence is studied, Both simulated a nd experimental penetration depth are compared and appear to be of several meters, varying with the stand's age.