Observed radar backscatter from forested areas with terrain variations

Analyses and quantifies topographic effects on the scattering behavior of forested areas, and to discuss the consequences for forest biomass estimation. In this study P-band polarimetric AIRSAR data is investigated. This for two reasons, namely (a) radar signals at low frequencies penetrate into the forest canopy and therefore are affected by topographic changes, and (b) this frequency has the best sensitivity to forest biomass. The AIRSAR data was collected over the hilly region of the Bonanza Creek Experimental Forest in Alaska. As a first step the synthetic aperture radar (SAR) data are calibrated considering the local topography using a Digital Elevation Model (DEM). The topographic effects on selected calibrated radar backscatter values for several forest stands located at different slopes and having approximately the same incidence angle are analysed and quantified. Results show that even at large incidence angles the backscattering coefficient is still affected by terrain changes. Therefore, if these variations are not considered, forest biomass errors of several tenths of tons/ha occur