THE EFFECT OF TOPOGRAPHY ON RADAR SCATTERING FROM VEGETATED AREAS

This paper shows how the radar scattering from vegetated areas is affe cted by the topography of the surface underneath the vegetation. In pa rticular, we show, using a discrete scatterer model, that the dominant scattering mechanism may change drastically when the ground surface i s tilted relative to the horizontal. In the case of a horizontal groun d surface, for example, the total scattering may be dominated by scatt ering off the tree trunks, followed by a reflection off the ground sur face. We show that for a relatively small tilt in the ground surface ( about 2-degrees from horizontal) the ground-trunk interaction term may be replaced by scattering from the branches alone as the dominant sca ttering mechanism. We also show that the effect of the topography is m ore pronounced for scattering by longer wavelengths, and discuss the i mplications on algorithms designed to infer forest woody biomass and s oil and vegetation moisture using polarimetric SAR data. The effect of the topography on the scattering behavior from forested areas is illu strated with images acquired by the NASA/JPL three-frequency polarimet ric SAR over the Black Forest in Germany.