THE EFFECT OF TOPOGRAPHY ON RADAR SCATTERING FROM VEGETATED AREAS

This paper shows how the radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation. In particular, we show, using a discrete scatterer model, that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal. In the case of a horizontal ground surface, for example, the total scattering may be dominated by scattering off the tree trunks, followed by a reflection off the ground surface. 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 scattering mechanism. We also show that the effect of the topography is more pronounced for scattering by longer wavelengths, and discuss the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric SAR data. The effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the NASA/JPL three-frequency polarimetric SAR over the Black Forest in Germany.