Characterization of the Amazon Rainforest Backscatter for X-Band SAR Calibration Using TanDEM-X Data

Abstract

The radiometric calibration of spaceborne SAR products plays a key role for ensuring a good performance of the whole end-to-end system and requires a precise knowledge of both the radar system and the illuminated target. The shape of the antenna pattern in elevation can be directly estimated by analyzing SAR detected images in presence of a flat backscatter profile in the slant range dimension. This is typically accomplished by acquiring SAR data over homogeneous distributed targets, under the assumption of isotropic scattering. This is the case of tropical rainforests, such as the Amazon and Congo forests, which have been established by the SAR community as well-known test sites for SAR calibration, thanks to their homogeneous and almost isotropic signature. Nevertheless, several studies using X- and C-band sensors have shown a slight dependency of the rainforest backscatter on the incidence angle, as well as on ground target properties and meteorological conditions. The aim of this work is to present a statistical characterization of radar backscatter at X-band over the Amazon rainforest using TanDEM-X data, and to provide insights on how to best utilize radar backscatter data in this region for SAR calibration and modeling purposes.