TerraSAR-X Antenna Pattern Estimation by a Complex Treatment of Rainforest Measurements

Abstract

Abstract—In this paper an elaborated development over the usual way of estimating a SAR antenna pattern with measurements over the rain forest is presented. The current standard procedure is to fit these data to a polynomial curve or sometimes to a power-cosine law. This antenna model is not a physical one but a convenient mathematical simplification to eliminate noise. This work’s contribution is the implementation of a physically meaningful model, i.e. a superposition of far-field wave fronts from each of the array elements, together with the Singular Value Decomposition (SVD) technique. In addition to eliminate noise, this method allows us to obtain an estimate of the in-flight corrected excitation laws of the antenna array. The motivation of the study is the characterisation of the German TerraSAR-X satellite antenna, a phased array consisting of 384 subarrays, each of which contains two slotted waveguides, one for horizontal and one for vertical polarisation. The utility of the technique is tested on data acquired by the ASAR instrument onboard the ESA ENVISAT satellite, more specifically from both image (IMP) and wide swath mode (WSM) products.