TOPS Imaging with TerraSAR-X: Mode Design and Performance Analysis

Abstract

This paper reports about the performed investigations for the implementation of the wide swath TOPS imaging mode with TerraSAR-X. The TOPS mode overcomes the limitations imposed by the ScanSAR mode by steering the antenna along-track during the acquisition of a burst. In this way, a uniform signal to noise ratio (SNR) is achieved, and consequently, scalloping and an azimuth-dependent distributed target ambiguity ratio (DTAR) are avoided. However, the use of electronically steered antennas leads to a quantization of the steering law and a non-ideal pattern for squinted angles (grating lobes and main lobe reduction). The former provokes spurious peaks, while the latter introduces a slight scalloping and DTAR deterioration. These effects are analyzed and quantified for TerraSAR-X and a TOPS system design approach is presented. Next, the requirements concerning interferometry are investigated. Finally, several results are shown with TerraSAR-X data, including a comparison between the TOPS and ScanSAR modes and the reporting of first TOPS interferometric results.