Assessment of Image Quality of Waveform-Encoded Synthetic Aperture Radar Using Real Data

Kurzfassung

Synthetic aperture radar (SAR) remote sensing is very attractive for the systematic observation of dynamic processes on the Earth’s surface since it allows high resolution imaging independently of weather conditions and sunlight illumination. Nevertheless, many limitations due to the SAR geometry, such as nadir returns and range ambiguities, typically constrain the PRF selection while designing conventional SAR systems, thus limiting both their swath width and their ambiguity performance. In this context, waveform-encoded SAR is a novel SAR concept based on pulse-to-pulse variation of the transmitted waveform that allows focusing the nadir echo and the range ambiguities and suppressing them through a multi-focus post-processing. However, the assessment of the ambiguity suppression performance for such a system is not trivial, as the processing involves a non-linear thresholding and blanking approach. This work proposes a novel methodology, which exploits real TerraSAR-X data to accurately simulate the effect of the range ambiguity on the useful signal and allows for a quantitative assessment of the image quality of a waveform-encoded SAR. The method considers different waveform variation schemes on transmit, i.e. cyclically-shifted and up- and down- chirps, as well as a multi-focus post-processing for suppressing range ambiguities. Specifically, a contrast-minimization technique for threshold selection is investigated, as well as the best achievable performance, i.e. optimal threshold. The results of this work further highlight the potentialities of the waveform-encoded SAR concept and also allow accounting for its ambiguity suppression capability in the design of novel SAR systems, as an increased system design flexibility can be achieved at the reasonable cost of employing different waveforms on transmit.