Ambiguous Staggered SAR: Rationale and Advanced Processing Techniques for Clutter Suppression

Conventional synthetic aperture radar (SAR) modes can only map wide swath at the expense of a degraded azimuth resolution, limiting the detection of weak or small targets. In order to overcome this limitation without increasing the system complexity (e.g., using digital beamforming), a novel ambiguous staggered SAR mode is proposed, which utilizes a wide beam for both transmission and reception while continuously varying the pulse repetition interval and waveform and achieves high resolution over ultra-wide swath. However, due to lower receive beam gain and overlapping echoes, the resulting SAR images are affected by noise and range ambiguities from both point and extended targets as well as clutter. Spaceborne experiments using the TerraSAR-X satellite demonstrated the effectiveness of this mode for ship monitoring in open sea and coastal regions, achieving swath widths over 160 km with an azimuth resolution of 2.2 m, an eightfold improvement compared to the TerraSAR-X ScanSAR mode. Postprocessing techniques for ambiguous clutter suppression can enhance ship detection performance. By exploiting waveform diversity, such as up- and down-chirps and different matched filters, range-ambiguous clutter can be mitigated, further improving target detection capabilities.