Ambiguous Synthetic Aperture Radar Modes for Wide Swath Ship Monitoring and Digital Elevation Model Generation in a Single Pass

One relevant application of synthetic aperture radar (SAR) is ship monitoring. Conventional SAR modes, however, are limited in their ability to detect small ships over wide swaths (> 100 km) due to their low azimuth resolution. A novel SAR mode is presented in which the pulse repetition interval (PRI) is continuously varied and is much smaller than the minimum PRI imposed by the swath width, producing images that are corrupted by strong range ambiguities. For the same observed swath, this mode has significantly better detection performance than ScanSAR due to higher azimuth resolution and ambiguity blurring effect due to the PRI variation. Waveform alternation can be moreover explored to further blur ambiguities and increase the mapped swath. Spaceborne demonstrations using experimental TerraSAR-X acquisitions are presented. The idea of SAR systems affected by SAR ambiguities is then extended to the case of a cluster of small satellites, whose acquired data are jointly processed to create an accurate, high-resolution digital elevation model (DEM) of the observed scene in a single pass. This technique is demonstrated through a dedicated multi-baseline airborne campaign, carried out using DLR’s F-SAR airborne sensor.