A Signal Model for PRF Dithering in Wide-Swath, Fine-Resolution InSAR

Abstract

Wide-swath radar imaging requires that the time interval to collect each radar pulse echo is large and can often exceed the interpulse period. As it is difficult to both transmit and receive from the same antenna simultaneously, there will be “blind ranges” when the receive and transmit times overlap. This leads to gaps in the radar echo and thus degradation of system performance. Today, most wide-swath systems address this by segmenting the swath in range, such as in the ScanSAR or Terrain Observation with Progressive Scan (TOPS) mode operation, so that each subswath is within the range ambiguity limit. Some groups have started experimenting with the variations in the sweepSAR technology, in which the receive antenna tracks the radar echo across the swath, realizing a complete wide-swath range scan but leading to the echo gaps. Here, we look at minimizing the effect of blind ranges by varying the radar pulse-repetition frequency (PRF) and interpolating across the gaps to preserve azimuth signal continuity. If the pulse times are selected properly, the main effect is to raise the noise floor of the echoes. Geocoded magnitude images, interferograms and correlation images, and deformation time series show strong robustness with respect to dithering, demonstrating that choosing essentially random PRFs allows for accurate generation of SAR and Interferometric Synthetic Aperture Radar (InSAR) data products while retaining wide-swath, fine-resolution coverage.