Burst-Mode Wide-Swath SAR Interferometry for Solid Earth Monitoring

Abstract

This work addresses the generation of large area maps of ground deformation originated by dynamic processes of the Earth using spaceborne Synthetic Aperture Radar (SAR) systems. The main focus is put on the development of new interferometric processing techniques for SAR data and on the proposal, design, experimental implementation and demonstration with TerraSAR-X of an acquisition mode with wide-swath capabilities, able to improve the accuracy of the measurements. Geoscientists have traditionally exploited StripMap mode to generate 2-D deformation maps by combining interferometric and correlation techniques. Correlation techniques have been applied in the first contribution to map the Mw9.0 Tohoku-Oki Earthquake occurred in 2011 in Japan by employing TerraSAR-X pairs. The terrain observation by progressive scans (TOPS) mode has been recently implemented as the baseline acquisition mode of the European Sentinel-1 System, providing a swath of 250 km at approximately 20 m resolution. The TOPS mode requires special techniques for the interferometric processing of the data, especially regarding accurate coregistration. The interferometric processing algorithms for handling pairs of Sentinel-1 TOPS data are provided in the second contribution. The coregistration approach exploits the SAR data for the retrieval of the required fine azimuth shifts. Since the performance of the method depends on the coherence, it can become an issue when working with very long time series, as temporal decorrelation dominates. A method for coregistering time series of Sentinel-1 TOPS data exploiting all images of the stack is proposed in the third contribution. In the last contribution, the novel 2-look TOPS mode is proposed which achieves wide swath (employing bursts of data and a steering of the antenna in azimuth, as TOPS) but exploiting spectral diversity techniques, in order to mitigate the poor accuracy on the along-track deformation retrieval. Taking into account that Earth Observation satellites orbit in quasi-polar configurations, a high sensitivity to the ground deformation in the North-South direction can be obtained. A demonstration with experimental TerraSAR-X data for the mapping of slow azimuth displacements with time series covering two years of postseismic deformation over the Hoshab fault, Pakistan, is provided, making evident the high potential of this mode.