Interferometric Processing of Sentinel-1 TOPS Data

Abstract

Sentinel-1 (S-1) has an unparalleled mapping capacity. In Interferometric Wide Swath (IW) mode, three subswaths imaged in the novel Terrain Observation by Progressive Scans (TOPS) SAR mode result in a total swath width of 250 km. Sentinel-1 has become the European workhorse for large area mapping and interferometric monitoring at medium resolution. The interferometric processing of TOPS data requires however special consideration of the signal properties, resulting from the ScanSAR-type burst imaging and the antenna beam steering in azimuth. The high Doppler rate in azimuth sets very stringent coregistration requirements, making the use of Enhanced Spectral Diversity (ESD) necessary to obtain the required fine azimuth coregistration accuracy. Other unique aspects of processing IW data, such as azimuth spectral filtering, image resampling and data deramping and reramping, are reviewed giving a recipe-like description that enables the user community to use Sentinel-1 IW mode repeat-pass SAR data. Interferometric results from Sentinel-1A are provided, demonstrating the mapping capacity of the S-1 system and its interferometric suitability for geophysical applications. An interferometric evaluation of a coherent interferometric pair over Salar de Uyuni, Bolivia is provided, where several aspects related to coregistration, deramping and synchronization are analysed. Additionally, a spatial and temporal evaluation of the along-track shifts, which are directly related to the orbital/instrument timing error, measured from the SAR data is shown that justifies the necessity to refine the azimuth shifts with ESD. The spatial evaluation indicates high stability of the azimuth shifts for several slices of a datatake.