Thermal Denoising of Cross-Polarized Sentinel-1 Data in Interferometric and Extra Wide Swath Modes

Abstract

An updated algorithm for the removal of thermal noise in Sentinel-1 synthetic aperture radar (SAR) level-1 ground range detected (GRD) data in cross-polarization is presented. The algorithm is comprised of two steps: correction of the annotated thermal noise magnitude (previously proposed in Park et al., 2018) and a novel correction of the annotated thermal noise range dependence. The magnitude of the annotated thermal noise is corrected by applying scale and offset coefficients tuned on a few hundred of Sentinel-1 data acquired over surfaces with low backscatter in interferometric wide and extra-wide swath modes in HV and VH polarizations. The values of coefficients for all modes and polarizations for data processing with the Instrument Processing Facility (IPF) version 3.1-3.3 are provided. The range dependence is corrected by minimizing a cost function between the annotated range profiles of thermal noise and antenna pattern gain (APG). An objective validation metric based on a comparison of averaged backscatter at interswath boundaries is proposed. Validation is performed on hundreds of Sentinel-1 scenes acquired over the open ocean, doldrums, deserts, and sea ice. It shows that the new algorithm outperforms the standard thermal noise removal algorithm proposed by European Space Agency in almost all cases. Analysis shows that the new algorithm worsens noise correction in cases when the range dependence of the annotated APG does not match with the observed signal, indicating either problems with signal processing on IPF or imprecise annotation of APG.