Analysis of ERS Tandem SAR coherence from glaciers, valleys, and fjord ice on Svalbard

Abstract

Interferometric satellite synthetic aperture radar (SAR) data was acquired from an area on Spitsbergen, Svalbard, during the European remote sensing satellite (ERS) Tandem mission in 1995-1996. Analyzing these data sets shows that the estimated SAR coherence is highly dependent on the satellite baseline length, and that corrections for this decorrelation effect is necessary if the baseline is a few hundred meters or more. Meteorological recordings are compared to SAR coherence estimates made at different seasons and surface categories: glaciers in motion, glacial forefields dominated by ice-cored moraines, lakes, rivers, and flat valleys with fine moraine materials like gravel and sand. It was found that temporal decorrelation effects are mainly due to changing surface conditions caused by precipitation and temperature variations around freezing, but that wind redistribution of snow also may play a role. Structures and cracks in the fjord ice as well as boundaries of lakes, rivers, and coastlines can be detected in SAR coherence images because of the contrast between high and low coherence areas. Low coherence is observed from those parts of moving glaciers that experience deformations shear, or zones of relative high velocity. The usefulness of 35-days interferometric SAR (e.g., the foreseen ENVISAT configuration) will be limited, even in sparsely vegetated areas like Svalbard, as compared to the ERS Tandem configuration.