SAR Signal Penetration Estimation over Ice Sheets and Glaciers Using Multiple Squints and Incoherent Shift Measurements

Abstract:
SAR interferometric elevation measurements of dry snow, firn, and ice are known to be substantially biased downward due to a penetration of the radar signals into the medium. The so-called penetration bias is commonly the main error source in surface elevation measurements over ice sheets. We propose a strategy to estimate the penetration of SAR signals for SAR mission scenarios in which two or more simultaneous or quasi-simultaneous SAR images with different squint angles are acquired, such as for ESA’s Harmony mission or the Co-Flier concepts from NASA JPL. The information is inherent in the processed SAR data as phase errors on the azimuth signals resulting from uncompensated non-linear propagation of the radar echoes through the glacial volume. The propagation effects result in almost linear phase errors for squinted acquisitions and hence in a shift of the imaged scene in azimuth direction. By measuring the shift between SAR images acquired with different squint angles, the penetration can potentially be inverted. We evaluate the potential of the approach using simulated SAR acquisitions for the Harmony mission based on real Sentinel-1 imagery.