Natural Target Analysis for the Radiometric Calibration of Radar Depth Sounder Data Products

Radar depth sounding of ice sheets provides a unique measurement capability of the ice sheet subsurface. Presently, much of the data are not radiometrically calibrated. Since dedicated calibration measurements of existing datasets are not available, a data dependent method is required. This work develops a system of linear equations linking flight paths via their crossovers with each other, and “naturally” occurring calibration target measurements. This work addresses the challenge of finding and using suitable “naturally” occurring calibration targets and extends our earlier work on crossovers. Specifically, we address this problem for airborne ice sounders and show results for automated detection of smooth water surfaces since the response for a specular water surface is well known and therefore can be used for calibration. We present the specular target detection process, analysis of specular metrics from multiple science missions, comparisons of radar measurements with ideal values, and estimates derived from a regional climate model. This work is incorporated into the Open Polar Radar toolbox; an open community effort to provide common data products and processing methods for all radar depth sounder datasets.