Crossover Analysis for the Radiometric Calibration of Radar Depth Sounder Data Products

Accurate knowledge of the Earth's melting polar regions is required to develop scientific models to understand and predict ice mass loss and sea-level rise. Data from airborne radar depth sounders have been a valuable asset for polar research groups for decades. Due to the lack of absolute radiometric calibration in many of these datasets, data users only have access to relatively calibrated datasets. System and processing variations over time, whether intentional or not, confound radiometric analysis of the data. Radiometric analysis is important, for example, to the mapping of basal characteristics such as the presence of liquid water and bed type. To solve the calibration problem, we present a data-dependent calibration solution that depends on natural targets that have known radar scattering characteristics (smooth lake and sea surfaces) and crossovers (where flight paths image the same target presenting the opportunity to link the calibration from one flight line to another). Our approach generates a system of linear equations which we can use to estimate the unknown calibration coefficients and use the residuals to provide an error analysis. The crossover analysis uncovered issues with the data products which we address in this work. We also present some interesting waveform properties that are dependent on various crossover parameters such as altitude differences and the angle between the crossing flight paths.