Toward a robust retrieval of snow accumulation over the Antarctic ice sheet using satellite radar

Abstract

The sensitivity of radar measurements to snow accumulation rate is determined by the firn volume characteristics of the ice sheets. Here we present a new approach for calculating the volume backscattering of dry firn, which is combined with recently developed empirical parameterizations of firn grain size and density as functions of depth, surface temperature, and accumulation rate. To this end, dense medium radiative transfer theory is applied to calculate the volume scattering and absorption coefficients. The coefficients for the density transition between snow and dense firn are evaluated using polynomial interpolation. For testing the method, we used measured accumulation rates, Envisat ASAR C‐band wide‐swath mode images, and QuikSCAT Ku‐band backscattering data from Dronning Maud Land, Antarctica. The comparison between measured and simulated backscattering coefficients shows that no tuning parameter is necessary to obtain the correct absolute level of scattering intensity. The robustness of accumulation rate retrievals depends on the consideration of technical and environmental factors. Due to the presence of sastrugi on the ice sheet surface the measured intensities are sensitive to the radar look direction. Wind compaction of snow and depth hoar formation change the depth‐dependent snow density and grain size profiles. Theoretical simulations revealed that the backscattering coefficient at C‐band is more sensitive to changes of accumulation rates than at Ku‐band. Penetration depths can vary significantly, dependent on radar frequency and firn characteristics. This has to be taken into account when comparing accumulation rates from different locations.