Seasonal variations of the backscattering coefficient measured by radar altimeters over the Antarctica Ice Sheet

Abstract

Abstract. Spaceborne radar altimeter is a valuable tool for observing the Antarctica Ice Sheet. The radar wave penetration into the snow provides information both on the surface and the subsurface of the snowpack due to its dependence on the snow properties. However this penetration also induces a negative bias on the estimated surface elevation. Empirical corrections of this space and time-varying bias are usually based on the backscattering coefficient variability. We investigate the spatial and seasonal variations of the backscattering coefficient at the S (3.2 GHz), Ku (13.6 GHz) and Ka (37 GHz) bands. We identified two clearly marked zones over the continent, one with the maximum of Ku band backscattering coefficient in the winter and another with the maximum in the summer. To explain this, we performed a sensitivity study of the backscattering coefficient at the S, Ku and Ka bands to surface snow density, snow temperature and snow grain size using an electromagnetic model. The results show that the seasonal cycle of the backscattering coefficient at the Ka band, is dominated by the volume echo and is mainly explained by snow temperature. In contrast, the cycle is dominated by the surface echo at the S band. At Ku band, which intermediate in terms of wavelength between S and Ka bands, the seasonal cycle is in the first zone dominated by the volume echo and by the surface echo in the second one. Such seasonal and spatial variations of the backscattering coefficient at different radar frequencies should be taken into account the for more precise estimation of the surface elevation changes.