Relating co-polarization phase difference at L-band over land ice to the structure of snow and firn layers

Spaceborne synthetic aperture radars (SARs) represent a powerful tool to perform cryospheric observations due to their high spatial resolution and capability to acquire data during the winter time. Especially at lower frequencies, SAR signals penetrate beneath the glaciers surface through the shallow snow cover, interacting with surface as well as sub-surface features. This makes the scattering scenario very complex and the interpretation of SAR backscattering from glaciers and ice sheets not straightforward. In the case of polarimetric SARs (PolSAR), the understanding of polarization phase differences represent one of the main open issues. In this paper, a physical model is employed to relate co-polarization HH-VV phase difference (co-pol phase) to structural and dielectric properties of snow and firn which characterize the first meters of glaciers subsurface. Modelled co-pol phase values are compared to values measured in experimental airborne L-band (1.3 GHz) SAR data, acquired over the Austfonna ice-cap, in Svalbard, in spring 2005 and 2007. A set of ground measurements is also exploited to properly set up the model and to validate the results. Finally, an interpretation of co-pol phase temporal variations over the period 2005-2007 is attempted based on the proposed model.