Microwave scattering in the Antarctic megadunes region: reconciling radar and radiometry

Icy surfaces across the solar system display unusual microwave radar and radiometry properties, including very high backscattering cross-sections and polarization ratios. At low temperature, snow and ice are very transparent to microwaves, leading to long path lengths and multiple scattering. Yet despite the large volume of available passive and active microwave satellite observations over the Earth cryosphere, physical interpretation of the co-variability of the multi-frequency observations is still challenging, especially when trying to reconcile radiometry and radar observations. To shed light on microwave scattering in icy regoliths, we focus on the Antarctic megadunes region, the coldest and driest area on Earth, which we propose as a new analog for icy satellites due to its very low precipitation (net zero snow accumulation) and temperature (averaging -50°C), combined with the highest microwave backscatter in Antarctica. We assemble a dataset consisting of 5.2 GHz ASCAT and 13.4 GHz QuikSCAT and OSCAT scatterometry, as well as AMSR2 radiometry at 6.9 to 89 GHz. Using the Snow Microwave Radiative Transfer (SMRT) model with a simplified snowpack with constant temperature and continuously increasing grain size and density with depth, we simulate simultaneously radar and radiometry. For the first time, we show that scatterometry and 6.9 to 37 GHz radiometry at V polarization can be successfully simulated with a unique simple snowpack model, indicating that incoherent volume scattering on subsurface heterogeneities dominates both the active and passive signal. The success of our approach encourages further work to analyze and simulate jointly active and passive microwave observations, both in the Earth cryosphere and on icy moons.