Snow thickness retrieval from L-band brightness temperatures: a model comparison

The Soil Moisture and Ocean Salinity (SMOS) satellite's L-band (1.4 GHz) measurements have been used to retrieve snow thickness over thick sea ice in a previous study. Here we consider brightness temperature simulations for 2.5-4.5 m thick Arctic multi-year ice and compare the results of the relatively simple emission model (M2013) used previously for the retrieval with simulations from a more complex model (T2011) that combines a sea-ice version of the Microwave Emission Model for Layered Snowpacks (MEMLS) with a thermodynamic model. We find that L-band brightness temperature is mainly determined by ice temperature. In the M2013 model, ice temperature in turn is mainly determined by surface temperature and snow thickness, and this dependence has been used previously to explain the potential for a snow thickness retrieval. Our comparisons suggest that the M2013 retrieval model may benefit from a more sophisticated thermodynamic calculation of the ice temperature or from using independent temperature data (e.g. from 6 GHz channels). In both models, horizontally polarized brightness temperatures increase with snow thickness while holding surface temperature, ice thickness and snow density near constant. The increase in the T2011 model is steeper than in M2013, suggesting a higher sensitivity to snow thickness than found earlier.