Improvement of Polar Snow Microwave Brightness Temperature Simulations for Dense Wind Slab and Large Grain

The Arctic snowpack, characterized mainly by a dense wind slab (WS) layer overlaying less dense and porous depth hoar (DH), generates large uncertainties in microwave radiative transfer models (RTM) used to interpret satellite observations. In this work, we tested two improvements recently implemented in the snow microwave radiative transfer (SMRT) model. First, an improvement of the snow microstructure parametrizations introduces a polydispersity geometrical parameter (K) related to the grain shape and microstructural arrangement. Second, the new electromagnetic model (EM) based on the strong contrast expansion (SCE) allows a continuous formulation of the scattering coefficient as a function of the density between low-density snow and hard and icy snow. The SCE model was compared with in situ observations to the commonly used improve Born approximation (IBA) EM. Results show improved brightness temperature simulations at 19, 37, and 89 GHz compared to surface-based and satellite microwave radiometric measurements using polydispersity values (<inline-formula> <tex-math notation="LaTeX">$K_{\text {WS}} = 0.80$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$K_{\text {DH}} = 1.33$ </tex-math></inline-formula>) for scaling the measured optical grain size of the different snow layers with IBA. The finding is that the polydispersity values found in this study are of general applicability for Polar-layered snowpack. The SCE model yields results similar to IBA for snow densities up to <inline-formula> <tex-math notation="LaTeX">$500 \; \text {kg}\,\text {m}^{-3}$ </tex-math></inline-formula> but no analysis was investigated for the range of 500–700 kgm3 (firn). These improvements in snow microstructure and the new SCE RTM allow better simulations of Polar snow and therefore better Polar snowpack monitoring by satellite.