Modeling the Microwave Emission of Bubbly Ice: Applications to Blue Ice and Superimposed Ice in the Antarctic and Arctic

Abstract

Passive microwave remote sensing is extensively used in polar regions to study the cryosphere. To better understand the measured signal above continental ice-covered areas, our objective is to estimate the microwave emission of bubbly-ice surfaces using a physically based multilayer electromagnetic model, i.e., the dense media radiative transfer—multilayer model (DMRT-ML). This model accounts for ice layers with variable amounts of bubbles. Each layer is fully described by its temperature, density, thickness, and air bubble radius. Simulations are performed using in situ data from two distinct sites: one in Antarctica on a coastal Blue Ice Area near the Cap Prud'Homme (CPH) station in Adelie Land and the other on the Barnes Ice Cap (BIC) located on Baffin Island in the Arctic. On this ice cap, superimposed ice with seasonal snow cover about 1 m thick was observed. In both cases, several ice parameters were measured or estimated, and the others were optimized. Results of the DMRT-ML simulations are compared with in situ surface-based radiometer (SBR) measurements at 11, 19, and 37 GHz at both horizontal and vertical polarizations. Results show that DMRT-ML is able to reproduce the microwave emission of different ice types with good accuracy when accounting for ice bubbles: final $\hbox{RMSE} = 7.37 \hbox{K}$ and 8.42 K, for CPH and BIC, respectively, compared with RMSE ranging from 15 K to 40 K without bubbles. Comparisons between SBR measurements and satellite data for the BIC also show good agreement ( $\hbox{RMSE} = 4.1 \hbox{K}$ for 19 and 37 GHz, both polarizations).