Microwave brightness temperature as an indicator of near-surface air temperature over snow in Canadian northern regions

During the past 50 years, winter temperatures have risen more rapidly than in summer in northern high latitudes. However, there are relatively few meteorological stations in these areas, and a better characterization of this trend is needed. This article investigates whether satellite microwave brightness temperature can be used as an indicator of near-surface air temperature over snow. The Helsinki University of Technology (HUT) snow emission model is used to generate a dry snow emissivity relationship between 19 and 37 GHz under the assumption that the air–snow interface temperatures and air temperatures (T_air ) are similar. This relationship allows the development of a near-surface air temperature retrieval model. A second empirical linear correction is also applied to reduce the residual observed bias. The comparison between retrieved near-surface air temperature and in situ air temperature for the Canadian northern regions shows a significant correlation (R ² of 0.76) but with a root mean square error (RMSE) of 4.94°C. Results also show that the satellite-derived temperatures can be compared to the thermal infrared skin temperature (RMSE of 5.9°C). The proposed approach gives better results than the direct correlation between brightness temperature (T _b) and in situ air temperature (RMSE reduced by 50%).