Unraveling the Impacts of Hyperspectral Microwave and Terahertz Sounding Channels on Temperature and Humidity Profile Retrieval

Abstract: The observations from satellite microwave sounding instruments have been proven to significantly impact severe weather monitoring and numerical weather prediction. Recent research indicates that the maturation of digitally channelized technology enables hyperspectral microwave sounding. However, the specific effects of these hyperspectral channels on the retrieval of temperature and humidity profiles remain uncertain. In this study, a novel Microwave to Terahertz Sounder (MTS) is explored. Specifically, the impacts of 50 - 60 GHz (V band) hyperspectral channels and 380 - 420 GHz (Y1 and Y2 band) terahertz channels on one - dimensional variational retrieval (1DVAR) results are investigated through various channel configurations. Initially, the information entropy of the channels is evaluated. When compared to the currently orbiting microwave sounders, the use of V - band hyperspectral channels can reduce the root - mean - square error (RMSE) of the retrieved temperature near the tropopause by approximately 14%. The inclusion of Y1 and Y2 band channels also positively contributes to the retrieved profiles. Compared to the currently deployed microwave sounders, this leads to a 2% reduction in temperature RMSE and a 5% reduction in humidity RMSE. The optimal channel configuration based on information entropy results in a temperature RMSE reduction of around 5.6% and a humidity RMSE reduction of 4.1%. Furthermore, the influence of observation noises on the retrieval results is examined. It is discovered that halving the noise can decrease the temperature RMSE by 13% and the humidity RMSE by 6%. Overall, the new sounding channels offer greater potential for enhancing temperature and humidity sounding, and they may potentially improve atmospheric measurements and the utilization of microwave observations in numerical weather prediction. Key Words: Satellite hyperspectral microwave sounding, terahertz channels, one - dimensional variational retrieval, atmospheric measurements