Use of Double Channel Differences for Reducing the Surface Emissivity Dependence of Microwave Atmospheric Temperature and Humidity Retrievals

摘要

Surface emissivity has a significant impact on atmospheric parameter retrievals from microwave sounding instruments. To reduce the dependence of retrievals on surface emissivity, a double channel differences equation is deduced, and a corresponding retrieval scheme is constructed. Retrieval experiments are performed using Advanced Microwave Sounding Unit‐A (AMSU‐A) and Microwave Humidity Sounder (MHS) simulations and global measurements. Simulation experiments show that the double channel differences scheme can reduce the root mean square errors (RMSE) of the temperature and humidity profiles in the middle and lower atmosphere. Retrieval experiments based on AMSU‐A and MHS global measurements show that the proposed scheme can significantly reduce the RMSE of temperature profiles in the lower atmosphere and humidity profiles in the middle and lower atmosphere for cloudy and cloudless conditions, different surface types, and different scan angles, with maximum reduction values of 0.64?K and 9.03%, respectively. Regarding RMSE improvement, that of the cloudy condition is greater than that of the cloudless condition, that of the land is greater than that of the coast and the sea, and there is no significant dependence on the scan angles. The double channel differences scheme is very sensitive to initial near‐surface temperatures. Reducing the initial near‐surface temperature error can significantly improve the temperature retrieval accuracy below 900?hPa, with maximum reduction value of 3.25?K. Plain language summary Microwave sounding instruments such as AMSU‐A/MHS provide an unique ability to acquire global atmospheric temperature and humidity profiles. However, at present, their ability to acquire temperature and humidity information in the lower atmosphere has not been fully exploited, mainly due to the impact of surface emissivity. Therefore, reducing the impact of surface emissivity is a key issue. In this paper, a temperature and humidity profiles retrieval scheme is constructed by using the relationship between the surface emissivity of adjacent channels. The research shows that the scheme can significantly improve temperature and humidity retrieval accuracy for cloudy and cloudless conditions, different surfaces types, different scan angles. Reducing initial values error in the scheme can further improve retrieval accuracy.