Water Vapor Retrieval Over Cloud Cover Area on Land Using AMSR-E and MODIS

This study mainly discusses atmospheric water vapor retrieval over cloud cover area on land with the help of a newly developed surface emissivity parameter estimation method in microwave bands. In the retrieval method, the atmospheric water vapor sensitivity parameter-ratio of brightness temperature polarization difference at frequencies 18.7 and 23.8 GHz (ΔTb_1.87/ΔTb_23.8)-is used to retrieve water vapor, and the surface emissivity parameter-ratio of surface emissivity polarization difference at frequencies 18.7 and 23.8 GHz (Δε_18.7/Δε_23.8) that corresponds to ΔTb_18.7/ΔTb_23.8 is a key parameter that affects the final precision of retrieved atmosphere water vapor. In order to estimate Δε_18.7/Δε_23.8 in cloudy condition, we first estimated the value of Δε_18.7/Δε_23.8 in clear condition using Advanced Microwave Scanning Radiometer for EOS (AMSR-E) brightness temperature and related MODIS atmospheric products. At the same time, it was found that gradient information derived separately from ΔTb_18.7/ΔTb_23.8 and Δε_18.7/Δε_23.8 and very good correlation with each other. Based on this good correlation, the Δε_18.7/Δε_23.8 in cloudy condition was estimated using corresponding==and adjacent 8 days Δε_18.7/Δε_23.8 in clear condition. With the estimated Δε_18.7/Δε_23.8, we retrieved atmospheric column water vapor using lookup table method in cloudy condition over land. As a validation source data, the SuomiNet GPS-retrieved precipitable water (PW) vapor is used to validate the retrieved water vapor in th- s study. According to validation, the correlation coefficient of the two is 0.94 and the root-mean-square-error (RMSE) is 4.85 mm. It is a great improvement in water vapor retrieval using microwave in cloud cover area on land.