Cloud Influence on Atmospheric Humidity Profile Retrieval by Ground-based Microwave Radiometer

There are a lot of limitations on measurement accuracy, cost and continuity of time in the meteorological sounding operations, which are two or four times a day. In order to obtain continuous atmospheric profile data, many methods are developed, among which the way of measuring atmospheric temperature and humidity profiles by the microwave radiometer is relatively mature. However, the ability of the microwave radiometer with infrared sensors is very limited in measuring the cloud, it can only get the height of cloud, and sometimes it brings large deviations. The deviation result in great uncertainty in distributed cloud microwave absorption, causing errors during the inversion of temperature and humidity profiles, so how to improve the accuracy of inversion on cloud is an urgent problem to solve. A method is implemented using atmospheric profiles from L-band sounding radar and brightness temperature observed with microwave radiometer, and MonoRTM is taken as a forward atmospheric radiative transfer model and the tool of retrieval is BP neural network. The matching cloud information is added and a new model of retrieval is created when retrieving atmospheric humidity profiles. Root mean square error (RMSE) values on each height layer with two kinds of inversion method are obtained and the impact of cloud information on atmospheric humidity profile retrieval is analyzed through comparison.Results show that the average of correlation between inversion humidity profiles is improved from 0.6850 to 0.8050 after adding cloud information. Compared with inversion profiles without cloud information, RMSE values on the vast majority of height layers after adding cloud information are reduced to various degrees, which is particularly obvious at layers with cloud.The study shows that the method of adding cloud information on the process of inversion is feasible. In order to improve the ability to observe the atmospheric profile lines in cloudy days, combined information of cloud distribution and brightness temperature of microwave radiation can be used to retrieve the temperature and humidity, in condition the joint observation of cloud radar and microwave radiation is available.