Research progress on retrieval algorithms of cloud liquid water over ocean based on remote sensing by satellite-borne passive microwave instruments

Space-borne visible and infrared instruments can only observe the information of the cloud top or within a limited depth below the top due to their lack of ability to penetrate clouds, while space-borne passive microwave instruments can obtain cloud body information because radiation generated from particles inside cloud can penetrate cloud. Therefore, space-borne passive microwave instruments have more advantages in cloud and precipitation observation. Since the end of 1970s, the United States has invested a large number of space-borne passive microwave instruments to obtain information of cloud and precipitation for weather forecasting and so on, which has also promoted the rapid development of retrieval algorithms on cloud and precipitation parameters remote sensed by passive microwave instruments. This paper focuses on the research progress of retrieval algorithms of cloud liquid water over ocean based on satellite-borne passive microwave remote sensing, aiming to improve the application ability of satellite-borne passive microwave instruments in China. Firstly, several kinds of microwave radiative transfer models are briefly introduced. Secondly, the sensitive studies on passive microwave channel (frequency) to cloud liquid water and oceanic surface parameters are presented. Then, retrieval algorithms of statistical algorithm, physical algorithm, combination method of physical and statistical algorithm, multi-parameter synchronous retrieval algorithm, algorithm based on passive microwave and visible/infrared, of cloud liquid water over ocean are introduced. Finally, the future study directions of this field are discussed.