1. 首先确定比湿q

   

   q是比湿，e是水汽压，P_d干空气分压，e,P_dCOSMIC产品可直接获取。

2. 确定水汽值
   

   

   PWV是可降水量，g是重力常数，P_t是顶层气压，P_s底层气压，气压值可由COSMIC数据直接获得。

3. 具体问题可以参考如下参考文献（Fonseca, Y. Burgos, et al. "Comparison between GNSS ground-based and GPS radio occultation precipitable water observations over ocean-dominated regions." Atmospheric research 209 (2018): 115-122；Zhang, Qin, et al. "Precipitable Water Vapor Retrieval and Analysis by Multiple Data Sources: Ground-Based GNSS, Radio Occultation, Radiosonde, Microwave Satellite, and NWP Reanalysis Data." Journal of Sensors 2018 (2018)；）。