The Accuracy Test of Retrieved Precipitation Water Vapor Based on Beidou Observations

The Beidou Navigation Satellite System is an independent system under construction in China. Observations of Beidou can be used to retrieve atmospheric precipitation water vapor (PWV) and provide information of water vapor with high precise and high real time. Beidou meteorological observation network is built by Shanghai Meteorological Bureau with PANDA (position and navigation data analysist) and M300C_GNSS, UNICORE-UB240 Beidou receivers, and the atmospheric precipitation water vapor is acquired. First, satellite data is received by Beidou meteorological observations and satellite orbit files are downloaded synchronously, and then zenith total delay (ZTD) is calculated by PANDA modules, and at last the PWV is retrieved based on surface meteorological parameters observed by automatic weather stations.Results of PWV retrieved by Beidou data (W_BD) are compared with both PWV retrieved by GPS data (W_GPS) and radiosonde data (W_Radio), as the technology of them are mature. W_GPS is retrieved by two methods: One is GAMIT (GPS at MIT) with the method of double difference phase observation, the other is PANDA with the method of precise point positioning. W_Radio is retrieved by the method of water vapor integration from different pressure levels. The horizontal distance difference between corresponding observations is no more than 10 km, the elevation difference between GPS and Beidou observations is no more than 5 m, and the elevation difference between radiosonde and Beidou observations is about 30 m. Results show that the root mean square error (RMSE) between W_BD and W_GPS is no more than 3.5 mm, the correlation coefficient between them is over 0.95, and the RMSE between W_BD and W_GPS-P is smaller than that between W_BD and W_GPS-G, which means that the retrieve method has certain influence on results of PWV. The RMSE between W_BD and W_GPS-Radio is about 3.6 mm, the correlation coefficient between them is over 0.96, and W_BD is on the high side compared with W_GPS-Radio. W_BD can well reflect the temporal changing characteristics of water vapor in the atmosphere and has corresponding relations with precipitation, which plays an important role in short-term weather forecast and climate analysis. The accuracy of W_BD relies much on the precise ephemeris of Beidou.With the development of the Beidou Navigation Satellite System, the accuracy of PWV based on Beidou observations can surpass that based on GPS observations. Therefore, making the best of the Beidou Navigation Statellite System and improving meteorological service with W_BD is important for the modernization of meteorology.