| Water vapor in earth's atmosphere plays a crucial role for climate, dynamics of weather system, atmosphere environment, hydrology and space geodesy. We are short of knowledge about the variations and structure of water vapor because of the limited spatio-temporal measurements of routine observing technology. Lack of information about three dimensional water vapor structure affects the precision of background field of numeric weather mode and the accuracy of weather forecast. GPS technology provides a new means for sensing atmosphere with the advantages of real-time, continuity, high precision and unaffected by weather et al, which has become powerful supplementation for routine atmosphere sensing system.For the purpose of application in meteorology, the theories and methods of real-time retrieving of PWV from local ground-based GPS network, sensing three dimensional water vapor structures, and the application in weather forecast are studied in this thesis. Some novel techniques have been put forward for solving a series of problems in application. Using observations from Shanghai GPS network, near continuous PWV series with high precision are provided for weather service in Shanghai area. The application and study of weather forecast over Yangtz river area have been improved by GPS/PWV, such as, judgement of Meiyu season in 2002 and 2003,monitoring and forecast of rain, analysis of rainstorms process.To the key problem of ground-based GPS meteorology (three dimensional water vapor information not enough), three dimensional water vapor tomography techniques is mainly studied in this thesis and some difficulties in inverse problem are removed. Using GPS slant water vapor from Shanghai GPS network, three dimensional water vapor structure over Shanghai area has been detected. The tomography results show that the forecast water vapor field from MM5 can be improved greatly by GPS slant observations. So the accuracy of numerical weather forecast can be advanced.The main contents of this thesis as followings: 1. We discussed some problems about real-time retrieving absolute PWV with high precision from local GPS network, including the choice of appropriate computation software and method, well determination and suitable constrain of station coordinates. In order to guarantee the absolute value of PWV, appropriate remote assistant stations more than 500 km should be combined. In this thesis, how many remote stations is best choice has been studied first. We found that two to three remote stations are enough for retrieving absolute PWV but relative value. And how to choose the satellite orbit also is introduced. The effect of ocean tide on real-time retrieving PWV, and the end problem of real application in weather forecast are also discussed. Comparisons between GPS/PWV and radiosonde observations show that GPS/PWV retrieved by above method can have the accuracy of millimeter level. 2. Comparisons between continuous GPS/PWV series with high precision and the output of MM5 show that GPS/PWV can be used as one tool for verifying the forecast quality of meso-scale numeric weather forecast mode. Assimilations of GPS/PWV into the background field using objective analysis and three dimensional variation integral methods both show that GPS/PWV is useful for improving the forecast ability. Especially for forecast of super rain, GPS/PWV has obvious advantage. 3. We analyzed GPS/PWV series from June 2002 to April 2004 monitored by Shanghai GPS network. The detail onsets of Meiyu season in Yangtz River Delta in 2002 and 2003 are provided first in China. GPS/PWV series show that, PWV increased rapidly by 30-40mm when Meiyu season was coming and it took only about half day to enter Meiyu season at each station. It also revealed that the onset of Meiyu season in Yangtz river delta was from south-west to north-east in 2002 and 2003. The spatio-temporal variety of GPS/PWV also consisted with the movement and direction of rainbands in each stage of the Meiyu season, which shows that GPS/PWV is very represent...
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