Error Analysis On Precipitable Water Derived From Ground-based GPS And Observations Appliactions

GPS meteorology theory makes GPS detection of atmospheric water vapor as possible, ground-based GPS atmospheric water vapor monitoring network building and shared with GPS network laid the foundation for high-altitude observations. GPS meteorology research is turning into the operational application. How to obtain the high-precision water vapor products by the high resolution datas, also based on the routine observational datas, the satellite images, radar datas and NECP1°×1°reanalysis datas, use all of them effectively in the rainstorm forecasting and other meteorological services is the study motivation in this paper. The study includes the improvement of GPS/PWV (precipitable water vapor) retrieval methods and the analysis of error source, established ground-based GPS atmospheric water vapor calculation system and gaven the preliminary study of the automatic calculative scripts, the application of ground-based GPS observations in severe weather nowcasting, made the assimilation and regional climate characters analysis. The methods and results are as follows:1. The atmospheric weighted mean temperature and the GPS/PWV (precipitable water vapor) retrieval methods has been localized by5radiosonde stations data in2007-2008years.the Tm from localization model can be well fitted by sounding Tm, the correlation coefficient compared with the Bevis Tm was improved. At the same time, after the improved the dry zenith delay models, the correctness is significantly improvd. Compared with the original models,the precision of the two improved methods were no change. In addition to the error of the model itself, The study found the dry zenith delay models were not only effected by the ground temperature, especially were impact by the ground pressure, so induce the error of surface pressure can improve ZHD precision;2. Based on the above improvements, estabilsed the ground-based GPS atmospheric water vapor calculation system and writed the automatic calculative scripts to achieve every30minutes high precision PWV datas. The scripts are suitable for Linux system; its portability is very good;3. Using2007-2008years atmospheric observation datas of the GPS/MET network in Chengdu, At the mean while, the PWV can be calculated according to the improved models, analyzed the daily variation and seasonal variation of the GPS/PWV. And also the characteristics of the PWV changes before and after the rain, in order to provide references information for severe weather forecast, got the threshold of precipitation and strong rainfall from the the high accuracy GPS/PWV datas, which have a good reliability, and would provide practical reference values for the forecaster;4. Because of the GPS/PWV only provides the water vapor in the atmosphere conditions, if we want to fully analyse the severe weather’s generation, we must combine the dynamic features and thermal features. This research makes full use of NECP materials, radar datas and satellite datas, automatic meteorological station datas and Sounding datas. It is shown that before the rainfall the water vapor of the middle and lower troposphere is sufficient, atmospheric stratification is extremely unstable; High temporal resolution observations of ground-based GPS not only can obtain the rapidly changing information of water vapor, but also have certain instructions for the occurrence time and the strength of the rainfall;Combined with the results of the mesoscale numerical simulation WRF, it is found that whether rainfall or the amount of rainfall depends on more the dynamical and thermodynamic conditions than the values of PWV, and the strength of moisture convergence plays a key role.