香港实时GPS水汽监测系统的若干关键技术

香港已经建成实时GPS水汽监测系统。主要介绍实时估计可降水分中的几个关键技术问题,如梯度模型、干分量模型的标定、湿分量至可降水分的区域性转换参数计算,以及预报卫星星历中粗差的探测方法等。最后,采用双差网解和非差精密单点定位两种数据处理方法,分别计算可降水份,并进行比较。

GPS Real-Time Estimation of Precipitable Water Vapor-Hong Kong Experiences

Since 1998 we have conducted GPS meteorology research to develop the methodology for accurate and real-time determination of PWV with GPS measurements at Hong Kong GPS active stations.The implementation system has been put in practical use in the Hong Kong Observatory for three years.This paper discusses some issues in this development,in particular the measures to improve the accuracy of real time GPS-derived PWV.These measures include the inclusion of a gradient model in the determination of Total Zenith Delay(TZD),calibration of Dry Zenith Delay(DZD) calculation model,and estimation of a local conversion factor for the transformation of derived Wet Zenith Delay(WZD) to PWV.Importance for the identification and elimination of those satellites with large predicted orbital errors is demonstrated.Tests are also conducted to compare two GPS data processing approaches,the Double Differencing(DD) method and Precise Point Positioning(PPP) method.To improve the accuracy of GPS derived PWV,several measures should be adopted,including the inclusion of a gradient model in the determination of TZD,calibration of DZD computation model,and estimation of local conversion factor.At the same time,the results of PWV with IGS prediction orbits and precise orbits are generally of small difference,but the bad satellite orbits can significantly degrade the estimated accuracy of PWV with IGS predicted orbits and must be eliminated in the nearly real-time application.Additionally,the tests indicate that both DD and PPP data processing approaches in general provide consistent results,but there exists a bias.Further research and comparison should be conducted.