MADOCA-LEX高频GPS卫星钟差短期预测精度分析
The prediction accuracy of the MADOCA-LEX high rate clock products
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摘要: 日本准天顶卫星系统(QZSS)卫星通过L波段实时播发高频全球卫星导航系统(GNSS)精密轨道和钟差产品,为GNSS导航用户提供实时精密单点定位(PPP)服务. 本文以JAXA MADOCA数据中心提供的1 s采样率GPS卫星钟差数据为研究对象,首先采用阿伦方差对卫星钟差的短期稳定性进行评估;然后分别采用一阶多项式、二阶多项式和灰色模型对高频钟差产品进行建模,在5 s,10 s和30 s的拟合窗口内预报后续10 s内钟差,并基于预报残差的均方根误差(RMS)评定不同类型GPS卫星钟差产品的短期预报精度. 基于2020年1月1日-21日连续21天的实时高频钟差统计分析结果表明,不同型号的GPS卫星钟差1 s,5 s和10 s的短期稳定性均能达到10-12量级;对比预报精度显示,10 s以内的拟合窗口采用最简单的一阶多项式最为稳定可靠,10 s延迟预报RMS精度可控制在0.1 ns以内;若采用30 s的拟合窗口,考虑钟差频漂特性的二阶多项式则更为稳定可靠,预报钟差的RMS精度能达到0.15 ns以内.由此可见,本文基于MADOCA-LEX钟差产品的实时预报精度可以满足厘米级PPP的需求.Abstract: The Japanese QZSS satellite will provide real-time PPP services by broadcasting the L-band augmentation signals with real time high rate GNSS precise orbit and clock corrections. This paper based on the 1Hz high rate GPS clock provided by JAXA MADOCA data center, we firstly evaluates the short-term stability of satellite clock corrections with Allan variance. To simulate the real time products latency, the first-order, second-order polynomials and grey model were used as the clock predictions model, and the fitting windows with 5, 10 and 30 s were used to predict the following 10 s clocks corrections. Over 21 continuous days data range from January 1 to 21 on 2020 were used on the clock stability analysis, the results show that the GPS clocks can reach 10-12with 1, 5 and 10 s intervals. On the prediction model comparison, a whole days analysis results show that, if less than 10 s fitting windows were used, the first-order linear model shows highest stability with accuracy less than 0.1 ns, and if the fitting windows were set to 30 s, the second-order polynomial model has the highest accuracy as the clock drift effects were taken into account. It can be concluded that the satellite clocks from MADOCA-LEX product could be precisely predicted to satisfy the real-time precise point positioning applications.