CAS实时轨道、钟差产品性能评估及完好性支持信息估计

Performance Assessment and Integrity Support Information Estimation of CAS Real-time Orbits and Clocks Products

  • 摘要: 实时轨道、钟差产品的精度和完好性是实现全球卫星导航系统精准可信定位服务的重要前提。以2022年中国科学院(chinese academy of sciences,CAS)实时轨道、钟差产品为例,从产品精度及精密单点定位精度两个方面评估实时轨道、钟差产品性能,并根据全球均匀分布的100个虚拟测站计算得到的瞬时空间信号用户测距误差(instantaneous signal-inspace user range error,IURE)分析实时轨道、钟差产品的空间信号用户测距误差分布特性,最后计算CAS实时轨道、钟差产品的完好性支持信息。试验结果表明:以GFZ提供的事后精密产品为参考,GPS和Galileo的轨道精度优于5 cm,钟差(standard deviation,STD)优于0.08 ns,BDS和GLONASS的轨道精度优于15 cm,STD优于0.3 ns;选取全球分布测站以静态仿动态方式进行PPP测试,四系统组合定位的3D方向精度RMS优于4 cm,收敛时间优于11 min。GPS和Galileo的IURE RMS(root mean squared,RMS)优于4 cm,同时IURE分布峰度基本在10以内,偏度绝对值基本在0.5以内,可接受为高斯分布; GLONASS的IURE RMS在10 cm以内,但是各卫星IURE的偏度和峰度之间差异较大,尖峰厚尾情况较为严重; BDS IURE RMS优于11 cm,但是不同类型卫星IURE分布不同且BDS-3 SECM卫星具有较为明显的双峰特性。对于星座故障和卫星故障先验概率,GPS星座故障先验概率最小为5.2×10-5,其他系统星座故障先验概率小于1.0×10-3; GLONASS卫星故障先验概率达到2.7×10-3,Galileo卫星故障先验概率最小为8.7×10-4。对于空间信号用户测距误差包络标准差σURA和空间信号用户测距误差标准差σURE ,GPS和Galileo各卫星σURAσURE差异在4 cm以内; GLONASS各卫星σURAσURE差异基本大于5 cm;相较于σURE ,BDS-2和BDS-3的σURA差异较大。

     

    Abstract: Objectives: The accuracy and integrity of real-time orbits and clocks are essential for achieving high-precision and assured positioning within the Global Navigation Satellite System (GNSS). Current assessments mainly focus on the short-term accuracy of real-time products from various analysis centers, there is a lack of extensive research on the integrity of real-time orbits and clocks. Methods: This study researches the real-time orbits and clocks of the Chinese Academy of Sciences (CAS) in 2022 as a case study. Evaluating the performance of real-time orbit and clock products from the perspectives of long-term products accuracy and dynamic precise point positioning (PPP) accuracy. Assessing the signal-in-space user range error (SIS URE) distribution characteristics of real-time orbit and clock products by analyzing the instantaneous signal-in-space user range error (IURE) calculated by 100 uniformly distributed stations worldwide. Finally, the integrity support information for the CAS real-time orbit and clock products is computed. Results: By comparing the CAS real-time orbits and clocks with post-processed precision products provided by GFZ, it is observed that the orbit accuracy of GPS and Galileo is better than 5 cm, with a standard deviation of clock errors better than 0.08 ns. However, the orbit accuracy of BDS and GLONASS is better than 15 cm, with a standard deviation of clock errors better than 0.3 ns. The kinematic precise point positioning using the CAS real-time products is conducted with observations collected from 28 globally distributed stations. The positioning accuracy of PPP with the combined four GNSS systems is better than 4 cm, and the corresponding convergence time is better than 11 min. The IURE RMS (Root Mean Squared) for GPS and Galileo is better than 4 cm, and the distribution of IURE can be accepted as a Gaussian distribution. GLONASS exhibits an IURE RMS within 10 cm, with noticeable differences among satellites, leading to an obvious leptokurtic and fat-tailed distribution; The BDS demonstrates an IURE RMS better than 11 cm, but the IURE distribution differs among different types of satellites, and the BDS-3 SECM satellites display distinct bimodal characteristics. Regarding the prior probability of constellation fault and satellite fault, the prior probability of GPS constellation fault is the smallest, which is 5.2×10-5, the prior probability of constellation fault of other systems is less than 1.0×10-3. The prior probability of GLONASS satellite fault reaches 2.7×10-3, the prior probability of Galileo satellite fault is the smallest, which is 8.7×10-4. Regarding the standard deviation of the SIS URE envelope σURE and the standard deviation of the SIS URE σURE , the difference between σURE and σURE of GPS and Galileo is within 4 cm; the difference between σURE and σURE of GLONASS is basically greater than 5 cm, compared with σURE , the difference of σURE between BDS-2 and BDS-3 is larger. Conclusions: Therefore, it can be concluded that the accuracy of the BDS and GLONASS real-time orbits and clocks products provided by CAS needs to be further improved to support high-precision and assured positioning.

     

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