多星定轨条件下北斗卫星钟差的周期性变化

基于地面监测网的多星精密定轨可以同时解算出北斗卫星轨道和卫星钟差。由于轨道和钟差的耦合影响,卫星钟差时序难免会出现周期性波动。此外,受限于目前并不完善的北斗全球监测网络分布、系统导航文件缺失以及定轨后处理软件的设置问题,3类卫星的钟差均存在大量数据间断问题。本文利用适用于间断数据的谱分析方法,对多星定轨条件下的北斗卫星钟差数据进行了周期项提取,并利用周期项改进后的钟差预报模型评估了24h以内的预报精度。基于近一年的数据分析表明,北斗GEO卫星钟差3个主周期依次为12、24和8h,IGSO卫星钟差的3个主周期依次为24、12和8h,而MEO卫星钟差的3个主周期依次为12.91、6.44和24h。与改进前相比,周期项改进后的钟差预报模型将北斗卫星钟差在24h以内的预报精度提高了20%~40%。

Periodic Variations of BeiDou Satellite Clock Offsets Derived from Multi-satellite Orbit Determination

Multi-satellite orbit determination based on global tracking network can generate satellite orbit and clock products for BDS at the same time. The errors in the two resulting products, however, are difficult to be decoupled completely. There might be periodic fluctuations existing in the satellite clock offsets. Restricted by current imperfect global tracking network, loses of navigation files and software settings, there exist a lot of data gaps in the BeiDou satellite orbit and clock products. A spectrum analysis method applicable to data with gaps was used, and the main periodic items of BeiDou satellite clock offsets were extracted with it. Two improved clock prediction models augmented with periodic corrections were proposed and the prediction accuracy within 24 hours was evaluated. The tested results with nearly one-year-long data showed that the three main periods in BeiDou GEO and IGSO satellite clock offsets are 12, 24 and 8 hours, respectively, while those for MEOs are 12.91, 6.44 and 24 hours. Compared with the conventional clock model of quadratic polynomial, the improved model can increase the prediction accuracy of BeiDou GEO and IGSO satellite clock offsets by 20 to 40 percent at spans less than 24 hours.