An Improved Multi-Satellite Method for Evaluating Real-Time BDS Satellite Clock Offset Products
An Improved Multi-Satellite Method for Evaluating Real-Time BDS Satellite Clock Offset Products
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实时北斗卫星钟差产品评估的改进多星方法
DOI：
10.3390/rs12213638
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发表时间：
2020-11
期刊：
影响因子：
5
通讯作者：
Cuilin Kuang
中科院分区：
文献类型：
--
作者：
Zhimin Yuan;Changsheng Cai;Lin Pan;Cuilin Kuang
卫星钟产品精度的评估主要有两种方法，即单星法和多星法。在卫星钟产品评估中，如何消除时标差异是一个重要的问题。SSM通过星间差分选择参考星来消除时标差异，但其评估结果易受参考星钟差粗差的影响。在MSM中，时间尺度差异首先被估计，然后被移除。与GPS不同，北斗导航卫星系统（BDS）由三种类型的卫星组成，即地球同步轨道（GEO），倾斜地球同步轨道（IGSO）和中地球轨道（MEO）卫星。这三种类型的卫星轨道精度参差不齐。在卫星钟产品的产生中，轨道误差被部分地同化到钟差中。如果忽略三种北斗卫星的轨道精度差异，MSM将得到时间尺度差异的有偏估计，最终影响时钟产品的评估。在这项研究中，一种改进的多卫星方法（IMSM）提出了评估的实时BDS时钟产品，通过消除同化的轨道误差的三种类型的BDS卫星时，估计的时标差异。三个实时BDS时钟产品分发的三个不同的国际GNSS服务（IGS）分析中心，即CLK16，CLK20，和CLK93，在两个月的时间内，用于验证这种方法。结果表明，同化的轨道误差对时间尺度差的估计有重要影响。将IMSM与严格选取参考卫星的SSM进行了比较，两者的均方根差仅为0.08 ns，说明IMSM的评估结果是准确的。与传统MSM相比，IMSM对于CLK16、CLK20和CLK93分别将RMS提高了0.16、0.11和0.07 ns。最后，三个实时BDS时钟产品使用所提出的方法进行评估，结果显示它们之间的显着精度差异。
Two methods are widely used for evaluating the precision of satellite clock products, namely the single-satellite method (SSM) and the multi-satellite method (MSM). In the satellite clock product evaluation, an important issue is how to eliminate the timescale difference. The SSM selects a reference satellite to eliminate the timescale difference by between-satellite differencing, but its evaluation results are susceptible to the gross errors in the referenced satellite clock offsets. In the MSM, the timescale difference is first estimated and then removed. Unlike the GPS, the BeiDou Navigation Satellite System (BDS) consists of three types of satellites, namely geosynchronous earth orbit (GEO), inclined geosynchronous orbit (IGSO), and medium earth orbit (MEO) satellites. The three types of satellites have uneven orbital accuracy. In the generation of satellite clock products, the orbital errors are partly assimilated into the clock offsets. If neglecting the orbital accuracy difference of the three types of BeiDou satellites, the MSM will obtain biased estimates of the timescale difference and finally affect the clock product evaluation. In this study, an improved multi-satellite method (IMSM) is proposed for evaluating the real-time BDS clock products by removing the assimilated orbital errors of the three types of BDS satellites when estimating the timescale difference. Three real-time BDS clock products disseminated by three different International GNSS Service (IGS) analysis centers, namely CLK16, CLK20, and CLK93, over a period of two months are used to validate this method. The results indicate that the assimilated orbital errors have a significant impact on the estimation of the timescale difference. Subsequently, the IMSM is compared with the SSM in which the referenced satellite is rigorously chosen, and their RMS difference is only 0.08 ns, which suggests that the evaluation results obtained by the IMSM are accurate. Compared with the traditional MSM, the IMSM improves the RMS by 0.16, 0.11, and 0.07 ns for CLK16, CLK20, and CLK93, respectively. Finally, three real-time BDS clock products are evaluated using the proposed method, and results reveal a significant precision difference among them.
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