Galileo在轨卫星钟性能评估与分析

Performance evaluation and analysis of Galileo satellite clock in orbit

Galileo系统是目前大范围、常态化装配高精度、高性能星载氢原子钟的唯一卫星导航系统,对其卫星钟长期性能进行分析有助于对该系统的整体评估。首先,基于德国地学研究中心(GFZ)的精密钟差产品,通过最小二乘法拟合钟差数据计算了卫星钟的频率准确度和频率漂移率,采用重叠哈达玛方差讨论了卫星钟的频率稳定度,同时对Galileo卫星钟差模型拟合残差序列长期变化特点进行了分析和精度统计;然后,根据频谱分析的方法提取了卫星钟差的周期项;最后,使用Lag1自相关法识别了卫星钟的噪声类型。综合上述方法所得到的指标较为全面地评估了Galileo在轨卫星钟的性能,结果表明:Galileo卫星钟的频率准确度均值为1.79×10^-11,日漂移率均值为1.46×10^-14,万秒稳均值为1.32×10^-14,模型拟合残差平均精度为0.102ns;Galileo卫星钟差序列周期特性显著,前三个主周期近似为其卫星轨道周期的0.5倍、1倍和0.33倍左右;不同平滑时间下Galileo卫星钟主要受调频白噪声、调频闪烁噪声和调频随机游走噪声的影响。

The Galileo system is currently the only satellite navigation system for large-scale,normalized assembly of high-precision,high-performance space-borne hydrogen atomic clocks.The analysis of the long-term performance of its satellite clocks contributes to the overall assessment of the system.Based on the precision clock offset products of GFZ,the frequency accuracy and frequency drift rate of the satellite clock are calculated by the least squares fitting clock offset data.The frequency stability of the satellite clock is discussed by the overlapping Hadamard variance.At the same time,the long-term variation characteristics of the residual sequence of the Galileo satellite clock offset model are analyzed and the accuracy statistics are obtained.Then the periodic term of the satellite clock is extracted according to the spectrum analysis method.Finally,the noise type of the satellite clock is identified by the Lag1 autocorrelation method.The indicators obtained by the above methods comprehensively evaluate the performance of the Galileo satellite clock in orbit.The results show that the mean of frequency accuracy,frequency daily drift rate,frequency stability in ten thousand seconds and model fitting residual accuracy of the Galileo satellite clock are 1.79×10^-11,1.46×10^-14,1.32×10^-14 and 0.102 ns,respectively.The Galileo satellite clock offset sequence has significant periodic characteristics,and the first three main periods are approximately 0.5,1 and 0.33 times of its satellite orbital period.The Galileo satellite clock is mainly affected by FM white noise(WFM),FM flicker noise(FFM)and FM random walk noise(RWFM)in different smoothing time.