上海佘山VLBI站的钟差补偿精度分析

Accuracy Analysis of Clock Offset Compensation of Shanghai Sheshan VLBI Station

甚长基线干涉测量(very long baseline interferometry,VLBI)台站钟差的补偿误差将导致VLBI时延观测量参考历元的偏离,进而对世界时(universal time,UT1)的准确估计产生影响。台站钟差包含格式器钟差和设备时延,设备时延是影响钟差补偿精准度的关键因素。上海佘山VLBI站是全球测地参考框架的基准站,有必要评估该站的钟差补偿精准度。利用该站2002—2017年国际测地观测数据的相关处理结果,分析了相关处理机对佘山站钟差的补偿精度。结果表明,不同VLBI相关处理机对佘山站模拟终端的设备时延补偿具有较好的一致性和长期稳定性,满足UT1测量精度需求,但是上海相关处理机对佘山站数字化终端的设备时延补偿存在大于1μs的系统差,有必要进一步改进钟差搜索方法和提高钟差补偿精度。

Objectives:The compensation error of clock offset for a very long baseline interferometry(VL-BI)station leads to the shift of delay observables in reference epochs,and further affects the estimation of universal time(UT1).The station clock offset includes the formatter clock offset and the instrumental de-lay,and the instrumental delay is essential for clock offset compensation.Since the Sheshan VLBI station is the fiducial station of the global geodetic reference frame,it is important to evaluate the compensation ac-curacy of the clock offset in the Sheshan station.Methods:We used the data of Sheshan station from all in-ternational geodetic observations from 2002 to 2017.In terms of different international VIBL service(IVS)correlators,data acquisition systems and recorded bandwidth,the compensation values of clock offsets were computed and analyzed by extracting clock parameters from correlator reports and formatter clock off-sets from station log files.Results:Different VIBL correlators show good agreement and stability in long term for the instrument delay compensation of the analog terminal in the Sheshan station.However,a sys-tematic bias of clock offset compensation of more than 1μs is revealed in Sheshan station.Conclusions:In most cases,the compensation accuracy of clock offsets for Sheshan VLBI station can meet the requirement of UT1 measurements.However,it is necessary to improve the searching algorithm of the clock offset and the accuracy of clock offset compensation due to the system bias.