Search

Objectives: Very long baseline interferometry (VLBI) is one of the main space geodetic techniques for monitoring Earth orientation parameters (EOP). China is building three VLBI global observing system (VGOS) antennas. In order to improve the EOP measurement accuracies, it is necessary to optimize VGOS observing network by extending the domestic VGOS network to an international network. Methods: We set three Chinese VGOS stations located at Shanghai, Urumqi and Beijing as core stations, by adding two international stations selected from four candidate sites located at Hobart of Australia or Bandung of Indonesia, as well as Johannesburg of South Africa or Hawaii of USA, we could form four different 5-station VGOS networks. The performance of EOP measurement accuracies for each network were analyzed based on generation of bulk observing schedules and subsequent large-scale Monte Carlo simulations. We used the repeatability value defined as standard deviation of EOP estimates as an indicator to evaluate the performance of each schedule and each network. We also compared the EOP formal errors of current VGOS observing sessions to our simulation results. Results: The experiment results show that:(1) The EOP measurement capability of the expanded 5-station networks are all much better than that of the 3-station domestic network. (2) The optimized 5-station network, which consists of 3 domestic antennas, Johannesburg in South Africa and Hobart in Australia, has the best EOP measurement results. Compared to the 3-station domestic network, the repeatability of dUT1, the pole motion XP and YP components are decreased by a factor of 5.7, 2.8 and 18.3, respectively. (3) The optimized 5-station network could reach equal or even better EOP estimates than that of the current IVS VGOS observing networks. We demonstrated that the EOP measurement accuracies can be improved by optimizing the observing network based on Monte Carlo simulations. Conclusions: The simulation results can be served as a start point for the future development of high-precision EOP observing program in China. [ABSTRACT FROM AUTHOR]

Objectives The very long baseline interferometry(VLBI) global observing system (VGOS) is a new generation of geodetic VLBI system which is equipped with broadband receiver and fast slewing antenna in order to achieve very high accuracy for measuring station coordinates, source positions as well as Earth rotation. Within the framework of the international VLBI service (IVS) for geodesy and astrometry, the first UT1 observing session was conducted using the VGOS stations at Kokee in USA and Wettzell in Germany, with a goal to validate VGOS data processing pipeline and estimate UT1 parameters. Methods The raw data were correlated at Shanghai VLBI correlator, followed by post-correlation processing and data analysis. The UT1 measurement results were derived and compared using VGOS database files produced from Shanghai correlator and the other correlator. Moreover, VGOS results were compared with those from the parallel UT1 session, which was conducted in the same time span using co-located legacy S/X-band stations. Results The UT1 estimation results obtained from Shanghai correlator output agree very well with those from the other correlator. The UT1 formal error obtained from VGOS observations is about 7 μs, approximately 2 times lower than the UT1 formal error obtained from the parallel legacy S/X-band observations. Conclusions VGOS system has the capability to obtain better UT1 measurement results than the legacy S/X-band system. The data processing pipeline established at Shanghai VLBI correlator has been validated and laid a foundation for regular VGOS data correlation in the near future. [ABSTRACT FROM AUTHOR]

Objectives: The compensation error of clock offset for a very long baseline interferometry (VLBI) 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 delay, 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 accuracy of the clock offset in the Sheshan station. Methods: We used the data of Sheshan station from all international 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 systematic bias of clock offset compensation of more than 1 μs 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. [ABSTRACT FROM AUTHOR]

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)