UT1 intensive measurements and evaluation based on China's VGOS Network

Objectives: The VGOS system, leveraging ultra-wide band signal reception and innovative rapidly rotating antenna technology, has emerged as the preferred choice for UT1 intensive observations, surpassing legacy S/X dual-frequency VLBI. China's 13-meter VGOS stations at Sheshan, Nanshan, and Tianma have successively been established, promptly initiating independent UT1 intensive observation services for domestic needs. Our objective was to analyze the precision of the first batch of intensive UT1 observations collected by China's VGOS network, compare it with the precision of international data and evaluate China's autonomous Earth Orientation Parameters (EOP) monitoring capabilities and contributions to international joint observations.
Methods: In the ΔUT1 calculation, we estimated ΔUT1, clock offsets as quadratic functions relative to the reference station, and zenith wet delays for each station, while adopting optimal model parameters for the remaining parameters. Additionally, we evaluated the impact of errors in the prior parameters of the model on ΔUT1 through theoretical derivation and adjustments to the prior model parameters. This included specific impacts from station coordinate errors, polar motion errors, celestial pole offsets and so on.
Results: We analyzed and processed UT1 intensive observations from May 2022 to May 2024 based on China’s VGOS network. The results demonstrate that China's ΔUT1(UT1-UTC) analysis outcomes, when compared to the IERS C04 20 sequence standards, exhibit a mean deviation as low as 12.3 µs, with an RMS error at 44.0 µs and a median formal error of just 14.3 µs. All of the priori model errors including the station coordinates, polar motion and nutation errors have certain impacts on the ΔUT1 calculation results. Specifically, a polar motion error of up to 1 mas can lead to a ΔUT1 error of 20 µs.
Conclusions: Our results are not only the first high-precision intensive resolution of ΔUT1 based on China's VGOS system, but also have already been successfully integrated into China's UT1 prediction service system. Despite China's relatively short baselines compared to the international networks, their precision is comparable to that of international traditional UT1 intensive observations, laying a solid foundation for China's independent achievement of high-precision EOP determination.