Subjects: Astronomy >> Astrophysical processes submitted time 2023-06-07 Cooperative journals: 《天文学进展》
Abstract： From the perspective of RNSS meter-level services, BDCS implementation accuracy evaluation methods are given, including broadcast ephemeris positioning method, precise ephemeris and broadcast ephemeris comparison method, and satellite laser ranging (Satellite Laser Ranging, SLR) coordinate estimation method. The broadcast ephemeris positioning method is suitable for users to realize real-time monitoring of the accuracy of the reference frame, but the monitoring accuracy is limited by the accuracy of the broadcast ephemeris. The orbital comparison method introduces post-precision products with high monitoring accuracy, but its timeliness is relatively poor. The SLR coordinate estimation method is less affected by the ionospheric delay and is not affected by satellite clock errors. It has the highest accuracy among the three methods. However, due to the small amount of laser data, it cannot be used for short-term monitoring. The results show that the accuracy of the three methods to evaluate the alignment of BDCS and ITRF is at the centimeter level. Finally, in the context of Sino-Russian satellite navigation system cooperation, the alignment accuracy of BDCS and PZ90 was evaluated. The results show that the two are aligned on the centimeter level, which can meet the application requirements of meter-level positioning users. With the improvement of Beidou-3 broadcast ephemeris accuracy and the development of SLR, the evaluation accuracy of the above three methods will be further improved.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-06-07 Cooperative journals: 《天文学进展》
Abstract： The thermal expansion of the radio telescope is an important element in geodesy and astrometric VLBI data analysis. In order to study the thermal expansion of the Tianma 13.2-m VGOS (VLBI Global Observing System) radio telescope, a monitoring system has been developed, which can automatically and in real time monitor the thermal deformation of the corresponding antenna structure. By continuously observing a target mounted on the antenna azimuth axis 1.5 m directly below the reference point, the monitoring system can determine the three-dimensional position variations of the prism. Based on continuous monitoring from 10 November 2020 to 31 August 2021 the results show that the maximum change of prism height is 2.6 mm in 10 months and 0.2 mm in one day. The horizontal displacement of the prism is not significant in 10 months. Finally, we verify the thermal expansion model of the IERS (International Earth Rotation Service) using the height thermal deformation of the Tianma VGOS telescope. The results show that the residuals between the observed data and the IERS model are less than 1.5 mm, and the RMS of the residuals is 0.43 mm. The IERS thermal expansion model can satisfy the current VLBI (Very Long Baseline interference) measurements, but not the accuracy requirements of VGOS. Therefore, the IERS thermal expansion model needs to be reconsidered for VGOS antennas.
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