High-precision geodetic datums are crucial for studying Earth's motion and deformation, positioning, and deep space exploration. The reference point coordinates of instruments from different geodetic techniques (i.e., local tie vector) constitute fundamental elements in the construction of high-precision geodetic data set. Constrained by physical limitations, the reference point coordinates of SLR telescopes cannot be obtained through direct observation. Traditional reference point determination measurements are time-consuming and prone to systematic errors. To address these challenges, we designed and implemented a self-driven prism system that enables automatic monitoring of target points moving with the telescope. Applying this system to the Sheshan SLR telescope, the experimental results demonstrate that a few hours monitoring can achieve a submillimeter error in the reference point coordinates, with the consistency of the coordinate components of ITRF2020 within 5 mm. The self-driven prism system enables more optimal target scatter observation with improved dispersion, which in turn reduces the correlations among the solved reference point horizontal coordinates, the tilt of the azimuth axis and other parameters. Moreover, this system is highly beneficial for the high spatio-temporal resolution monitoring of reference points and local tie vectors, as well as for the construction of multi-technology geodetic reference frames. (c) 2025 The Author(s). Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Abstract The determination of reference points for telescopes is crucial for obtaining the local‐tie vector for a multi‐technology co‐located station. Traditional methods suffer from labor‐intensive fieldwork, long execution cycles, and systematic errors due to the incident angle of the total station's laser beam on the prism. In this paper, we propose an algorithm aligning the prism pointing vector with the prism‐to‐total station vector and introduce a pan‐tilt platform and the Tianma VGOS telescope for sub‐millimeter unmanned reference point monitoring. Our results show that the prototype system based on the pan‐tilt achieves a formal error of ±100 μm (1σ) in reference point positions with just 2.5 hr of automated monitoring. The consistency of reference point positions is comparable to the local control network accuracy. Single‐direction observations may introduce a deviation of ±1 mm in the reference point compared to multiple direction observations. Preliminary experiments on the Tianma VGOS telescope have also shown that this system can efficiently automate the monitoring of prism scatter points (one measurement every minute) and achieve sub‐millimeter horizontal precision in reference point positions within a single day.

为解决常规射电望远镜归心测量工作耗时耗力的问题,引入GNSS(Global Navigation Satellite System)同步监测技术实现了一种针对射电望远镜参考点的无人值守监测方法.设计了针对GNSS靶标点观测数据的归算方法,包括数据匹配、数据检核以及后续精度评估等步骤,并对2018年佘山25-m射电VLBI(Very Long Baseline Interferometry)望远镜的GNSS靶标点实测数据开展了数据预处理、解析与归心解算等,证明了该方法的可行性.结果表明基于该方法,采用单日内部分(5％)数据(约7600个靶标点),所测定的VLBI望远镜参考点的点位形式精度可达3 mm.总结了针对射电望远镜采用GNSS开展无人值守归心测量先行试验中的一些经验教训,明确了利用该方法测量过程中应该注意的问题,为今后更高精度射电望远镜参考点无人值守归心监测提供重要参考.

Abstract According to Newton's law of universal gravitation, the movement of matter and the change in density cause a gravitational variation. Due to the anisotropic distribution of matter, the vertical and the normal directions at a point on the ground are probably inconsistent, which is referred to as the deflection of the vertical (DOV) and is indispensable to astrogeodetic and geophysics research. Two new non‐optical methods, including small network transformation and azimuth‐axis inclination inversion, are proposed to determine the DOV at a very long baseline interferometry (VLBI) telescope at the Urumqi station. A generalized expression of the pointing calibration model considering axis‐related errors is also presented. Therefore, the pointing calibration model and indirect model used for reference point (RP) determination are unified by redefining their coordinate system, angle direction, and axis‐related errors. The DOV given by the small network transformation agrees well with the DOVs determined by the real surveying and other different models. Due to the possible asymmetric coverage of calibrating sources in the north‐south direction in antenna pointing calibration, the north‐south DOV component based on azimuth‐axis inclination inversion differs from the surveyed value. However, the west‐east DOV component fits well in both direction and magnitude. The proposed methods enable the VLBI telescope to sense the direction of the local plumb line by introducing local leveling. We also establish the connections among VLBI delay observation, RP determination, and telescope pointing calibration, which has a benefit to multi‐tech systematic error identification, monitoring, and correction. The research indicates that telescope point calibration can also be taken as a regular technique to monitor systematic error.

The complete expression of pointing calibration model (PCM) for the axis related errors (ARE) of the radio telescope is derived directly. The definition of the common axis related parameters in both pointing correction model of ARE and Lösler's indirect model (IM) is unified, then the relationship between PCM and IM of the radio telescope is established. Thus, the deflection of the vertical (DOV) determination of VLBI stations is realized by using radio telescope azimuth axis information. As a direct surveying approach, this method does not rely on special DOV surveying equipment. It could only depend on pointing calibration surveying data for telescope aperiodic maintenance and the local surveying data including leveling. Verified by a variety of DOV surveying methods, the DOV obtained by our method shows a good agreement with real surveyed DOV in west-east component. Owing to the non-uniform distribution of the radio sources sky coverage of the station during its pointing calibration, the north-south component of DOV has the same direction as the surveyed DOV, but has a difference in value. In the future, further providing an optimized telescope pointing calibration, the high precision surveying of DOV will be obtained by using VLBI telescope azimuth axis.

为了提高射电天线的目标跟踪精度,采用直接法推导了射电天线轴系误差对指向的影响,并给出轴系误差指向改正模型的完全表达式,明确了指向改正模型中各轴系参数的定义,传统分项以及球谐函数所推导的轴系误差项为该模型的简化形式.基于此,评估得出基本参数改正模型中,因忽略轴系误差高次谐项而引起的指向精度损失可能达到1"量级,具体需结合轴系误差大小而定;同时明确了基本参数改正模型(如22项指向模型)中与轴系误差有关的部分高次谐项系数的物理意义.为高精度轴系误差指向改正模型的建立提供了理论依据.

推导了传统全球卫星导航定位系统(GNSS)测定垂线偏差(Deflection of theVertical,DOV)形式误差的表达式;提出一种可用以解算并置站DOV的小网参数转换法.利用乌鲁木齐南山多技术并置站控制网观测信息,开展了算法验证,并对该站内多个地点DOV开展了实测.结果表明,高精度的小网DOV仅由点位观测精度最高、覆盖面积最广的3个站点决定.个别精度较差的点会为DOV的测定值带来较大的不确定性;采用小网转换法所解算的DOV与实测值间的一致性分别为?2.3′′±4.3′′(子午分量)和0.2′′±4.6′′(卯酉分量);小网转换求取DOV的方法在精度上与经典的GNSS水准方法相当,但步骤更加简便.鉴于多技术并置站会不定期地开展本地测量,可利用该方法实现多技术并置站DOV的零成本长期监测.