We report the results of position ties for short baselines at eight geodetic sites based on phase delays that are extracted from global geodetic very-long-baseline interferometry (VLBI) observations rather than dedicated short-baseline experiments. An analysis of phase delay observables at X band from two antennas at the Geodetic Observatory Wettzell, Germany, extracted from 107 global 24-hr VLBI sessions since 2019 yields weighted root-mean-square scatters about the mean baseline vector of 0.3, 0.3, and 0.8 mm in the east, north, and up directions, respectively. Position ties are also obtained for other short baselines between legacy antennas and nearby, newly built antennas. They are critical for maintaining a consistent continuation of the realization of the terrestrial reference frame, especially when including the new VGOS network. The phase delays of the baseline WETTZ13N–WETTZELL enable an investigation of sources of error at the sub-millimeter level. We found that a systematic variation of larger than 1 mm can be introduced to the Up estimates of this baseline vector when atmospheric delays were estimated. Although the sub-millimeter repeatability has been achieved for the baseline vector WETTZ13N–WETTZELL, we conclude that long term monitoring should be conducted for more short baselines to assess the instrumental effects, in particular the systematic differences between phase delays and group delays, and to find common solutions for reducing them. This will be an important step toward the goal of global geodesy at the 1 mm level.

中文翻译：

---

通过站点内基线的无线电干涉仪相位延迟实现亚毫米级的基线矢量可重复性

我们根据从全球大地测量超长基线干涉测量 (VLBI) 观测中提取的相位延迟，而不是专门的短基线实验，报告了八个大地测量站点的短基线的位置关系结果。从 2019 年以来的 107 个全球 24 小时 VLBI 会话中提取的德国大地测量天文台 Wettzell 的两个天线在 X 波段的相位延迟观测值分析产生了关于 0.3、0.3 和 0.3 的平均基线向量的加权均方根散布东、北、上方向分别为 0.8 mm。对于传统天线和附近新建天线之间的其他短基线，也可以获得位置关系。它们对于维持地面参考系实现的连续性至关重要，尤其是在包括新的 VGOS 网络时。WETTZ13N – WETTZELL可以调查亚毫米级的误差源。我们发现，在估计大气延迟时，可以将大于 1 毫米的系统变化引入到该基线向量的 Up 估计中。尽管基线矢量WETTZ13N – WETTZELL已经实现了亚毫米可重复性，但我们得出结论，应该对更短的基线进行长期监测，以评估仪器效应，特别是相位延迟和群延迟之间的系统差异，并找到减少它们的通用解决方案。这将是朝着 1 毫米级别的全球大地测量目标迈出的重要一步。