An effective approach for accurate estimation of VLBI–GNSS local-tie vectors

Abstract

Abstract The local-tie vectors, which connect coordinate frames of different space geodetic techniques, are indispensable for the construction of the International Terrestrial Reference Frame (ITRF). To obtain the local-tie vector connecting very long baseline interferometry (VLBI) sites with high measurement accuracy, it is crucial to accurately determine the antenna invariant point (IVP), which does not change its position under any tracking conditions. In the 2018 co-location survey at Ishioka station, we employed two methods to determine the IVP; “inside” and “outside” methods. We observed a target mirror from inside or outside of the antenna and derived trajectories of the target used for estimation of the rotation axes. Both the methods successfully estimated the IVPs with the measurement error of less than 1 mm, meeting the requirement of measurement accuracy by the International Earth Rotation and Reference Systems Service (IERS). The striking point is that the difference between the IVP positions was less than 1 mm, suggesting that both the methods could determine almost the same position independently. While they both can determine the IVPs with high measurement accuracy, it should be noted that the inside method substantially improved the operational efficiency. For the outside method, we had to repeat the target observations from four or more pillars around the VLBI antenna, with the reinstallation of a total station (TS) if needed. In contrast, for the inside method, we can observe the target from one place inside the antenna in a short time with only one TS no matter where the mirror is attached in the azimuth cabin. We concluded that the inside method is an effective and practical approach to accurately estimate the IVP. Graphical Abstract

Keywords

• Local-tie vector
• Co-location
• Very Long Baseline Interferometry (VLBI)
• Invariant point
• Inside method
• Outside method