ALBERT

Description: The Geospatial Information Authority of Japan (GSI) has operated two space geodetic techniques, VLBI and GNSS, at the Ishioka Geodetic Observing Station (hereafter Ishioka). We regularly conduct local-tie surveys to determine the local-tie vector connecting those techniques. In 2021, we submitted the results of the surveys to the International Earth Rotation and Reference Systems Service (IERS) to contribute to the construction of the International Terrestrial Reference Frame (ITRF). In ITRF2020, Ishioka was registered as one of the IERS stations for the first time. Reference points of VLBI antennae generally cannot be measured directly and thus need to be estimated in the local-tie survey. In Ishioka, we estimate the position of the reference point of the VLBI antenna by a method called the ‘inside method’, in which targets attached to the inner wall of the azimuth cabin are used for observation. This method is applied only to the specific antenna with an observation pillar constructed in it, but this method is effective to improve efficiency of local-tie survey. We combine the results of the inside-method observation and various other observations using total stations, geodetic leveling and static GNSS, and calculate the local-tie vector with the software called pyaxis. In this report, we will compare the local-tie vector obtained from the surveys with that derived from the ITRF2020 after describing the outline of the local-tie survey technique at Ishioka.