2.3 Geodetic VLBI activities at GSI

The Geographical Survey Institute (GSI) has been performing geodetic VLBI observations to correct the positions of geodetic control points in Japan and to detect plate motion and crustal deformation around Japan. In 1981, GSI began development of a mobile VLBI system in cooperation with the Communications Research Laboratory, and used this system from 1986 to 1993 in the VLBI Experiment for Geodetic Application (VEGA) project. The most remarkable achievement of the VEGA project was the first detection of motion of the Philippine Sea plate. The GSI also carried out VLBI observations between Japan and Korea in 1995 by transporting a mobile system with a 3.8-m antenna to Korea. In 1994, ownership of the Kashima 26-m antenna was transferred from CRL to GSI, and with this antenna, GSI started to participate in international global observations. The coordinates of the Kashima 26-m antenna in the International Terrestrial Reference Frame (ITRF) have become the primary point of a new Japanese Geodetic Datum. At present, GSI's VLBI network in Japan consists of five stations that are used to perform regular VLBI observations. More than 30 years have passed, however, since the construction of the Kashima 26-m antenna, and its role has been passed on to the Tsukuba station, which will now participate in international global observations and act as the key station of the Japanese VLBI network.