Activity Report of the National Committee for
Shuhei OKUBO Chair of the National Committee for Geodesy
N ational Committee (NC) for Geodesy, Japan hosted the IUGG XXIII General Assembly at Sapporo in 2003 as a member of Science Council of Japan. More than 4100 researchers from 79 countries and regions attended the Assembly. In August, 2005, NC sent official delegates to a Joint Assembly of the IAG, IAPSO and IABO held in Cairns, Australia. Besides these General Assemblies, several international meetings related to geodesy were held in Japan, e.g. “International Workshop on GPS Meteorology - GPS Meteorology: Ground-Based and Space-Borne Applications” at Tsukuba in 2003 , and “The 3-rd International e-VLBI Workshop” at Chiba in 2004 .
In addition to international activities, the Geodetic Society of Japan (GSJ) holds general meetings twice a year. In 2004, GSJ celebrated her fiftieth anniversary. As part of the commemorative activities, GSJ published two books in Japanese: an introductory book on geodesy for the general public  and a CD-ROM textbook on geodesy for researchers and university students .
During the period 2003 to 2006 a variety of geodetic activities have been undertaken in Japan. We may name some major ones out of them. The Japanese continuous GPS observation network (GEONET: GPS Earth Observation Network System) has been reinforced qualitatively and quantitatively. The number of continuous sites has been increased to about 1200, and the acquired data are transferred on a real time basis. Analysis strategy has been updated to realize a better accuracy. GEONET, the world’s largest regional GPS network, serves not only for geodesy but also for meteorology, seismology, volcanology and ionosphere sciences.
The first geodetic VLBI observation within the VERA (VLBI Exploration of Radio Astrometry) network was carried out in November 2004 by the National Astronomical Observatory of Japan. Regular observations scheduled three times per month started in December 2004. The VERA network, composed of 1020 km to 2270 km baselines, attains the observation precision of 2 mm in horizontal coordinates and 7-8 mm in vertical ones with one 24-hour observation in S/X bands.
Another new important geodetic facility is “Daichi”, the Advanced Land Observing Satellite (ALOS), which was successfully launched in January 2006. Daichi, equipped with the L-band Synthetic Aperture Rader (SAR) sensor, can be used to monitor changes in the deformation of the surface regardless of vegetation.
Research and development studies of seafloor positioning using GPS/Acoustic techniques have been continued by two university groups (Nagoya University and Tohoku University) and by the Japan Coast Guard (JCG). The former succeeded in detecting horizontal seafloor crustal movement as large as 30 cm during the 2004 Off the Kii Peninsula earthquake [5,6] while the latter revealed an intraplate crustal movement of 7.3 cm/yr WNW relative to the stable part of Eurasian Continent at a seafloor reference station located landward of Japan Trench .
The development of the onboard instruments for the coming lunar exploration mission SELENE has already been finished and proto-flight tests are continued under various conditions. SELENE is expected to be launched in the summer of 2007.
International geodetic activities have also been made intensively. Continuous observations with five superconducting gravimeters have been maintained under the Global Geodynamics Project (GGP). The domestic GGP group succeeded in submicrogal coseismic gravity change with excellent agreement to