Large permanent GPS networks in Japan

C. Rocken1, T. Sagiya2, and H. Tsuji2

1University Corporation for Atmospheric Research/University Navstar Consortium; 2Geographical Survey Institute, Tsukuba, Japan

Japanese government agencies and Universities operate several of the worlds largest permanent GPS networks. The Geographical Survey Institute (GSI) of Japan alone has been operating two GPS networks with over 210 GPS receivers for over one year. These two networks, called GRAPES and COSMOS, will be combined and expanded, and a 610-station permanent GPS network will assume operation in Spring 1996. The Japanese arrays deploy the latest in dual frequency receiver technology and data are analyzed daily with state-of-the-art GPS processing software. The main purpose of the arrays is the determination of crustal strain in the Japanese island arc system. There are also plans to make the data available to the public for geodetic surveys and other applications. Future use of the GSI network for monitoring atmospheric water vapor is currently being discussed between scientists from GSI and the Japanese Meteorological Agency.

GSI's 610-station network will combine the 100-station nationwide "GRAPES" network, the 110-station "COSMOS" network which is centered around Tokyo, plus 400 new sites distributed over the entire country. Average spacing between sites will be ~ 30 km for all of Japan.

Data from the sites are transmitted daily to the central processing facility in Tsukuba. Sites are accessed via ISDN and public telephone lines. The new 610-station network will collect and download at 30 seconds for 24 hours/day resulting in ~ 1 GigaByte/day of data in the uncompressed standard Receiver Independent Exchange (RINEX) format. High-rate 1-second data are buffered at 120 stations and will be analyzed kinematically in case of an earthquake.

The primary purpose of the network is the determination of crustal strain in Japan. We show estimated station velocities after one year of analysis of data from the COSMOS network. Interesting results from the GRAPES network can be found on the GSI homepage at http://www.gsi-mc.go.jp/gsihome-e.html.

Three high accuracy software packages are currently in use at GSI: (1) Bernese/BPE, developed at the University of Bern, Switzerland, (2) GAMIT/GLOBK developed at MIT and SIO, and (3) GIPSY, developed at JPL. GSI plans to use all three packages for the analysis of data from the new 610-station GPS network. UCAR scientists are installing the BPE and coordinating the operation of the three software packages in collaboration with teams from GSI, Hitachi Zosen Information System Co., LTD., the University of Bern, MIT, SIO and JPL.

All three software packages will be operated from the same user interface, and three solutions will be computed for the entire network. These three solutions shall be compared and combined to form a "best" solution. GSI selected this approach to benefit from the different strengths and new developments in each of the three software packages, and to ensure that scientific competition and collaboration of the software groups will help to improve GSI products in the future.

Figure1. The 610-station GSI permanent GPS Network, Spring 1996. Island sites to the south are not shown.


Figure 2. Measured deformation velocities (small black arrows) superimposed with red plate motion vectors, and blue plate interaction vectors that were used to interpret the observed deformation of the COSMOS GPS network. Crustal deformation velocities for the Tokyo/Yokohama metropolis and surroundings were estimated at GSI from 1 year of data with the Bernese Processing Engine. (Figure courtesy of Takeshi Sagiya, GSI.)