Vol.45-1 ABSTRACT1

Abstract

The Geographical Survey Institute (GSI) is constructing a new geodetic reference frame of Japan using space geodetic techniques. The current framework based on Tokyo Datum was established at the end of the nineteenth century and has served as a national reference since then. However, it has a large internal distortion and a shift from a geocentric reference frame, which was revealed by space geodetic techniques.
A new framework is being built by referring to ITRF94 (International Terrestrial Reference Frame 1994) at the epoch of 1997.0. The coordinates of the Kashima VLBI station are determined in ITRF94 using the data from international VLBI observations. Positions of two additional VLBI stations are determined referenced to Kashima VLBI station using the data from domestic VLBI observations. The coordinates of 950 stations of the nationwide permanent GPS array are determined using these three VLBI stations as anchor points. The coordinates of the first- through third-order triangulation points are calculated by referring to the GPS array. GSI resurveyed 6300 of first- to third-order triangulation points using EDM or GPS. Survey records by theodolite since 1883 were archived for 30,000 triangulation points that were not resurveyed. The fourth-order triangulation points will be mapped by an interpolation method.
The coordinates newly determined for VLBI stations, GPS stations, and triangulation points are the realization of Japan's new geodetic reference system. Reflecting its intention to legally enforce the new reference system in the year 2000, GSI named it "Japanese Geodetic Datum 2000" (JGD2000).