日本の測地基準系と水路部ジオイド

抄録

Astrogeodetic deflections of the vertical in Japan with respect to Bessel′s ellipsoid are mostly directed to the northwest due to the unfitness of Bessel′s ellipsoid to the geoid in and around Japan. This kind of unsuitableness for the position of Bessel′s ellipsoid is based on the assumption that the astrogeodetic deflection is taken as zero at the geodetic datum . A correction computation is desired for best-fitting the ellipsoid to the geoid. Astrogeodetic deflections of the vertical in Japan have been observed at 324 trian gulation points during the period from 1947 to 1977 by the Geographical Survey Insti tute. And the geoidal heights in and around Japan have been computed by the Hydrographic Department of the Maritime Agency. The present study is devoted to transforming the Geodetic Reference System of Japan into an ellipsoid best-fitting the Japan Hydrographic Department Geoid. The result shows that the correction for the deflection of the vertical at the Tokyo geodetic datum amounts to ξ0=-11″.98 and ηo= +10″.24. These values are well consistent with the results previously obtained by the various methods.