Deviation of Japanese Vertical Datum and Reference Surface with Respect to the Global Geoid
The deviation of the Japanese vertical reference surface from the geoid is discussed. The analysis method is based on Rapp (1994); GPS-derived geoid heights at benchmarks (BMs) are compared with the geoid undulations calculated from a global geopotential model, EGM96. The Geographical Survey Institute (GSI) conducted GPS observation at some 800 BMs throughout Japan and determined the ellipsoidal heights with reference to a nationwide continuous GPS array of Japan. The published normal orthometric heights at BMs were adjusted in 1969/71 with local corrections for ground subsidence afterwards. Since the Japanese islands are located in an island and arc region, we have to be careful in handling the orthometric heights because of the existence of vertical crustal movements during the leveling and GPS observation periods. The mean differences in areas of about 1.5 degree width in both longitude and latitude show geographically gradual variations of the peak to peak amplitude of around 60 cm. With evaluation of height changes estimated from preliminary adjustment results of the latest leveling survey in the period from 1987 to 1995, the p-p amplitude is slightly reduced to 50 cm. When the area of approximately 300 km by 300 km around the vertical datum station is considered, the mean deviation is derived as 14 cm and 18 cm below the EGM96 geoid with and without height change corrections, respectively.
KeywordsGeopotential Model Geoid Model Vertical Data Geoid Undulation Orthometric Height
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