Detailed gravimetric geoid around Japan based on 30′ × 30′ block gravity means

Abstract

A detailed gravimetric geoid around Japan has been computed on the basis of 30’ × 30’ block mean free‐air gravity anomalies and GSFC GEM‐8 geopotential coefficient set. The 30’ × 30’ block means were read from various gravity maps around Japan, and the block means have been compiled into the JHDGF‐1 gravity file. Since the gravity file is restricted around Japan (see Figure 1), additional gravity data are needed to perform the Stokes’ integration in the cap with radius ψ₀ = 20°. The 1° × 1° block gravity means have been used outside the JHDGF‐1 region. The remarkable features of the gravimetric geoid occur over the trench areas. The geoidal dents over the trenches amount to ‐20~ ‐25 m in comparison with the geoidal heights in the land areas of Japan. The mean error of the 30’ × 30’ detailed gravimetric geoid obtained is estimated to be around 1.4 m, and the relative undulation of the geoid between the distance of a few hundred kilometers may be more accurate.