Wavelet approach to improvement of gravity field-geoid modeling for Japan

An improved gravimetric geoid model for Japan, JGEOID2004, on a grid of 1 × 1.5 minutes, was constructed by the one‐dimensional fast Fourier transform method with EGM96 as a foundation model. The model geoid heights in the nontidal system refer to the GRS80 ellipsoid aligned in the ITRF94 (epoch 1997.0). Newly acquired terrestrial gravity data supplemented the data gaps of the previous model, JGEOID2000. A “semidiscrete” wavelet analysis/reconstruction with two‐dimensional (2‐D) Halo wavelets were developed and successfully applied to a combination of marine gravity data and an altimetric gravity model, KMS02. The method is used to localize 2‐D signal components in the spatio‐frequency domain and to screen them as a locally adjustable band‐pass filter. Compared with 816 GPS/leveling benchmarks, JGEOID2004 showed significant improvement over JGEOID2000: the standard deviation of the differences from the best fit planes is reduced from 15.3 cm to 9.2 cm. Substantial localized errors, which are due to systematic errors of the marine gravity data as well as to data gaps on land and in the inland sea, were effectively removed.