Improvement of Japanese geoid with lD- FFT method and its comparison with altimetry-derived geoid

An improvement of the Japanese gravimetric geoid over a pre-existing model, JGEOID93, is studied with the 1D-FFT method as a strict realization of Stokes’spherical integration in a remove-restore manner and in consideration of possible mean offset errors in the network-adjusted ship gravity data used. Simulation shows that the offset errors of about 4.9 mGal in a limited distribution in space, result in geoid errors of a few meters of amplitude in the medium wavelength, a situation which should not be ignored. The differences between the 1D-FFT and single-band 2D-FFT geoids range from 15 cm to -25 cm with a 2-3 cm RMS. We prepare an approximated error response function of Stokes’kernel, which well indicates the geographical distribution of the differences. The 1D-FFT geoid obtained, provides better accuracy in magnitude and a slight improvement in precision, in comparison with a nation-wide network and several local networks of GPS at benchmarks. Comparison of the gravity field and geoid with an altimeter- derived global model (Sandwell and Smith, 1997) reveals the existence of significant discrepancies in the southeastern edge of the Sea of Japan, which is attributed to the altimeter model errors.