Abstract
An improved high-resolution gravimetric geoid model covering the four main islands of Japan (Hokkaido, Honshu, Shikoku, and Kyushu) was developed on a 1 × 1.5 arc-minute grid from EGM2008, GOCO02S/EGM2008, and terrestrial gravity data. A modified form of the Stokes-Helmert scheme was applied for the determination of the geoid using an empirically determined optimal spherical cap size. Handling of the topographical effects on gravity was accomplished using the integral formulae of Martinec and Vanicek, which were found to be more suitable for geoid modeling over Japan than the classical formulae. EGM2008 was used in Hokkaido, Honshu, and Kyushu Islands, whereas a combination of GOCO02S and EGM2008 was used in Shikoku Island and its immediate surroundings. The global geopotential models (GGMs) used in this study were chosen based on our earlier evaluation of the performance of EGM2008- and GOCE-related GGMs in Japan. In comparison with the previous geoid model for Japan, our new model shows an improvement in the standard deviation from ±8.3 to ±7.5 cm.
Highlights
Geoid determination over Japan has been the focus of numerous studies over the past few decades (e.g., Ganeko 1976; Kuroishi 1995, 2001a, b, 2009; Fukuda et al 1997; Kuroda et al 1997; Kuroishi et al 2002; Kuroishi and Denker 2001; Kuroishi and Keller 2005; Odera et al 2012; Odera and Fukuda 2013), precise geoid modeling remains a challenge
The choice of global geopotential models (GGMs) used in this work is based on our earlier evaluation of GGMs that have recently been developed over Japan (Odera and Fukuda 2013)
The classical Moritz formula (Moritz 1980) was used to estimate direct topographical effect (DTE) in the previous geoid model for Japan, here, we evaluated DTE using the integral formula of Martinec and Vaníček (1994b)
Summary
Geoid determination over Japan has been the focus of numerous studies over the past few decades (e.g., Ganeko 1976; Kuroishi 1995, 2001a, b, 2009; Fukuda et al 1997; Kuroda et al 1997; Kuroishi et al 2002; Kuroishi and Denker 2001; Kuroishi and Keller 2005; Odera et al 2012; Odera and Fukuda 2013), precise geoid modeling remains a challenge. An improved high-resolution gravimetric geoid model is developed from EGM2008 (Pavlis et al 2012), GOCO02S (Goiginger et al 2011) combined with EGM 2008 (GOCO02S/EGM2008), and local terrestrial gravity data. The performance of EGM2008 and GOCE-related GGMs over Japan was shown by Odera and Fukuda (2013) to be almost identical at a harmonic expansion to degree 150, EGM2008 performs better at the 180-, 210-, and 240-degree spectral bands. The current geoid model for Japan has been developed using the integral formulae of Martinec and Vaníček (1994a, b) for the computation of DTE and PITE. In this work, a combination of GOCO02S (up to degrees) and EGM2008 (from to 2,190 degrees) is used to improve the geoid model over the Shikoku area, and EGM2008 is used in Hokkaido, Honshu, and Kyushu. These two formulae (classical Moritz and planar) are hereafter referred to as the classical formulae and are given respectively as
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