Towards an improvement of the geoid model in Japan by GOCE data: A case study of the Shikoku area

The performance of the recently-released global geopotential models (GGMs) based on 2, 8 and 12 months of data collected by the Gravity field and steady-state Ocean Circulation Explorer (GOCE) is evaluated using geoid undulations and free-air gravity anomalies over Japan. Comparisons over the four main islands reveal that EGM2008 performs better than GOCE and related GGMs in Hokkaido, Honshu and Kyushu. However, GOCE and related GGMs perform better than EGM2008 in Shikoku. GOCO02S, GOCE-DIR3 and GOCE-TIM3 have a similar performance, and the best, in Shikoku. Given that GOCE-TIM3 relies exclusively on GOCE data, it is assessed further for geoid determination in Shikoku. To evaluate the actual improvement of the geoid model in the Shikoku area by GOCE-TIM3, the geoid over Shikoku is determined from EGM2008 and a combination of GOCE-TIM3 with EGM2008. There is an improvement in the standard deviation from ±8.7 cm, when EGM2008 is used, to ±6.6 cm, when GOCE-TM3/EGM2008 is used. The first improvement of the geoid model over Japan by GOCE data is evident in Shikoku.