Development of a New Japanese Geoid Model, "GSIGEO2000"

Hiroyuki NAKAGAWA, Kojin WADA, Tadayuki KIKKAWA, Hisao SHIMO, Hisashi ANDOU, Yuki KUROISHI, Yuki HATANAKA, Hiromi SHIGEMATSU, Kauyuki TANAKA, Yoichi FUKUDA


 GSI developed a new Japanese geoid model "GSIGEO2000" as a surface for converting from GPS-derived ellipsoidal heights to orthometric heights. Least squares collocation was applied to fit JGEOID2000, the latest gravimetric geoid model made from denser land gravity data obtained by improved calculation method, to 844 bits of geoid undulation data derived from a geoid survey (GPS/Leveling survey) conducted from 1995 to 2000.
       In order to adapt the geoid undulations to the new Japanese geodetic reference system, that is, the Japanese Geodetic Datum 2000, and new national vertical datum in the orthometric height system, the GPS/Leveling data were re-analyzed in advance, in terms of leveling-derived orthometric heights and GPS-derived ellipsoidal heights with tighter constraints to the permanent GPS array of Japan, GEONET (the GPS Earth Observation Network of the GSI) in ITRF94 (epoch 1997.0) frame. The geoid undulation difference between old and new analyses ranges from - 30 to + 58 cm with a 12.5-cm SD about the mean of 5.0 cm in geoid undulation.
       The signal covariance matrices for least squares collocation were determined from the analytical covariance function, which was modeled by fitting an empirical variance function from the data. The estimated error variance of the geoid undulation from the GPS/Leveling was dealt as a smoothing parameter in the process and the value which gave the smoothest result was chosen.
       The formal error of the least squares collocation is about 4.0cm, and the geoid undulation discrepancies between GPS/Leveling and GSIGEO2000 range from -35.8cm at the Sata-misaki Peninsula to +23.8cm at the Nemuro Peninsula.


1. Introduction
2. Re-analysis of the geoid survey data
  2.1 Re-analysis of GPS data
    2.1.1 Software
    2.1.2 GPS data
    2.1.3 Baseline analysis
    2.1.4 Network adjustment of GPS baseline analysis by GLOBK
    2.1.5 Evaluation of the GPS re-analysis
  2.2 Calculation of the orthometric height at the geoid survey points
  2.3 Calculation of the geoid undulation
3. Gravimetric geoid model
4. Combination procedures of JGEOID2000 and GPS/Leveling data
  4.1 Preparation and modification for the procedure (Kuroishi, 2001)
  4.2 Final process
5. Geoid model for isolated islands
6. Evaluation of the GSIGEO2000
  6.1 Comparison between the geoid undulation data and GSIGEO2000
  6.2 Verification by the geoid undulation at GEONET sites
7. Summary