5:15 PM - 7:15 PM
[SGD02-P02] Development of new geoid model for Japan, “JPGEO2024”
Keywords:geoid, GNSS, elevation
The Geospatial Information Authority of Japan aims to realize a society where GNSS can be used to easily and accurately determine elevation. To achieve this, it has developed the “GEOID 2024 JAPAN AND ITS SURROUNDINGS” (“JPGEO2024”), which represents the elevation standard that will serve as the foundation for such a society. JPGEO2024 will be officially available from April 1, 2025. On the same day, the elevation results of GNSS-CORS, triangulation points, benchmarks, etc. will be updated to “Geodetic Coordinates 2024” and shifted to a height reference system based on GNSS.
JPGEO2024 was developed by applying corrections to the precise gravimetric geoid model JGEOID2024 to comply with land surveying standards under the Survey Act. JGEOID2024 is a seamless geoid model for both land and ocean, created through the spatial integration of gravity data from satellite, airborne, ground, shipborne, and ocean-bottom gravimetry as well as marine gravity field model from satellite altimetry. The accuracy of JGEOID2024 was confirmed to meet the target of 3 cm by comparing it with geoid height data obtained by the GNSS/level method (Nakashima et al., 2023). JGEOID2024 is referred to the global mean sea level, with its geopotential value W0 set to 62 636 853.4 m2s-2. The permanent tide system is a tide-free system, where all tidal forces, including lunar and solar tidal effects, are removed.
On the other hand, the elevations in Japan are defined with reference to the mean sea-level of Tokyo Bay (elevation 0 m) according to the Survey Act. The permanent tide system is an approximate mean-tide system, where only the cyclic component of tidal forces is removed, because the elevations in Japan have traditionally been maintained through spirit leveling and do not account for tidal corrections. Therefore, JPGEO2024 applies an offset correction and a permanent tide correction to JGEOID2024 to align it with the current definition of elevation. The offset correction is applied to convert the reference sea level from the global mean sea level to the mean sea level of Tokyo Bay. The permanent tidal correction is applied to derive the mean-tide elevation from the tide-free ellipsoidal height obtained via GNSS by using the geoid model.
Regarding the elevation of remote islands, due to the inability to conduct spirit leveling surveys from the Japanese vertical datum in marine areas, a unique local vertical datum has been established using the mean sea level of the remote island as the reference (elevation 0 m). The elevations have been determined through spirit leveling surveys relative to this local vertical datum.
The current official geoid model GSIGEO2011 applies a reference surface correction parameter to convert the reference sea level from the mean sea level of Tokyo Bay to the local mean sea level on remote islands. Therefore, when GSIGEO2011 is used on remote islands, the elevation relative to the local mean sea level of the island could be obtained by subtracting the geoid height of GSIGEO2011 from the ellipsoidal height obtained via satellite positioning. In contrast, JPGEO2024 does not apply such a correction parameter for remote islands. As a result, when JPGEO2024 is used on southern remote islands, there may be a discrepancy of about 80 cm between the elevation obtained and the elevation referenced to the local mean sea level. To address this, for these remote islands, a reference surface correction parameter will be established. By adding this correction parameter to the geoid height derived from JPGEO2024, the elevation relative to the local mean sea level can be calculated from the ellipsoidal height obtained via satellite positioning. This reference surface correction parameter will be officially available from April 1, 2025, along with JPGEO2024.
JPGEO2024 was developed by applying corrections to the precise gravimetric geoid model JGEOID2024 to comply with land surveying standards under the Survey Act. JGEOID2024 is a seamless geoid model for both land and ocean, created through the spatial integration of gravity data from satellite, airborne, ground, shipborne, and ocean-bottom gravimetry as well as marine gravity field model from satellite altimetry. The accuracy of JGEOID2024 was confirmed to meet the target of 3 cm by comparing it with geoid height data obtained by the GNSS/level method (Nakashima et al., 2023). JGEOID2024 is referred to the global mean sea level, with its geopotential value W0 set to 62 636 853.4 m2s-2. The permanent tide system is a tide-free system, where all tidal forces, including lunar and solar tidal effects, are removed.
On the other hand, the elevations in Japan are defined with reference to the mean sea-level of Tokyo Bay (elevation 0 m) according to the Survey Act. The permanent tide system is an approximate mean-tide system, where only the cyclic component of tidal forces is removed, because the elevations in Japan have traditionally been maintained through spirit leveling and do not account for tidal corrections. Therefore, JPGEO2024 applies an offset correction and a permanent tide correction to JGEOID2024 to align it with the current definition of elevation. The offset correction is applied to convert the reference sea level from the global mean sea level to the mean sea level of Tokyo Bay. The permanent tidal correction is applied to derive the mean-tide elevation from the tide-free ellipsoidal height obtained via GNSS by using the geoid model.
Regarding the elevation of remote islands, due to the inability to conduct spirit leveling surveys from the Japanese vertical datum in marine areas, a unique local vertical datum has been established using the mean sea level of the remote island as the reference (elevation 0 m). The elevations have been determined through spirit leveling surveys relative to this local vertical datum.
The current official geoid model GSIGEO2011 applies a reference surface correction parameter to convert the reference sea level from the mean sea level of Tokyo Bay to the local mean sea level on remote islands. Therefore, when GSIGEO2011 is used on remote islands, the elevation relative to the local mean sea level of the island could be obtained by subtracting the geoid height of GSIGEO2011 from the ellipsoidal height obtained via satellite positioning. In contrast, JPGEO2024 does not apply such a correction parameter for remote islands. As a result, when JPGEO2024 is used on southern remote islands, there may be a discrepancy of about 80 cm between the elevation obtained and the elevation referenced to the local mean sea level. To address this, for these remote islands, a reference surface correction parameter will be established. By adding this correction parameter to the geoid height derived from JPGEO2024, the elevation relative to the local mean sea level can be calculated from the ellipsoidal height obtained via satellite positioning. This reference surface correction parameter will be officially available from April 1, 2025, along with JPGEO2024.