Technical Details of the Alpha prototype of GEOID2022

GEOID2022 alpha is the last prototype of GEOID2022. It covers three regions: the North America–Pacific region, Guam and Northern Mariana Islands, and American Samoa. The spatial resolution of the geoid model is 1 arcminute. The geoid heights, which are in the tide-free system, are with respect to the reference ellipsoid of the Geodetic Reference System 1980 (GRS80) in the ITRF2020 geometric reference frame. GEOID2022 alpha includes static and dynamic components for the geoid heights. For detailed fundamental parameters of the geoid model, refer to NOAA Technical Report 78.

The following data sets are used for geoid computation:

• GOCO06S satellite gravity model (Kvas et al., 2021)
• Terrestrial gravity:
• National Geospatial-Intelligence Agency (NGA) data covers the area -5 ̊ ≤ latitude ≤ 85 ̊; 170 ̊ ≤ longitude ≤ 350 ̊.
• National Geodetic Survey (NGS) data provides supplemental coverage to the NGA data
• Canadian Geodetic Survey (CGS) data covers Canada lands
• INEGI data provides supplemental coverage to NGA data in Mexico
• Reprocessed GRAV-D airborne gravity data (96% completion)
• Arctic Gravity Project (ArcGP) data provided by NGA in a 3-arcmin. grid covering 60 ̊ ≤ latitude ≤ 90 ̊; 0 ̊ ≤ longitude ≤ 360 ̊
• DTU21, a 30-arcsec. grid of marine gravity anomalies derived from satellite altimetry data (Andersen personal communication)
• DEM2022, a 3-arcsec. digital elevation model (Krcmaric and Li., 2023)
• BedMachine Greenland ice thickness grid (Morlighem M. et al., 2017)
• Goddard Space Flight Center L1B GRACE/GRACE-FO mascon trend solutions (dynamic component)

The geoid computation follows the same approach as the experimental geoid 2020 (NOAA Technical Report 78). The final alpha geoid model combination and selection are also the same. However, a major difference is that the ice thickness in Greenland is used to compute the geoid-quasigeoid separation term. The ice and bedrock layers are treated separately and their effects on the separation term are then added together. The binary and ascii geoid layers for the static (SGEOID at 2020.0) and dynamic (DGEOID) geoid can be downloaded from the GEOID 2022 Data Download page. Additional grids and tools will be available in the near future.

References

Andersen OB, Rose SK, Abulaitijiang A, Zhang S, and Fleury S (2023) The DTU21 global mean sea surface and first evaluation, Earth Syst. Sci. Data, 15, 4065-4075, https://doi.org/10.5194/essd-15-4065-2023, 2023

Krcmaric J and Li X (2023). The experimental xDEM2022 and its uses for geoid modelling at NGS, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10030, https://doi.org/10.5194/egusphere-egu23-10030, 2023.

Kvas A, Brockmann JM, Krauss S, Schubert T, Gruber T, Meyer U, Mayer-Gürr T, Schuh W-D, Jäggi A, and Pail R (2021) GOCO06s — a satellite-only global gravity field model, Earth Syst. Sci. Data, 13, 99–118, https://doi.org/10.5194/essd-13-99-2021.

Moritz H (2000) Geodetic Reference System 1980. Journal of Geodesy 74, 128–133 (2000). https://doi.org/10.1007/s001900050278

Morlighem M, CN Williams et al. (2017) BedMachine v3: Complete Bed Topography and Ocean Bathymetry Mapping of Greenland From Multibeam Echo Sounding Combined With Mass Conservation

National Geodetic Survey, 2024. Geoid Monitoring Service (GeMS) (https://beta.ngs.noaa.gov/GEOID/gems/index.shtml)

Wang YM, Li X, Ahlgren K, Krcmaric J, Hardy R, Véronneau M, Huang J, and Avalos D (2022). Technical Details of the Experimental GEOID 2020, NOAA Technical Report NOS NGS 78, June 2022. https://geodesy.noaa.gov/library/pdfs/NOAA_TR_NOS_NGS_0078.pdf