Description:
xGEOID20 is the first gravimetric geoid model jointly computed by the National Geodetic Survey (NGS), the Canadian Geodetic Survey (CGS) of Natural Resource Canada and the National Institute of Statistics and Geography of Mexico (INEGI). It covers the entire region of North America, including the contiguous United States, Alaska, Hawaii, the U.S. territories of Puerto Rico and Virgin Islands, and neighboring countries such as Canada and Mexico. The geoid grid is defined in the geocentric coordinate system IGS14 and geoid heights are relative to the GRS80 ellipsoid. The geoid is tide-free, and it has the geopotential value W0=62,636,856.0 m2/s2. The model has a 1'x1' spatial resolution in latitude and longitude. It is based on the same dataset of the previous version xGEOID19 with the addition of new GRAV-D blocks of airborne data (for a total of 63 GRAV-D blocks). The reference models are updated using the GOCO06S global gravity model (at the epoch of 2020.0) and a 3"x3" digital elevation model, obtained from TanDEM-X, MERIT and USGS 3D Elevation Program in all areas south of 85°N latitudes. xGEOID20A is the solution without airborne gravity, while xGEOID20B is the one with airborne gravity. In the latter case, the airborne gravity data are included by using the so-called Spherical Harmonic Analysis (SHA) method. The geoid models are computed under Molodensky's theory (NGS) and the Stokes-Helmert scheme (CGS), then the geoid models are combined. Both methods use the one-dimensional spherical Fast Fourier Transform (FFT) with a modified Stokes kernel. Accompanying the geoid grids, the deflections of the vertical grids are also computed. The geoid accuracy for xGEOID20B is estimated using the full error covariance matrix of GOCO06S and propagated errors in gravity data. For more details of xGEOID20 computation and validation, see the corresponding NOAA Technical Report (in preparation).
References:
Y.M. Wang, J. Saleh, X. Li, D.R. Roman (2012). The U.S. Gravimetric Geoid of 2009 (USGG2009): Model Development and Evaluation. Journal of Geodesy, 86(3), pp. 165-180. DOI: 10.1007/s00190-011-0506-7
X. Li, K. Ahlgren, R. Hardy, J. Krcmaric, Y.M. Wang (2019). The Development and Evaluation of the Experimental Gravimetric Geoid Model 2019. Technical Report, NOAA/National Geodetic Survey.
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