Description:
xGEOID19B is a gravimetric geoid model computed by the National Geodetic Survey (NGS) and covering the entire region
of North America, including the conterminous United States, Alaska, Hawaii, the U.S. territories of Puerto Rico and
Virgin Islands, and neighboring countries such as Canada and Mexico. The reference ellipsoid is GRS80. The model has
a 1'x1' spatial resolution in latitude and longitude. It is based on 1,650,169 terrestrial gravity points from NGS,
NGA, NRCan, and DTU; marine gravity data from the DTU15 model; 53 blocks of the GRAV-D airborne data. The remove-restore
procedure is implemented by using the xGEOID16RefA spherical harmonic model, which is a combination of EGM2008 and GOCO05S
up to degree and order 2160, and a 3"x3" digital elevation model, obtained from SRTMv4.1 for all areas south of 60°N and
from a combination of other models at higher latitudes. Airborne gravity data are included by exploiting the so-called
Spherical Harmonic Analysis (SHA) method. The geoid determination is then the same of the one used for the previous releases
(USGG2009 and USGG2012), namely it is based on the use of the one-dimensional spherical Fast Fourier Transform (FFT) with a
modified Stokes kernel. By comparing the xGEOID19B model with GPS/levelling data along two traverses that cross eastern Texas
and central Iowa, residuals show a standard deviation of about 1 cm. The GEOID18 hybrid model is computed by fitting the
xGEOID19B gravimetric model to 32,357 GPS/levelling data points. The fitting is performed by least-squares collocation after
removing a two-dimensional planar surface to the residuals. Therefore, the GEOID18 model directly relates NAD83(2011)
epoch 2010.0 ellipsoid heights and NAVD88 orthometric heights. The differences between GEOID18 and GPS/levelling benchmarks
have an rms of 1.39 cm in conterminous United States, Canada and Mexico.
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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