Description:
G96SSS is a gravimetric geoid model for conterminous United States computed by the National Geodetic Survey (NGS).
It is referred to the GRS80 normal ellipsoid in the ITRF94 frame (epoch 1996.0). It has a 2'x2' spatial resolution in
latitude and longitude. It is based on over 1.8 million terrestrial and marine gravity values, augmented by gravity data
contributions from NIMA. The geoid determination is based on the use of the one-dimensional spherical Fast Fourier Transform
(FFT) to evaluate Stokes' integral. This computation is performed in the framework of a remove-restore procedure, where long
wavelengths come from the EGM96 geopotential model. The digital elevation model used for the terrain correction is mainly based
on the 30"x30" TOPO30 database. By comparing the G96SSS model with GPS/levelling data (ITRF94/NAVD88), a systematic offset at
the level of 30-45 cm is present, with an overall rms of 15.6 cm. The GEOID96 hybrid model is computed by fitting 2951 GPS/levelling
points (NAD83/NAVD88) with the G96SSS gravimetric model, also taking into account the relationships between NAD83 and ITRF94 reference
frames. The fitting is performed by collocation after removing a tilted-plane from the residuals. Therefore the GEOID96 model directly
relates NAD83(86) ellipsoid heights and NAVD88 orthometric heights. The differences between GEOID96 and GPS/levelling (NAD83/NAVD88)
benchmarks have an rms of 5.5 cm (no tilts, zero average), due primarily to GPS error. The differences between GEOID96 and GEOID93 range
from -1.22 to 3.74 m, due primarily to the non-geocentricity of the NAD83 ellipsoid.
References:
D.A. Smith, D.G. Milbert (1999). The GEOID96 high-resolution geoid height model for the United States. Journal
of Geodesy, 73(5), pp. 219-236. DOI: 10.1007/s001900050239
Web of Science ID:
DRCI:DATA2019017015400566
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