The G96SSS model is a gravimetric geoid model for the conterminous United States, suitable for scientific investigations. Geoid heights are referred to the GRS80 ellipsoid, and the computations were performed in the ITRF94(1996.0) reference frame.
The G96SSS model is not suitable for direct conversion between NAD 83 GPS ellipsoid heights and NAVD 88 orthometric heights.
In the conterminous United States, geoid heights range from a low of -52.8 meters in the Atlantic (magenta) to a high of -7.7 meters (red) in the Rocky Mountains.
It is necessary to subtract 12.0 cm from the G96SSS values
to obtain the geoid undulation between the best-fit global
geopotential surface and the GRS80 ellipsoid
(when both are expressed in a tide-free system).
