DETERMINATION OF THE GEOPOTENTIAL AT THE TIDE GAUGE DEFINING THE NORTH AMERICAN VERTICAL DATUM 1988

The methodology for connecting existing vertical datums and for the establishment of a global vertical datum has been developed and tested on the North American Vertical Datum 1988 (NAVD88). Using the EGM96 geopotential model and the four adopted primary constants (GM, [omega], [J.sub.2], [W.sub.0]), the geopotential value of 62636861.4 [+ or -] 0.5 [m.sup.2][s.sup.-2]for the zero tide gauge defining the NAVD88 Vertical Datum has been determined from 1830 GPS Revelling points in the USA and 1248 points in Canada. This implies that the NAVD88 zero tide gauge is about 57 cm below the reference equipotential surface (geoid) defined by [W.sub.0]=(62636855.8 [+ or -]0.5) [m.sup.2][s.sup.-2]. The separate, mean NAVD88 geopotential determinations in the USA and Canada agreed within .94 [m.sup.2][s.sup.-2], which is equivalent to 9.5 cm in height.