The equatorial radius of the Earth and the zero-order undulation of the geoid

Recent determinations of equatorial gravity, the earth’s flattening, and the product of the gravitational constant and the earth’s mass have been combined to yield an equatorial radius and the potential of the geoid. These elements make it possible to determine the zero-order undulation that must be added to the undulation obtained from the Stokes equation in order to yield an absolute undulation with respect to a given reference ellipsoid. Adopting the parameters γe = 978.0421 ± 0.002 gals (Potsdam system), KM = 3.986013 ± 0.000010 × 1020 cm³/sec², 1/ƒ = 298.25 ± 0.02, and a Potsdam correction of −13.7 ± 1.0 mgal yielded the following values: a = 6378157.5 ± 10.8 m, Wo = 6263678.768 ± 10.6 kgal m, and No = −200.6 ± 10.8 m with respect to the International Ellipsoid.