World Geodetic Datum 2000

Abstract

Based on the current best estimates of the fundamental geodetic parameters, i.e., W ₀ (Grafarend and Ardalan, Journal of Geodesy 71 (1997) 673-679), GM (Ries et al, Geophys. Res. Letters 19 (1992) 529-531), J ₂ (Lemoine et al, GRAGEO-MAR 1996, International Association of Geodesy, Symposia 117, (1996) 461-469) and Ω (given in Internal Communications of IAG/IUGG Special Commission 3, Darmstadt (1997)), the form parameters of a Somigliana-Pizetti level ellipsoid, namely the semi-major axis a and semi-minor axis b (or equivalents the linear eccentricity ɛ = √a ² - b ²) are computed. There are six parameters namely the four fundamental geodetic parameters {W ₀ , GM, J ₂ , Ω} and the two form parameters {a, b} or {a, ɛ}, which determine the ellipsoidal reference gravity field of Somigliana-Pizetti type constraint to two nonlinear condition equations. Their iterative solution leads to best estimates a = (6378136.572 ±0.053)m, b = (6356751.920 ±0.052)m, ɛ= (521853.580 ±0.013)m for the tide-free geoid of reference and a = (6378136.602 ±0.053)m, b = (6356751.860 ± 0.052)m, ɛ= (521854.674 ±0.015)m for the zero-frequency tide geoid of reference. The best estimates of the form parameters of a Somigliana-Pizetti level ellipsoid, {a, b}, differ significantly by -0.398m, -0.454m, respectively, from the data of the Geodetic Reference System 1980.