On the use of Australian geodetic datums in gravity field determination

The treatment of gravity and terrain data prior to any gravimetric geoid computation is critical. If errors remain in the gravity or terrain data or both, these will propagate into any subsequently determined gravimetric geoid. The effects of horizontal and vertical datums on gravity reduction and, hence, the gravimetric geoid are discussed. Free-air gravity anomalies should be computed on the normal ellipsoid, after a coordinate transformation from the Australian Geodetic Datum, and incorporate a second-order free-air reduction. Their combined effect can reach -0.120mgal or an estimated -12cm in the resulting geoid. Also, the separation between the AHD and the geoid has an effect on the gravimetrically determined geoid. A combined oceanographic and levelling estimate implies that this effect can reach 0.216mgal and 22cm in the geoid. If this rigorous gravity data preparation is employed, centimetric improvements can be expected in all wavelengths of the resulting gravimetric geoid.