1Attempts to Unify the Australian Height Datum Between the Mainland and Tasmania

Abstract. AUSGeoid98 is used with GPS and Aus-tralian Height Datum (AHD) heights at 1013 points, and subsets thereof, to estimate the offset between the AHD(Mainland) and AHD(Tas). It appears that the AHD(Tas) is offset below the AHD(Mainland) between (26±33)cm and (12±12)cm, which agree with previous estimates and sea-surface topography models. The offsets are heavily influenced by the spatial distribution of the GPS-AHD-AUSGeoid98 points, being a function of latitude and proximity to the Australian coast. This is possibly due to the fixing of multiple tide-gauges to mean sea level in the adjustment of the AHD. For any future unifica-tion of the AHD(Mainland) and AHD(Tas) into a global vertical datum, appropriate datum connection points must first be chosen