Towards a new absolute datum for Australian gravity

Abstract

The Australian Fundamental Gravity Network (AFGN) defines the datum, currently Isogal84, and scale for gravity surveys conducted in Australia and the surrounding oceans. It consists of over 900 stations at over 250 locations. The network was initially established in the early 1950?s with stations added at various times up to the present. All of these stations were established using relative gravimeters to measure gravity differences between stations. The errors in these measurements were distributed by least squares adjustments of the network. The network datum was based on relative gravity ties to overseas gravity stations until the Isogal 84 datum was established. Isogal84 is based on five absolute gravity sites that were established in 1979 by a Soviet absolute gravimeter. Geoscience Australia has conducted absolute gravity measurements with a portable absolute gravimeter at 54 AFGN stations. These measurements show that the Isogal84 datum is 75 microgals (1 microgal = 1x10-8 m/s2) higher than the absolute datum and that the accuracy of the network is 30 microgals. Geoscience Australia is planning to adjust the Australian Fundamental Gravity Network and define a new datum based on these absolute gravity measurements to improve the accuracy of the network and provide a consistent framework for gravity surveyors.