AAGD07: A new absolute gravity datum for Australian gravity and new standards for the Australian National Gravity Database

Abstract

The current Australian gravity datum, Isogal84, is defined by the Australian Fundamental Gravity Network (AFGN). The AFGN consists of about 950 stations at over 250 locations throughout Australia with the first stations in the network being established in the early 1950s. Prior to Isogal84, the datum was based on relative ties to overseas sites. The Isogal84 datum is based on 5 absolute gravity sites within Australia that were established in 1979 using a Soviet absolute gravimeter. Absolute gravity measurements conducted at 60 AFGN sites by Geoscience Australia using a portable absolute gravimeter have shown that the Isogal84 datum is 78 microgals (1 microgal = 1´10-8 m/s2) higher than the absolute measurements. A new gravity datum, the Australian Absolute Gravity Datum 2007 (AAGD07), has been defined based on these absolute gravity measurements and the AFGN and the Australian National Gravity Database (ANGD) have been adjusted to this new datum. Concurrent with implementing AAGD07, the formulae used for reducing gravity data in the ANGD have been reviewed and updated. These changes include using the 1980 International Gravity Formula, global horizontal and vertical datums, and a spherical cap Bouguer correction that accounts for the Earth?s curvature. These new formulae provide more accurate anomalies, particularly in longer wavelengths which will be beneficial to regional studies.