Complete Bouguer Anomalies for the Australian National Gravity Database

Abstract

The Australian National Gravity Database (ANGD) contains over 1.8 million gravity observations from over 2,000 surveys conducted in Australia over the last 80 years. Three processes are required to correct these observations for the effects of the surrounding topography: (a) a Bouguer correction (Bullard A), which approximates the topography as an infinite horizontal slab; (b) a correction to that horizontal slab for the curvature of the Earth (Bullard B); and (c) a terrain correction (Bullard C), which accounts for the undulations in the surrounding topography. These three corrections together produce complete Bouguer anomalies. Since February 2008, a spherical cap Bouguer anomaly calculation has been applied to data extracted from the ANGD. This calculation applies the Bullard A and Bullard B corrections. Terrain corrections, Bullard C, have now been calculated for all terrestrial gravity observations in the ANGD allowing the calculation of complete Bouguer anomalies. These terrain corrections were calculated using the Shuttle Radar Topography Mission 3 arc-second digital elevation data and Geoscience Australia?s 2009 Bathymetry and Topography Grid. The complete Bouguer anomalies calculated for the ANGD provide users of the data with a more accurate representation of crustal density variations through the application of a more accurate Earth model to the gravity observations.