Terrain corrections for airborne gravity gradiometry data are calculated from a digital elevation model (DEM) grid. The relative proximity of the terrain to the gravity gradiometer and the relative magnitude of the density contrast often result in a terrain correction that is larger than the geologic signal of interest in resource exploration. Residual errors in the terrain correction can lead to errors in data interpretation. Such errors may emerge from a DEM that is too coarsely sampled, errors in the density assumed in the calculations, elevation errors in the DEM, or navigation errors in the aircraft position. Simple mathematical terrains lead to the heuristic proposition that terrain-correction errors from elevation errors in the DEM are linear in the elevation error but follow an inverse power law in the ground clearance of the aircraft. Simulations of the effect of elevation error on terrain-correction error over four measured DEMs support this proposition. This power-law relation may be used in selecting an optimum survey flying height over a known terrain, given a desired terrain-correction error.

The Bass Strait FALCON airborne gravity gradiometer (AGG) survey was flown over an area of the Gippsland Basin in Bass Strait in July 2002. The survey, centred on the gas-producing Marlin and Snapper fields. coincided with a contemporary, detailed marine gravity survey. These marine gravity data, as well as pre-existing data from satellite gravity and sparse marine gravity surveys, were used in comparisons with the FALCON data.The vertical gravity gradient data outlined a major Eocene channel. Interpretation, including modelling of representative seismic lines, revealed the particular usefulness of these data for mapping shallow faults. Conventional vertical gravity from the FALCON survey was better at the longer wavelength features, typically the major tectonic elements such as basin bounding faults, and relative sediment thickness. Comparisons with the marine and satellite gravity data showed that the FALCON gravity reproduced all the information nailable in the other surveys at wavelengths up to the survey size. At shorter wavelengths, the FALCON data had higher sensitivity than all other datasets, including the detailed marine gravity. Incorporation of longer wavelengths from the satellite or other gravity into the FALCON gravity proved successful in improving the longer wavelength information and regional context. As a result of this study, the standard FALCON processing has been improved to allow such incorporation on all surveys where separately acquired sparse gravity data are available.

No abstract