A set of recommendations for application of automated terrain correction of gravity anomalies in Australia.
Recent improvements in position and elevation determinations due to Differential GPS have led to substantial improvements in the accuracy and precision of observed gravity data, and a general renaissance in the use of gravimetry in Australia. Increasingly, users of the data are specifying levels of precision in derived measurements such as the Bouguer Anomaly, that reflect only these positioning improvements without considering topographic effects on precision. The consequence has been that most gravity data routinely submitted to the National Gravity Database are Simple Bouguer Anomalies only, and contain a range of unquantifiable acquisition noise that degrades the quality of the overall dataset. This paper briefly describes the principles behind the terrain correction of observed gravity data, and outlines one method of rapidly calculating the value of a 'first pass' terrain correction for gravity values in Australia. This method makes use of the widely available 9 second Digital Elevation Model of Australia and the IntrepidTM geophysical software package developed jointly by the Australian Geological Survey Organisation and Des Fitzgerald & Associates. The assumptions and pitfalls behind this particular method are also described. A comparison between the Intrepid method and traditional Hammer-chart manual methods is described using a test dataset from northern Tasmania. The comparison shows that the IntrepidTM method is suitable for applying coarse corrections using the generally available DEM. However, the limitations of the DEM itself prevent use in extreme topographic situations, where a more detailed DEM is needed. Overall, in Australian conditions, the method should prove practical. Finally, test data are also provided on an ftp site to allow users to test their own terrain correction algorithms.
