This grid is derived from gravity observations stored in the Australian National Gravity Database (ANGD) as at February 2016 as well as data from the 2013 New South Wales Riverina gravity survey. Out of the approximately 1.8 million gravity observations 1,371,998 gravity stations in the ANGD together with 19,558 stations from the Riverina survey were used to generate this image. The grid shows isostatic residual gravity anomalies over onshore continental Australia. The data used in this grid has been acquired by the Commonwealth, State and Territory Governments, the mining and exploration industry, universities and research organisations from the 1940¿s to the present day.

Continental Australia has a base coverage of 11 kilometres, with South Australia, Tasmania and part of New South Wales covered with gravity stations at a spacing of 7 kilometres. Victoria has station coverage of approximately 1.5 kilometres. Federal, State and Territory Government initiatives have systematically infilled at a station spacing of 2 to 4 kilometres to improve coverage in areas of scientific or economic interest. Other areas of detailed coverage have been surveyed by private companies for exploration purposes. Only open file data held in the ANGD at February 2016 were used in the creation of the grid. The 2013 Riverina survey was added to the gridding process as this survey was not in the ANGD at the time.

The depth to mantle model and subsequent isostatic corrections were calculated using a modified version of the USGS program AIRYROOT (Simpson et al., 1983) provided by Intrepid Geophysics (1). The 2009 Bathymetry and Topography Grid (Whiteway, 2009) was used to calculate the depth to Mohorovi¿i¿ discontinuity (Moho) following the Airy-Heiskanen crustal root model. The bathymetry and topography grid was subsampled to 1 km cell size and then low pass filtered to remove spatial wavelengths greater than 50 km. A crustal density of 2670 kg/m3 was used for the isostatic correction, with an assumed density contrast between the crust and mantle of 400 kg/m3. An initial average depth to Moho at sea level of 37 km was used in the calculation. This was derived from refraction and wide-angle reflection seismic experiments and receiver function analyses around Australia (Goncharov et al., 2007). The isostatic corrections were then applied to the Complete Bouguer Gravity Anomaly Grid of Onshore Australia 2016 to produce the Isostatic Residual Gravity Anomaly Grid of Onshore Australia 2016.

The original grid was converted from ERMapper (.ers) format to netCDF4_classic format using GDAL1.11.1. The main purpose of this conversion is to enable access to the data by relevant open source tools and software. The netCDF grid was created on 2016-08-04.

References:

(1) http://www.intrepid-geophysics.com

Goncharov, A., Deighton, I., Tischer, M. and Collins, C., 2007. Crustal thickness in Australia: where, how and what for? ASEG Extended Abstracts, 2007, 1-4, ASEG 2007 19th Geophysical Conference.

Simpson, R.W., Jachens, R.C. and Blakely, R.J., 1983. AIRYROOT: A FORTRAN program for calculating the gravitational attraction of an Airy isostatic root out to 166.7 km. US Geological Survey Open File Report 83-883.

Whiteway, T. G., 2009. Australian bathymetry and topograhy grid. Geoscience Australia, Canberra. http://dx.doi.org/10.4225/25/53D99B6581B9A

20170906 NetCDF file restructured to be indexed Southward-positive for improved performance and interoperability