This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied.
The 2009 gravity grid over the Australian Region is derived from onshore observations recorded at approximately 1.4 million gravity stations held in the Australian National Gravity Database (ANGD) by Geoscience Australia (GA), and free-air gravity anomaly data derived from satellite altimetry by Sandwell and Smith (1997) over marine areas. The onshore data were acquired by the Commonwealth, State and Territory Governments, the mining and exploration industry, universities and research organisations from the 1950s to the present day.
Continental Australia has a basic station spacing coverage of 11 kilometres, with South Australia, Tasmania and part of New South Wales covered at a spacing of 7 kilometres. Victoria has station coverage of approximately 1.5 kilometres. Recent Federal, State and Territory Government initiatives have funded systematic infill at a grid station spacing of 2, 2.5 or 4 kilometres to provide improved coverage in areas of scientific or economic interest. Other areas of detailed coverage have been surveyed by private companies for exploration purposes.
Over the continental region only open file data as held in the ANGD at May 2009 were used in the creation of the grid. Data derived from satellite altimetry were used exclusively over the marine region.
The data values contained in the grid are Spherical Cap Bouguer gravity anomalies over Continental Australia while free-air anomalies are used offshore. The onshore Spherical Cap Bouguer gravity anomalies were calculated using a density of 2.67 tm-3. Offshore Ellipsoidal Free-air gravity anomalies were based on gravity (V16.1) and topography (V9.1) data extracted from the Marine Gravity from Satellite Altimetry dataset (Sandwell and Smith, 1997, 2005). These data were combined with the GA onshore gravity data and gridded using a variable density gridding technique provided by the INTREPID Geophysics software package. The data were gridded to a cell size of 0.5 minutes of arc = 0.00833333 (approximately 800m) for the geodetic grid and to a cell size of 800m for the Lambert Conformal Conic Projection grid.
The parameters of the geodetic grid are:
Grid spacing : 0.5 minute = 0.0083333 degree (approximately 800 m)
Projection : Rectangular in latitude and longitude
Datum : GDA94
Grid size : 5278 rows x 8399 columns
Grid origin : 8:0:33.9958 South, 100:0:20.9934 East (0,0)
Scaling : Nil. Values are in decimal units (ms-2)
Null value : -99999.00
Data accuracy : 5 ms-2, maximum error 100 ms-2 onshore
Data precision : 1 ms-2
The gravity data as supplied are based on the Australian Absolute Gravity Datum (AAGD07) (Tracey et al., 2008). The gravity unit used is micrometres per second squared (ms-2) which is equivalent to 0.1 milligals (mGal).
Geoscience Australia (2009) Onshore geodetic Spherical Cap Bouguer gravity anomalies. Bioregional Assessment Source Dataset. Viewed 07 December 2018, http://data.bioregionalassessments.gov.au/dataset/90c0e7ac-587b-45d7-adfd-931e53ba5ead.