Geoscience Australia, in collaboration with the States and the Northern Territory, has produced a map showing the surface distribution of potassium, uranium and thorium over 80 per cent of the continent. Almost all the gamma-rays detected near the Earth's surface result from the natural radioactive decay of these three elements, while their distribution indicates a lot about the relative age, stability, composition and processes which have helped to create the Australian landscape.
The new radiometric map has been produced by combining more than 450 individual surveys collected over the past 40 years into a single seamless compilation. The individual surveys were conducted using low flying aircraft and helicopters to measure the gamma radiation emitted from the rocks and soils below.
The map reveals the distribution of bedrock and regolith materials at a national scale, but has sufficient detail to show variations at local scales.
Interpreters can use the new radiometric map to make comparisons between radiometric signatures at different locations around Australia. They also can recognise and appreciate the significance of broad-scale and local features in the data.
Play the movie to learn more about how the map was developed, how to interpret it and its range of applications.
Revealing Australia's Secrets
Flash movie is 17.7MB, 5 Minutes
The gridded digital data which underpins the Radiometric Map of Australia is available free of charge for download using the Geophysical Archive Data Delivery System (GADDS). Because the grids are large (approximately 5.5 GB each), users planning to access entire grids at full resolution should contact minerals@ga.gov.au to arrange alternative means of acquiring the digital data.
The Radiometric Map of Australia dataset comprises grids of potassium (K), uranium (U) and thorium (Th) element concentrations and derivatives of these grids which were developed by seamlessly merging over 550 airborne gamma-ray spectrometric survey grids in the national radioelement database using the method described by Minty et. al. (2009).
Cell sizes: The cell sizes of the original 550 survey grids range from 50 m through to 800 m, but most have a cell size of about 100 m. The original survey grids were levelled and then re-sampled, using minimum curvature (Briggs, 1974), onto the Radiometric Map of Australia grids with a cell size of about 100 m (0.001 degrees).
Filtering: Potassium, uranium, thorium and dose rate grids are available in both filtered and unfiltered versions. The low-pass filtering was achieved by applying a 7-point, degree-3 Savitzky-Golay filter (Savitzky and Golay, 1964) to each of the original survey grids prior to grid merging.
File sizes: At full resolution, each Radiometric Map of Australia grid has 34 761 rows and 40 771 columns. Each grid has a file size of approximately 5.5 GB in ERMapper format.
Projections and datums: The grids are stored as geodetic grids based on the GDA94 datum, but can be re-projected prior to downloading.
Grid data types: The Radiometric Map of Australia dataset is made up of 12 separate grids. Grid data types [PDF 30KB]
The Radiometric Map of Australia is available as a free PDF or JPG and can be purchased as an A0 printed wall map from our Sales Centre.
Explore and visualise the datasets over different parts of Australia using the 3D World Wind Viewer.
The Radiometric 3D Atlas is a series of interactive X3D Models that can be viewed in your web browser.
Briggs, IC 1974, 'Machine contouring using minimum curvature', Geophysics, vol.39, pp. 39-48.
Minty, BRS, Franklin, R, Milligan, PR, Richardson, LM and Wilford, J, 2009. 'The Radiometric Map of Australia', paper presented at the 20th International Geophysical Conference and Exhibition, Australian Society of Exploration Geophysicists, Adelaide, 22-25 February 2009.
Savitzky, A and Golay, MJE 1964, 'Smoothing and differentiation of data by simplified least squares procedures', Analytical Chemistry, vol.36, pp. 1627-1639.