The vast sandy deserts of Australia are poised to yield up their mineral secrets to a unique airborne radar system, AIRSAR (Airborne Synthetic Aperture Radar).

Sand is impenetrable to the more common remote sensing imaging systems widely used for airborne minerals exploration, but not to AIRSAR, which uses echoes from the radar wave to create valuable pictures of the terrain beneath the sand.

The system, which becomes available in 1999, operates from a NASA DC-8 aircraft which flies at 8500 metres transmitting radar microwaves capable of penetrating dry sand up to 1.5 metres deep.

AIRSAR was invented by America's NASA and the Jet Propulsion Laboratory and deployed to Australia for evaluation by the Co-operative Research Centre for Landscape Evolution and Mineral Exploration (CRC LEME), CSIRO, and University of New South Wales.

Dr Ian Tapley, of CRC LEME, says the potential of AIRSAR to conquer the sand barrier problem has opened up hundreds of thousands of square kilometres of arid and semi-arid desert to faster and more cost-effective airborne exploration.

"Gaps in companies' exploration data-sets can now be filled. Previously hidden land forms are being revealed and with them are coming valuable clues to the prospectivity of these areas," Dr Tapley says.

Analysis of AIRSAR data from the Great Sandy Desert region, near to the Telfer gold mine in Western Australia, was recently completed. The study revealed several significant new insights into the geological structure of the region, including new folds, shears and a buried river system.

"A previously unmapped fold formation (syncline) with properties similar to those of the Telfer Dome - the sedimentary rock formation which hosts the Telfer gold deposit - was identified," Dr Tapley said.

"In previously recorded Landsat TM and airborne magnetic survey images of the same area the syncline is not visible, because it is masked by the sand cover and the spinifex vegetation and has no magnetic signature."

Other key areas in line to benefit from AIRSAR's penetration of sand are the Birindudu Basin (adjacent to the Tanami Desert on the WA-NT border), and the Granites-Tanami Block (North West of Alice Springs).

Dr Tapley says AIRSAR's microwave radar brings a string of other benefits to miners' portfolios of exploration techniques, including:

• Radar is non-selective in its detection of underground structures. Unlike magnetic radiation, which only detects land forms that contain particular iron-bearing minerals or 'magnetic signatures', radar detects all land forms and objects so long as the overlying sand veneer is homogeneous and free of moisture.
• AIRSAR images are provided at a very large scale - 10m x 10m spatial resolution and they are complete images. Magnetic survey systems rely on interpolation of data collected by aircraft whose flightpaths might be several hundred metres and sometimes several kilometres apart.
• AIRSAR's radar is unaffected by cloud, light rain or smoke, and can be flown day or night.

The value of the radar-based data to Australian mining and exploration can be gauged by the strong commercial support for the AIRSAR project.

Several of the nation's largest miners have sponsored NASA's deployment of its aircraft in Australia, including WMC Resources, Rio Tinto, Stockdale, the Normandy Group, Sumitomo Metal Mining and Hamersley Iron. The most recent deployment was from November to December 1996 when the NASA aircraft targeted sites extending from New Zealand to Taiwan, half of which were in Australia.

Dr Tapley said that while access to AIRSAR was presently limited to companies sponsoring the aircraft's deployment in Australia, the system is expected to be available commercially for use in light aircraft by 1999.

More information: Dr Ian Tapley, CRC for Landscape Evolution and Mineral Exploration, CSIRO Division of Exploration and Mining.
(08) 9333 6263 (W) 08 9448 3544 (H)