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15 December 1998 |
Ref 98/289 |
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A CSIRO breakthrough will help turn mines back into greener landscapes after they have yielded their mineral wealth, assist in discovering new mineral deposits and cut industry costs.
Scientists have developed a correction technique for a problem in imagery known as BRDF (Bi-directional Reflectance Distribution Function), producing a dramatic improvement in the precision of aerial remotely-sensed survey images. These images are used for planning and monitoring minesite restoration and rehabilitation programs.
Developed by CSIRO Exploration & Mining's Minesite Rehabilitation Research team based in Perth, the BRDF correction technique gives significant improvement to raw images and the information they contain.
The amount of the sun's reflected energy can reveal whether the object is a flourishing tree or a dying one, and so is important to understand quantitatively what is going on in the landscape.The research has overcome a problem caused by variation in solar illumination on different parts of images. Under certain viewing angles, the image will show more of the shaded sides of the trees and other materials at one side of the image than those on the other side.
An added complication is that the behaviour of the surface materials in reflecting light can cause dramatic changes in the intensity of the measured signal. For example, some surfaces behave like mirrors and others like paper under certain viewing angles. These brightness variations have distorted aerial photography for decades, leaving uncertainty about the true situation at ground level.
The BRDF correction process eliminates these distortions by incorporating satellite images of the same ground into the analysis.
While the satellite images have less detail because they are taken from a much greater height, they show little BRDF effect and the correction is based on this difference.
"Our successful marriage of the data from the two sources (satellite and aerial) has given us an accuracy previously only dreamt about," says CSIRO's Ms Cindy Ong. "These days you can't get away with non-quantitative remote sensing. Government and industry now demand very high standards with revegetation work and in the accuracy of monitoring."
Ms Ong says the BRDF correction process can be used with both digital cameras and airborne scanners - the two most common remote sensing formats used by the mining industry.
The new levels of data accuracy will be a significant cost-saver for the industry where minesite rehabilitation work can cost $30,000 per hectare, per year.
If the miners know where the rehabilitation is struggling, they can go back and apply discreet management, thus ensuring there is no unnecessary delay in signing off on the environmental conditions set by government.
The process will also be a boon for minerals exploration. Some vegetation is an indication of particular minerals lying beneath it. The technique developed by the CSIRO team enables this vegetation to be identified more accurately, leading to the discovery of potential areas of mineralisation.
Another promising use for the technique is in giving new value to old aerial survey photographs. "Data from decades back, which until now has had limited use because of questionable accuracy, can be resurrected and used as a baseline for measuring the success of rehabilitated areas," says Ms Ong.
"The process costs slightly more because of the satellite images and extra computing. But, without corrections the best images can give up to 15-20% error. Our processing eliminates almost all of the error. It's a giant leap forward!" she says.
BRDF is undergoing further tests and trial applications with funding provided by the CSIRO Earth Observation Centre.
More information:
Ms Cindy Ong, CSIRO 08 9333 6243
mobile 0418 273 306
(Australia's largest scientific research organisation)
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