Calibration, processing and interpretation of hyperspectral data over the Broken Hill region

Abstract

In March 2002, the New South Wales Department of Mineral Resources contracted an airborne hyperspectral remote sensing survey of the Broken Hill region in New South Wales. It covered 4 000 square kilometres and involved the acquisition at a ground sampling distance of 3 m. HyMaptm was selected as the hyperspectral system as it is a 126 band sensor that provides a combination of high spatial resolution, spectral coverage, signal-to-noise ratio and image quality. The HyMaptm sensor utilises four 32-element detector arrays to provide 126 spectral channels covering the 450 nm to 2 500 nm spectral range over a 512 pixel swath. The HyMap?s instantaneous field of view of 3 m ´ 3 m, corresponded to a flight altitude of 1.4 km above ground level and an aircraft ground speed of 110 knots. The ground swath coverage corresponded to 1.6 km for each flightline resulting in a 20% overlap. The data processing and data products were radiance calibrated, atmospheric corrected and geometric corrected. Spectral and radiometric calibration of the HyMaptm sensor was accomplished prior to the survey and this information was used to allow the conversion of the raw DN counts to radiance values in uW/cm²/nm/sr. Using the ENVI image processing package, preliminary lithology maps have now being generated using the Mixture Tuned Matched Filtered method. The maps identify stratigraphic units; regolith; alteration zones; sulphate; hydroxyl-bearing minerals; iron oxides; and green and dry vegetation. These maps will now be taken into the field for verification and then released to the mineral industry as a GIS set of geo-referenced mineralogical map layers, along with other geological and geophysical data.