The 24-channel Geoscan scanner includes six grating-dispersed thermal infrared channels, co- registered with the 18 VNIR and SWIR bands. Considerable silicate (hydroxyl) discrimination can be seen in the SWIR band images but will not be treated further in this paper. Each of the TIR bands has a bandpass of 530 nm, centered between 8.64 and 11.28 micrometers band centers dispersed onto a linear detector array of HgCdTe. The system has been flown over Ludwig, Nevada three times (May 1989/June 1990), and twice over Virginia City, Nevada (June 1989/Aug. 1990). Pixel sizes ranged from 3 m to 6 m in this ''research-mode'' flying. In flight the scanner is operated in a noncalibrated, relative-radiance mode in all of the 24 channels. A sample of the terrain to be mapped is overflown, during which the offsets of each channel are set to mid-range (DN equals 127), with the data spread by the gain setting so as to occupy all of the 8-bit range. The recording therefore is of the 8 bits of data spread about the average (relative) brightness of the terrain in that band. In this manner, this scanner differs from almost every other unit either in airborne use or in the Landsat satellites. These units record absolute brightness from which, by use of the calibration parameters, the absolute radiance of the terrain may be reconstructed. The problem is to perform a transformation of the imagery to apparent reflectance allow comparison of the spectra extracted from the airborne imagery to ground-measured spectra. TIR spectra have also been obtained in ground-based stationary laboratory-type operation of the aircraft scanner, viewing warm samples (heated by the sun to about 45 C) for fifteen of the major rock-type assemblages. These laboratory-scanner match the airborne-scanner spectra abstracted from the imagery data as well as direct exitance spectra obtained previously from other sun-warmed samples.
Analysis of the Geoscan Mk II scanner imagery obtained over the past twelve months in Australia and in the USA has shown that this advanced system can effect direct mineral identification (DM1) with only a minimum of processing and in an operational commercial mode of use. This paper attempts to show some of these results with imagery flown over goldmineralizaon (Leonora W. Australia) porphyry-copper mineralization and associated higher-level advanced argiffic alteration (Yerington NV--Ann Mason and Buckskin Ra. ) and a copper-gold skarn nearby (Ludwig NV). In all cases simple banddifferencing is all the processing that is required and this can be effected minutes after landing from a flight using a proprietary image-display system (GIPSy) which accepts the optical disks directly. [3 1.