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B.C.
Geophysical Society Thursday
January 11, 2001, Placer Dome Boardroom, Second Floor, Bentall 2 Building,
Vancouver, B.C. (Note
change of location from United Kingdom Building) Dr,
Gary Borstad, G.A. Borstad and Associates, Sidney, B.C., will present "An
overview of the SFSI-2 (SWIR Full Spectrum
Imager) and some examples of its use for mapping clay alteration minerals at
Cuprite Nevada". Several
short reports available at http://www.borstad.com/mineral.html will be
summarised in the presentation. Abstract: Electronic
and vibrational processes at the atomic scale create narrow diagnostic features
in the visible and particularly in the Short Wave Infra-Red (SWIR) reflectance
spectra of rocks (e.g. Hunt and Ashley, 1979) and SWIR spectroscopy can be used
to identify sulfates, carbonates, chlorites, silicates and phosphates. Minerals,
such as kaolinite, dickite, alunite, muscovite, jarosite and illite, which are
present in gold-bearing alteration systems can be identified through their
absorption spectra. These minerals are important constituents of altered rocks
and there are now several commercially manufactured hand-held SWIR spectrometers
in common use on the ground. A number of airborne SWIR sensors have also
appeared, with the aim of producing detailed image maps of much larger areas
than can be produced by a geologist walking the terrain. Much of the science of
airborne mineral mapping has come from a NASA program involving the AVIRIS
Airborne Visible/Infrared Imaging Spectrometer). AVIRIS acquires 224 channels in
the Visible and Near Infra-Red (VNIR) and SWIR, and has been shown in a long
series of scientific papers to be a very effective mineral mapping tool (e.g.
Goetz, et al., 1985). It has become the standard by which all other SWIR
instruments are measured. The
Canada Centre for Remote Sensing (CCRS) of Natural Resources Canada has designed
and constructed another SWIR airborne sensor, called the SWIR Full Spectrum
Imager (SFSI). SFSI was originally intended to provide an alternative source of
SWIR data for research and to provide higher spatial resolution imagery than the
20 m pixels produced by AVIRIS (Neville et al, 1995). Borstad Associates Ltd
took over the SFSI in 1996 and have redeveloped it for commercial survey
purposes. SFSI-2 also operates in the Short Wave range, from 1220 nm to 2420 nm
and has the ability to simultaneously acquire the full spectrum (230 bands) at
high spatial (4 m) and spectral (10.4 nm) resolution. The instrument utilizes a
two-dimensional detector array, refractive optics and a transmission grating
with an angular field of view of 32 degrees. The sensor has been in commercial
operation since 1998 and has now flown in Siberia, Nevada, Utah, Arizona, Peru,
Chile, North West Territories, British Columbia and
Saskatchewan. In
this talk we will present examples of image maps made from SFSI-2 in Utah and
Nevada, and compare mineral maps produced by the SFSI at 4 m ground resolution,
using a process of spectral unmixing, with maps produced from 20 m resolution
AVIRIS data, using the TRICORDER 3.3 algorithm. Dr.
Gary Borstad G.
A. Borstad Associates Ltd 114
- 9865 West Saanich Road Sidney,
British Columbia, CANADA V8L 5Y8 Ph
250-656-5633 Fx 250-656-3646 email
[EMAIL PROTECTED] |
