Calibration of Evaluation of Imaging Spectrometer Data: Cripple Creek, Colorado

R. N. Clark, B. J. Middlebrook, G. A. Swayze, T. V. V. King, K. E. Livo, D. H. Knepper, K. Lee

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and Geophysical Environmental Imaging Spectrometer (GERIS) data were obtained over Cripple Creek and Canon City, Colorado, on October 19, 1987, and September 16, 1988, respectively. The region contains Tertiary volcanic rocks and Precambrian metamorphic and plutonic rocks, including areas of well-known alteration and mineralization.

Many ground calibration sites in the area were measured with a field spectrometer, and samples were returned to the laboratory for more detailed spectral characterization. The laboratory data were used to calibrate the imaging spectrometer field data to ground reflectance. Laboratory reflectance spectra of samples collected at the calibration sites were convolved to match the resolution and sampling interval of each of the imaging spectrometers. Next, the corresponding raw spectral data, the laboratory calibration data, and the dark spectra were extracted. The imaging spectrometer spectra were then dark corrected and calibrated to ground reflectance.

Once calibrated, selected spectra in the image were extracted and examined and the signal-to-noise performance was computed. (The calibrated data sets can be used to derive reflectance spectra for direct analysis.) A simple spectral analysis was conducted to map specific absorption band depths in the image. Absorption bands were chosen for minerals and vegetation that are known or likely to occur in the Cripple Creek area.

Band-depth images were computed for a number of minerals, including the 1.7-µm band of gypsum, the 1.27-µm band of biotite, the 2.34-µm band of calcite, the 2.32-µm band of dolomite, the 2.21-µm band of montmorillonite, the 2.20-µm band of kaolinite, the 0.45-µm and 0.93-µm bands of jarosite, the 0.85-µm band of hematite, and the 0.94-µm band of goethite. A band-depth image for the 0.68-µm band of Lodgepole pine was also computed.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.