Proceedings PaperExtracting Spectral Information From Imaging Spectrometer Data: A Case History From The Northern Grapevine Mountains, Nevada/California
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Seven flightlines of Airborne Imaging Spectrometer (AIS) data were analyzed for an area of hydrothermally altered rocks in the northern Grapevine Mountains, Nevada and California. Atmospheric and solar irradiance effects were removed from the raw data by first normalizing the data using an equal-area normalization and then dividing each spectrum (pixel) in an AIS flightline by an average spectrum calculated from all of the flightlines in a given mission. These procedures produced "Internal Average Relative (IAR) Reflectance" spectra that closely resemble laboratory and field reflectance spectra. Once the data were reduced to IAR reflectance, then removal of a continuum from the data was used to put all of the absorption bands on a common reference plane. The strongest absorption feature in each spectrum was analyzed by automatically calculating band position, band depth, and band width, and mapping these parameters into a hue, saturation, intensity (HSI) coded image for pixels with absorption features deeper than a selected cutoff depth. The color coded image allowed rapid identification of mineral groups based upon band position (hue). Band width was shown as variation in color saturation while image intensity allowed a subjective estimate of the band depth to be made. Examination of individual spectra and comparison to spectra of laboratory standards allowed positive identification of sericite (muscovite), montmorillonite, calcite, and dolomite.