Mineral predominance map for Nabesna, Alaska, derived from imaging spectrometer reflectance data

Reflectance data from HyMap™ were processed using the Material Identification and Characterization Algorithm (MICA), a module of the USGS PRISM (Processing Routines in IDL for Spectroscopic Measurements) software (Kokaly, 2011), programmed in Interactive Data Language (IDL; Harris Geospatial Solutions, Broomfield, Colorado). The HyMap reflectance data are provided and described in this data release. MICA identifies the spectrally predominant mineral(s) in each pixel of imaging spectrometer data by comparing continuum-removed spectral features in the pixel’s reflectance spectrum to continuum-removed absorption features in reference spectra of minerals, vegetation, water, and other materials. Linear continuum removal is a technique to isolate an absorption feature from background spectral variations (Clark and Roush, 1984). Following continuum removal of a spectral feature in a reference spectrum and the corresponding channels in an imaging spectrometer pixel, the coefficient of determination (r2) of a linear regression of these continuum-removed values is used as the metric to judge the degree of match (or fit) between the unknown and reference spectra. MICA analysis is controlled by a command file, which lists the reference spectra for comparison to imaging spectrometer pixel spectra, the wavelength regions for continuum removal and spectral feature comparison, and other parameters (see Kokaly, 2011). For each pixel, the reference spectrum with the highest fit value identifies the predominant mineral class. The reference spectra used in this MICA analysis are available to the public in the USGS spectral library (Kokaly and others, 2017). The MICA command file used in this study was adapted from that used to process HyMap data covering Afghanistan (Kokaly and others, 2013). The MICA command file is provided in this data release and also in the digital appendix of Graham and others (2018).