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Imaging spectroscopy of geological samples and outcrops:
                           Novel insights from microns to meters

GSA TODAY | DECEMBER 2015  Rebecca N. Greenberger, Dept. of Earth, Environmental and            presence of clays, sulfates, carbonates, and other minerals formed
                           Planetary Sciences, Brown University, Providence, Rhode Island       through interaction with water on Mars, illuminating potentially
                           02912, USA, and Jet Propulsion Laboratory, California Institute of   habitable past environments (e.g., Bibring et al., 2006; Mustard et
                           Technology, 4800 Oak Grove Drive, Pasadena, California 91109,        al., 2008; Murchie et al., 2009). The Moon Mineralogy Mapper
                           USA, Rebecca.N.Greenberger@jpl.nasa.gov; John F. Mustard,            (M3) provided new insights into the formation, igneous evolution,
                           Dept. of Earth, Environmental and Planetary Sciences, Brown          and composition of the Moon and discovered small and varying
                           University, Providence, Rhode Island 02912, USA; Bethany L.          amounts of hydroxylated or water-bearing materials in its regolith
                           Ehlmann, Jet Propulsion Laboratory, California Institute of          (Green et al., 2011; Pieters et al., 2009, 2011). The Near Infrared
                           Technology, 4800 Oak Grove Drive, Pasadena, California 91109,        Mapping Spectrometer (NIMS) on the Galileo spacecraft (Carlson
                           USA, and Division of Geological & Planetary Sciences, California     et al., 1992) detected hydrated salts on Europa (McCord et al.,
                           Institute of Technology, Pasadena, California 91125, USA; Diana L.   1998) and mapped SO2 volcanism on Io (Douté et al., 2001). The
                           Blaney, Jet Propulsion Laboratory, California Institute of           Visible and Infrared (VIR) Mapping Spectrometer mapped litho-
                           Technology, 4800 Oak Grove Drive, Pasadena, California 91109,        logic units on Vesta’s surface (de Sanctis et al., 2012a, 2012b) and
                           USA; Edward A. Cloutis, Dept. of Geography, University of            has arrived at the dwarf planet Ceres. The Visual and Infrared
                           Winnipeg, 515 Portage Ave., Winnipeg, Manitoba R3B 2E9,              Mapping Spectrometer (VIMS) on the Cassini spacecraft mapped
                           Canada; Janette H. Wilson, Headwall Photonics, Inc., 601 River       surface compositions on satellites of Saturn and discovered a large
                           Street, Fitchburg, Massachusetts 01420, USA; Robert O. Green,        ethane cloud on Titan (Brown et al., 2006; Griffith et al., 2006).
                           Jet Propulsion Laboratory, California Institute of Technology, 4800  Closer to home, imaging spectrometers flown on aircraft, such as
                           Oak Grove Drive, Pasadena, California 91109, USA; and Abigail A.     the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)
                           Fraeman, Division of Geological & Planetary Sciences, California     and HyMap, and in space, such as Hyperion, have mapped miner-
                           Institute of Technology, Pasadena, California 91125, USA             alogies and monitored dynamic changes in ice, vegetation, and
                                                                                                other surface processes on Earth (e.g., Vane et al., 1993; Cocks et
                           ABSTRACT                                                             al., 1998; Green et al., 1998; Painter et al., 2003; Pearlman et al.,
                                                                                                2003; Asner et al., 2004, 2007).
                             Imaging spectroscopy is a powerful, non-destructive mineral-
                           ogic tool that provides insights into a variety of geological          For geological applications, at the typical tens to hundreds of
                           processes. This remote measurement technique has been used for       meters spatial resolutions of these imaging spectrometers (Fig. 1),
                           decades from orbital or aerial platforms to characterize surface     regional or global lithologic units can be distinguished, and some
                           compositions of Earth and other solar system bodies. These           components of the mineral assemblages can be identified. The
                           instruments have now been miniaturized for use in the laboratory     highest-resolution airborne imaging spectrometers currently
                           and field, thereby enabling petrologic analyses of samples and       achieve spatial resolutions of meters, permitting discrimination of
                           outcrops. Here, we review the technique and present four exam-       mineralogies at scales of boulders or larger outcrops. However,
                           ples showing the exciting science potential and new insights into    spatial resolutions of a centimeter or less are generally necessary
                           geological processes.                                                to investigate the mineralogic and petrologic relationships within
                                                                                                rocks—essential to understanding the geologic history—and
                           INTRODUCTION                                                         airborne and orbital imaging spectrometers cannot achieve these
                                                                                                resolutions. The next revolution is field- and laboratory-based
                             Imaging spectroscopy is a technique whereby images are             imaging spectroscopy at sub-millimeter to centimeter resolutions
                           acquired in hundreds of wavelengths simultaneously, permitting       capable of petrologic analyses (e.g., Fig. 1).
                           spectral analysis of each discrete pixel (Goetz et al., 1985).
                           Compositionally distinct materials reflect and absorb light differ-    Recently, visible-shortwave infrared (VSWIR) imaging spec-
                           ently as a function of wavelength, creating unique spectra that are  trometers have been miniaturized and are now commercially
                           used to identify and map compositional units remotely. The appli-    available for use in the field and laboratory (e.g., manufactured by
                           cation of imaging spectroscopy to planetary surfaces has trans-      Headwall Photonics, Inc., Norskk Elektro Optikk AS, and
                           formed our understanding of surface compositions throughout          SPECIM), and prototypes have been deployed and demonstrated
                           the solar system. The Observatoire pour la Minéralogie, l’Eau, les   for use on planetary missions (Blaney et al., 2014; Ehlmann et al.,
                           Glaces et l’Activité (OMEGA) and the Compact Reconnaissance          2014; Van Gorp et al., 2014; Pilorget and Bibring, 2013).
                           Imaging Spectrometer for Mars (CRISM) have revealed the              Specifically, the Ultra Compact Imaging Spectrometer (UCIS) is
                                                                                                in development by the Jet Propulsion Laboratory for a future

     GSA Today, v. 25, no. 12, doi: 10.1130/GSATG252A.1.

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