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