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Field- and lab-based Regional and global
imaging spectroscopy geologic units identified
Fine-scale units within
rocks identified
Headwall CAO- CRISM
AToMS
hyperspectral OMEGA determined
M3
UCIS AVIRIS Hyperion
Spectral bands HyMap
multispectral WorldView-3 differences distinguished
Mastcam/ ASTER
Pancam ThemLaisTnhVdesISmatis IRMODIS
HiRISE
µm m km
Spatial resolution
Figure 1. Conceptual plot of the relative spectral sampling versus the spatial
scales of observations by various imaging systems and the gap that ground-
based imaging spectroscopy fills (dashed box). Blue text indicates imaging
systems on Earth, red italicized text is for Mars, and gray bolded text is for the
Moon. The number of spectral bands and the spatial resolutions used in this
plot are generally those in the visible-shortwave infrared regions. The Headwall
and Ultra Compact Imaging Spectrometer (UCIS) imagers were used to
acquire data presented in this paper. ASTER—Advanced Spaceborne Thermal
Emission and Reflection Radiometer; AVIRIS—Airborne Visible/Infrared
Imaging Spectrometer; CAO-AToMS—Carnegie Airborne Observatory–
Airborne Taxonomic Mapping System; CRISM—Compact Reconnaissance
Imaging Spectrometer for Mars; M3—Moon Mineralogy Mapper; OMEGA—
Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité; HiRISE—High
Resolution Imaging Spectrometer Experiment; MODIS—Moderate Resolution
Imaging Spectrometer; THEMIS VIS/IR—Thermal Emission Imaging System
(visible/infrared).
mission (Van Gorp et al., 2014), and the MicrOmega instrument
will be on the upcoming ExoMars rover and Hayabusa-2 mission
(Pilorget and Bibring, 2013). An orbital VSWIR imaging spec-
trometer has also been selected to fly to Europa. The shortwave
infrared wavelengths are critical for mineralogic analyses
because unique overtones and combination tones of vibrations
within mineral structures occur in this region. The visible wave-
lengths alone cannot distinguish mineralogies. While not the
focus of this paper, similar systems are in development to
measure thermal infrared emissivity in the laboratory (e.g.,
Edwards and Christensen, 2013). There is a steadily growing
suite of literature on the use of imaging spectroscopy of outcrops
and samples, including core scanning, to answer geologically
relevant questions (e.g., Kruse et al., 2012; Kurz et al., 2012;
Murphy et al., 2012, 2014; Butz et al., 2015; Greenberger et al.,
2015a, 2015b; Yokoyama et al., 2015). Here we highlight some
exciting applications of this emerging, non-destructive tech-
nology and the science discoveries enabled.
1 GSA supplemental data item 2015342, imaging spectroscopy methods and calibration, is online at www.geosociety.org/pubs/ft2015.htm. You can also request a copy
from GSA Today, P.O. Box 9140, Boulder, CO 80301-9140, USA; gsatoday@geosociety.org.
EXAMPLE 1: CHARACTERIZING HABITABILITY AND
SEARCHING FOR BIOSIGNATURES IN SERPENTINE-
BEARING ROCK
The serpentinization process liberates molecular hydrogen that
can sustain microbial communities and react through biotic and
Mineral associations Basic compositional abiotic processes to form methane (e.g., Kelley et al., 2001, 2005;
Sleep et al., 2004; Oze and Sharma, 2005; Schulte et al., 2006;
Cardace and Hoehler, 2009; Etiope and Sherwood Lollar, 2013;
McCollom and Seewald, 2013). The oxidation states and coordi-
nation environments of iron produce diagnostic absorption
features readily detected and mapped with imaging spectroscopy
but not so easily spatially resolved with traditional analysis tech-
niques. In serpentinized bodies, the oxidation state and iron coor-
dination chemistry are related to the volume of hydrogen
produced and the availability of reduced gasses capable of
supporting microbial metabolisms (Marcaillou et al., 2011;
Andreani et al., 2013). Though degrees of serpentinization are not
readily apparent visually, work by Greenberger et al. (2015b) used
imaging spectroscopy in the 0.42–1.1 µm region to map the depth
of an electronic transition of tetrahedrally coordinated Fe3+ occur-
ring at 0.45 µm as a proxy for hydrogen production. Using new
imaging data that cover an extended wavelength range (0.40–2.5
µm; Fig. 2), the 0.45 µm feature is shown with the two dominant
minerals, carbonate and serpentine, which exhibit sharp vibra-
tional absorptions mapped through calculation of the depths of
these features (Clark and Roush, 1984) and other spectral param-
eters (data processing algorithms are described in the GSA
Supplemental Data Repository1). Different portions of this sample
have undergone different degrees of serpentinization; those areas
with tetrahedral Fe3+ have undergone advanced serpentinization
and are promising areas to search with still higher spatial resolu-
tion compositional or isotopic techniques (e.g., scanning electron
microscopy, mass spectrometry) for microbial biosignatures and
to understand the production of reduced gases.
EXAMPLE 2: HYDROTHERMAL ALTERATION AND
DIAGENESIS OF LACUSTRINE PILLOW BASALTS
Alteration rinds illuminate conditions of water-rock interac-
tions, and progressive changes from interior to exterior reflect
increasing degrees of alteration (e.g., Hausrath et al., 2008). With
sub-millimeter spatial resolutions, imaging spectroscopy GSA TODAY | www.geosociety.org/gsatoday
measurements of alteration rinds resolve fine changes in miner-
alogy with alteration. Data from an Early Jurassic lacustrine
pillow lava from the Hartford Basin are shown in Figure 3
(Greenberger et al., 2015a). In this work, coordinated imaging
spectroscopy, electron microprobe, microscopic X-ray diffraction,
microscopic thermal emission spectroscopy, and microscopic
Raman spectroscopy analyses of a thick section across an altera-
tion rind (Fig. 3C) characterized spectral, mineralogic, and chem-
ical transformations. Unexpected key identifications with imaging
spectroscopy include calcic clinopyroxenes interpreted to have
formed through >400 °C hydrothermal alteration (e.g., Bird et al.,
1984; Manning and Bird, 1986), pervasive oxidation, Fe/
Mg-phyllosilicate signatures that increase in strength toward the
exterior, and higher water content of calcites in the rind, either as
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