IEEE Geoscience and Remote Sensing Magazine - June 2019 - 69

If a classified mineral map is required, a more sophisticated algorithm than the Wavelength Mapper may be necessary. An example would be the USGS's Tetracorder algorithm, which uses a so-called confidence score and several
expert rules to express the resemblance of a pixel spectrum
to a typical laboratory spectrum from the USGS Spectral
Library [23]. This matching score can then be translated
into a classification of a pixel into a particular mineral or
group of minerals. The Tetracorder's expert rules make use
of all of the diagnostic parts of a mineral's spectrum and go
far beyond the absorption wavelength and depth on which
the Wavelength Mapper focuses. As a consequence, the
Tetracorder is truly an expert system, while the Minimum
Wavelength Mapper may be more intuitively accessible to
experts and nonexperts alike.
The main applications for the Wavelength Mapper are in
the early stages of a spectral mapping project. It will give
immediate answers on the general information content of
a data set, an assessment of the image quality the users are
dealing with, and, at the same time, a first-pass idea of the
mineralogical distribution patterns in a study area. It can
then serve as a stepping-stone to more advanced methods,
including guiding spectral endmember collection efforts, classifying spectra into mineral classes, directing a
field sampling campaign, or providing a basis for communicating with geologic experts outside the image processing community.
ACKNOWLEDGMENTS
The hyperspectral image data for the proximal-sensing
case study were acquired by Abigail Agus (formerly of the
University of Twente, Enschede, The Netherlands) with the
help of Rainer Bärs and Harri Karjalainen of Spectral Imaging Ltd. Ancillary data were provided by Marinus Dalm
and Mike Buxton of the Technical University of Delft, The
Netherlands. AVIRIS-NG Cuprite data were provided by
the NASA/Jet Propulsion Laboratory through the AVIRISNG data portal. We would like to express thanks to Gregg
Swayze for information on the geology and alteration for
the Cuprite case study and to the AVIRIS-NG team for helpful discussions on data characteristics. We thank Ed Cloutis
and two anonymous reviewers for their constructive comments that helped to improve the consistency and readability of this article.
AUTHOR INFORMATION
Christoph Hecker (c.a.hecker@utwente.nl) received his

M.Sc. degree in Earth sciences from the University of Basel, Switzerland, in 1999 and his Ph.D. degree in remote
sensing of earth resources from the University of Twente,
Enschede, The Netherlands, in 2012. From 2000 to 2001,
he was with the Belize Audubon Society, Belize. In 2001,
he joined the Faculty of Geo-Information Science and
Earth Observation, University of Twente, The Netherlands where he currently works as an assistant professor.
His research focuses on the mineralogy of hydrothermal
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IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE

and geothermal alteration systems to facilitate the exploration of mineral deposits and renewable energy sources.
To study these systems, he applies laboratory, field, and
imaging spectroscopy in the shortwave and thermal-infrared wavelength bands.
Frank J.A. van Ruitenbeek (f.j.a.vanruitenbeek@utwente
.nl) received his M.Sc. degree in geology from Utrecht University, The Netherlands, in 1993 and his Ph.D. degree in
geological remote sensing from Utrecht University in 2007.
In 1997, he started working for ITC, first as a lecturer and
since 2007 as an assistant professor for the Department of
Earth Systems Analysis. He uses infrared hyperspectral data
sets to measure rock composition and microstructure. He
applies these methods to study hydrothermal systems, ore
deposits, early life environments, and planetary surfaces.
Harald M.A. van der Werff (harald.vanderwerff@utwente
.nl) received his M.Sc degree in structural geology and
imaging spectrometry from Utrecht University, The Netherlands, in 1999, and his Ph.D. degree in spatial-spectral
image processing techniques from Utrecht University in
2006. He is currently assistant professor with the Faculty of
Geo-Information Science and Earth Observation, University of Twente, The Netherlands. His research interest is remote and proximal sensing for Earth science applications.
Specifically, these are the porting of hyperspectral mineral
indices to operational and freely available satellite imagery;
analysis of multi-temporal satellite imagery data for monitoring Earth dynamics; and the analysis of time-lapse camera data for monitoring Earth dynamics.
Wim H. Bakker (w.h.bakker@utwente.nl) received his
bachelor's degree in electrical engineering from the University of Twente, The Netherlands, and his M.Sc degree in
geoinformatics from ITC, The Netherlands, in 2002 and
is at present working on his Ph.D. degree in imaging spectrometry at the University of Twente. He is currently a lecturer and researcher with the Faculty of Geo-Information
Science and Earth Observation, University of Twente, The
Netherlands. His research interests are in remote sensing
and data processing, specifically the acquisition and analysis of hyperspectral images.
Robert D. Hewson (r.d.hewson@utwente.nl) received
his B.Sc. degree (honors) in geophysics at Melbourne University, Australia, in 1981 and worked from 1982 to 1989
at Shell Australia. After receiving an M.Sc. degree in geophysics study at Macquarie University (1991), he undertook a Ph.D. in geological remote sensing at the University of New South Wales in 1998. He worked at Australia's
CSIRO from 1998 to 2010 in geoscience applications of
remote sensing. Since 2011, he has been a part-time lecturer and research fellow at RMIT University, Melbourne,
until his current appointment that began in 2016 at the
Faculty of Geo-Information Science and Earth Observation, University of Twente. His research activities include
geoscience applications of multispectral satellite imagery
and night-time thermal imagery and integration of remote sensing and regional airborne geophysics.
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IEEE Geoscience and Remote Sensing Magazine - June 2019

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