IEEE Geoscience and Remote Sensing Magazine - June 2019 - 63

an earlier adularia-sericite-type hot-spring alteration comprising the famous buddingtonite outcrops of the eastern
center (Figure 11).
More details on the geology and alteration mineralogy of the Cuprite area can be found in [57]. For this case
study, we use airborne hyperspectral images from NASA's
AVIRIS-NG instrument to investigate the spatial distribution of three iron-bearing minerals (hematite, goethite, and
jarosite); the OH-bearing minerals alunite, kaolinite, white
mica, chlorite, nontronite, and montmorillonite; and the
carbonate mineral calcite.

Reno

Eastern Center

Western Center

Nevada

Cuprite
Las Vegas

4,156,000

4,158,000

IMAGE ACQUISITION
AVIRIS-NG is an imaging spectrometer that measures
reflected radiance at 5-nm intervals in the visible/SWIR
spectral range from 380 to 2,500 nm. The Cuprite data
used here were flown on 25 June 2014 and cover the
study area in five overlapping strips. The flying height was
18,000 ft, which resulted in a ground pixel size of approximately 3.7 m. The level 2 atmospherically corrected and
georeferenced data were ordered and downloaded from
the AVIRIS-NG data portal (https://avirisng.jpl.nasa.gov/
alt_locator/). The flight lines were individually processed
with the Wavelength Mapper, and the resulting products
were mosaicked.

PROCESSING
From the literature [57], the alteration minerals in the area
are already known. If prior knowledge of the spectral shape
of these minerals is absent, IDL DISPEC can be used on laboratory spectra to determine the characteristic wavelength
positions for this set of alteration minerals. The IDL DISPEC output table can be used to set the spectral subsets of
the Wavelength Mapper and interpret the final Wavelength
Mapper results.
The reflectance spectra of the three iron-bearing minerals, 10 OH-bearing minerals, and one carbonate mineral
are first analyzed with IDL DISPEC (Table 4). From this table, it appears that the diagnostic wavelength ranges are in
the VNIR for the iron-bearing minerals (882-949 nm) and
in the SWIR for the OH-bearing and carbonate minerals
(2,115-2,355 nm). Based on the IDL DISPEC results, four
Wavelength Mapper products were calculated. With buddingtonite having a spectral feature that partially overlaps
with the 1,900-nm atmospheric water feature in the data,
a compromise in the step 1 spectral subset needed to be
found that included enough of the rather wide buddingtonite 2,115-nm feature but stayed away from the water
feature. The parameters used are listed in Table 5.
The SWIR overview product is calculated to give an
overview of the positions of major vibrational absorption

Alteration Zones
Advanced Argillic
Hydrated Silica
Alunite

4,154,000

Argillic
Kaolinite
White Mica + Montmorillonite
Adularia-Smectite
Buddingtonite ± Smectite
4,152,000

Propylitic

0
480,000

482,000

484,000

486,000

Chlorite
(km)
0.5 1

Reference System:
UTM Zone 11 North, WGS-84 Datum

FIGURE 11. A spectroscopic alteration map showing the alteration zonation in the western and eastern centers of the Cuprite district

(modified after [57]). UTM: Universal Transverse Mercator projection; WGS-84: World Geodetic System WGS84 datum.
JUNE 2019

IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE

https://avirisng.jpl.nasa.gov/alt_locator/ https://avirisng.jpl.nasa.gov/alt_locator/

IEEE Geoscience and Remote Sensing Magazine - June 2019

Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - June 2019