James K. Crowley

Airborne imaging spectrometer data of the Ruby Mountains, Montana: Mineral discrimination using relative absorption band-depth images

Abstract Airborne imaging spectrometer data collected in the near-infrared (1.2–2.4 μm) wavelength range were used to study the spectral expression of metamorphic minerals and rocks in the Ruby Mountains of southwestern Montana. The data were analyzed by using a new data enhancement procedure—the construction of relative absorption band-depth (RBD) images. RBD images, like bandratio images, are designed to detect diagnostic mineral absorption features, while minimizing reflectance variations related to topographic slope and albedo differences. To produce an RBD image, several data channels near an absorption band shoulder are summed and then divided by the sum of several channels located near the band minimum. RBD images are both highly specific and sensitive to the presence of particular mineral absorption features. Further, the technique does not distort or subdue spectral features as sometimes occurs when using other data normalization methods. By using RBD images, a number of rock and soil units were distinguished in the Ruby Mountains including weathered quartz - feldspar pegmatites, marbles of several compositions, and soils developed over poorly exposed mica schists. The RBD technique is especially well suited for detecting weak near-infrared spectral features produced by soils, which may permit improved mapping of subtle lithologic and structural details in semiarid terrains. The observation of soils rich in talc, an important industrial commodity in the study area, also indicates that RBD images may be useful for mineral exploration.

Mapping playa evaporite minerals with AVIRIS data - A first report from Death Valley, California

Abstract Efflorescent salt crusts in Death Valley, California, were mapped by using Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data and a recently developed least-squares spectral band-fitting algorithm. Eight different saline minerals were remotely identified, including three borates, hydroboracite, pinnoite, and rivadavite, that have not been previously reported from the Death Valley efflorescent crusts. The three borates are locally important phases in the crusts, and at least one of the minerals, rivadavite, appears to be forming directly from brine. Borates and other evaporite minerals provide a basis for making remote chemical measurements of desert hydrologic systems. For example, in the Eagle Borax Spring area, the AVIRIS mineral maps pointed to elevated magnesium and boron levels in the ground waters, and to the action of chemical divides causing subsurface fractionation of calcium. Many other chemical aspects of playa brines should have an expression in the associated evaporite assemblages. Certain anhydrous evaporites, including anhydrite, glauberite, and thenardite, lack absorption bands in the visible and near-infrared wavelength range, and crusts composed of these minerals could not be characterized by using AVIRIS. In these situations, thermal-infrared remote sensing data may complement visible and near-infrared data for mapping evaporites. Another problem occurred in wet areas of Death Valley, where water absorption caused low signal levels in the 2.0–2.5 μm wavelength region that obscured any spectral features of evaporite minerals. Despite these difficulties, the results of this study demonstrate the potential for using AVIRIS and other imaging spectrometer data to study playa chemistry. Such data can be useful for understanding chemical linkages between evaporites and ground waters, and will facilitate studies of how desert ground-water regimes change through time in response to climatic and other variables.

Hydrothermal formation of Clay-Carbonate alteration assemblages in the Nili Fossae region of Mars

Abstract The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has returned observations of the Nili Fossae region indicating the presence of Mg-carbonate in small (

Mapping playa evaporite minerals and associated sediments in Death Valley, California, with multispectral thermal infrared images

Efflorescent salt crusts and associated sediments in Death Valley, California, were studied with.

Near-infrared reflectance spectra of mixtures of kaolin-group minerals; use in clay mineral studies

Near-infrared (NIR) reflectance spectra for mixtures of ordered kaolinite and ordered dickite have been found to simulate the spectral response of disordered kaolinite. The amount of octahedral vacancy disorder in nine disordered kaolinite samples was estimated by comparing the sample spectra to the spectra of reference mixtures. The resulting estimates are consistent with previously published estimates of vacancy disorder for similar kaolin minerals that were modeled from calculated X-ray diffraction patterns. The ordered kaolinite and dickite samples used in the reference mixtures were carefully selected to avoid undesirable particle size effects that could bias the spectral results.NIR spectra were also recorded for laboratory mixtures of ordered kaolinite and halloysite to assess whether the spectra could be potentially useful for determining mineral proportions in natural physical mixtures of these two clays. Although the kaolinite-halloysite proportions could only be roughly estimated from the mixture spectra, the halloysite component was evident even when halloysite was present in only minor amounts. A similar approach using NIR spectra for laboratory mixtures may have applications in other studies of natural clay mixtures.

MAPPING HYDROTHERMALLY ALTERED ROCKS ON MOUNT RAINIER, WASHINGTON, WITH AIRBORNE VISIBLE/INFRARED IMAGING SPECTROMETER (AVIRIS) DATA

Mount Rainier has produced numerous Holocene debris flows, the largest of which contain clays and other minerals derived from hydrothermally altered rocks on the volcano’s edifice. Imagery from an advanced airborne sensor was used to map altered rocks at Mount Rainier and demonstrates their distinctly nonuniform distribution. The mapping of altered rocks helps to identify edifice failure surfaces and to recognize the source areas for the largest debris flow events. Remote sensing methods like those used at Mount Rainier can enhance ground-based mapping efforts and should prove useful for rapidly identifying hazardous sectors at other volcanoes.

Comparative alteration mineral mapping using visible to shortwave infrared (0.4-2.4 /spl mu/m) Hyperion, ALI, and ASTER imagery

Advanced Land Imager (ALI), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and Hyperion imaging spectrometer data covering an area in the Central Andes between Volcan Socompa and Salar de Llullaillaco were used to map hydrothermally altered rocks associated with several young volcanic systems. Six ALI channels in the visible and near-infrared wavelength range (0.4-1.0 /spl mu/m) were useful for discriminating between ferric-iron alteration minerals based on the spectral shapes of electronic absorption features seen in continuum-removed spectra. Six ASTER channels in the short wavelength infrared (1.0-2.5 /spl mu/m) enabled distinctions between clay and sulfate mineral types based on the positions of band minima related to Al-OH vibrational absorption features. Hyperion imagery embedded in the broader image coverage of ALI and ASTER provided essential leverage for calibrating and improving the mapping accuracy of the multispectral data. This capability is especially valuable in remote areas of the earth where available geologic and other ground truth information is limited.

Mapping mine wastes and analyzing areas affected by selenium-rich water runoff in southeast Idaho using AVIRIS imagery and digital elevation data

Abstract Remotely sensed hyperspectral and digital elevation data from southeastern Idaho are combined in a new method to assess mine waste contamination. Waste rock from phosphorite mining in the area contains selenium, cadmium, vanadium, and other metals. Toxic concentrations of selenium have been found in plants and soils near some mine waste dumps. Eighteen mine waste dumps and five vegetation cover types in the southeast Idaho phosphate district were mapped by using Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) imagery and field data. The interaction of surface water runoff with mine waste was assessed by registering the AVIRIS results to digital elevation data, enabling determinations of (1) mine dump morphologies, (2) catchment watershed areas above each mine dump, (3) flow directions from the dumps, (4) stream gradients, and (5) the extent of downstream wetlands available for selenium absorption. Watersheds with the most severe selenium contamination, such as the South Maybe Canyon watershed, are associated with mine dumps that have large catchment watershed areas, high stream gradients, a paucity of downstream wetlands, and dump forms that tend to obstruct stream flow. Watersheds associated with low concentrations of dissolved selenium, such as Angus Creek, have mine dumps with small catchment watershed areas, low stream gradients, abundant wetlands vegetation, and less obstructing dump morphologies.

Mapping hydrothermally altered rocks by analyzing hyperspectral image (AVIRIS) data of forested areas in the Southeastern United States

Abstract Analysis of Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data of the Carolina slate belt, a region in the Southeastern United States, has shown that certain types of hydrothermally altered rocks can be delineated based on the spectral reflectance characteristics of forest vegetation growing on them. These altered rocks are typically highly silicified and commonly associated with gold, silver, and pyrophyllite ores. Field evaluation of the resulting forest classification identified several previously unmapped areas of altered rocks, and no areas that were mapped erroneously. Distinction of the altered rocks from unaltered siliceous volcanic bedrock areas, also silica-rich, is especially significant as chestnut oak forests are characteristic of both. We conclude that the dominant chestnut oak canopy and the lack of other species that are usually present here on the unaltered rocks, result in lower apparent canopy density at the altered sites, which is expressed in the AVIRIS data by lower O–H absorption intensity. These differences in species composition and canopy architecture may be caused by one or several factors, including soil depth and physical properties, direction and steepness of slope, moisture availability, and the amount of nutrients present and their availability to the trees.

Digital classification of contact metamorphic rocks in Extremadura, Spain, using Landsat thematic mapper data

Landsat Thematic Mapper (TM) images of an extensively cultivated part of Extremadura, Spain, have been used to distinguish soil developed on contact metamorphic rocks in aureoles around late Hercynian granitic plutons from soil formed on stratigraphically equivalent Late Proterozoic slate and metagraywacke that has been regionally metamorphosed to the greenschist facies. Reflectance spectra of contact metamorphic soil have lower reflectance, especially in the 1.6 mu m wavelength region, and weaker Al-OH, Mg-OH, and Fe (super 3+) absorption features than do spectra of the slate-metagraywacke soil. These spectral differences are attributed to highly absorbing carbonaceous material in the contact metamorphic soil that was subjected to high temperatures during emplacement of the plutons. These spectral reflectance differences are evident in a density-sliced TM band 5 image, in color-ratio composite images that incorporate TM 4:5, 4:3, and 3:1 ratios, and in principal-component composite images. Digital classification of the numerous tilled, vegetation-free fields was used to map the contact metamorphic soil in an August 1984 TM scene of the Caceres study area. First, TM 4:3 was used to identify these fields. Then ranges of TM 5 and TM 3:1 values were determined for selected tilled fields within and outside the contact aureoles. Field evaluation of a classification map based on TM 5 plus TM 3:1 shows more extensive aureoles than published geologic maps and few misclassified areas. Similar results were achieved using TM 4:5 instead of TM 5. This approach was subsequently used to map two linear zones of contact metamorphic rocks in the San Nicolas mine area where only two small exposures of granite have been documented. Landsat Multispectral Scanner (MSS) images can also be used to map contact aureoles in the study areas, but extensive field evaluation is required because of more frequent misclassification.