James V. Taranik

SEBASS hyperspectral thermal infrared data: surface emissivity measurement and mineral mapping

This study focuses on mapping surface minerals using a new hyperspectral thermal infrared (TIR) sensor: the spatially enhanced broadband array spectrograph system (SEBASS). SEBASS measures radiance in 128 contiguous spectral channels in the 7.5- to 13.5-μm region with a ground spatial resolution of 2 m. In September 1999, three SEBASS flight lines were acquired over Virginia City and Steamboat Springs, Nevada. At-sensor data were corrected for atmospheric effects using an empirical method that derives the atmospheric characteristics from the scene itself, rather than relying on a predicted model. The apparent surface radiance data were reduced to surface emissivity using an emissivity normalization technique to remove the effects of temperature. Mineral maps were created with a pixel classification routine based on matching instrument- and laboratory-measured emissivity spectra, similar to methods used for other hyperspectral data sets (e.g. AVIRIS). Linear mixtures of library spectra match SEBASS spectra reasonably well, and silicate and sulfate minerals mapped remotely, agree with the dominant minerals identified with laboratory X-ray powder diffraction and spectroscopic analyses of field samples. Though improvements in instrument calibration, atmospheric correction, and information extraction would improve the ability to map more pixels, these hyperspectral TIR data nevertheless show significant advancement over multispectral thermal imaging by mapping surface materials and lithologic units with subtle spectral differences in mineralogy.

Mapping alteration minerals at prospect, outcrop and drill core scales using imaging spectrometry

Imaging spectrometer data (also known as ‘hyperspectral imagery’ or HSI) are well established for detailed mineral mapping from airborne and satellite systems. Overhead data, however, have substantial additional potential when used together with ground-based measurements. An imaging spectrometer system was used to acquire airborne measurements and to image in-place outcrops (mine walls) and boxed drill core and rock chips using modified sensor-mounting configurations. Data were acquired at 5 nm nominal spectral resolution in 360 channels from 0.4 to 2.45 μm. Analysis results using standardized hyperspectral methodologies demonstrate rapid extraction of representative mineral spectra and mapping of mineral distributions and abundances in map-plan, with core depth, and on the mine walls. The examples shown highlight the capabilities of these data for mineral mapping. Integration of these approaches promotes improved understanding of relations between geology, alteration and spectral signatures in three dimensions and should lead to improved efficiency of mine development, operations and ultimately effective mine closure.

Effect of Reduced Spatial Resolution on Mineral Mapping Using Imaging Spectrometry—Examples Using Hyperspectral Infrared Imager (HyspIRI)-Simulated Data

The Hyperspectral Infrared Imager (HyspIRI) is a proposed NASA satellite remote sensing system combining a visible to shortwave infrared (VSWIR) imaging spectrometer with over 200 spectral bands between 0.38 and 2.5 μm and an 8-band thermal infrared (TIR) multispectral imager, both at 60 m spatial resolution. Short Wave Infrared (SWIR) (2.0-2.5 μm) simulation results are described here using Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data in preparation for the future launch. The simulated data were used to assess the effect of the HyspIRI 60 m spatial resolution on the ability to identify and map minerals at hydrothermally altered and geothermal areas. Mineral maps produced using these data successfully detected and mapped a wide variety of characteristic minerals, including jarosite, alunite, kaolinite, dickite, muscovite-illite, montmorillonite, pyrophyllite, calcite, buddingtonite, and hydrothermal silica. Confusion matrix analysis of the datasets showed overall classification accuracy ranging from 70 to 92% for the 60 m HyspIRI simulated data relative to 15 m spatial resolution data. Classification accuracy was lower for similar minerals and smaller areas, which were not

Analysis of the northern Sierra accreted terrane, California, with airborne thermal infrared multispectral scanner data

Sedimentary and igneous rocks of the northern Sierra accreted terrane and the Sierra Nevada batholith have been distinguished and mapped with the help of data from the airborne thermal infrared multispectral scanner (TIMS). TIMS acquires radiant spectral emittance data in the 8.2 to 12.2 μm (thermal infrared) part of the electromagnetic spectrum, where diagnostic spectral emission features of rocks and minerals occur. These features allow the discrimination of major rock types, because a distinct relation exists between the emissivities of the types of silicate minerals in rocks and the colors in the TIMS false-color imagery. Using a computer-enhanced TIMS image, we have been able to separate silica-rich metasedimentary and felsic igneous rocks from intermediate and mafic igneous rocks. In addition, several previously unmapped phases within the Mesozoic batholith were identified and mapped. These rocks are inseparable on conventional color aerial photography, but they are distinguishable on TIMS imagery. These results suggest that TIMS data should have widespread applicability to geologic mapping in many tectonic settings, including well-exposed batholithic belts, accreted terranes, and Precambrian shield areas.

Comparison of techniques for discriminating hydrothermal alteration minerals with Airborne Imaging Spectrometer data

Abstract High spectral and spatial resolution Airborne Imaging Spectrometer (AIS) data were used to map hydrothermal alteration mineralogy in the Tybo mining district, Hot Creek Range, Nevada. Kaolinite and montmorillonite—clinoptilolite alteration zones and limestone formations, which had been identified from field mapping and laboratory analyses were delineated using three methods: band ratios, principal component analysis, and a signature matching algorithm. The signature matching algorithm was the most effective method for discriminating alteration minerals and has the potential of identifying mineralogy by matching AIS image spectra with library reference spectra. Principal components was the second most successful method, and band ratioing was the least useful. With each of the methods, localities with kaolinite could be distinguished from areas with clinoptilolite or calcite and from unaltered rocks and alluvium. Kaolinite and montmorillonite could be distinguished from each other only with the signature matching algorithm. AIS bands in the portion of the spectrum between 2048 and 2337 nm which were found to account for the greatest amount of variance, and were not related to albedo, slope, or aspect, were: 2067, 2076, 2132, 2141, 2169, 2178, 2188, 2197, 2206, 2300, 2309, 2318, 2328, and 2337 nm. Most of these bands are located within spectral absorption features for kaolinite, montmorillonite, clinoptilolite, and calcite. The mapping of hydrothermal alteration minerals with high resolution remote sensing instruments provides us with a rapid method to extend the limits of field mapping and can be used to direct future exploration efforts.

Mapping Rock-Forming Minerals at Daylight Pass, Death Valley National Park, California, using SEBASS Thermal-Infrared Hyperspectral Image Data

Rock-forming minerals comprise the bulk of the rocks found at the surface of the Earth. These include, amongst others, quartz, feldspars, pyroxenes, micas and carbonates, all of which possess diagnostic emission features in the thermal-infrared portion of the electromagnetic spectrum. Using established emission spectra libraries we sought to map the distribution of these minerals using aerial remotely-sensed data centered on Daylight Pass, an alluvial wash dissecting the Grapevine Mountains to the northwest and the Funeral Mountains to the southeast, both of which effectively form the northeast perimeter of Death Valley. An abundance of Late Proterozoic and Cambrian sedimentary beds of dolomite, siltstone and sandstones, in addition to low- to moderate-grade metamorphic rocks form the bulk geology of the area of study, which is largely devoid of vegetation. Thermal-infrared spatially enhanced broadband array spectrograph system (SEBASS) hyperspectral image data was collected at Daylight Pass in mid-July of 2007. Standard reflectance hyperspectral processing techniques were implemented to reduce data dimensionality and, by referencing the emission spectra of both library and laboratory-measured ground specimens, we were able to successfully map the distribution of dominant rock-forming minerals in the form of outcrops and weathering products with a high degree of confidence.

Reconnaissance geologic mapping of a portion of the rain-forest-covered Guiana Shield, northwestern Brazil, using SIR-B and digital aeromagnetic data

This paper documents the result of an integrated analysis of spaceborne radar (SIR-B) and digital aeromagnetic data carried out in the heavily forested Guiana Shield. The objective of the research is to interpret the geophysical data base to its limit to produce a reconnaissance geologic map as an aid to ground work planning in a worst‐case setting. Linear geomorphic features were identified based on the interpretation of the SIR-B image. Digital manipulation of aeromagnetic data allowed the development of a color‐shaded relief map of reduced‐to‐pole magnetic anomalies, a terrace‐magnetization map, and a map showing the location of maximum values of the horizontal component of the pseudogravity gradient (magnetization boundary lines). The resultant end product was a reconnaissance geologic map where broad terrane categories were delineated and geologic faults with both topographic and magnetic expression were defined. The availability of global spaceborne radar coverage in the 1990s and the large number o...

Regional analysis of tertiary volcanic calderas (Western U.S.) using landsat thematic mapper imagery

Abstract The Basin and Range province of southern Nevada is an excellent setting to study Landsat imagery over volcanic rock assemblages. The area is semiarid, sparsely vegetated, and contains relatively youtful (6–14 Ma) volcanic calderas with compositionally diverse volcanic rock assemblages. Investigation of rock spectra, whole rock geochemistry, desert varnish, and Landsat imagery indicates that the longer wavelength visible and near infrared Thematic Mapper (TM) bands 3, 5, and 7 provide more effective lithologic discimination than the shorter wavelength bands due partly to deeper penetration of lower frequency energy and greater primary rock compositional response. (Spectral contamination of vegetation degrades lithologic information in TM Band 4.) Thus ratios, color composites, and intensity - saturation - hue images using TM Bands 3, 5 and 7 generally lead to superior lithologic contrast. Shorter wavelength, TM Bands 1 and 2 are affected more by surficial weathering products including desert varnish which may or may not provide an indirect link to lithologic identity. These relationships lead to a rock-varnish albedo difference that aids identification of desert varnish on leucocratic rocks, using TM Band 2, 5, and 5 2 ratio images. Principles component color composites provide best overall lithologic contrast but not specific lithologic identification. PC2 tends to contain lithologically dominant variance and combines favorably with other images influenced strongly by lithology. Late magmatic differentiates that are “evolved” with respect to alkalies and the “incompatible” elements exhibit steep spectral curves throughout the TM Bands 5–7 interval, leading generally to low 5 7 ratios and dark contrast on 5 7 ratio images. Guidelines for lithologic analysis of volcanic terrain using Landsat TM imagery are outlined.

Characterization of hydrothermal systems using simulated HyspIRI data

The Hyperspectral Infrared Imager (HyspIRI) is a proposed NASA satellite remote sensing system combining a visible to shortwave infrared (VSWIR) imaging spectrometer with over 200 spectral bands between 0.38 – 2.5 micrometers and an 8-band thermal infrared (TIR) multispectral imager. ©± We have begun data and analysis simulations using airborne data in preparation for the future launch. Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data with 224 spectral bands and multispectral TIR data from the MODIS/ASTER Airborne Simulator (MASTER) and the MODIS Airborne Simulator (MAS) sensors are being used to simulate the spectral and spatial HyspIRI response. The combined datasets, applied to measurement of geothermal and hydrothermal systems, successfully identify and map minerals such as goethite, hematite, jarosite, kaolinite, dickite, alunite, buddingtonite, montmorillonite, muscovite-illite, calcite, and hydrothermal silica. The TIR data were also used to extract elevated surface temperatures at active hot springs areas. The simulations demonstrate that HyspIRI data, while limited by their relatively coarse (60m) spatial resolution should still be useful for many geologic applications.

Differentiating volcanic rock assemblages using Landsat Thematic Mapper data - Influence of petrochemistry and desert varnish

Abstract Composition, distribution, spectral properties, and Landsat thematic mapper (TM) imagery influences of desert varnish were investigated at three study sites in southern Nevada, U.S.A. Thematic mapper signatures of diverse volcanic rock assemblages were found to depend largely on primary petrochemical characteristics. Results indicate that desert varnish exerts minimal influence on TM imagery at longer wavelengths (bands 4–7) but absorbs higher frequency radiation (TM bands 1–3), leading to relatively high TM band 5 2 values and dark contrast on 5 2 images over units with a high rock-varnish albedo difference (RVAD). Highly evolved volcanic deposits exhibit steep positive spectral slopes in the TM band 5–7 region, resulting in low 5 7 values and dark tonal contrast on 5 7 images.