Jonathan F. Huntington

Comparison of airborne hyperspectral data and EO-1 Hyperion for mineral mapping

Airborne hyperspectral data have been available to researchers since the early 1980s and their use for geologic applications is well documented. The launch of the National Aeronautics and Space Administration Earth Observing 1 Hyperion sensor in November 2000 marked the establishment of a test bed for spaceborne hyperspectral capabilities. Hyperion covers the 0.4-2.5-/spl mu/m range with 242 spectral bands at approximately 10-nm spectral resolution and 30-m spatial resolution. Analytical Imaging and Geophysics LLC and the Commonwealth Scientific and Industrial Research Organisation have been involved in efforts to evaluate, validate, and demonstrate Hyperionss utility for geologic mapping in a variety of sites in the United States and around the world. Initial results over several sites with established ground truth and years of airborne hyperspectral data show that Hyperion data from the shortwave infrared spectrometer can be used to produce useful geologic (mineralogic) information. Minerals mapped include carbonates, chlorite, epidote, kaolinite, alunite, buddingtonite, muscovite, hydrothermal silica, and zeolite. Hyperion data collected under optimum conditions (summer season, bright targets, well-exposed geology) indicate that Hyperion data meet prelaunch specifications and allow subtle distinctions such as determining the difference between calcite and dolomite and mapping solid solution differences in micas caused by substitution in octahedral molecular sites. Comparison of airborne hyperspectral data [from the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)] to the Hyperion data establishes that Hyperion provides similar basic mineralogic information, with the principal limitation being limited mapping of fine spectral detail under less-than-optimum acquisition conditions (winter season, dark targets) based on lower signal-to-noise ratios. Case histories demonstrate the analysis methodologies and level of information available from the Hyperion data. They also show the viability of Hyperion as a means of extending hyperspectral mineral mapping to areas not accessible to aircraft sensors. The analysis results demonstrate that spaceborne hyperspectral sensors can produce useful mineralogic information, but also indicate that SNR improvements are required for future spaceborne sensors to allow the same level of mapping that is currently possible from airborne sensors such as AVIRIS.

ICE: a statistical approach to identifying endmembers in hyperspectral images

Several of the more important endmember-finding algorithms for hyperspectral data are discussed and some of their shortcomings highlighted. A new algorithm - iterated constrained endmembers (ICE) - which attempts to address these shortcomings is introduced. An example of its use is given. There is also a discussion of the advantages and disadvantages of normalizing spectra before the application of ICE or other endmember-finding algorithms.

Characterising the hydrothermal alteration of the Broadlands–Ohaaki geothermal system, New Zealand, using short-wave infrared spectroscopy

Abstract Hydrothermal clay minerals present in the Broadlands–Ohaaki geothermal field were characterised by field portable short-wave infrared spectroscopy. Three major alteration zones, an upper smectite, a middle illite and a lower illite–chlorite, are spectrally separable. The zoning pattern is generally consistent with the thermal structure of the geothermal field, although occasionally zone boundaries cut present-day isotherms. The data indicate that temperature is the major control on clay zoning and permeability plays a subordinate role. Both beidellite and montmorillonite are common in the upper, low-temperature smectite zone. Kaolinite, mainly of low crystallinity, marks the margin of the field where cool acidic ground waters inflow. In the middle alteration zone, illite, dominantly K-rich, shows a narrow compositional variability. Some highly permeable zones are characterised by illite with low octahedral Al contents. Ammonium-bearing illite and buddingtonite are present locally in permeable horizons within the illite zone, where temperatures are above 200°C. Chlorite is most abundant in the lower alteration zone (temperature >250°C), although it also occurs unevenly in the upper and middle alteration zones. Chlorite varies from Mg- to Fe-rich varieties (but mostly with Mg# values

Geologic and alteration mapping at Mt Fitton, South Australia, using ASTER satellite-borne data

The Japanese ASTER sensor on board the US Terra satellite was launched in December 1999 to establish a spaceborne capability for high spatial, multispectral visible-shortwave infrared and thermal infrared remote sensing data mapping of the Earths environment. The Mt Fitton test site in South Australia was chosen to test the ability of the ASTER instrument for geological mapping having been previously surveyed by several visible-shortwave IR and thermal IR airborne remote sensing instruments and several field campaigns collecting relevant spectral measurements. These previous airborne remote sensing surveys and field campaigns successfully mapped a suite of intrusives and sedimentary units with some greenschist metamorphic and localised hydrothermal alteration. Visible-NIR ASTER channels successfully mapped green vegetation and iron oxide information. ASTER SWIR data were spectrally unmixed into four spectrally recognizable endmembers that relate to areas rich in talc, chlorite, white mica and carbonate mineralogies. This result was confirmed using IRIS field spectra resampled to ASTER resolution wavelengths. Quartz, carbonate and talc-tremolite rich units at Mt Fitton were also discriminated using ASTERs thermal infrared data. These results from low level ASTER data products indicated that ASTER could discriminate mineral groups not achievable from Landsat TM, though more precise mineral species mapping is not possible.

The performance of the satellite-borne Hyperion hyperspectral VNIR-SWIR imaging system for mineral mapping at Mount Fitton, South Australia

Satellite-based hyperspectral imaging became a reality in November 2000 with the successful launch and operation of the Hyperion system on board the EO-1 platform. Hyperion is a pushbroom imager with 220 spectral bands in the 400-2500 nm wavelength range, a 30 meter pixel size and a 7.5 km swath. Pre-launch characterization of Hyperion measured low signal to noise (SNR<40:1) for the geologically significant shortwave infrared (SWIR) wavelength region (2000-2500 nm). The impact of this low SNR on Hyperions capacity to resolve spectral detail was evaluated for the Mount Fitton test site in South Australia, which comprises a diverse range of minerals with narrow, diagnostic absorption bands in the SWIR. Following radiative transfer correction of the Hyperion radiance at sensor data to surface radiance (apparent reflectance), diagnostic spectral signatures were clearly apparent, including: green vegetation; talc; dolomite; chlorite; white mica and possibly tremolite. Even though the derived surface composition maps generated from these image endmembers were noisy (both random and column), they were nonetheless spatially coherent and correlated well with the known geology. In addition, the Hyperion data were used to measure and map spectral shifts of <10 nm in the SWIR related to white mica chemical variations.

An infrared spectral reflectance study of hydrothermal alteration minerals from the Te Mihi sector of the Wairakei geothermal system, New Zealand

Abstract Hydrothermal alteration minerals and their zoning with depth in the Te Mihi sector of the Wairakei geothermal field have been characterised in this study by using field portable short-wave infrared spectroscopy. Observed variations in the spectral reflectance of hydrothermally altered volcanic and sedimentary rocks indicate a downward gradation in the dominant alteration minerals from mordenite, smectite, illite, to illite + chlorite (epidote). The variations result from temperature and permeability controlled fluid-rock interactions. Mordenite is abundant in the shallowest samples. Dioctahedral, aluminous smectites (discrete phase or as mixed-layer species) are common in the upper part of the sequence, but decrease in abundance below 200 m. In the smectite-rich zone, beidellite is common and locally may predominate over montmorillonite. Illite, including the illite component in mixed-layer illite/smectite, becomes a significant component below 150–200 m. Illite has an octahedral cation composition close to that of muscovite, with insignificant amounts of Fe and Mg. Chlorite is nearly undetectable in the upper part (0–200 m) of the altered sequence, and may become a minor component below 200 m. Chlorite is abundant only in andesitic rocks. Chlorite from the lower alteration sequence is Fe-rich, probably with the Mg# values around 0.2–0.4. Epidote is abundant locally at depth.

HyLogger-3, a visible to shortwave and thermal infrared reflectance spectrometer system for drill core logging: functional description

ABSTRACT Australian Geological Surveys are the custodians of a major national asset in the form of historically drilled and archived drill cores of the top few kilometres of the continent acquired by government agencies and companies over many decades. The AuScope National Virtual Core Library (NVCL) component of the AuScope Earth Model comprises geological/rock samples, technology, people and database/delivery infrastructure located in six nationally distributed nodes and is aimed at extracting additional value from this asset. The technology components of the NVCL comprise an integrated suite of hardware (HyLogger-3) and software (TSG-Core) systems for the imaging and hyperspectral characterisation of drill cores in their original core trays and the interpretation of their contained oxide, carbonate, hydrous and anhydrous silicate mineralogy. The HyLogger-3 includes state-of-the-art Fourier Transform Spectrometers that continuously measure calibrated spectral reflectance from nominal 10 by 18 mm fields of view. These spectra are in turn passed through a series of automatic and semi-automatic pre-processing and mineralogical unmixing algorithms. These, along with numerous other tools in TSG-Core, output a variety of mineralogical and image products for use by scientists in many branches of the earth sciences. This paper provides a functional overview of the HyLogging hardware and software tools available in each of Australias Geological Surveys.

Evaluation and validation of EO-1 Hyperion for geologic mapping

NASAs EO-1 Hyperion sensor, launched in November 2000, provides the first opportunity to evaluate short-wave-infrared (SWIR) spaceborne hyperspectral capabilities. Hyperion covers the 0.4 to 2.5 /spl mu/m range with 242 spectral bands at approximately 10 nm spectral resolution and 30 m spatial resolution. Selected validation results for geology over USA sites with abundant ground truth and airborne hyperspectral data are described.

Geological fracture mapping in coalfields and the stress fields of the Sydney Basin

Abstract In the fracture pattern of the Sydney Basin, various fracture and stress domains that are spatially related can be recognised. At least for the western region of the Basin, periodic, relatively narrow domains (termed fault and joint swarms) that have a submeridional trend are believed to be similar to the Lapstone Monocline‐Kurrajong Fault structures, and may extend into the Lower Palaeozoic basement. An overall, horizontal N‐S and NE‐SW oriented principal compressive stress (σ1) measured in collieries and inferred from earthquake events at depths of 10–20 km is a regional phenomenon (possibly Basin‐wide), which can be expected to be locally modified close to geological structures, especially in and close to fault and joint swarms, near major normal faults, and near minor thrust and strike‐slip faults. The interaction of colliery roadway drivage, local structures (faults and/or cleat) and the stress field permits inferences to be made about virgin stresses in coal seams. Some earthquakes coincide...

Comparison of airborne and satellite hyperspectral data for geologic mapping

Airborne hyperspectral data have been available to researchers since the early 1980s and their use for geologic applications is well established. The launch of NASAs EO-1 Hyperion sensor in November 2000 marked the establishment of a test bed for spaceborne hyperspectral capabilities. Hyperion covers the 0.4 to 2.5 mum micrometer range with 242 spectral bands at approximately 10nm spectral resolution and 30m spatial resolution. Initial Hyperion analysis results for a site at Cuprite, Nevada, with established ground truth and years of airborne hyperspectral data show that Hyperion is performing to specifications and that data from the SWIR spectrometer can be used to produce useful geologic (mineralogic) information. Minerals mapped at Cuprite include kaolinite, alunite, buddingtonite, calcite, muscovite, and hydrothermal silica. Hyperion data collected at other sites under optimum conditions (summer season, bright targets) allow subtle distinctions such as determining the difference between calcite and dolomite and mapping spectral differences in micas caused by substitution in octahedral molecular sites. Comparison of airborne hyperspectral data (AVIRIS) to the Hyperion data establishes that Hyperion provides similar information content, with the principal limitations being reduced spatial distinctions caused by the 30m spatial resolution and limited mapping of fine spectral detail based on lower signal-to-noise ratios.