Fred A. Kruse

The spectral image processing system (SIPS) interactive visualization and analysis of imaging spectrometer data

Abstract The Center for the Study of Earth from Space (CSES) at the University of Colorado, Boulder, has developed a prototype interactive software system called the Spectral Image Processing System (SIPS) using IDL (the Interactive Data Language) on UNIX-based workstations. SIPS is designed to take advantage of the combination of high spectral resolution and spatial data presentation unique to imaging spectrometers. It streamlines analysis of these data by allowing scientists to rapidly interact with entire datasets. SIPS provides visualization tools for rapid exploratory analysis and numerical tools for quantitative modeling. The user interface is X-Windows-based, user friendly, and provides “point and click” operation. SIPS is being used for multidisciplinary research concentrating on use of physically based analysis methods to enhance scientific results from imaging spectrometer data. The objective of this continuing effort is to develop operational techniques for quantitative analysis of imaging spectrometer data and to make them available to the scientific community prior to the launch of imaging spectrometer satellite systems such as the Earth Observing System (EOS) High Resolution Imaging Spectrometer (HIRIS).

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.

Use of airborne imaging spectrometer data to map minerals associated with hydrothermally altered rocks in the northern grapevine mountains, Nevada, and California

Abstract Three flightlines of Airborne Imaging Spectrometer (AIS) data, acquired over the northern Grapevine Mountains, Nevada, and California, were used to map minerals associated with hydrothermally altered rocks. The data were processed to remove vertical striping, normalized using an equal area normalization, and reduced to reflectance relative to an average spectrum derived from the data. An algorithm was developed to automatically calculate the absorption band parameters band position, band depth, and band width for the strongest absorption feature in each pixel. These parameters were mapped into an intensity, hue, saturation (IHS) color system to produce a single color image that summarized the absorption band information, This image was used to map areas of potential alteration based upon the predicted relationships between the color image and mineral absorption band. Individual AIS spectra for these areas were then examined to identify specific minerals. Two types of alteration were mapped with the AIS data. Areas of quartz-sericite-pyrite alteration were identified based upon a strong absorption feature near 2.21 μm, a weak shoulder near 2.25 μm, and a weak absorption band near 2.35 μm caused by sericite (fine-grained muscovite). Areas of argillic alteration were defined based on the presence of montmorillonite, identified by a weak to moderate absorption feature near 2.21 μm and the absence of the 2.35 μm band. Montmorillonite could not be identified in mineral mixtures. Calcite and dolomite were identified based on sharp absorption features near 2.34 and 2.32 μm, respectively. Areas of alteration identified using the AIS data corresponded well with areas mapped using field mapping, field reflectance spectra, and laboratory spectral measurements.

Expert system-based mineral mapping in northern Death Valley, California/Nevada, using the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)

Abstract Integrated analysis of imaging spectrometer data and field spectral measurements were used in conjunction with conventional geologic field mapping to characterize bedrock and surficial geology at the northern end of Death Valley, California and Nevada. A knowledge-based expert system was used to automatically produce image maps showing the principal surface mineralogy from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data. Linear spectral unmixing of the AVIRIS data allowed further determination of relative mineral abundances and identification of mineral assemblages and mixtures. The imaging spectrometer data show the spatial distribution of spectrally distinct minerals occurring both as primary rockforming minerals and as alteration and weathering products. Field spectral measurements were used to verify the mineral maps and field mapping was used to extend the remote sensing results. Geographically referenced image maps produced from these data form new base maps from which to develop improved understanding of the prosesses of deposition and erosion affecting the present land surface.

Characterization of saline soils using airborne radar imagery

Abstract Complex dielectric constants determined by inversion of the polarized returns of AIRSAR images acquired in wet conditions delineate the distribution of saline soils in irrigated regions around the town of Pyramid Hill, in western Victoria, Australia. There is good agreement between the areas delineated as having anomalous dielectric constants by the radar backscatter inversion techniques with saline areas as defined by electrical conductivity and as inferred from dielectric constants determined in the field. Surface roughness maps and vegetation classification maps derived from AIRSAR data provide useful ancillary information regarding the extent of salinity in the region, but they are not as diagnostic as the determined dielectric constants. The magnitudes of P band radar-determined dielectric constants most closely approach those expected from field determinations, although the distribution of L-band-determined dielectric constants gives the best discrimination between saline and nonsaline areas as seen at the surface. C-band-determined dielectric constants are much lower than expected from field determinations and show saline areas as anomalous only in the bare, most severely affected, areas. The more general regional distribution of high dielectric areas seen at P band may be a more accurate indication of the salinity at depth. The AIRSAR image inversion techniques generally underestimate the magnitude of the complex dielectric constant. AIRSAR data for salinity mapping should be acquired under wet conditions. In such conditions there is an electrical continuum between the wet ground surface and saline water within the pores in the upper soil horizons. A wet ground surface results in a higher total power return than that which would occur under dry conditions and in a higher contrast between the radar-dark and radar bright areas within the scene.

Quantitative geochemical mapping of ammonium minerals in the southern Cedar Mountains, Nevada, using the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)

Abstract Imaging spectrometer (hyperspectral) data, field spectral measurements, and laboratory analyses were used to quantitatively map the concentration of mineral-bound ammonium (buddingtonite) in hydrothermally altered volcanic rocks in the southern Cedar Mountains, Esmeralda County, Nevada. Mineral-bound ammonium is a product of ion exchange in silicate minerals and has no visible distinguishing characteristics, however, diagnostic infrared spectral features are ideal for identification using both field and airborne/spaceborne spectrometers. Establishment of a laboratory- or field-based geochemical calibration is presently a prerequisite to quantitative mapping. For this study, ammonium content of rock samples was determined by chemical analysis and reflectance spectra were measured on whole-rock samples. A linear relation was found between ammonium concentration and the depth of a 2.12 μm ammonium absorption feature in buddingtonite. An image-map of ammonium concentration in ppm was derived from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data by applying the linear calibration to the AVIRIS reflectance-calibrated spectrum at each pixel. Field spectral measurements, made with a PIMA field spectrometer on a 40 m grid, were used to create a ground-truth concentration map that confirmed the AVIRIS results. Field mapping, X-ray diffraction, and petrologic studies performed in conjunction with the AVIRIS analysis show that buddingtonite is the dominant ammonium mineral in the southern Cedar Mountains, that the ammonium is located along northeast-trending basin and range normal faults, and that it is restricted to two of four crystal-rich rhyolitic tuff units of Oligocene age. This study establishes that remote geochemical mapping using imaging spectrometer data is possible, and presents a methodology that could be extended to quantitatively map other minerals that have absorption features in the short-wave infrared.

Characterization and mapping of kimberlites and related diatremes using hyperspectral remote sensing

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and commercially-available HyMap hyperspectral data were used to study the occurrence and mineralogical characteristics of limberlite diatremes in the State-Line district of Colorado/Wyoming. A mosaic of five flightlines of AVIRIS data acquired during 1996 with 20-m resolution is being used to locate and characterize the kimberlite diatremes. Higher spatial resolution data (1.6 m AVIRIS and 4m HyMap acquired in 1998 and 1999, respectively) are being used to map additional detail. Poor exposures, vegetation cover, and weathering, however, make identification of characteristic kimberlite minerals difficult except where exposed by mining. Minerals identified in the district using the hyperspectral data include calcite, dolomite, illite/muscovite, and serpentine (principally antigorite), however, most spectral signatures are dominated by both green and dry vegetation. The goal of this work is to determine methods for characterizing subtle mineralogic changes associated with kimberlites as a guide to exploration in a variety of geologic terrains.

Knowledge‐based geologic mapping with imaging spectrometers

Abstract A knowledge‐based expert system has been developed that allows automated mineralogical mapping using data from imaging spectrometers. An algorithm for extraction of absorption features from digital spectral libraries produces “fact tables” characterizing the individual absorption features. An “expert” (knowledgeable user) then interactively analyzes these results to determine key absorption features for mineral identification. These key features are in turn used in simple rules to examine each picture element (pixel) in an imaging spectrometer data set. An information data cube is produced that contains a measurement of the certainty of occurrence of specific materials in the library at each pixel. An image map is also produced showing the best mineral match for each pixel. Interactive programs for analysis and visualization of the results allow display of specific certainty thresholds and automatic building of spectral end member libraries to be used in quantitative procedures such as linear spe...

Comparison of EO-1 Hyperion and airborne hyperspectral remote sensing data for geologic applications

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 spaceborne hyperspectral capabilities. Hyperion is a satellite hyperspectral sensor covering the 0.4 to 2.5 micrometer spectral range with 242 spectral bands at approximately 10 nm spectral resolution and 30 m spatial resolution from a 705 km orbit. AIG and CSIRO, as members of the NASA EO-1 science validation team, have been involved in efforts to evaluate, validate, and demonstrate Hyperions utility for geologic applications. Comparison of airborne hyperspectral data to the Hyperion data establishes that Hyperion provides the ability to remotely map surface mineralogy, with the principal limitations being reduced spatial distinctions caused by the Hyperion 30 m spatial resolution (versus 2-20 m spatial resolution for the airborne sensors) and limited mapping of fine spectral detail based on lower signal-to-noise ratios (approximately 50:1 in the SWIR for Hyperion versus >500:1 for the airborne sensors). Initial results at selected Hyperion validation sites in the USA and Argentina establish that Hyperion is performing to specifications and that data from the SWIR spectrometer can be used to produce useful geologic (mineralogic) information.

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.