Crustal Imaging and Characterization Team
Task Contact: Roger N. Clark
The development of the USGS Tetracorder expert system will be continued in this Task. This Task will also continually expand the number of high quality spectra from well-characterized samples contained in the USGS digital spectral libraries and make these data available on a regular basis to support spectroscopic analyses in the USGS and elsewhere. In addition, the Task will address two areas of research. The first area is the effect of cation substitution in mineral structures. Previous research results have shown that mineral absorption features shift with small changes in mineral composition. The ability to detect and map small changes in the chemical composition of mineral species is important for accurate geologic and geochemical interpretation of mineral maps derived from all imaging spectroscopy studies, whether using commercial software, or the USGS Tetracorder expert system. Consequently, spectral variability in selected mineral series that are important to geologic and geochemical interpretations will be studied in the laboratory and imaging spectroscopy mapping based on these characterizations will be tested in areas where these mineral species are known to occur. For example, aluminum substitution in muscovites can be an indicator of geologic processes, and these substitutions are expressed as a shift in the 2.2-micron absorption feature.
The second area of research involves the refinement and development of computer algorithms that allow remotely sensed data, especially airborne imaging spectrometer data, to be more easily and accurately orthorectified. This is a difficult, yet essential, undertaking that will result in georectified data suitable for locating a specific pixel of mineralogical interest in the field, as well as integrating mineral map information with other GIS layers. The orthorectification correction procedure uses an internally consistent Digital Elevation Model derived from the atmospheric abundance of CO2. Tests show ten times the accuracy over conventional registration techniques achieved in about one fourth the time.
The Task will continue to provide technical support for spectral studies conducted by the Health Dust Project, as defined in cooperative agreements with other State and Federal agencies.
Data sets representative of various geologic processes will be tested by adding expert system instructions to the Tetracorder system and verifying mapping accuracy at our standard test sites, which include volcanic and hydrothermal (Cuprite, NV test site), sedimentary (Arches National Park test site), city (Lakewood, Colorado test site), metamorphic (Joshua Tree National Park test site) and other environments. Accuracy of mapping is defined in the Tetracorder Paper (Clark et al., JGR, 2003a) and numerically modeled and tested (Swayze et al., JGR, 2003). The knowledge base for spectral work is a digital spectral library. We have completed a new spectral library (Clark et al., JGR, 2003b).
As the samples used in the spectral library become standards, their composition must be documented. A variety of sample analysis techniques are used to document the samples in the library, including X-Ray Diffraction, X-Ray Fluorescence, electron microprobe, scanning electron microscopy with energy dispersive spectroscopy. Not all samples require all analyses for all applications. Spectroscopic measurements and associated documentation are assembled in computer readable formats for publication and distribution. We have written new software for verification of sample documentation and assembly of spectral libraries. This software ensures that a computer readable database is created.
Spectroscopy measures the vibrational wavelengths of molecular bonds, which reveals a host of information about the atomic structure of minerals, such as the degree of solid-solution and other elemental components. Minerals may be directly identified with spectroscopy using data from airborne or orbital instruments, which can be used to assess environmental conditions over wide areas.
The Tetracorder expert system was published in Journal of Geophysical Research (Clark et al., 2003a) and a study of it’s accuracy was also published in Journal of Geophysical Research (Swayze et al., 2003). A new spectral library was published (Clark et al., 2003b), and a paper describing calibration of imaging spectroscopy data (Clark et al., 2003c) was published. Thus, major objectives documenting our methodologies have now been completed. We have also completed application papers resulting from the above research, including vegetation (Kokaly et al., 2003), and geologic mapping (Swayze et al., 2002, 2005). This research has also been critical to environmental research, including the World Trade Center post-disaster environmental evaluations (Clark et al., 2001, 2004a), spectral detect of asbestos (Clark et al., 2003d, Swayze 2004a), and mapping natural occurrences of potentially asbestos-bearing rocks in El Dorado County, California (Swayze et al., 2004b).
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Mineral Resources |
Eastern / Central / Western / Alaska / Minerals Information |
| Crustal Imaging & Characterization / Spatial Data |
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://crustal.usgs.gov
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