Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p11a0955h&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P11A-0955
Other
5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
Thermal infrared (TIR) spectroscopy is widely implemented in attempts to determine the composition of the Mars's surface. Discoveries include basaltic rocks, possible andesites, and hematite-rich terrains associated with areas of probable hydrothermal alteration [Bandfield et al., 2000; Christensen et al., 2001; Glotch et al., 2004]. Some of the basaltic rocks appear to be covered by either a weathering rind or a varnish. The presence of a varnish would be interesting because it is believed to form through multiple wetting and drying events [reference]. The presence of these coatings can potentially be identified through unique nonlinear effects where both the substrate and varnish have strong spectral features. For example, varnished terrestrial quartz-rich rocks have a low-emissivity ~8.4-micron reststrahlan band diagnostic of a silicate-rich substrate which remains present while the longer wavelength reststrahlen band is obscured by the clay-rich varnish. In general, this non-linearity will conform to the Beer-Lambert Law, with additional reflection and scattering terms, so that the light emitted from the varnished stone will be similar to I=Io e-ax, where `Io' is the light emitted from a bare substrate, `a' is the absorption constant for the varnish coating, and `x' is the thickness of the coating. If the effect were linear, as expected for dusty surfaces [Johnson et al., 2002] or discrete patches of rock and clay, the emissivity of the emitted light would, at all wavelengths, possess equal contributions from the varnish and substrate; thus the clay feature would not completely dominate the longwave reststrahlan band without also erasing the shortwave reststrahlan band. After having theoretically determined a nonlinear at some wavelengths is probable, we have focused on laboratory spectral analyses of terrestrial varnished rocks. We have collected over 100 varnished stones from various pavements and unvarnished stones from other surfaces and have acquired over 200 spectra from which we have developed a preliminary, empirical TIR spectral algorithm for the detection of varnished rocks. Developed for terrestrial rocks, the current algorithm relies on 18 bands, each ~ 50 to ~100nm wide, in the 8-12-micron region. We will modify this model for best detecting nonlinear mixing of light emitted from the substrate basaltic rocks covered by a varnish that is spectrally dominated by the ubiquitous Martian dust.
Gillespie Anna
Hansen Gary B.
Hibbitts Ch. A.
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