Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p42a0543r&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P42A-0543
Mathematics
Logic
3934 Optical, Infrared, And Raman Spectroscopy, 5460 Physical Properties Of Materials, 5464 Remote Sensing, 5494 Instruments And Techniques
Scientific paper
The remote sensing data sets that typically are used to assess dust cover on Mars are thermal inertia and albedo measurements. Thermal inertia measurements are well suited to identifying surfaces that are dust covered but are ineffective for dust layers less than a few centimeters thick. Albedo measurements can be used to infer the presence of dust layers both thick and thin, where high albedo commonly is associated with dust covered surfaces. However, albedo alone is not a unique predictor of dust cover. With the advent of spectral data from the Mars Global Surveyor Thermal Emission Spectrometer, it is possible to identify the presence of surface dust down to a few 10s of microns thick by exploiting the well known fact that fine particulate surfaces produce distinctive spectral features. Martian surface dust particles have been found to be a few 10s to just a few microns in diameter, a size range that produces significant changes in laboratory IR spectra of any geologic material compared with coarser equivalents. I find that TES spectra of classical bright regions on Mars that have been identified previously as dust-covered show clear indications of particle size effects when compared to dark, dust-free regions. In particular, the high wavenumber range of TES spectra (>1300 cm-1) shows an absorption attributable to a broad transparency feature found in fine-particulate silicates. A global map of this feature (the dust cover index) produces a remarkable correlation with global albedo measurements from the TES instrument, corroborating the previously recognized relationship between high albedo and dust cover. However, I have found localized areas on Mars where high albedo surfaces do not show the spectral particle size effects of dust, i.e., they are dust-free. The most significant of these occurrences are the many locations where MOC images reveal finely-layered, alternating bands of brighter and darker sedimentary materials. Examples are "White Rock" in Pollack crater, the intracrater mounds in Gale, Becquerel, and Crommelin craters, and a similar deposit in Schiaparelli Basin. These sites demonstrate that not all bright surfaces are dust covered. The reverse situation of a dark, dust-covered surface has yet to be observed. The dust cover index is well suited to investigating the character of the upper-most layer of the martian surface.
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