Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p31b1541o&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P31B-1541
Mathematics
Logic
[5460] Planetary Sciences: Solid Surface Planets / Physical Properties Of Materials, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
We have completed a laboratory study on the effects of surface roughness on the thermal emission spectra of a diverse suite of rock samples, including igneous, metamorphic, and sedimentary compositions. We roughened our samples with abrasives, which created average roughnesses that range from < ~1μm to > ~10μm and compare mid-infrared emissivity spectra from initial and roughened surfaces. The initial and roughened surfaces were characterized by using a profilometer to calculate the length scale-dependent root mean square deviation (Rqɛ). Initial results indicate that 1) rock classes vary in the degree that they are susceptible to abrasion, 2) absorption features shallow with increasing roughness across all rock groups, 3) in general, absorption features do not change shape with increasing surface roughness, 4) we see no first order correlations between increasing surface roughness and reduction in spectral contrast, and 5) we do not see complete obscuration of features in any of our roughened spectra. One of the fundamental goals of acquiring spectroscopic observations of planetary surfaces is to determine the composition of rocks and minerals, which can provide insight into a wide variety of geological processes that may have shaped the region. The mid-infrared region is able to provide such information because wavelength dependent molecular vibrations within the lattice structure cause absorption and emission of infrared radiation. Emission spectra from most mineral groups contain distinctive absorptions and it is these spectral signatures that can be exploited to determine mineralogy. However, previous studies have shown that surface roughness can change the contrast or obscure the diagnostic spectral signatures in the mid-infrared wavelength region. A solid laboratory basis for interpreting remotely acquired data is imperative to understanding the mineralogy of a surface. If the detectability of all minerals in the infrared may be dependent in part on their surface roughness, it is critical to establish which classes of rocks display this effect and to what degree. The roughness effect discussed by previous researchers is similar to a blackbody cavity effect in which multiple reflections reduce the number of photons measured at the sensor, resulting in shallowing of spectral features. However, reduction in spectral contrast may also be the result of surface or volume scattering, but the majority of previous investigations have focused on particulate samples. The surface morphology created from our abrasion process, and similar to most roughening techniques, does not create pits that can be described as blackbody cavities. True blackbody cavities produced by geologic processes, such as dissolution features in limestone or vesicles in lava flows, are difficult to simulate and/or recreate through most mechanical abrasion techniques in the laboratory. Instead, the surfaces created here are more accurately described as half spherical pits that likely cause a reduction in spectral contrast through surface scattering.
Anderson Scott F.
Hamilton Victoria E.
Osterloo Mikki Michele
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