Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p71a0452h&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P71A-0452
Other
3934 Optical, Infrared, And Raman Spectroscopy, 3994 Instruments And Techniques, 5464 Remote Sensing
Scientific paper
Optical Constants of Planetary Analogs Using KBr Pellet Transmission G. B. Hansen, C. A. Hibbitts Optical constants of bulk materials are needed for radiative transfer models used to simulate remote sensing measurements. Many minerals are difficult orimpossible to study in bulk form, leading to various attempts to derive optical constants in other ways (e.g. measuring the Fresnel reflection from a polished or packed surface, which is not sensitive to regions of small absorption). We are starting a campaign to remeasure, or measure for the first time, many planetary analog materials (clays, oxyhydroxides, etc.) using a potassium bromide pellet technique, where the mineral powder is sparsely dispersed in KBr matrix such that the pellet is transparent through much of the mid-infrared (2.5-30 μm). The strongly absorbing regions can be measured if the grain size is small enough, and the weakly absorbing regions are measured by increasing the density of particles. The KBr pellet method has long been used because scattering at the matrix-particle interface is minimized due to the similarly high real indices of refraction between the matrix and particles, but interpretation of the measured extinction is still not straightforward because one is not measuring the absorption of a thin bulk film, but rather the absorption extinction of particles of comparable size to the wavelength. There is also the possible presence of scattering voids or bubbles in the matrix. In our case, there is also a weak absorption spectrum present due to impurities in the KBr powder. We will present the results from our first measurements of the clay Montmorillionite. The extinction of the Montmorillionite cloud in an absorbing medium will be modeled using Mie scattering and a full plane parallel radiative transfer model, utilizing available information on the size distribution and densities of the powder. The measurements will be matched by adjusting the optical constants input into the model. The need to match several measurements at each wavelength provides for a robust determination of the optical constants.
Hansen Gary B.
Hibbitts Ch. A.
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