Abstract-Bidirectional visible and near-infrared and off-axis biconical Fourier transform infrared reflectance spectra of Almahata Sitta meteorite stone samples, fragments of asteroid 2008 TC 3 , have been measured. These meteorites represent the first freshly fallen polymict ureilites available for such studies. Although the chip samples show varying degrees of terrestrial weathering depending on their environment on Earth, many of them are much fresher than other ureilites known to date. The majority of the Almahata Sitta chips studied here show only a weak near-UV absorption, a flat spectrum at visible and near-IR wavelengths, and varying depths of the 1 and 2 lm pyroxene and olivine bands. The astronomical reflectance observations of the asteroid 2008 TC 3 over the range 0.55-1.0 lm provide a constraint on what a combination of the measured spectra can represent in the surface reflectance of the asteroid over the 0.32-2.55 lm range measured in this study. Most of the recovered samples of Almahata Sitta have textures and albedos similar to stones #27 (largest recovered fragment), #4, and #47. Results of linear least-square fits of the asteroid 2008 TC 3 spectrum with two sets of the meteorite spectra suggest that the asteroid had 10-12% albedo and no fine regolith on its surface. We note that other lithologies may be at the surface of other fragments of the asteroid family from which 2008 TC 3 originated. In that case, reflectance spectra could vary significantly among family members.
The accuracy of the perturbation model to predict the effect of scattering and absorbing inhomogeneities on photon migration has been investigated by comparisons with experimental and numerical results. Comparisons for scattering inhomogeneities showed that the model gives satisfactory results both for the intensity and for the temporal profile of the perturbation over a large range of values for the scattering properties of the defect. As for absorbing inhomogeneities, the model provides an excellent description for the temporal profile, but the results for the intensity are accurate only when the perturbation is small. For absorbing inhomogeneities an empirical model that has a significantly more extended application range has been proposed. The model is based on an expression for the time-resolved mean path length that detected photons have followed inside the inhomogeneity. The application range of the proposed model covers the values expected for the optical properties and for the volumes of inhomogeneities of practical interest for optical mammography.
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