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W. D. Smythe, R. M. Nelson (Jet Propulsion Laboratory), A. S. Hale (Jet Propulsion Labotatory), B. W. Hapke, J. L. Piatek (University of Pittsburgh)
The apparent composition of ice mixtures, when determined from spectral reflectance measurements, depends critically on details of light transport within the media. It is of paramount importance that the absorption effective pathlength be well characterized to understand the relative abundance of end members within the mixture. Several approaches to developing scattering models that characterize the absorption effective pathlength have been taken by a number of investigators in the past five decades, with differing degrees of success. One general weakness of these models is, that while the input parameters used reproduce the bi-directional reflectance distribution function (BRDF) reasonably well, it has not been possible to map reliably these input parameters to the physical variables describing the transport path, such as particle size and particle shape. This is emphasized by recent results that found the relative contributions of coherent backscattering and shadow hiding exhibit little dependence on particle size (Nelson et al., 2000, 2002). The choice of model used for analysis can have a significant effect on the estimate of composition with an ice mixture. Several of these models have been used to re-examine the apparent composition of areas on the surfaces of Galilean satellites. The effects of model on the apparent composition are discussed. Nelson, R. M. , B. W. Hapke, W. D. Smythe, and L. J. Spilker. 2000. The opposition effect in sumulated planetary regoliths. Reflectance and circular polarization ratio change at small phase angle. Icarus, 147, 545-558. Nelson, R. M. , W. D. Smythe B. W. Hapke, A. S. Hale, J. L. Piatek. 2002. Low phase angle studies of the opposition effect: Search for wavelength dependence. Planetary and Space Science, 50, 849-856. This work done at JPL under contract with NASA.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.