Mathematics – Probability
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p11a0350s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P11A-0350
Mathematics
Probability
5410 Composition, 5415 Erosion And Weathering, 5460 Physical Properties Of Materials, 5464 Remote Sensing, 5494 Instruments And Techniques
Scientific paper
For remote sensing observations of planetary regoliths it is well known that as phase angle becomes small, the reflectance of a particulate material will increase non-linearly and exhibit the 'opposition effect' [1]. The phase curve, the size of the opposition surge and the width of the phase curve near zero degrees, have been attributed to two processes commonly called 'shadow hiding' (SHOE) and 'coherent backscattering' (CBOE)[2,3,4] Understanding the relative contribution of the SHOE and CBOE components to the integrated phase curve is a prerequisite for developing models that can confidently determine fundamental regolith textural properties such as particle size and packing density from remote sensing data. Laboratory experiments have attempted to distinguish the contribution of SHOE and CBOE by illuminating samples with circularly polarized monochromatic light and measuring the ratio of circular polarization to linear polarization in the returned signal. If the returned signal is singly scattered then this ratio should decrease as phase angle decreases. If the returned signal is multiply scattered then the circular polarization ratio should strongly increase as phase angle decreases. We have observed this increased ratio with decreasing phase angle in many highly reflective particulate media [5,6,7]. For materials with low reflectance, the expectation is that most of the returned signal is singly scattered because of the high probability absorption at each scattering event. Hence, for absorbing media the circular polarization ratio is not expected to sharply increase as phase angle decreases. In general we have found this to be true [5]. However, we have encountered recently an interesting exception. Measurements on a suite of boron carbide samples (reflectance =~ 5%) have shown a significant increase in circular polarization ratio with decreasing phase angle, a result that is not consistent with our interpretation of the process. This result suggests that albedo is not only parameter determining the amount of multiple scattering in the medium. This unusual behavior is as yet unexplained; one conjecture is that a unique particle shape may create a very unusual single scattering phase function in boron carbide. It is important to understand this unusual behavior and its implications for models that retrieve surface textural properties from remote sensing data. This work performed at JPL under a contract from NASA's Planetary Geology and Geophysics Program. 1. Geherels, T. Astrophys. J, 123, 331-338, 1956 2. Hapke, B. W. Icarus, 67, 264-280, 1986 3. Shkuratov, Yu. SA-A.J., 27, 581-583, 1983 4. Hapke, B.W. Icarus, 88, 264-280, 1986 5. Nelson, R. M., B. W. Hapke, W. D. Smythe, L. J. Horn. Icarus 131, 223-230, 1998 6. Nelson, R. M., B. W. Hapke, W. D. Smythe, L. J. Spilker. Icarus, 147, 545-558, 2000 7. Nelson, R. M., W. D. Smythe, B. W. Hapke, A. S. Hale. to appear in Planet. Space Sci, 2002
Hale Scott A.
Hapke Bruce W.
Nelson Robert M.
Piatek J. A.
Smythe William D.
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