Computer Science
Scientific paper
Nov 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........8c&link_type=abstract
Ph.D dissertation, 2005. 124 pages; United States -- New York: Cornell University; 2005. Publication Number: AAT 3162190. DAI-B
Computer Science
Mantling, Venus, Regoliths, Asteroids, Radar Polarimetry
Scientific paper
Dual-polarization radar images of Venus were obtained and analyzed with the aim of studying regional variations in the surface properties. Subsurface scattering of an incident circularly polarized radar wave produces a linearly polarized echo component because the transmission coefficients at the atmosphere-surface boundary are different for the horizontal and vertical linearly polarized components of the incident wave. Mapping the degree of linear polarization across the surface can therefore reveal the presence of mantling deposits.
Arecibo 12.6 cm wavelength radar observations provided images of the surface of Venus in all four Stokes polarization parameters of the reflected echo, from which images of the degree of linear polarization were derived. These images show that substantial areas of Sedna, Guinevere and Lavinia Planitias produce a radar echo with a significant linear-polarized component. The areas showing linear polarization enhancements are strongly correlated with surface features visible in Arecibo and Magellan images, primarily impact craters, dome fields, highland regions and aeolian deposits, including dune fields. A strong linearly polarized echo component (~10-40% linear polarization) is found from regions near 45 impact craters, including from 5 of the parabolic-shaped impact deposits seen in earlier radar images of Venus. These linear polarization features typically correspond to diffuse, higher backscatter cross section (bright) regions in Magellan images. The linearly polarized component in these regions is attributed to subsurface echoes from a mantled substrate or from buried rocks. Enhanced linear polarization signatures are also present in three highland areas (Theia Mons, Tepev Mons, and Maxwell Montes) with high radar reflectivity and anomalously low emissivity, providing evidence that at least some portions of these mountaintops are covered by fine-grained material.
Radar polarimetry can also be applied to the search for regolith on asteroids. Degree of linear polarization images of the asteroid 1999 JM8 show that it is possible to measure linear-polarized ethos from an asteroid and infer coverby a fine-grained material such as regolith. Analysis of archival radar data of asteroids and future observations will allow comparison of asteroid size and possibly composition with the presence of regolith.
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