Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p31b1056c&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P31B-1056
Astronomy and Astrophysics
Astronomy
5420 Impact Phenomena (Includes Cratering), 5470 Surface Materials And Properties, 6295 Venus, 6949 Radar Astronomy, 6969 Remote Sensing
Scientific paper
Magellan spacecraft images of Venus revealed several different types of impact crater related deposits on Venus. Examples include the hundreds of kilometers in length parabolic-shaped deposits and the smaller (tens of km) dark halos. Wind streaks are associated with some of these features, confirming the presence of mantling material. These areas on Venus may look significantly different at optical wavelengths, since radar can penetrate several wavelengths into the surface and reveal underlying terrain. Linear polarization analysis can be used to investigate whether there is a surficial deposit in a given region. A circularly polarized wave can be decomposed into two orthogonal linear-polarized waves of equal magnitude. If a circularly polarized radar signal penetrates into a surface that is smooth at wavelength scales, and is scattered by embedded rocks or a sub-surface layer, the received echo will have a linear-polarized component. This linear polarization is produced because the "horizontal" and "vertical" components of the incident circular wave have different transmission coefficients into and out of the surface layer. If there is no sub-surface reflection, there will be no linear polarization. We used the 13-cm wavelength Arecibo radar system to observe Venus during two inferior conjunctions. We transmitted a circularly polarized wave and received both of the reflected circular polarizations. From these data, delay-Doppler images in all four Stokes polarization parameters were created, and a map of the degree of linear polarization was formed. Our data reveals linear polarization associated with impact craters, volcanic dome fields, and areas of wind streaks. In particular, we note significant linear polarization from areas near 44 craters, including 5 of the craters with parabolic deposits. The linear polarization signature is usually associated with the diffuse, featureless radar-bright areas near the crater. In addition, the craters that show a linearly polarized echo component often have dark halos or bright floors, and thus are likely be younger in age. This technique can be used for other objects as well, including possibly determining whether there is regolith covering the polar ice deposits on Mercury and searching for regolith on asteroids.
Campbell Bruce A.
Campbell Don B.
Carter Lynn Marie
Margot Joelle
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