Multi-Wavelength Radar Studies of Lunar Pyroclastic Deposits
Lunar pyroclastic deposits were formed early in the history of volcanism on the Moon. These low-albedo features are typically associated with mare boundaries, sites of mare volcanism, and fractures in and around impact craters. Optical and infrared data have been used to map the locations of over one hundred pyroclastic deposits and to study their compositional differences (e.g. Gaddis et al., Icarus, 161, 262, 2003; Weitz et al., JGR, 103, 22725, 1998). We use multi-wavelength radar observations to study the distribution, depth and embedded rock abundance of these deposits. Data were acquired at S-band (12.6 cm wavelength) and P-band (70 cm wavelength) using Arecibo Observatory and the Green Bank Telescope in a bistatic configuration. The P-band images have resolutions of 150 m/pixel; S-band images have resolutions between 20 and 60 m/pixel.
Pyroclastic deposits appear dark to the radar at both observed wavelengths because they are smooth, easily penetrable by radar waves, and generally contain few embedded blocks. At S-band wavelengths, changes in radar reflectivity across some of the pyroclastic deposits highlight areas with increased rock abundance. Radar circular polarization ratio maps can be used to identify fine-grained deposits in cases where optical or near-infrared data are ambiguous about the presence of pyroclastics. In some cases, data from multiple radar wavelengths (including 3.8 cm wavelength data) can place constraints on the depth of the deposits. We will present results for pyroclastic deposits surrounding Mare Serenitatis, including Sulpicius Gallus, Rima Menelaus, and Taurus-Littrow, as well as new polarimetry of the Aristarchus Plateau that compliments work done by Campbell et al. (2008, Geology, 36, 135). The S-band data are part of a larger study to map the entire lunar nearside at ~80 m/pixel resolution.
1. Carter et al. (2008), Multi-Wavelength Radar Studies of Lunar Pyroclastic Deposits.
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