Earth-based radar observations for lunar geologic investigations R.R. Ghent 1 , B.A. Campbell 2 , D. B. Campbell 3 , L. M. Carter 2 , M. Nolan 4 , and B. R. Hawke 5 , 1 Department of Geology, University of Toronto, Earth Sciences Centre, 22 Russell St., Toronto, Ontario M5S 3B1, Canada , 2 Center for Earth and Planetary Studies, Smithsonian Institution, MRC 315, Washington, D. C., 20013-7015, 3 Dept. of Astronomy, Cornell University, Ithaca, NY 14853, 4 Arecibo Observatory, Arecibo, PR , 5 Hawai’i Institute of Geophysics and Planetology, University of Hawai’i, 1680 East-West Road, Honolulu, HI 96822. Introduction: Over the past three years we have carried out high resolution 13 cm and 70 cm multi- polarization radar studies of high-interest terrain on the Moon using the Arecibo/GBT radar systems [1-4]. These studies support planning for future robotic and human landings, in situ resource utilization, and a number of lunar mapping and geologic investigations. Beginning in 2008, our team will collect a complete 12.6-cm wavelength radar map of the near side, at 80 m spatial resolution, to complement a PDS-archived 70-cm map and upcoming lunar- orbital radar investigations. Radar Observations: The Arecibo Observatory/Green Bank Telescope (GBT) bistatic radar system can be used to obtain multi-polarization images of the Moon at 13 cm and 70 cm wavelengths. The resolution of the 13 cm images is as fine as 20 m per pixel, and is 200-500 m/pixel for the 70 cm images. The 13 cm system has similar characteristics and capabilities to the 13-cm radar system on the LRO, and can image large areas (~300x600 km) of the lunar surface in each one-hour observation. One of the advantages of radar is its sensitivity to both surface and near-surface properties. This is especially true for the Moon, with a dry regolith that has low enough microwave losses to allow penetration of the radar signal to depths of ten wavelengths or more. The reflected signal is modulated by the abundance of rocks and blocky material, both on the surface and suspended within the probing distance of the radar. The circular polarization ratio (CPR), the ratio of the echo power in the same sense of circular polarization as that transmitted to the power in the opposite sense, is a useful indicator of the presence of surface or sub-surface wavelength scale roughness, while the degree of linear polarization derived from analysis of the Stokes’ polarization parameters of the reflected echo can help to distinguish between the two. Fig. 1. Radar image at 12.6-cm wavelength of the distal end of Vallis Schröteri, where thick (radar-dark) and thin (radar-bright areas with numerous small, bright craters and streaks) mantling materials flank the rille. Inset shows LO-IV photo of the rille end, with small craters labeled to match on both images. Note the lack of optical albedo features associated with the radar-bright secondary ejecta streaks across this area. Looking Inside Regional Pyroclastic Deposits: Fig. 1 shows a high-resolution 13 cm image of part of the Aristarchus plateau, which has been used in conjunction with 70-cm data to characterize variations in pyroclastic thickness, mare flooding from Vallis Schroteri, the abundance of impact-derived rocks, and to identify the best sites for excavation and resource extraction. What shows up clearly in this image are areas with high concentrations of sub-surface scatterers due to a probable lava flow feature near the image center, which is covered by a thin veneer of NLSI Lunar Science Conference (2008) 2065.pdf