Radar Images of the Candidate Spacecraft Landing Sites on the Moon

Abstract

We present new radar images and polarimetric data for the candidate landing sites of the Russian Luna-25 spacecraft near the Manzinus and Boguslawsky craters in the south polar region of the Moon. The images were obtained with the 64-m TNA-1500 antenna at the Bear Lakes Satellite Communications Center of the Special Design Bureau of the Moscow Power Engineering Institute and the 13.2-m RT-13 radio telescope at the Svetloe Observatory of the Institute of Applied Astronomy of the Russian Academy of Sciences in a bistatic configuration at a wavelength of 4.2 cm. At this wavelength the radar signals can penetrate into the lunar regolith to a depth up to 1 m and are sensitive to surface and suspended rocks with a diameter of about 1 cm or more. A spatial resolution ${\sim}80$ m per pixel was achieved through the focused processing algorithm that avoids the radar image smearing at a long integration time. The receiving-system noise temperature measurements during the entire observation session provided a reliable estimate of the circular polarization ratio (CPR) of the echo signal. Analysis of the radar images obtained revealed regions with high radar backscatter and CPR. The number and distribution of rocks and irregularities with sizes comparable to the radar wavelength on the surface and in the near-surface layer of regolith were estimated. As a result of the radar data analysis, we conclude that the surface and the near-surface regolith layer of the main site are smoother than those of the reserved site, which makes it preferable for landing. Thus, the resulting new radar images and CPR maps can be used in planning future lunar missions.