High Resolution Topographic Maps of the Lunar South Pole

J. L. Margot, D. B. Campbell (Cornell University), R. F. Jurgens, M. A. Slade (JPL/Caltech), N. J. Stacy (DSTO, Australia)

Topographic maps of the South Polar region of the Moon are derived from new high resolution ground-based radar maps. The images were obtained with the Goldstone X-band system ( tex2html_wrap_inline20 = 3.5 cm) using the 70 m antenna to transmit and two 34 m antennas to form a receive interferometer. In this interferometric mode, heights above a reference surface can be derived from the relative phase between the two radar signals [1]. A focused delay-Doppler technique [2] is used to generate backscatter maps with a surface resolution of 75 m. The combination of the complex reflectivities is expected to yield surface heights at a similar resolution.

Current map coverage includes an area tex2html_wrap_inline22 450 km in range by tex2html_wrap_inline22 300 km in Doppler, with latitudes ranging from -80 degrees on the near side to -85 degrees on the far side. Future observations are planned to map two regions of similar extent to the East and West of the South Pole, as well as the North Polar area.

The topographic maps will be used to estimate solar illumination around the poles, taking the 18.6 year lunar precessional cycle into account. This effort is motivated by an attempt to identify areas of permanent shadow, and may provide a valuable tool in evaluating the likelihood of the presence of volatiles on the Moon. The topographic data will also be useful in complementing Clementine's altimetry and extending its coverage into the polar regions [3].

As one of the two receiving antennas had dual polarization capability, new circular polarization ratio maps of the South Pole can be derived. These will complement similar maps obtained at Arecibo at 12.6 cm [4] and refine the search for unusual polarization signatures that may be indicative of ice.

[1] I. I. Shapiro et al. (1972). Science, 178, 939. [2] N. J. Stacy (1993). Ph.D. Thesis, Cornell University. [3] D. E. Smith et al. (1997). JGR, 102, 1591. [4] N. J. Stacy et al. (1997). Science, 276, June 6.