LUNAR TOPOGRAPHY FROM EARTH-BASED RADAR INTERFEROMETRIC MAPPING
Jean-Luc C. Margot, Ph.D.
Cornell University 1999

An incomplete knowledge of the topography of the Moon has hindered the solution to several problems in lunar science and comparative planetology. The lack of elevation data over the polar regions and the generally sparse coverage in non-equatorial areas have restricted investigations related to the global shape of the Moon, impact cratering processes, and the possible presence of water ice at the lunar poles.

Three-dimensional maps of the nearside and polar regions of the Moon can be obtained with an Earth-based radar interferometer. This technique allows surface heights to be accurately measured from the relative phase between radar echoes recorded at two separate receiving stations.

The 70 m antenna and several 34 m stations of the Deep Space Network in California were configured as a radar interferometer for a sequence of observations in 1997. This experiment provided the first detailed topographic maps of the lunar polar regions, with a coverage of 300 x 1200 km at each pole. Elevation maps and radar imagery were also obtained for a 200 x 200 km region centered on Tycho Crater, the freshest large crater on the Moon. With a surface resolution of 150 m and a height resolution of 50 m or better, the radar maps represent significant improvements compared to existing lunar topographic data sets.

The digital elevation model of Tycho Crater was used to determine the fundamental parameters of the crater's shape. The data revealed an asymmetry in floor elevations, rim heights, and wall slump zones, which may be related to an oblique nature for the impact.

The topographic maps of the polar areas were used to verify previous estimates of global shape parameters for the Moon, and to locate regions which are in permanent shadow from solar illumination. The actual locations of the cold traps, potential reservoirs of ice deposits, are delineated on radar images of the lunar polar areas.