13.05

Reanalysis of Clementine Bistatic Radar Data

R.A. Simpson, G.L. Tyler (Stanford Univ.)

Reports by Nozette and other Clementine investigators (Science, 266, 1835, 1994; Science, 274, 1495, 1996) that ice deposits may be present near the lunar south pole have stimulated discussion both as to the significance of the discovery and the validity of the detection and its interpretation. We are conducting a systematic reanalysis of these data and will present a progress report.

The data were collected at stations of the NASA DSN when Earth was in the plane of the Clementine orbit and when the spacecraft-pole-DSN angle tex2html_wrap_inline11 was within a few degrees of zero. Models for icy surfaces, such as those proposed by Hapke (Icarus, 88, 407, 1990) suggest that a coherent backscatter opposition effect leads to enhanced scatter in the backward direction and that a peak at tex2html_wrap_inline13 should be observable in the bistatic geometry.

Our analysis includes features which distinguish it from the earlier work reported by Nozette et al. We are digitally "equalizing" the non- uniform response of baseband filters in both receiving channels; this simplifies removal of the noise baseline and allows for coherent analysis of the polarization. We are also coherently removing the drift of the echo signal, which simplifies mapping between frequencies in the spectra and points on the lunar surface.