Reports

The Clementine Bistatic Radar Experiment

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Science  29 Nov 1996:
Vol. 274, Issue 5292, pp. 1495-1498
DOI: 10.1126/science.274.5292.1495

Figures

  • Fig. 1.

    Orbital geometry of the Clementine bistatic radar experiment. The lunar polar tilt relative to the ecliptic (1.6°), the lunar tilt toward Earth (∼5°), and the bistatic angle β between spacecraft, lunar surface, and Earth receiver are shown.

  • Fig. 2.

    Composite Clementine orbital images of the poles of the moon, where more than 50 separate images have been summed together over one lunar day. In these views, areas of near permanent illumination are white and areas of near permanent darkness are black. Within 100 km of each pole, the south pole (B) shows considerable darkness (= cold traps) whereas the immediate surroundings of the north pole (A) show at least an order of magnitude greater illumination, and are therefore warmer. The scale bar is 100 km. [Ed. note: This has been corrected from what appears in the print product where the poles were incorrectly identified.]

  • Fig. 3.

    (A) Circular polarization ratio (RCP/LCP) as a function of β for orbit 234 for a 2.5° radius latitude band centered on the lunar south pole and for orbit 235, for a 2.5° radius periodically illuminated band centered at 82.5°S, and for orbits 301 and 302, originating from a 2.5° radius band centered at the north pole. The area sampled is approximately 45,000 km2 (orbits 234, 301, and 302) to 170,000 km2 (orbit 235). (B) Individual polarization channel (RCP and LCP) echo power response used on a frequency bin-by-bin basis to compute the orbit 234 and 235 polarization ratios.

  • Fig. 4.

    Clementine mosaic of the south pole region of the moon showing area sampled on orbit 234.The white outline indicates the nominal area at the time of peak RCP response on orbit 234, as shown in Fig. 3. The limits of this area are defined by contours of constant Doppler shift of the received signal and the RF terminator on an idealized spherical moon. The spread of Doppler shift was chosen to maximize the fraction of permanently shadowed ground in the area sampled. On the actual moon, the true boundaries are irregular, owing to topography, and the fraction of the sampled area occupied by permanently shadowed ground probably is higher than in the idealized case.

Tables

  • Table 1.

    Circular polarization ratio (RCP/LCP) median value with 95% confidence interval for data sorted as a function of incidence angle, not as a function of β. All frequency bins representing 82° to 90° angle of incidence are included and presented as a median value. Because the orbit 234 RCP/LCP ratio is statistically greater than the other orbits, it is unlikely that this larger ratio would be found for other orbits when sorted on the basis of high angle of incidence.

    OrbitRCP/LCP median value (dB)
    2340.449 ± 0.019 (−3.476 ± 0.178)
    2350.325 ± 0.011 (−4.885 ± 0.151)
    3010.354 ± 0.014 (−4.512 ± 0.171)
    3020.318 ± 0.012 (−4.978 ± 0.166)