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Clementine Bistatic Radar Experiment

NSSDC ID: 1994-004A-09
Mission Name: Clementine
Principal Investigator: Dr. Eugene M. Shoemaker

Description

The Clementine Bistatic Radar Experiment made use of the radio transmitting equipment aboard Clementine to search the Moon's polar regions for evidence of ice in permanently shadowed craters. The basic method of bistatic radar involves a spacecraft transmitting a radio signal at a point on the target body. Reflections of these signals from the target are received on Earth. Properties of the received reflections can be interpreted to give information on the target surface.

In this experiment the Clementine spacecraft transmitted an unmodulated S-band right-circularly polarized signal through the 1.1 meter high-gain antenna. The signal had a frequency of 2.273 GHz (13.19 cm wavelength) and net power of about 6 watts. The high gain antenna has a half-power half-beamwidth of 4.0 degrees. Reflections were received on Earth by the 70 meter antennae of the Deep Space Network (DSN) at Goldstone (United States), Madrid (Spain) and Canberra (Australia). During these passes, the lunar axial tilt toward Earth at the DSN stations was 4.5 to 5.5 degrees. The experiment can be done when the target and DSN receiver are coplaner with the spacecraft orbital plane. The bistatic radar experiment was performed for the lunar south pole during orbits 234, 235, 236, and 237 on 9 and 10 April 1994 (received at Goldstone, Madrid, and Canberra). Observations of the north pole were made on orbits 299, 301, and 302 on 23 and 24 April 1994 (received at Madrid and Canberra). Systematic errors made the results from orbits 236, 237, and 299 unusable.

The properties of the reflected radio signal which are of particular interest in the search for water ice and other frozen volatiles are the echo magnitude and the sense of polarization. The echo magnitude, or amplitude of reflectivity, is higher for frozen volatiles than for typical silicate rocks. Total internal reflection, characteristic of volatile ices, tends to preserve the original sense of circular polarization, in this case right-circular polarization, or RCP, in the reflected signal. There is also a detection, known as a coherent backscatter opposition effect, which can be made as the spacecraft-target-receiver angle approaches zero, which may indicate scattering centers embedded in ice. Results of the experiment showed a significant RCP to LCP (left-circular polarization) ratio enhancement on orbit 234 over the south pole and a coherent backscatter opposition effect, possibly indicative of volatile ices (presumably well-mixed with soil and dust) in the permanently shadowed craters in this region. However, other scattering mechanisms, such as roughness, can not be ruled out as the cause of these results. The other orbits did not show statistically significant RCP/LCP enhancements.

Facts in Brief

Mass: 13.6 kg

Funding Agencies

  • Department of Defense-Department of the Navy (United States)
  • NASA-Office of Space Science (United States)

Discipline

  • Planetary Science: Geology and Geophysics

Additional Information

Questions or comments about this experiment can be directed to: Dr. David R. Williams.

 

Personnel

NameRoleOriginal AffiliationE-mail
Mr. Eric EliasonTeam MemberUS Geological Surveyeeliason@usgs.gov
Prof. Jacques E. BlamontTeam MemberCNRS, Service d'Aeronomie 
Dr. Bonnie J. BurattiTeam MemberNASA Jet Propulsion Laboratorybburatti@scn1.jpl.nasa.gov
Dr. Alfred S. McEwenTeam MemberUS Geological Surveymcewen@pirl.lpl.arizona.edu
Dr. Paul D. SpudisDeputy Team LeaderLunar and Planetary Institutespudis@lpi.usra.edu
Dr. Daniel N. BakerTeam MemberNASA Goddard Space Flight Centerdaniel.baker@colorado.edu
Mr. Thomas C. DuxburyTeam MemberNASA Jet Propulsion Laboratorytduxbury@gmu.edu
Dr. Eugene M. ShoemakerTeam LeaderUS Geological Survey 
Mr. Merton E. DaviesTeam MemberRand Corporation 
Mr. Charles H. ActonTeam MemberUS Geological Surveycacton@mail3.jpl.nasa.gov
Dr. Paul G. LuceyTeam MemberUniversity of Hawaiilucey@pgd.hawaii.edu
Dr. Carle M. PietersTeam MemberBrown Universitycarle_pieters@brown.edu
Dr. David E. SmithTeam MemberNASA Goddard Space Flight Centerdavid.e.smith@nasa.gov

Selected References

Nozette, S., et al., The Clementine bistatic radar experiment, Science, 274, No. 5292, 1495-1498, Nov. 1996.

Simpson, R. A., and G. L. Tyler, Reanalysis of Clementine bistatic radar data from the lunar South Pole, J. Geophys. Res., 104, No. E2, 3845-3862, Feb. 1999.

Stacy, N. J. S., et al., Arecibo radar mapping of the lunar poles: A search for ice deposits, Science, 276, No. 5324, 1527-1530, June 1997.

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