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K. E. Drew, P. G. Brown (University of Western Ontario), S. Close, D. Durand (MIT Lincoln Labs, Boston, USA)
Meteoroids entering the earth’s atmosphere create an ionized plasma through collisions with air molecules. This plasma both surrounds and moves with the meteoroid as well as leaves an enduring trail in its wake. The term ``head echo" refers to the radar signal when the plasma directly surrounding the meteoroid is observed. In this study, meteoroid bulk densities and orbits are determined from meteor head echoes observed by the ARPA Long-Range Tracking And Instrumentation Radar (ALTAIR) at 422 and 158 MHz. ALTAIR is very well suited to the detection of meteor head echoes, being capable of detecting upwards of 1000 meteor head echoes per hour. The ALTAIR beam was directed primarily at the North Apex sporadic meteor source during our observation collection periods, which total approximately 80 minutes, on Aug 12, 1998, Nov 17, 1998 and Nov 17, 1999. Meteoroid masses have been determined by applying both the overdense scattering and a new full wave scattering theory (Close et al., 2004) to the observed radar cross section. Observed meteoroids are predominantly in the 10-10-10-6 kg mass range. Densities are calculated using the classical physical theory of meteors. We find median densities near 1000 kg per cubic meter consistent with our observed orbital inclination distribution, which is primarily retrograde, indicative of a long-period cometary origin for most of our observed meteoroid population. We are grateful to NASA's Space Environments and Effects Program (SEE) for making this project possible.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.