Computer Science
Scientific paper
Jul 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........14c&link_type=abstract
Thesis (PhD). BOSTON UNIVERSITY, Source DAI-B 65/01, p. 254, Jul 2004, 220 pages.
Computer Science
5
Scientific paper
Meteoroids are solid objects in space that typically originate from the breakup of comets and asteroids. Meteoroids are of fundamental importance to our understanding of the Earth and our solar system because they are composed of the material from which everything in our solar system was originally made. Outstanding questions include how many meteoroids enter Earth's atmosphere, how much material do they deposit, what is their origin, and what are their densities. When a meteoroid enters into the Earth's atmosphere, it ablates and forms localized plasma near 100 km altitude; the luminous phenomenon associated with a meteoroid's entry is referred to as a meteor. Large-aperture, narrow- beam radars often detect the meteor plasma that surrounds a meteoroid and moves at its speed; these signals are called head echoes. Head echoes contain a wealth of information about the meteor and meteoroid, however, no compelling explanation has been proposed for the nature of the head echo. This thesis contains the first comprehensive description of head echoes and the subsequent analysis of head echo properties to determine meteoroid properties. Using multi-frequency, high- resolution radars, we analyze radar head echo data to determine the meteoroid flux and speed. We determine the inter-dependence of head echo properties such as altitude, radar-cross-section, speed, deceleration and radar frequency. We develop a new scattering theory for head echoes by modeling the interaction of a radar wave with the plasma, which enables us to calculate the head echo plasma density and its dependence on altitude. Using ablation and ionization models, we convert plasma density to meteoroid mass and use the corresponding speed and position to determine the meteoroid's density and radius with unprecedented accuracy. Our results indicate that our detected meteoroids have masses ranging from 10-9 to 1 gm with a peak near 10-6 gm. The interstellar meteoroids, which comprise a small percentage of the total number of detections, have the lowest masses. The average meteoroid density utilizing all of our multi- frequency data is 1.6 g/cm3, which indicates that these particles are mostly cometary in origin.
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