Determination of meteoroid physical properties from tristatic radar observations

摘要

In this work we give a review of the meteor head echo observations carriedout with the tristatic 930 MHz EISCAT UHF radar system during four 24 h runsbetween 2002 and 2005 and compare these with earlier observations. A totalnumber of 410 tristatic meteors were observed. We describe a method todetermine the position of a compact radar target in the common volumemonitored by the three receivers and demonstrate its applicability for meteorstudies. The inferred positions of the meteor targets have been utilized toestimate their velocities, decelerations and directions of arrival as well astheir radar cross sections with unprecedented accuracy. The velocitydistribution of the meteoroids is bimodal with peaks at 35–40 km/s and55–60 km/s, and ranges from 19–70 km/s. The estimated masses are between10−9–10−5.5 kg. There are very few detections below 30 km/s. Theobservations are clearly biased to high-velocity meteoroids, but not sobiased against slow meteoroids as has been presumed from previous tristaticmeasurements. Finally, we discuss how the radial deceleration observed with amonostatic radar depends on the meteoroid velocity and the angle between thetrajectory and the beam. The finite beamwidth leads to underestimatedmeteoroid masses if radial velocity and deceleration of meteoroidsapproaching the radar are used as estimates of the true quantities in amomentum equation of motion.