ASTRONOMICAL AND PHYSICAL DATA FOR METEOROIDS RECORDED BY THE ALTAIR RADAR

摘要

We present preliminary results of orbital and physical measurements of a small selection of meteoroids observed at UHF frequencies by the ALTAIR radar on Kwajalein island on November 17, 1998. The head echoes observed by ALTAIR allowed precise determination of velocities and decelerations from which orbits and masses of individual meteoroids derived from numerical modelling have been measured. During these observations, the ALTAIR radar detected average head echo rates of 1665 per hour. The effective system limiting magnitude is found to be between magnitude +10.5 and +11 corresponding to masses near 6 x 10~(-10) kg using an observed mean velocity of our analyzed sample of 56 kms~(-1). This compares favorably to a mean modelled initial mass from the observed decelerations of the largest events of near 2 x 10~(-9) kg. All observations were made with the antenna beam pointing very near the center of the north apex sporadic source. The resulting orbits determined from modelling arc largely consistent with the orbital characteristics of that source derived from other radar orbital surveys. Despite these observations occuring near the time of the expected Leonid maximum in 1998, no definite Leonids were detected in our analyzed sample.