Abstract
Abstract. In this work we give a review of the meteor head echo observations carried out with the tristatic 930 MHz EISCAT UHF radar system during four 24 h runs between 2002 and 2005 and compare these with earlier observations. A total number of 410 tristatic meteors were observed. We describe a method to determine the position of a compact radar target in the common volume monitored by the three receivers and demonstrate its applicability for meteor studies. The inferred positions of the meteor targets have been utilized to estimate their velocities, decelerations and directions of arrival as well as their radar cross sections with unprecedented accuracy. The velocity distribution of the meteoroids is bimodal with peaks at 35–40 km/s and 55–60 km/s, and ranges from 19–70 km/s. The estimated masses are between 10−9–10−5.5 kg. There are very few detections below 30 km/s. The observations are clearly biased to high-velocity meteoroids, but not so biased against slow meteoroids as has been presumed from previous tristatic measurements. Finally, we discuss how the radial deceleration observed with a monostatic radar depends on the meteoroid velocity and the angle between the trajectory and the beam. The finite beamwidth leads to underestimated meteoroid masses if radial velocity and deceleration of meteoroids approaching the radar are used as estimates of the true quantities in a momentum equation of motion.
Highlights
Meteor head echoes are radio wave reflections from the plasma generated by the interaction of meteoroids with the atmosphere at about 70–140 km altitude
The position of a compact target observed by the three EISCAT UHF receivers can be visualized as situated at the intersection point of three geometrical shapes: a sphere centered around the Tromsø antenna and two prolate spheroidal surfaces, both with Tromsø in one focal point and one of the remote antennae in the other
The tristatic EISCAT UHF system has been used in a series of measurement campaigns from 2002–2005 to study meteoric head echoes. 410 meteors were simultaneously detected with all three receivers and contained enough data points for time-of-flight velocity calculations to be compared with the Doppler velocity measurements
Summary
The first meteor investigations with what today is termed a High Power Large Aperture (HPLA) radar were conducted by Evans (1965, 1966) with the 440 MHz Millstone Hill radar. To study head echoes with a monostatic radar requires that the geometry of the detections be carefully taken into consideration, as only the radial component of the velocity is observed. There was a 30-year pause in the use of narrow beam HPLA radars for meteor observations, and when they resumed, the improved signal processing techniques and large data handling capacities proved them suitable for studies of sporadic meteor head echoes (Pellinen-Wannberg and Wannberg, 1994; Mathews et al, 1997). The tristatic capability of the EISCAT UHF system makes it a unique tool in determining meteoroid physical properties and investigations of the head echo scattering process. We present the methods used for meteor head echo observations carried out during four 24 h runs between 2002 and 2005 as well as a summary of the determined physical characteristics of the observed meteoroids
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