Determination of meteoroid physical properties from tristatic radar observations

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.

A meteor head echo analysis algorithm for the lower VHF band

“…The way target range and Doppler velocity are extracted from the raw data in a multi-step matched-filter procedure (Sects. 3-4) largely follows the EISCAT analysis technique detailed by Wannberg et al (2008) and Kero et al (2008a).…”

“…It is similar to the meteor data analysis performed on EISCAT VHF and UHF radar data described by Wannberg et al (2008) and Kero et al (2008a). The scanning procedure performs a search in the power domain by computing the boxcar function of 26 consecutive range gates (the length of a point target echo) and compares the result to the noise.…”

“…It also provides a way to remedy the signal processing issues in already existing data. The EISCAT meteor code described by Wannberg et al (2008) and Kero et al (2008a) is a 32-bit BPSK-coded sequence oversampled by a factor of 4 at reception. Our simulations show that ripples with an amplitude of 13 %, or −0.6 dB should be present in the data.…”

“…The angle between the trajectory and the beam is υ, and the radial component of the velocity vector varies as cosυ. Kero et al (2008a) showed that this gives rise to an apparent acceleration/deceleration term (depending on if the meteoroid is approaching or receding from the radar) that is of the same order of magnitude (and often larger) than the true meteoroid deceleration.…”

“…Wannberg et al (2008) detailed description of this improvement and the signal processing development following the installation of the new digital signal processing and raw data recording systems in 2001, which enabled phase-coherent pulse-by-pulse analysis. Kero et al (2008a) present a method for finding the position of a compact meteor target in the common volume monitored by the three UHF receivers, and how velocity, deceleration, RCS and meteoroid mass were estimated from the improved tristatic observations. The EISCAT UHF radar provided excellent precision and accuracy of meteors observed with all three widely separated receiver systems, but low rate of such events ( 10 h −1 ), mainly due to the small tristatic measurement volume .…”