Abstract
Abstract. Incoherent scatter radars (ISR) are versatile instruments for continuous monitoring of ionisation processes in the Earth's atmosphere. EISCAT, The European Incoherent Scatter facility has proven effective also in meteor studies. The time resolution of the radar can be reduced to a few milliseconds, sufficient to resolve the passage of individual meteors through the narrow ISR beam. Methods for group and phase velocity determination of the meteoroids and the discrepancy between the results related to the target behaviour are presented. The radar cross sections of echoes associated with moving meteoroids ("meteor head echoes") are very small and increase with decreasing wavelength. The parent meteoroids are found to have visual magnitudes far below the detection limit of most optical observations. The equivalent visual magnitude limit of the smallest objects observed by EISCAT in the current experiments has been estimated by two different methods, both from the cross-section measurements and from the measured event rates. Both methods give a limit value of +10 for the smallest objects while the upper limit is +4. The lower limit of the visual magnitude for the collocated optical measurement system is +4. Thus the two detection systems observe two different meteor size ranges, with the radar almost reaching micrometeorite population. Meteor fluxes estimated from the event rates and the radar system parameters agree well with previous extrapolated values for this size range.Key words. Ionosphere (ionization mechanisms). Radio science (ionospheric physics). Space plasma physics (ionization processes)
Highlights
In the early 1960s, a series of meteor studies were performed at the 440 MHz Millstone Hill radar (Evans, 1965, 1966)
Since 1994, measurements have been performed at the Jicamarca, EISCAT and Arecibo incoherent scatter radars (ISR) and numerous papers have been published (Chapin and Kudeki, 1994; Pellinen-Wannberg and Wannberg, 1994, 1996; Zhou et al, 1995; Wannberg et al, 1996; Malnes et al, 1996; Mathews et al, 1997; Zhou and Kelley, 1997)
Earlier studies comparing visual and in that case meteor radar observations on meteor head echoes have been done by Jones and Webster (1991)
Summary
In the early 1960s, a series of meteor studies were performed at the 440 MHz Millstone Hill radar (Evans, 1965, 1966). The VHF radar, located in Tromsù in Norway is monostatic, while the UHF radar is tristatic with the transmitter and one receiver located in Tromsù and the other receivers at Kiruna, Sweden and SodankylaÈ , Finland In their standard mode of operation, these radars observe the incoherent scatter from collective densityuctuations, organized by plasma waves created at thermal nearequilibrium conditions in the ionosphere (Evans, 1969; Farley, 1979). The range resolution was set at 450 m, which required the use of 3 ls pulses and 2 ́ 176.8 kHz detection band width in the radar receiver With such a wide passband, strongly Doppler shifted`meteor head echoes'' were passed by the ®lters, and not cut away as they would be in most standard incoherent scatter program modes, where the detection band widths are of the order of 25 kHz
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