METEOR FLUXES AND VISUAL MAGNITUDES FROM EISCAT RADAR EVENT RATES - ACOMPARISON WITH CROSS-SECTION BASED MAGNITUDE ESTIMATES AND OPTICAL-DATA

Incoherent scatter radars (ISR) are versatile instruments for continuo us monitoring of ionisation processes in the Earth's atmosphere. EISCA T, 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 me teors through the narrow ISR beam. Methods for group and phase velocit y determination of the meteoroids and the discrepancy between the resu lts related to the target behaviour are presented. The radar cross sec tions of echoes associated with moving meteoroids (''meteor head echoe s'') are very small and increase with decreasing wavelength. The paren t meteoroids are found to have visual magnitudes far below the detecti on limit of most optical observations. The equivalent visual magnitude limit of the smallest objects observed by EISCAT in the current exper iments has been estimated by two different methods, both from the cros s-section measurements and from the measured event rates. Both methods give a limit value of +10 for the smallest objects while the upper li mit is +4. The lower limit of the visual magnitude for the collocated optical measurement system is +4. Thus the two detection systems obser ve two different meteor size ranges, with the radar almost reaching mi crometeorite population. Meteor fluxes estimated from the event rates and the radar system parameters agree well with previous extrapolated values for this size range.