Dual frequency measurements of meteor head echoes simultaneously detected with the MAARSY and EISCAT radar systems

Abstract

We present dual frequency measurements of common meteor head echoes, conducted with the VHF radar MAARSY (53.5 MHz) and the UHF EISCAT (930 MHz) radar located in Northern Norway. With temporal resolutions of 1ms, we find most head echoes show a continuous increase/decrease in radar cross section (RCS) with time at both frequencies. In some cases a sudden drop of several dBsm is detected by both radars, which we interpret as direct evidence for gross fragmentation. The mean difference of the RCS between both frequencies is about 17 dBsm at an average altitude of 100 km. We find a clear positive correlation between both RCS’s as well as a trend of RCS increasing with altitude, as expected (Close et al. 2002b). We were not able to find physically allowable fits to our dual frequency measurements for plasma radial distributions following either a 1r or 1r2 fall-off around the ablating meteoroid (Marshall et al. 2017). Assuming an overdense Gaussian plasma distribution, we estimated our typical meteoroid masses as ≈100 micrograms and a mean meteoroid density of ∼600kgm3. Two other plasma distribution functions (exponential and parabolic exponential) lead to slightly larger meteoroid densities of about ∼800kgm3. All of our meteor head echoes followed cometary-type orbits prior to Earth impact.