Simultaneous radar and video meteors—II: Photometry and ionisation

Abstract

Simultaneous radar and video measurements of meteors were made using the Canadian Meteor Orbit Radar (CMOR) and several Gen-III image-intensified CCD cameras primarily to relate radar meteor electron line density, q, to video meteor photon radiant power, I. We find that log10q=log10I+(12.56±0.49) leading to M=(38.7±1.2)−2.5log10q, where M is the meteor magnitude in the Gen-III video bandpass (470–850nm) corresponding to q at the radar specular point. The ratio of the ionisation coefficient to luminous efficiency, β/τI, was estimated from our observations of q/I to functionally depend on speed and radiant power. For our average meteor photon radiant power of I=64W, we find log10β/τI=(3.00±0.62)log10v−(4.27±1.37). By adopting β computed according to Jones (1997), which we approximate as log10β=5.84−0.09v0.5−9.56/log10v (roughly proportional to v4 between 20 and 40km/s), a corresponding estimate of τI for our intensified spectral bandpass was made using our measurements of q/I. We find a peak bolometric value of τI=5.9% at 41km/s. The main uncertainties associated with our analysis are the unknown spectra of individual meteors which affect our estimate of absolute radiant power, and uncertain values of the initial trail radius which makes estimates of q problematic. Our results suggest that the video meteor mass scale is an order of magnitude smaller than previously thought at these higher speeds, and implies that the total meteoroid mass influx between 10−5 and 10−8kg is lower than previous studies would suggest.