Simultaneous radar and video meteors-Ⅱ: Photometry and ionisation

摘要

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 log_(10)q = log_(10)I + (12.56 + 0.49) leading to M = (38.7 + 1.2)-2.5 log_(10)q, where M is the meteor magnitude in the Gen-Ⅲ video bandpass (470-850 nm) corresponding to q at the radar specular point. The ratio of the ionisation coefficient to luminous efficiency, β/τ_1. was estimated from our observations of q/I to functionally depend on speed and radiant power. For our average meteor photon radiant power of / = 64W, we find log_(10)β/τ_1; = (3.00 ± 0.62)log_(10) v-(4.27 + 1.37). By adopting β computed according to Jones (1997), which we approximate as log_(10)β = 5.84-0.09 v~(0.5)-9.56/log_(10) v (roughly proportional to υ~△ between 20 and 40 km/s), a corresponding estimate of τ_1 for our intensified spectral bandpass was made using our measurements of q/I. We find a peak bolometric value of τ_1 = 5.9% at 41 km/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~(-8) kg is lower than previous studies would suggest.