Correcting radar meteor fluxes for observing biases

TL;DR

This study uses an eight-year optical and radar survey to identify biases in radar meteor detection and proposes correction factors to improve flux estimates, revealing overcorrections for some showers and undercorrections for others.

Contribution

It introduces a method to correct radar meteor fluxes for observing biases based on simultaneous optical and radar data over eight years.

Findings

Radar echoes missed by optical detection are quantified.

Correction factors vary with meteor velocity and height.

Current correction methods overestimate some showers and underestimate others.

Abstract

We report on an eight year survey of simultaneous optical and radar meteor detections with the goal of isolating the fraction of meteors missed by specular radars. A total of 10,503 Electron Multiplied Charge Couple Device (EMCCD) meteors with peak brightness above +7 were simultaneously detected by the Canadian Meteor Orbit Radar (CMOR) and used to estimate the fraction of radar echoes missed as a function of speed and height. During the time period that our cameras were recording, we found some 34,119 and 18,008 meteor echoes in total occurred within the field of view of the EMCCD cameras at 29 and 38 MHz respectively. This demonstrated that a significant fraction of the specular radar echoes remain below the detection threshold of the EMCCD cameras. We used these data to derive corrections for radar-specific observing biases. The optical height distributions for six velocity bins, spanning 10 - 72 km/s were used to determine the fraction of potential radar echoes which are observed for meteors with higher begin heights ($k_c$>96) and for those with lower begin heights. When compared to the correction factors currently used in calculating shower fluxes with CMOR, mid-velocity showers such as the Geminids and South Delta Aquariids are found to have been overcorrected, while high velocity showers like the Perseids and Leonids are significantly undercorrected.