Determination of the meteoroid velocity distribution at the Earth using high-gain radar

Abstract

Plasma formed in the immediate vicinity of a meteoroid as it descends through Earth's atmosphere enables high-gain radars such as those found at Kwajalein, Arecibo, and Jicamarca to detect ablating meteoroids. In the work presented here, we show that these head echo measurements preferentially detect more energetic meteoroids over less energetic ones and present a method of estimating the effects of this bias when measuring the velocity distributions. To do this, we apply ablation and ionization models to estimate a meteoroid's plasma production rate based on its initial kinetic energy and ionization efficiency. This analysis demonstrates that, almost regardless of the assumptions made, high-gain radars will preferentially detect faster and more massive meteoroids. Following the model used by Taylor (1995, Icarus 116, 154–158), we estimate the biases and then apply them to observed meteoroid velocity distributions. We apply this technique to observations of the North Apex meteoroid source made by the Advanced Research Project Agency Long Range Tracking and Instrumentation Radar (ALTAIR) at two frequencies (160 and 422 MHz) and compare results from the Harvard Radio Meteor Project (HRMP) at High Frequency (HF, 40.9 MHz). Both studies observe a peak in the distribution of North Apex meteoroids at approximately 56 km s −1. After correcting for biases using Taylor's method, the results suggest that the mass-weighted peak of the distribution lies near 20 km s −1 for both studies. We attribute these similarities to the fact that both radar systems depend upon similar ablation and ionization processes and thus have a common mass scale.