Optical Observations of Meteors Generating Infrasound - I: Acoustic Signal Identification and Phenomenology

We analyze infrasound signals from 71 bright meteors simultaneously detected by video to investigate the phenomenology and characteristics of meteor-generated near-field infrasound and shock production. A taxonomy for meteor generated infrasound signal classification has been developed using the time-pressure signal of the infrasound arrivals. Based on the location along the meteor trail where the infrasound signal originates, we find most signals are associated with cylindrical shocks, with about a quarter of events evidencing spherical shocks associated with fragmentation events and optical flares. The video data indicate that all events with ray launch angles >117 deg from the trajectory heading are most likely generated by a spherical shock, while infrasound produced by the meteors with ray launch angles <117 deg can be attributed to both a cylindrical line source and a spherical shock. We find that meteors preferentially produce infrasound toward the end of their trails with a smaller number showing a preference for mid-trail production. Meteors producing multiple infrasound arrivals show a strong infrasound source height skewness to the end of trails and are much more likely to be associated with optical flares. While a significant fraction of our meteors producing infrasound (~1/4 of single arrivals) are produced by fragmentation events, we find no instances where acoustic radiation is detectable more than about 60 deg beyond the ballistic regime at our meteoroid sizes (grams to tens of kg) emphasizing the strong anisotropy in acoustic radiation for meteors which are dominated by cylindrical line source geometry, even in the presence of fragmentation.