Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Physics
Supervisor
Brown, Peter G.
2nd Supervisor
Vida, Denis
Abstract
When meteoroids fall into a planetary atmosphere, such as the Earth’s atmosphere, it deposits energy in the form of shock wave, radially from the center of the trajectory vector. These shock waves quickly decay from a strong shock into acoustic waves, which can be observed by seismic and infrasonic stations on the ground. These waveforms can determine information about the meteor, which has been done in previous works, such as position triangulation, using methods similar to earthquake epicenter triangulation. This study aims to further develop the methods of gathering information from meteors acoustically. In the first study, we looked at getting energy estimates from fragmentations using acoustic data. This was completed by using a case study with an independent energy estimate and com- paring to our acoustically found energy estimate using blast wave theory, assuming a spherical chemical explosion as the meteoroid. We found that our estimate aligned with the independent energy estimate within a factor of two, and produced reasonable results, given the uncertainties in energy calculation and atmospheric propagation of acoustic waves. The second study built off of this study, where fragmentation (and ballistic) energies of meteors were used to calculate the luminous efficiency at an instantaneous point in time for several case studies. This was used to validate the luminous efficiency models produced by Boroviˇcka et al. (2020). The final study applied acoustic wave propagation from meteors from air-based propaga- tion to water-based propagation. We showed that it was possible for the acoustic waves to pass through the air-water boundary and travel through the SOFAR channel to a hydroacoustic station. We present the time and location of both the meteor and the hydroacoustic signal, and constrain the ray-path through temporal and back-azimuth observations. We show multi- pathing to stations from reflections off of real bathymetric features to further constrain these arrivals as meteor source. Using several case studies, we present candidates for the first ever meteor detection from underneath the ocean’s surface. Overall, this thesis aims to improve the available data pipelines of meteor acoustics and hy- droacoustics so that these detections are easier to process. This work will increase the number of acoustic detections, the number of meteor parameters of each detection (such as fragmenta- tion energy), and acoustic detections will provide independent validation of meteors detected by multiple sources (optical, radar, etc.).
Summary for Lay Audience
When a meteor occurs in the Earth’s atmosphere, it releases energy in the form of shock waves, due to how fast the meteoroid body travels (30 - 240 times the speed of sound). These shock waves will propagate through the atmosphere at the speed of sound to seismic stations on the ground, and infrasound stations, which are microphones that observe low frequency sound (Hz). The signals observed by these stations can provide information about the meteor, such as triangulation, similar to how earthquake triangulation is done. This has been done in previous studies, and this thesis aims to further develop such methods. In the first study, we looked at getting estimates of the energy released from fragmentations using the acoustic data observed at infrasonic stations. This was completed by using a case study with an independent estimate of this energy, and comparing to our energy found acous- tically, using blast wave theory with the fragmentation. We found that the energy estimates agreed within reasonable amounts, given the uncertainty of the atmosphere that the acoustic waves traveled through. The second study built off of this study, where the acoustic energies of the meteors at specific points along the trajectory were measured, and used to constrain the optical energy models given by Boroviˇcka et al. (2020). The final study applied the propagation of acoustic waves into the ocean. We showed that is was possible for the acoustic waves to pass through the boundary between the atmosphere and the ocean, and travel through a channel in the ocean a long distance to a hydroacoustic station, which is effectively an underwater microphone. We conduct a survey of large meteors that exploded over the ocean, and show that for four events, the timing and angles of the observation at a hydroacoustic station are consistent with the fireball. We also show that some of the arrivals take multiple paths, reflecting off of real underwater mountains, which we use to further constrain these arrivals. Using these case studies, we present candidates for the first ever meteor detection from underneath the ocean’s surface. Overall, this thesis aims to improve the available data pipelines of meteor acoustics and hydroacoustics so that these detections are easier to process. This work will increase the number of acoustic detections, will increase the amount of information obtained from each detection (such as the energy released by fragmentation), and will provide independent validation of meteors detected by multiple sources (optical, radar, etc.).
Recommended Citation
McFadden, Luke, "Meteor Acoustics and Hydroacoustics" (2025). Electronic Thesis and Dissertation Repository. 10827.
https://ir.lib.uwo.ca/etd/10827