Meteor Acoustics and Hydroacoustics
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.).