Assessing the Temporal Coherency of the Stratosphere Using Infrasound Signals from Repeating Explosions

Abstract:

Advancements in infrasound science have been restricted by the lack of constraints on atmospheric dynamics at altitudes where waves are refracted. However, recent detections of repetitive signals, with a temporal distribution suitable for assessing the impact of short time-scale atmospheric variations on infrasonic wave propagation, provide data to unravel these difficult problems. These signals, generated by explosions conducted at the McAlester Army Ammunitions Plant, are recurrent over 20 second time intervals and exhibit apparent multi-pathing. Summer-time detections made at a regional infrasound array located approximately 250 km northwest of the source were used to conduct a preliminary analysis of the data. Blasting logs provide ground truth source location and the time intervals in which the explosions occurred. Frequency-wave number analysis and sliding-window array processing methods are applied to the signals in order to quantify the impact of time-varying atmospheric effects on back azimuth and trace velocity estimates. Ray tracing is implemented in conjunction with pertinent G2S atmospheric models to gain insight into potential propagation paths from source to receiver. We present results based on a preliminary analysis of these signals with an aim of achieving a better overall understanding of how and why acoustic waveform temporal coherency varies over short time intervals.