Observation and Modeling of Infrasound Signals Generated By Rocket Motor Tests and Rocket Motor Demolitions in the Western US

Abstract:

Ground-truth for infrasonic sources enables the documentation of time-varying atmospheric effects on infrasound observations. The associated source and observation data provide a basis for assessing current atmospheric models and estimating their contribution to infrasound detection and location. In this study, we utilize both seismic and acoustic data recorded at USArray Transportable Array (TA) stations and additional regional infrasound arrays in Utah and Nevada. Ground truth consists of a total of 25 rocket motor tests (static rocket motor burn tests) and 6 rocket motor demolitions in Utah for the time period from 2003 to 2013. Characteristics of infrasound signals generated by the rocket motor tests and rocket body demolitions are compared. The typical signal frequency band from the rocket motor tests is 5-10 Hz with durations of up to 60 seconds, while those from rocket body demolitions have relatively shorter durations (10 seconds) and lower frequencies (1-5 Hz). The distributions of stations that detect signals are quite variable in terms of both distance and azimuth and dependent on atmospheric conditions. Infrasound amplitudes document strong energy attenuation with range that must be quantified in order to assess the source strength. Ray tracing and parabolic equation (PE) modeling were conducted utilizing the ground-to-space (G2S) atmospheric specifications at the time of each event, in order to understand the predictability of the models and assess their utility in estimating amplitudes as a function of range. This unique dataset quantifies the contribution of temporal atmospheric conditions to infrasound detection and documents the predictive capabilities of current atmospheric model.