Initial characterization of infrasound sources using the phase and amplitude gradient estimator method for acoustic intensity

The phase and amplitude gradient estimator (PAGE) method for vector acoustic intensity [Thomas et al., J. Acoust. Soc. Am. 137, 3366–3376 (2015)] has been used previously to improve source characterization over broad frequency ranges. This paper describes initial applications of the PAGE method to the infrasound region for outdoor sources using multi-microphone probes. Measurement challenges include wind noise, which reduces signal-to-noise ratio and coherence, low-frequency phase and amplitude mismatch between microphones, and determining an appropriate microphone spacing to maximize bandwidth. Analysis challenges include phase unwrapping above the spatial Nyquist frequency, source statistical stationarity, and balancing frequency resolution with averaging across finite record lengths. This paper discusses how these challenges are being addressed for specific sources of infrasound, namely, wind turbines and large rocket motors. [Work supported by NSF.]The phase and amplitude gradient estimator (PAGE) method for vector acoustic intensity [Thomas et al., J. Acoust. Soc. Am. 137, 3366–3376 (2015)] has been used previously to improve source characterization over broad frequency ranges. This paper describes initial applications of the PAGE method to the infrasound region for outdoor sources using multi-microphone probes. Measurement challenges include wind noise, which reduces signal-to-noise ratio and coherence, low-frequency phase and amplitude mismatch between microphones, and determining an appropriate microphone spacing to maximize bandwidth. Analysis challenges include phase unwrapping above the spatial Nyquist frequency, source statistical stationarity, and balancing frequency resolution with averaging across finite record lengths. This paper discusses how these challenges are being addressed for specific sources of infrasound, namely, wind turbines and large rocket motors. [Work supported by NSF.]