The application of acoustic particle velocity sensors to airborne infrasonic signals

Abstract

Infrasound arrays, because of the wavelengths involved and the necessity for minimal spatial aliasing, can be quite large, e.g. an array layout often used for beamforming for frequencies up to 10 Hz is a centered, 17-m radius equilateral triangle. Available real estate is often limited such that optimally sized arrays are not possible. An acoustic particle velocity sensor, in principle, can perform the same job as a large infrasound array, but in a much smaller package (less than the size of a single infrasound sensor) since it provides, in post processing, a direct measurement of the wavefront normal. However, localized meteorological perturbations to the wavefront normal could cause significant bearing estimate errors when using a particle velocity sensor. Recently, as part of the characterization of a mobile infrasound source and during the collection of sounds from space station resupply rockets, acoustic particle velocity sensors were positioned next to infrasound sensors in order to test the concept of using these sensors for accurate pointing at infrasound frequencies. Results from these experiments will be discussed.Infrasound arrays, because of the wavelengths involved and the necessity for minimal spatial aliasing, can be quite large, e.g. an array layout often used for beamforming for frequencies up to 10 Hz is a centered, 17-m radius equilateral triangle. Available real estate is often limited such that optimally sized arrays are not possible. An acoustic particle velocity sensor, in principle, can perform the same job as a large infrasound array, but in a much smaller package (less than the size of a single infrasound sensor) since it provides, in post processing, a direct measurement of the wavefront normal. However, localized meteorological perturbations to the wavefront normal could cause significant bearing estimate errors when using a particle velocity sensor. Recently, as part of the characterization of a mobile infrasound source and during the collection of sounds from space station resupply rockets, acoustic particle velocity sensors were positioned next to infrasound sensors in order to test the concept...