Secondary: GPS Array for Ionospheric Sounding
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Journal of the Acoustical Society of America
We evaluate the acoustic coda phase delay method for estimating changes in atmospheric phenomena in realistic environments. Previous studies verifying the method took place in an environment with negligible wind. The equation for effective sound speed, which the method is based upon, shows that the influence of wind is equal to the square of temperature. Under normal conditions, wind is significant and therefore cannot be ignored. Results from this study con rm the previous statement. The acoustic coda phase delay method breaks down in non-ideal environments, namely those where wind speed and direction varies across small distances. We suggest that future studies make use of gradiometry to better understand the effect of wind on the acoustic coda and subsequent phase delays.
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It is therefore of paramount importance to quantify the three dimensional propagation characteristics of infrasound from buried sources. Despite initial success with using an octocopter to quantify ground motion with a seismic hammer (Jones et al., 2015), attempts to capture buried explosion sources using this method have proven very difficult. Even when successful, octocopter-borne sensors suffer from high levels of background noise, have limited flight time due to battery life, and require substantial resources to deploy.
Low frequency sound waves transmit information on both natural and anthropogenic phenomena, transfer energy between the lower and upper atmosphere, and often propagate for thousands of kilometers. These sound waves are typically in the "infrasound" (below human hearing) range. Although the vast majority of geoacoustic sensor networks have existed on the Earth's surface, microphones drifting in the atmosphere may have much greater sensitivity as well as sample regions inaccessible from the ground.
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