Infrasound Signal Classification

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The local infrasound environment in Alaska is rich in both natural and human-generated sources. Identifying the source and localizing it is a challenge with many different applications. The Infrasound group at UAF has operated arrays in Alaska and Antarctica for several years. The primary arrays are comprised of eight microphones arranged to obtain wide-band operation with no spatial aliasing over the frequency band of interest. These arrays are operated and maintained by the UAF group as part of the International Monitoring System (IMS) of the United Nations Comprehensive Nuclear Test-Ban Treaty Office (CTBTO). A second array of four microphones is operated by the UAF group as a research array. The group has used this array to test methods of wind-noise reduction, microphone performance and array performance under varying array geometries. As part of the process of identifying infrasound signal sources a prototype locator algorithm was developed that allows estimation of the range to the signal source for locations of the signals source of up to 10 to 15 times the array diameter. The locator algorithm has been used extensively in cases where signal-to-noise levels are high and it appears to be robust. Investigators will continue to study the method and investigate its behavior under a range of signal-to-noise conditions, as well as develop an estimator of the variance in the estimates of range and azimuth. The description and classification of signal sources will improve the ability to discriminate against known natural and man-made sources in signal detection operations. The development of an algorithm to estimate source range to accompany the traditional azimuth estimates will also benefit the general area of source localization using acoustic methods. This algorithm should be transferable to any detection program using arrays of sensors.