Research: Infrasound direction-finding, positioning system

By John P. McIntire, Duy K. Nguyen, Eric T. Vinande, and Frederick C. Webber
U.S. Air Force Research Laboratory / Presented at ION ITM, January 2017

Detection of artillery blasts at a near distance (0.15 miles or 0.24 km) using a single infrasound sensor, with the sensor amplitude trace over time shown on Infiltec’s Amaseis software data and visualization package, and using some basic bandpass filtering (5 to 25 Hz). The spikes are clearly visible as high amplitude impulses in the traces, confirming sensor detection.

Infrasound refers to sound frequencies below the threshold of human hearing, around 20 Hz or less. There are a variety of natural sources of infrasonic emissions, including thunderstorms, avalanches, meteors, earthquakes, volcanos, and windstorms as well as manmade sources of emissions, such as aircraft, heavy machinery, artillery, missile testing and road traffic. Infrasound is especially attractive from a sensing perspective due to its ability to propagate long distances while suffering little from atmospheric or environmental attenuation.

Blasts detected at 5.22 miles (or 8.4 km) are still detectable, but additional signal processing or wind-filtering techniques may make these impulsive signals more prominent above the noise.

In this work, we describe the development of a man-portable “tactical” infrasound field sensor array that is small, lightweight and can be rapidly set-up and torn-down as needed. The system is able to provide direction-finding capabilities to infrasound impulse sources with a directional accuracy of +/–3 degrees. Such information could be used for alternative positioning schemes, described in detail, or perhaps for direction-finding (homing) to acoustic sources of interest. Possible users could be military or search-and-rescue teams operating in GPS-denied environments; field researchers studying volcanology or seismology; or other geo-acoustic scientists and engineers.