Alessio Medda, PhD –
Robert Funk, PhD –
Krish Ahuja, PhD –
Aerospace, Transportation & Advanced Systems Laboratory
Georgia Tech Research Institute
Georgia Institute of Technology
260 14th Street NW
Atlanta, GA 30332

Walter Carr, PhD –
Bradley Garfield –
Walter Reed Army Institute of Research (WRAIR)
503 Robert Grant Avenue
Silver Springs MD 20910

Popular version of 3pPA4 – Infrasound Signature Measurements for U.S. Army Infantry Weapons During Training
Presented Wednesday morning, December 1, 2021
181st ASA Meeting, Seattle, WA
Click here to read the abstract

Infrasound is defined as an acoustic oscillation with frequencies below the typical lower threshold of human hearing, typically 20 Hz. Although infrasound is considered too low in frequency for humans to hear, it was shown that infrasound could be heard down to about 1 Hz. In this low-frequency range, single frequencies are not perceived as pure tones but are experienced as shocks or pressure waves, through the harmonics generated by the distortion from the middle and inner ear. Moreover, it has been shown that infrasound exposure also can have an effect on the human body, when sound of sufficient intensity is absorbed and stimulates biological tissue to produce effects similar to whole-body vibrations.

United States military personnel are exposed to blast overpressure from a variety of sources during training and military operations. While it is known that repeated exposure to high-level blast overpressure may result in concussion like symptoms, the effect of repeated exposure to low-level blast overpressure is not well understood yet. Exposure to low-level blast rarely produces a concussion, but anecdotal evidence from soldiers indicates that it can still produce transient neurological effects. During interviews, military personnel described the effect of firing portable antitank weapons like “getting punched in your whole body.” In addition, military personnel involved with breaching operations often use the term “breacher’s brain” to identify symptoms that include headache, fatigue, dizziness, and memory issues.
Impulsive acoustic sources such as pressure waves generated by explosions, artillery launches, and rocket launches are typically characterized by a broadband acoustic energy with frequency components well into the infrasound range. In this study, we explore how routine infantry training can result in high level repeated infrasound exposures by analyzing acoustic recordings and highlighting the presence of infrasound.

We present results in the form of time-frequency plots, which have been generated using a technique based on wavelets, a mathematical approach that represents a signal at different scales and uses unique features at each scale. This technique is called Synchrosqueezed Wavelet Transform and it was proposed by Daubechies et al. in 2011. In Figure 1 we show examples of high energy infrasound for three weapons commonly used during infantry training in the US military. Figure 1(A) shows the time-frequency plot of a grenade explosion, Figure 1(B) shows the time-frequency plot obtained from recordings of machine gun fire, and Figure 1(C) shows the time-frequency plot obtained from a recording of a rocket launched from a shoulder-held weapon.

Results indicate that high infrasound levels are present during military training events where impulsive noise is present. Also, service members that are routinely part of these training exercises have reported concussion-like symptoms associated with training exposures.

Through this research, we have an opportunity to establish the nature of the potential threat from infrasound in training environments as a preparation for future studies aimed at developing dose-response relationships between neurophysiological outcomes and environmental measurements.

Time-frequency spectrum for recordings of (A) Grenade Blast, (B) Machine Gun fire, and (C) Rocket Launcher from shoulder weapon. Regions characterized by high energy appear hotter (red) while normal conditions are cooler (blue).


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