In the depths of the United States’ coastal and inland waters lie silent relics of past conflicts—unexploded ordnance (UXO)—that have lain dormant for decades yet continue to pose significant risks to human safety and environmental health. Estimates reveal that more than 400 underwater sites throughout the country are contaminated with these hazardous remnants. Their concealed presence beneath the seafloor demands advanced detection methods, as traditional techniques grapple to identify and classify them accurately amid the complex marine environment.
A promising breakthrough emerges from the lab of Connor Hodges, a doctoral researcher at the University of Texas at Austin, who has been pioneering acoustic methods to understand how corrosion and biological encrustations alter the acoustic profile of underwater UXOs. As these ordnances are submerged over long periods, they undergo profound physical and chemical transformations, including rust and layers of marine growth such as barnacles and algae. These processes modify the bombs’ surface texture, shape, and material composition, rendering conventional sonar imaging both unreliable and prone to false negatives.
“Many of these underwater UXO sites are located in shallow waters, areas frequently accessed by the public,” Hodges explains. “The combination of corrosion and biological fouling blurs the acoustic signature of these objects, making them harder to pick out against the natural seafloor.” Such conditions not only complicate detection but also increase the risk of accidental detonation if stepped on or disturbed. This urgent safety concern fuels Hodges’s research to develop acoustic sensing techniques that can penetrate the layers of environmental alteration affecting these hazards.
Hodges’s recent study utilized a collection of AN-Mk 23 practice bombs, a type of miniature ordnance commonly used for dive-bombing training, which had been submerged and buried in a brackish pond on Martha’s Vineyard for approximately eighty years. These samples, having endured prolonged corrosion and marine encrustation, were systematically compared to pristine counterparts in controlled acoustic scattering experiments. The goal was to analyze how the resonant acoustic behavior of these bombs changed as they deteriorated, and to evaluate how these changes influence detection fidelity.
Fundamental to Hodges’s approach is understanding acoustic resonance and scattering—the physical phenomena whereby sound waves interact with objects underwater. Those interactions produce characteristic wave reflections and signals that sonar systems detect and interpret. Corrosion and biofouling modify the geometry and material properties of UXOs, altering their resonant frequencies and scattering patterns. This complicates their identification based on acoustic signatures, as signals become weaker or more ambiguous, often mimicking natural debris or geological features on the seafloor.
The experimental results confirmed that corrosion reduces the size and changes the shape of the bombs, while biofouling layers obscure their original material properties. Such changes shift their acoustic fingerprints significantly, diminishing the signal strength returned to sonar detectors and increasing misclassifications. “These altered acoustic responses are a critical obstacle in UXO detection because they cause many traditional sonar algorithms to miss or misinterpret the presence of underwater ordnance,” Hodges notes.
Despite these challenges, acoustic scattering provides a unique window into detecting UXOs beneath sediment and seafloor surfaces. Unlike optical or magnetic methods, acoustic techniques can provide insights into internal structural changes of submerged objects. Hodges emphasized the advantage of sonar-based imaging, which is not only faster and cost-effective but also capable of “seeing” through sedimentary layers to locate these dangerous remnants without disturbing them.
The broader implications of this research extend beyond military sites transitioning back to civilian use. As former training grounds and bombing ranges make way for public access and recreational activities, the imperative for safe, reliable UXO identification technology grows louder. Hodges advocates that improving acoustic detection methodologies will greatly enhance environmental demining efforts, offering safer water access and reducing risks of accidental blasts.
Looking ahead, Hodges and his team plan to extend their work to encompass a wider variety of munitions and to investigate diverse corrosion and biofouling scenarios. By developing comprehensive acoustic models that capture these variables, they aim to create predictive tools capable of distinguishing even heavily degraded UXOs. This innovation promises to revolutionize underwater hazard detection, blending cutting-edge acoustic physics with practical environmental safety.
“Detecting and safely recovering underwater UXOs is an ongoing technical and humanitarian challenge,” Hodges stresses. “Our hope is that through refined acoustic imaging and targeted research, we can ultimately save lives and mitigate the risks posed by these silent, submerged threats.” As awareness about underwater UXO hazards grows, Hodges’s acoustic advances represent a pivotal step toward safer marine environments worldwide.
The intersection of environmental science, acoustic physics, and historical ordnance analysis embodies a multidisciplinary frontier where technology meets safety imperatives. Through focused experimentation and modeling of acoustic scattering behaviors in corroded UXOs, this research exemplifies how scientific ingenuity can confront enduring legacies of conflict impacting modern society. The quest to acoustically see beneath the seafloor promises a future where hidden dangers are unveiled and neutralized more effectively than ever before.
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Subject of Research: Acoustic characterization and detection of corroded underwater unexploded ordnance (UXO) altered by corrosion and biofouling.
Article Title: Using Acoustics to Detect Corroded Unexploded Ordnance Invisible to Traditional Sonar
News Publication Date: May 19, 2025
Web References:
– https://acoustics.org/asa-press-room/
– https://acoustics.org/lay-language-papers/
– https://acousticalsociety.org/
– https://www.icacommission.org/
Image Credits: Kevin Lee, Connor Hodges, and Preston Wilson
Keywords
Acoustics, Underwater acoustics, Corrosion, Unexploded ordnance, Sonar imaging, Biofouling, Acoustic resonance, UXO detection, Environmental demining, Marine safety
