Hundreds of underwater sites across the United States have concealed a dangerous secret with their seemingly calm surface: unexploded bombs and other military ordnances that never detonated as expected. These silenced threats pose a significant risk to human security, especially when previous military testing grounds transitioned to public use. Now, researchers are using advanced acoustic techniques to locate these deteriorating weapons before they can hurt anyone.
At this week’s joint meeting between the American Acoustic Society and the 25th International Conference on Acoustics in New Orleans, scientists presented new discoveries on how sound waves detect corrosive ammunition that may be missed by visual methods. This study could revolutionize how we find these dangerous leftovers from military activities.
There are over 400 underwater locations across the United States that may contain unexploded ordnance (UXO), many of whom are in shallow waters where people swim, boat and dive. Decades after underwater, these weapons are almost unrecognizable when corroded and covered by marine life.
Challenges of finding degraded weapons
“Many of these sites are in shallow water, which can pose a threat to human safety and can go back decades,” said Connor Hodges, a doctoral student at the University of Texas at Austin. “Long-term exposure to the environment can lead to corrosion and in the form of barnacles or algae growth.”
This conversion makes standard sonar detection extremely difficult. As weapons rust and are covered by marine life, they merge into the underwater environment, no longer resemble the original shapes in sonar images.
Hodges and his team looked at practical bombs recovered from Martha’s vineyard, which had been submerged for about 80 years. They compared these severely corroded weapons to the original version to see how their acoustic marks change over time.
How much “see” the sound can’t be seen
What makes acoustic detection particularly valuable is its ability to penetrate the surface and reveal what is underneath it. Unlike visual methods that only show appearance, sound waves interact with the internal structure of the object.
“Acoustic scattering technology gives a deeper understanding of the internal structure of an imaged object, and a way to “see” the seabed,” Hodges explained. This capability is crucial when ammunition is buried under sediments or is heavily masked by ocean growth.
The study reveals several key findings on how corrosion affects acoustic detection:
- Corroded ammunition is weaker than complete ammunition
- As the metal deteriorates, the resonance pattern changes significantly
- Changes in size and shape of corrosion can produce different acoustic characteristics
- These changes can cause the detection system to miss or misclassify dangerous objects
Public safety issues promote research
As former military testing sites transition to public recreational areas, this study urgently requires new urgency. As seaside property becomes more valuable, more people may encounter these dangerous artifacts without realizing it.
“If stepped on or otherwise disturbed, there is a risk of explosion,” Hodges warned. “This poses a greater human security risk in shallow waters, and as old sites move from military use, UXO identification and recovery becomes crucial.”
How dangerous are these underwater ammunitions? Although many practice bombs cost less to explode than the combat version, they still pose a great risk. Some may also contain toxic substances that can leak into surrounding waters when degraded.
Future safety instructions
The research team tested the AN-MK 23 practice bomb, the bomb originally used for submersible bomb practice – re-approved from a salt pond in Martha’s vineyard. These weapons have been submerged for about eighty years, providing excellent examples of long-term corrosion effects.
Going forward, Hodges plans to study extensions to include different types of ammunition and various corrosion patterns. This extended dataset will help create more accurate detection systems that can detect even severely deteriorate weapons.
“Underwater UXO can be difficult to find and recover, so this must be done safely and effectively,” Hodges said. “We hope this work will ultimately help save lives.”
In addition to safety, acoustic detection has practical advantages over alternative methods. “Using Sonar to map the seabed and detect ammunition is also faster and cheaper than other technologies,” Hodges noted.
As previous military sites continue to be reused for public use, this study represents a crucial step in ensuring that these waters are truly safe for recreational activities. By understanding how time changes these dangerous objects, scientists can develop better tools to find and delete them before they can harm unsuspecting visitors – sometimes the best way to see danger is to listen to it.
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