A University of Texas at Austin scientist has demonstrated a technique for using sound waves to detect unexploded munitions (UXOs) on the seafloor. This novel application of sound could offer an alternative to detecting UXOs only by visual identification.
The lead researcher believes that discovering new methods for spotting UXOs will help prevent accidental injury or even death resulting from people encountering them, especially since differentiating between UXOs and the seafloor by visual inspection becomes increasingly difficult as time passes and the objects corrode.
“There is a risk of detonation if they are stepped on or otherwise disturbed,” said UT at Austin doctoral student and the study’s lead researcher, Connor Hodges. “This poses a larger risk to human safety in shallow waters, and UXO identification and recovery become vital as old sites are transitioned away from military use.”
Detecting Unexploded Munitions: Just One Ability of Sound Waves
Several marine animals and human-made vessels use sound waves in the form of SONAR to navigate the world’s seas. Scientists have used similar technologies to map the ocean floor and to explore the uncharted depths with drones.
More recently, clever scientists and engineers have found numerous uses for sound waves beyond imaging. Some science fiction-sounding examples include using sound waves to move objects like a Star Trek-style tractor beam, magically levitating objects with sound and metamaterials, treating cancer with sound, or even creating an artificial black hole with sound that powers a warp drive spacecraft.
According to Hodges’ presentation at the joint 188th Meeting of the Acoustical Society of America and 25th International Congress on Acoustics, tracking down aging UXOs that tend to blend in with their surroundings as they become covered in barnacles and other sea growth could represent the latest applications of sound wave technology. The situation is even more urgent since over 400 such sites are in the United States alone.
“Many of these sites are in shallow water, potentially posing a threat to human safety, and date back several decades,” said Hodges. “This long exposure to the environment leads to corrosion as well as encrustation in the form of barnacles or algal growth.”
Tests Show Potential of Acoustic Scattering for UXO Detection
To test his theory, Hodges and colleagues studied the acoustics of sound waves as they bounced off a selection of AN-Mk 23 ‘fake’ bombs used for military dive-bombing practice. To simulate the different ages of munitions scattered around the shallow US seafloor, they used munitions recovered from a brackish pond in Martha’s Vineyard that were in various stages of corrosion due to the 80 years they spent submerged. The team also collected acoustic signatures of pristine AN-Mk 23 munitions. This effort included monitoring the “scattering response” of sound waves directed at the targets from different angles and directions.
When comparing the signatures from the different targets, the team found that the acoustic signal of pristine bombs becomes “weaker” as the unexploded munitions corrode. The more corroded, the weaker the signal. According to Hodges, these changes could result in misidentifications of UXOs as natural formations. However, the doctoral candidate says that training military and civilian officials tasked with detecting these dangerous munitions on how to look for these variations could result in increased detection and saved lives.
“Acoustic scattering techniques give an insight into the internal structure of the object imaged, as well as a method to ‘see’ into the seafloor,” Hodges explained.
Regardless of the approach, Hodges says that finding an alternative to visual detection of unexploded munitions will become even more critical as some military waters previously used for practice bombing are transferred to civilian oversight.
“Underwater UXO can be tricky to find and recover, so it is important that this can be done safely and effectively,” said Hodges. “We hope this work will ultimately help save lives.”
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.