Newswise — Many bodies of water around the globe contain discarded and unexploded munitions, a.k.a. “underwater ordnance” or “UXOs.” These UXOs, most commonly associated with former military training sites or the result of post-war disposal, pose public safety hazards as well as chemical contamination risks.
Cleanup requires being able to locate and differentiate engineered objects from natural ones. And a team of physicists is working on a way to do just that, thanks to low-frequency acoustics. Aubrey España, a research associate in the Acoustics Department of the University of Washington’s Applied Physics Laboratory, and colleagues will describe their research at the Acoustical Society of America’s 162nd annual meeting in San Diego, Calif.
Sound is a particularly useful tool for classifying objects either on or embedded in the ocean floor. “Low-frequency sound has the advantage of being able to excite specific vibrations of an object of interest, which in turn results in re-radiation of sound back to the observer,” explains España. “This scattered sound is used to generate an acoustic template or fingerprint of the object, which can aid in distinguishing between manmade and natural objects.”
Acoustic fingerprints are made up of several key components, with the most obvious being the shape and material of the object, as well as the type of ocean floor (sand, silt, mud) it is in contact with.
“Our research not only aims to generate these acoustic fingerprints for various objects, but also to understand the physics or the ‘why’ behind what we see in the acoustic fingerprint – such as how sound couples to the object/UXO, the subsequent vibration that ensues, and how the sound radiates from the object back to the viewer,” she says.
Currently, the researchers are turning their attention to a combination of modeling techniques including the finite-element method, to provide insight into what’s happening when sound hits an object. Using simple models that exploit the symmetry of the object and environment, and which require only a minimum amount of information about the surrounding environment, they were able to generate acoustic fingerprints that, according to the researchers, “agree phenomenally well” with actual experimental data acquired in a test pond.
“Our model results also enable examination, in extreme detail, about how the object is vibrating and how sound will radiate away from it. Again, the hope is that this new knowledge about the driving forces of acoustic fingerprints can help improve existing techniques for detecting and classifying objects near the ocean floor,” says España.
Next, the team plans to run experiments at sea, with a goal of generating acoustic fingerprints for many more human-made objects. Development of models for these objects will continue, and the validity of each will be tested against the experimental data acquired at sea.
The paper 1aUW2, “Acoustic scattering from unexploded ordnance in contact with a sand sediment: Mode identification using finite element models,” will be presented Monday morning, Oct. 31.
A webcast featuring this research will be held 11 a.m. EDT on Oct. 31. Register at http://www.aipwebcasting.com
USEFUL LINKS:Main meeting website: http://acousticalsociety.org/ Searchable index: http://asa.aip.org/asasearch.html Hotel site: http://www.towncountry.com/index.cfm Webcast registration and viewing: http://www.aipwebcasting.com
WORLD WIDE PRESS ROOMIn the week before the meeting, the ASA's World Wide Press Room (www.acoustics.org/press) will be updated with lay-language papers, which are 300-1200 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio, and video.
****************************ABOUT THE ACOUSTICAL SOCIETY OF AMERICAThe Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world's leading journal on acoustics), Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. For more information about ASA, visit our website at http://www.acousticalsociety.org.