Underwater ears

Jason Holmes, a mechanical engineering graduate student at

and guest researcher at

, has devised a low-cost, highly sensitive hydrophone array that is perking up interest in both homeland security and ocean research circles.

Holmes' underwater hydrophone array is designed to be towed by a small, autonomous submarine and can monitor for ocean-going threats to America's waterways or for sound for ocean acoustics studies.

He presented research on his underwater listening device in Vancouver on May 20 at the semi-annual meeting of the Acoustical Society of America.

Holmes' prototype system comprises six underwater microphones, or hydrophones, spaced inside a 30-foot plastic tube filled with mineral oil. The array tube is filled with mineral oil to create neutral buoyancy, allowing the array to float behind the underwater towing vehicle.

Signals from the hydrophones are captured and stored on mini-disc recorders aboard an unpiloted submarine called Remus. Designed by Woods Hole Oceanographic Institution, Remus looks like a small torpedo and can navigate autonomously underwater around obstacles and through harbours using GPS sensors, sonar, and electronic maps.