Magazine article National Defense

Dolphin's Brain Holds Secret to More Sophisticated Sonar

Magazine article National Defense

Dolphin's Brain Holds Secret to More Sophisticated Sonar

Article excerpt

SAN DIEGO - The Navy's submarine-hunting sonars have been accused of harming marine mammals. It now appears that in the brains of one of those mammals - the bottlenose dolphin - could reside the secret to even more powerful underwater sensors.

By studying how the marine mammals interpret the signals they emit and receive in the water, researchers believe they can eventually develop a short range, high-resolution sonar to detect man-made objects in the noisy coastal waters and on the littered sea floor.

Dolphins, like bats, have a biological sonar system called echolocation. They produce ultrasonic sounds that reflect off objects to "see" the environment around them. Whales have similar abilities, but the bottlenose dolphin resides in regions of the ocean where the Navy wants to deploy advanced sonar: in the littorals, or coastal waters of the world.

The research is part of the Navy's Marine Mammal Program, which works under the auspices of the Space and Naval Warfare Systems Center San Diego.

Dolphins emit short echolocation clicks on the order of 100 microseconds in beam patterns that shift in frequencies, source levels and bandwidth. Those impulse signals range from 35 to 135 kilohertz in frequency and 80 to 100 kilohertz of bandwidth.

Dolphins are able to "tune" their sonar for various tasks. For example, in waters where snapping shrimp generate background noise like sizzling bacon, to human ears - dolphins echolocate at higher frequencies that are optimal against the din.

"They can do things like steer the beam and change the beam width on a click-to-click basis," says Patrick Moore, a scientist and former head of the biosonar program office.

Scientists want to build sonars that can do the same thing. It's called environmentally adaptive sonar.

By virtue of being mobile when they echolocate, dolphins are able to perceive objects from multiple points of view.

"It swims around the target and looks at it from all these different aspects and creates an image, somehow," says Moore.

The researchers have attempted to mimic the blosonar by putting a multi-beam, mechanically scanned sonar on the nose of an unmanned underwater vehicle. As it moves through the water, the beams pick up multiple perspectives of an object says Steve W. Martin, senior project engineer. Those snippets of data are then assembled for image analysis.

But researchers don't know how dolphins "see" their environment using the information from those echolocation signals.

"We don't know if they form images," says Martin. …

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