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U.S. Navy Looks to Bats, Dolphins for Better Sonar

John Roach
for National Geographic News
December 12, 2002
 
The ability of bats and dolphins to see at night and navigate the
murky depths of the sea has long garnered the interest of the United
States military.

"We would like to emulate this capability for the quick, accurate detection and classification of buried mines," said Harold Hawkins, a program manager with the biosonar program at the Office of Naval Research in Arlington, Virginia.

Hawkins and his colleagues seek to understand how bats and dolphins make sounds and process the sounds' echoes to create three-dimensional reconstructions of objects in their environment.

Reception of echoes is the basis of conventional sonar systems designed by humans. But many of these devices are not nearly as sophisticated as the ones that have evolved in bats and dolphins, according to James Simmons, a neuroscientist at Brown University in Providence, Rhode Island.

Simmons studies the biological sonar systems of bats and cooperates with people who study dolphins in the Navy Marine Mammal Program in San Diego, California. The collaborative research is funded in part by the Office of Naval Research.



Mine Detection

"The Navy has a problem with mines," said Simmons. "They are easy and cheap to get and they can damage or sink a large ship."

Naval mines are designed to float on the surface of the sea or are moored just below its surface to blow up ships. Other types can be planted on the seafloor or hidden among rocks to cripple submarines.

The Navy currently uses trained dolphins to help detect mines. The dolphins are carried in holding tanks on warships and released upon entering mine-infested waters. The dolphins use their sonar to find the mines and later communicate that information to sailors.

One goal of the Office of Naval Research's Biosonar Program is to build a sonar system as good as the dolphins. Simmons' research on bats is crucial to the success of the program.

"Since bat work has a large and formal foundation in neurophysiology and the neuronal wiring of the bat is more or less well understood, the hope is that similar echolocation performance by bats and dolphins may have roots in similar neurophysiology," explained Patrick Moore, a researcher with the Navy Marine Mammal Program.

Bat Lab

Simmons and his colleagues conduct their research out of the bat lab, a suite of rooms in a basement laboratory at Brown University. They work with big brown bats, Eptesicus fuscus, which are commonly found in household attics, forests, and caves across North America and Europe.

The bats are relatively inexpensive for the researchers to keep in captivity and study. The knowledge the researchers gain about bat sonar is tested out on dolphins and applied to human sonar systems.

"We do experiments that measure how accurately they determine the timing of echoes and how they form images of scenes," said Simmons.

Bat lab experiments have shown that the animals are able to differentiate between sounds that are 2 to 3 millionths of a second apart, giving bats the ability to tell the difference between objects and shapes that are separated by only about the width of a human hair.

This unexpected finding suggested to the researchers that the bats use their sonar for purposes greater than simply tracking their prey. To find out what bats actually do with their sonar, Simmons and his colleagues filmed the animals with an infrared camera.

The camera recorded the bats body heat. Footage captured by the researchers showed bats zipping across the sky like comets, said Simmons. Their movies highlighted the bats' ability to navigate around the full range of objects in their environment, including trees and bodies of water.

"We see them doing things never imagined," said Simmons. "They spend a lot of time doing dogfights chasing each other."

Military Application

The knowledge learned from these studies is being used by the Office of Naval Research to build a better sonar system.
 

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