Quiet but deadly: diesel-electric submarines, the U.S. Navy's latest annoyance.

Contrary to popular belief, sonar is not like radar, which gives complete visibility of "hits" in the air. What sonar technicians see is a screen that is filled with vertical lines representing echoes from objects in the water Discerning which line is a submarine and which one is a coral reef is a difficult and complex task, sailors say.

The Navy spent 40 years building a training range on the coast of Southern California--one of the most extensive in the world, officials say. Underwater sensors track ships' locations and record operations during exercises.

Because the water and ocean bottom conditions are representative of many areas around the world, the range is an ideal location for training strike groups in antisubmarine warfare, says Locklear.

But the Navy's training there has been curtailed by ongoing litigation over the harmful effects of active sonar on marine mammals.

Under a federal judge's ruling, ships were forbidden from using active sonar within 12 nautical miles of shore and had to steer clear of waters between the Santa Catalina and San Clemente islands during a joint training exercise in January for the Abraham Lincoln carrier strike group. Sightings of marine mammals at certain distances also prompted ships to take protective measures, such as powering down sonar or shutting the sensors off completely.

"We're not able to employ the sonar, given those restrictions, in a realistic manner, and it just makes it real tough to assess whether the fleet is proficient at using the technology," says Capt. Pete Tomczak, deputy director for training at Third Fleet.

The use of sonar by the Navy has been linked to mass marine mammal strandings on beaches in the Bahamas and the Canary Islands. Pending necropsy results, the death of a northern right whale dolphin that washed up Jan. 29 on the Navy's San Nicolas Island could be connected to sonar use.

Locklear says the Navy tries to balance its responsibility to protect the environment with its job to prepare sailors for war. He expresses concern that the judge's ruling, if extrapolated beyond Southern California, could hamper Navy training around the world.

"If this becomes precedence setting, I think it will be very difficult for the United States Navy," he says. "If there was a new technology on the horizon that made this irrelevant, we would be all over it. We just haven't found it yet."

With prospects of at-sea training diminishing, not only because of the litigation, but also as a result of rising fuel costs and other budget constraints, the Navy is searching for alternative ways to prepare its sailors for anti-submarine warfare.

One option is to rely on simulators, says Waickwicz. But he points out that current simulations in the Navy do not replicate sonar accurately.

"It's like playing 'Pong' in today's game world," he says. While the submarine forces have higher fidelity trainers, much of the rest of the fleet--especially surface ships--have sub-par simulations.

"Computer simulations can only go so far. There is still no substitute for at-sea practice against a real submarine," says Pacific Fleet's Walsh.

Because the U.S. Navy no longer operates diesel-electric submarines, it invites allied countries that own these boats to participate in exercises at Navy ranges on the east and west coasts.

The Swedish Navy's HMS Gotland collaborated most recently with various Navy commands in San Diego.

"It was very advantageous to have a diesel submarine crew for two years, to see how they thought, how they approached the issues to go against the ships," says Waickwicz. "It really opened our eyes to diesel submarines and how active sonar is what you have to have in the strike group."

The experience led to recent changes in the Navy's anti-submarine warfare doctrine and tactics.

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Dolphin's Brain Holds Secret to More Sophisticated Sonar

* 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 biosonar 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.

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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.

That signal processing capability in their brains is something the scientists are trying to unravel.

"We're dealing with an acoustic animal, not a visual animal. So it's hard for us as visual creatures to try to get inside the head of acoustic animals," says Moore.

But that's exactly what the researchers are planning to do. The scientists have received funding from the Office of Naval Research to do brain imaging work on echolocating dolphins to discover what parts of the brain are actively engaged in processing the echoes.

There's a theory that the dolphin has two hearing systems. One is devoted to communication sounds--the whistles and other noises they make in social settings. The scientists believe the other one is a passive system that has special timing considerations in a portion of the brain that becomes engaged when they begin to echolocate. When dolphins generate a click, they somehow know when the echo will return, and they can ignore other incoming signals until they receive the echo.

The scientists plan to experiment with the dolphins by using controlled electronic targets. They will place earphones on the jaw and the dolphin's forehead. When the dolphin produces a click, the scientists can manipulate the sound and present it back to the animal when they believe it would return from a target. By conducting the brain images, the scientists will begin finding clues into the dolphin's signal processing abilities.

The team works closely with the Navy's explosive ordnance disposal community, which employs dolphins as mine hunters. The EOD units also deploy UUVs, which have met much success clearing mines in the Middle East harbors. But the sea floor there is relatively uncluttered. Such robotic technologies do not fare so well in other regions where the ocean bottom is not as pristine, researchers say. In such cases, dolphins continue to prove their mettle with their echolocation abilities.

Progress has been made in biomimetic sonar. Martin built a biosonar that could detect underwater buried objects in a previous $4.5 million project funded by the Defense Advanced Research Projects Agency. But there was insufficient funding to take the prototype to the next level, says Moore. It's a recurring problem that frustrates the research team.

The scientists are conducting small business innovative research-funded work to apply the concept to small side-scan sonars for unmanned underwater vehicles.

"We'll get our technology to the fleet, one way or another," says Moore.

Undersea Combat Simulators Needed, Navy Says

* ORLANDO -- The Navy is worried about quiet diesel-electric submarines that are proliferating around the world and particularly in the western Pacific. But officials say the bigger challenge is training sailors to find and engage those submarines.

Rising fuel prices, restrictions on the use of sonar and less availability of ships are curtailing training, officials say.