Technology heads recovery effort

Police are using sonar device to search the bay for missing publisher


The pace of this week's search for the body of publisher Philip Merrill, which enters its sixth day today, is set in part by a yellow, torpedo-shaped piece of technology known as a "side sonar scanner."

When switched on and in motion, the device gives recovery workers a superherolike ability to see beneath even the murkiest waters.

"Fish schools will show up real well," said Natural Resources Police Cpl. Paul Carey, aboard a motorboat at Sandy Point State Park yesterday, where he demonstrated the scanner for reporters before casting off to continue the search.

Carey gestured toward a grainy image on a computer screen that, to the untrained eye, looked like a rust-colored blur. Carey could make sense of the fuzz, pointing to bright squares he said were crab pots.

The sonar device, about four feet long, is tethered to a computer aboard the boat by hundreds of feet of black cable and towed behind.

When it's operational, the sonar (technically called a towfish) skims the sea floor, emitting pulses of a high-frequency sound. These sound waves bounce off submerged objects and the waves return to the device. The pulses are displayed as grainy images that, after some training, reveal surprising detail.

The device works a lot like an ultrasound machine - and this is no coincidence. John Wilcox, who owns the company that makes these devices, spent decades developing obstetric imagers for various medical companies, said John C. De Mille, a sales representative with Marine Sonic Technology Inc., the Virginia-based company that sold scanners to the NRP and to the Anne Arundel County and Baltimore City fire departments.

The NRP bought its scanner for $30,000 in July, and it has been used to find evidence cast into the sea, sunken boats and bodies. The Baltimore City Fire Department bought its device in 2003 after a water taxi flipped over. De Mille said he brought a scanner to the Inner Harbor and helped authorities recover three bodies from that tragedy.

In their search for Merrill, technicians had scanned 18 square miles of bay bottom by yesterday morning, Carey said. During the day they hoped to search an additional nine square miles south of Kent Island and east of the Severn River.

"We haven't had anything suspicious," said Carey before going out for yesterday's search. If they do find something suspicious, NRP officers will mark the spot with a buoy and send down divers, Carey said.

If the buoy drifted, divers still could find the flagged object, because the digital images are stored and each pixel on each image has a GPS coordinate. The GPS encoding also means that if someone reviewing the images later saw a shadow or an object missed the first time around, that person would be able to figure out exactly where on the sea floor it is, De Mille said.

Recovery workers pull the tow-

fish at 4 1/2 knots while a technician views the image on the screen in real time. Searchers use a "mowing the lawn" pattern - methodically moving up and down swaths of the Chesapeake near the mouth of the Severn River and Kent Island where Merrill tended to sail.

The sonar can "see" an area that stretches about 100 feet on either side of it. "You can cover the area of a football field in less than a minute," De Mille said.

The search area extends about 150 square miles - from the Severn down to Plum Point, where Merrill's boat was found unmanned with the sails hoisted on Saturday evening. The GPS navigational system onboard Merrill's 41-foot sailboat didn't reveal anything about his journey, so investigators have relied on his known sailing patterns to guess where to focus their search, Tucker said.

Recovery workers seemed optimistic yesterday. "We're having real good pictures for this operation," Carey said. "Fresh objects will sit on top of the floor."

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