Sonar, GPS, Robots: The Science of Underwater Recovery

Aug. 2, 2007 — -- Sonar scans, Global Positioning Systems and robotics could play primary roles as Minnesota and federal authorities continue recovery efforts today after the fatal bridge collapse over the Mississippi River.

The collapse of the Minneapolis bridge left as many as 30 people missing and cars and debris jutting out from the water below, making efforts to retrieve the dead very tricky.

In this morning's news conference, Hennepin County Sheriff Rich Stanek said the recovery would include the use of sonar, heavy barges and trained diving teams. Those efforts were initially stymied Wednesday evening and this morning by safety concerns for divers and other recovery workers.

Traditionally in recovery missions, divers were used for both the searching and recovering, but this method can be time-consuming and exhausting for authorities and divers.

According to John L. Saunders, the director of the National Underwater Rescue Recovery Institute, the first step in any underwater recovery situation is to use sonar scanning technology. Founded in 1970, the institute trains divers around the country in underwater rescue and recovery. Institute members have collectively recovered 617 drowning victims.

"Before, everything would have been done by hand, but now the technology is so good we just put the instruments in the water and we know everything that's down there," Saunders said. "We don't have to put the diver in the water. It makes it 100 percent safer and a lot quicker."

With side-scan sonar machines, authorities can look under and around bridges to scan the wreckage for submerged cars and people and also look out for any debris — in this case concrete and rebar — that might be dangerous to diving teams, Saunders said.

"Safety is the No. 1 thing. All these things will make this thing a safe recovery and make it safe for the divers," he said. "You don't want to put anyone else's life in danger."