Rescue becomes recovery
Sadly after the 35W bridge collapse rescue efforts quickly turned into recovery operations. In an effort to recover the bodies of still missing victims rescue workers will be diving into the Mississippi River to look through the murky water for cars that are trapped under the water and submerged sections of the bridge.
Recovery operations are using side-scan sonar to detect vehicles, parts of the bridge, and very sadly bodies under the water.
Side-scan sonar creates an image of structures underwater that is similar to an aerial photograph of an area of land.
In the example side-scan sonar image above you can see remnants of two ships, the Frank A. Palmer and Louise B.Crary, that collided and sank in Massachusetts Bay in 1902.
How does side-scan sonar work?
Side-scan sonar is specifically designed to image the sea floor (or in this case a river bottom). A SONAR (SOund Navigation And Ranging) device is pulled from behind a boat traveling very slowly. This sonar device emits a sound and then a detector senses the return sound or echo to paint a picture of the river bed and any other obstructions.
Side-scan sonar: Courtesy NOAA.
Graphic courtesy NOAA.