scan sonar which identifies objects that stands out from the sea bed. it's not taking pictures, right it's measuring sound? >> it's actually -- converting sounded the electricity and turning that electrical value into numerical value then turn it into an image. >> reporter: when it returns to the surface scientists download the sonar data to computers. the results may look something like this. >> what we're looking at here, this is a ship wreck in boston harbor. it's different. there's parts of the steam engine flight. >> reporter: if something catches their eye the navy will send down a high resolution camera on the bluefin-21. it can take black and white photos covering about 15 square miles a day. it's a slow process. moving at just three nautical miles per hour. made worse by conditions,