16 hours. it scans the ocean floor as if it's mowing a lawn, using side scan sonar, which identifies objects that stand out from the seabed. . >> when it's working with the side scanners, it's not actually taking pictures, right? >> correct. it's converting sound to electricity and then turning that electrical value into numerical values and then turns 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, for example, this is a ship wreck in boston harbor. you can see that there are parts of the steam engine right there. >> if something captures the eye, the navy will send down a high resolution camera and can take black and white photos covering 15 square mile as day. it's a slow process, moving three nautical miles per hour,