so, right around here. hopefully there's not a lot below that, where they are actually hearing this device. hopefully it's not at the deepest point. >> all right, we are going to continue to look now beneath the surface. thank you very much, as we have been mentioning, surfaces may be scouring a specific part of the ocean floor, and some of that searching will involve sonar using sound waves to map out the bottom of the ocean. we will look at the technology that makes it all possible. >> the idea of searching the ocean floor is a huge undertaking. we want to show you a different in the couple of technologies that are likely being used in the indian ocean. and he is going to show us first when a hydrophone does. >> exactly, this is a hydro phone, it's an underwater microphone. it's a device like this. either strung together in a tail that they tow behind the boat or dipped over the side, or dipped