How search teams could use sound to find the Titan sub -- and why it's a challenge

Search teams racing to find the missing Titanic submersible have detected underwater noises but it won’t be easy to find the source of that sound in the ocean. There are many other potential sources of sound under water, including from fish, other animals and human-made instruments. The Coast Guard said search teams heard banging noises at 30-minute intervals. But even this could come from an underwater instrument making repeated noise. Sound also gets bent as it travels underwater, because of how pressure and temperature change at different depths. This can create echo-like effects and make it hard to locate the source of a particular sound.