CNN New Day Saturday April 5, 2014 10:50:00
I'll bring you an example that we can talk about. passive sonar is the idea of pinger listener. it's device that is towed behind the ship and it's listening passively to the sound of the flight data recorders. and it has to be within a mile of two of hearing them. if it does, it can be a sense whereof the plane might be. very slow process. the ship's not moving fast at all. beyond that, there's the question of active sonar and that involves a robot. essentially if we drive below the water here, we can talk about this device that sort of looks like a torpedo. it's put into the water and can ope...
Source: archive.org