If you click on the link to this
Canadian oil company, they have a great animation on their homepage that shows what I do. Click on it and you can see a boat pulling a cable. There are guns located very near to the boat, that go off about every 10-15 seconds. On the cables there are hundreds of receivers (or hydrophones), that pick up or "hear" the sound of the guns. The receivers hear the direct sound, but also the sound that bounces off of the ocean bottom, and off of geological layers below the surface. The result is the black and white picture / diagram that you can also see in the animation. One difference though between the animation and us, is that we have 8 cables and not one.