Lowering a camera to a position just above the sea floor is a critical operation. The "pinger" method of camera-to-bottom positioning has proved to be an excellent technique. A sonar transducer on the camera sends one sound signal directly to the surface, and another to the bottom. The bottom signal, reflected from the sea floor, rises to the surface where its delayed arrival time is measured against the camera signal beamed to the surface. An Alden recorder is used to record each direct or reflected signal as received.