Geophysical methods of underwater survey. Some of these methods are: 1) towing a proton magnetometer behind a survey vessel to detect iron and steel objects, 2) using side-scan sonar that transmits sound waves in a fan-shaped beam to produce a graphic image of surface features on the sea-bed, and 3) using a sub-bottom profiler that emits sound pulses which bounce back from features and objects buried beneath the sea floor.