underwater reconnaissance

Surveyal of the seafloor, especially in underwater archaeology, for buried objects. It employs diving apparatus, sonar, and other 20th-century technological developments. Submersibles are also used in underwater exploration.

Equipment used includes the proton magnetometer, towed behind a survey vessel to detect iron and steel objects that distort the Earth's magnetic field; the side-scan sonar, which transmits sound waves in a fan-shaped beam to produce a graphic image of subsurface features on the seabed; and the sub-bottom profiler, which emits sound pulses that bounce back from features and objects buried under the seafloor.