Geophysical methods provide a non-invasive, non-destructive means of investigating and defining subsequent excavation targets in areas of known or suspected archaeological potential. Terrestrial methods rely on measuring contrasts in the properties, such as magnetism and electrical resistance, of buried archaeological features and the soils in which they lie. For submerged sites, contrasts with host sediments are measured in properties such as sound velocity and magnetism. The choice of method, order and mode of deployment is governed by the site type, the archaeological objectives, available archaeological, geological/morphological information, the nature of potential targets and the area under investigation.