Archaeologists can see below the surface of the ground using specially designed geophysical instruments. Several different forms of geophysical survey exist, and some suit certain conditions better than others. SicTransit geophysicists Helen and Lyall explored the possibilities offered by the following forms of geophysics:
- Magnetometry maps disturbances to the earth's natural magnetic field caused by ancient sources of heat such as buried hearths.
- Resistivity sends an electric current through the ground which detects good and poor conductors of electricity. Stone walls are poor conductors, while ditches and foundation trenchs - which often hold water better than the surrounding soil - are good conductors.
- Ground-penetrating radar (also known as soil-sounding radar) send radiowaves into the ground which bounce back when they hit a harder materials such as walls or buried roads.
The results of the surveys were plotted geographically to inform us where best to conduct excavation and other forms of survey.