Geophysics studies the physical properties of the earth to find possible archaeological features without digging. There are three main types: resistivity, magnetometry, and ground penetrating radar.
Resistivity measures the resistance to an electrical current between two probes in the soil. Walls and buried features have high resistance, and pits and ditches have low resistance.
Magnetometry measures the differences in magnetic fields of different soils and features. Magnetometry is good for finding metal-working sites, hearths and fireplaces, and rubbish pits.
Ground penetrating radar sends electromagnetic waves into the soil and records variations in the reflected return signal caused by buried features.
The data collected by geophysics are used to create computer pictures, which can show up where archaeological features are underneath the ground. Geophysics is therefore used before an excavation to try and decide the best places to dig.
An archaeologist carrying out a resistivity survey © Nicky Milsted