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The various techniques used in resistivity survey are to a great extent gotten from those made use of in engineering, geology and mining. Most archaeological sites are close to the surface. There are different methods used this kind of survey, some modern and others slightly ancient. The commonest techniques applied are magnetometers, conductivity meters, ground penetrating radars as well as electrical resistance gauges. These are able to operate under vast conditions and provide very high sample density surveys. This is unlike metal detectors that cannot generate high resolution imagery. There are other technologies in use too. Electrical resistance meters involve insertion of into the earth of metal probes. These obtain the required readings of local electrical resistance. The method utilizes different probe configurations that are mounted on rigid frames. The number of probes used is usually four. Their use is similar to using ohmmeters in testing circuits. In places in which direct contact with the ground is undesired, Electromagnetic conductivity instruments are preferred. Their response can be compared to that of resistance meters. One major advantage of the method is that it is suitable in conditions not favorable for resistance meters. Their response is faster and they are able to measure magnetic susceptibility, a feature that makes them preferable to most methods. Magnetometers can be used too. They measure total magnetic field strength using single sensors, or gradient of magnetic field using two and above sensors. The latter is preferred in most mining applications. The best known modern technique is perhaps the use of ground penetrating radars. The radar signals are directed to the ground. Objects below the ground cause reflections that are picked by receivers. The depth is showed by the time the signals take to travel. There are several other techniques use in resistivity survey that are not as modern. These are metal detectors, data collection and the use of data processing and imaging.
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