Electrical resistance meters measure how well electricity can flow through the ground. In most of the settings where we work, this comes down to how much soil moisture is in the ground. Thus, resistance surveys are weather dependent, but they can produce some very different, and sometimes better, results in different soil moisture conditions.
Resistance meters are good at detecting compact surfaces like old roads that have become buried, house foundations, and gravel and/or sand layers–basically, any kind of scenario where a drier, less conductive material replaces soil that can hold moisture. They also can work well when looking for filled in excavations because these tend to hold moisture differently than their surrounding soil matrix. For example, graves sometimes show up in resistance data because they hold moisture well. We typically use the resistance meter as a second, supporting data set in cemetery surveys and at earthwork sites.
Examples of Electrical Resistance Surveys
- Ancient Native American Earthworks