Performing an Electrical Resistivity Tomography Survey
Resistivity imaging involves measuring a series of readings along a profile with the electrodes at a set spacing. The resistivity data can be collected using a variety of electrode array configurations, the choice being selected by the geophysicist on-site to meet the objectives of the survey.
Electrical resistivity imaging provides a complete data set from very close to the surface to a considerable depth. The depth of investigation and the resolution achieved are dependent on the electrode spacing and electrode configuration used. Longer spreads will achieve a greater depth, trading resolution to do so.
The apparent resistivity values are affected by a number of factors and it is important, therefore, that the geophysicist considers all relevant information when interpreting resistivity data. Different materials have different resistivity values, which means that the interpretation of ERT profiles requires an understanding of the geology and hydrogeology in the area under investigation.
High resistivity values indicate a low conductivity and are usually associated with materials such as air, sand or gravel. A low resistivity value indicates a high conductivity and is usually associated with materials such as clay or water.