When performing electrical resistivity tomography (ERT) surveys, it is possible to add Induced Polarization (IP) to the measurement with most modern instruments such as an ABEM TerraMeter LS2 or an AGI SuperSting R8.

The software that we use to process this data is RES2DINV, which was originally developed by Dr. Menh Heng Loke at Geotomo Software. Geotomo Software was recently acquired by Aarhus Geosoftware, which was recently acquired by Bentley Software.

With ERT, the resistivity measurement is made while the current is flowing. With IP, the measurement are made once the current is turned off. ERT measures the electrical resistivity (inverse of electrical conductivity) of the medium, which is a measurement of loss in the earth system. With IP, the system is measuring how much energy the system can store and release later.

Typical ERT/IP measurements are made in the time domain. If the measurement is made in the frequency domain, it may be called spectral induced polarization (SIP), complex resistivity (CR), or non-linear complex resistivity (NLCR). All of the names listed so far are specific to the test performed, while the very general name for all of these types of measurements is impedance spectroscopy.