“Apparent” Resistivity:   The resistivity which is measured at the surface and calculated making the assumption of a homogenous substance.  The apparent resistivity is calculated by measuring the potential drop between two “potential electrodes” positioned between two “current electrodes”.  The formula for apparent resistivity is:

(from Milson 1991)

Transmitter:    An instrument which controls and measures current and resistivity and induced polartization surveys.

Receiver:   An instrument which measures voltage in resistivity and induced polarization surveys.

Electrodes:   Usually metal stakes driven in the ground with wires attached, but sometimes consisting of “porous pots” which contain salt water to enhance current flow.

Electrical Polarization:    To establish a current, voltage and electromagnetic field enhancing the flow of electrons with a specified flow path (highly variable in shape).

Telluric Currents:   Naturally occurring electrical currents which travel in large sheets induced just below the earth’s surface, which are influenced by ionospheric currents related to diurnal changes in the earth’s magnetic field.