With all E&EM methods the Earth is excited through the injection of current, either galvanically, capacitvely or inductively, and a resulting voltage response is measured using electrodes, magnetic sensors or a combination of these. The depth of investigation is controlled by the electrode array configuration for electrical methods, and time-varying fields for EM sounding methods. There are two basic EM sounding techniques: the transient electromagnetic (TEM), and the magnetotelluric (MT) methods, which include audiomagnetotelluric (AMT) and controlled-source AMT (CSAMT). Electrical resistivity surveys are often deployed on the surface and in boreholes. EM data can be acquired on the ground or from the air on a fix-wing or helicopter platform.   

Data can be used to create thematic maps in plan view or inverted to create a two-dimensional (2D) or quasi 2-D resistivity sections from several meters to tens of kilometers. Resistivity can be related to basic geological structure, such as depth to basement, stratigraphy, faults, fractures, paleochannels, and hydrogeological features such as depth to groundwater and aquifer characterization. Full three-dimensional modeling is available for electrical resistivity data and the MT method, but data acquisition can be expensive. The choice of method depends on the geophysical target, local geology and required resolution.