EM-field transformations and their use in interpretation

Two large groups of methods used to transform electromagnetic fields are discussed. The first of them includes methods based on the linear relations between the components of the MT-fields measured at a single or several points at the earth's surface. In this context special attention is paid to the consideration of impedance transformations, apparent resistivity and inductive operators, most frequently used in interpretation.The second group of methods concerns integral transformations of data. Firstly techniques are considered which are used for the division of the EM-fields into external and internal, normal and anomalous, surface and deep parts. Finally electromagnetic analogs of seismic methods are mentioned briefly.All transformations discussed are accompanied by examples of their use in data interpretation.