A term used with magnetotelluric methods (q.v.) for the apparent resistivity based on the magnetotelluric impedance tensor, Z:
where is the angular frequency and is the permeability of free space. This parameter is rotationally invariant and thus independent of the choice of coordinate axes, as contrasted with other apparent resistivity definitions based upon individual components of Z. See Berdichevsky and Dimitriev (1976).