Migration of the Electromagnetic Field

The previous chapter dealt with the theory of analytical continuation of the electromagnetic field in a well-conducting medium. The examination was confined to a monochromatic field. As indicated in our study (Zhdanov 1981), similar techniques can be also elaborated for transient electromagnetic fields. But the latter can be continued using a method somewhat different from that utilized in ordinary analytical continuation. This method is known as migration of the electromagnetic field (Zhdanov and Frenkel 1982 a, b, 1983 a, b). As will be shown below, this procedure is very much similar to the method used for seismic data interpretation and called seismoholography or seismic migration (Petrashen and Nakhamkin 1973; Timoshin 1978; Berkhout 1984; Claerbout 1985). It extends, in turn, the ideas of optical or radio holography (Caulfiled 1979: Handbook of Optical Holography) to the case of seismic (wave) fields.