Abstract: The 3D whole-space response characteristic of the sheet conductive body located in uniform medium has been imitated with a magnetic dipole, and adopting non-uniform grid and time step length, the 3D time domain finite-difference formula has been deduced, the contour figure of the magnetic field and itshave also been plotted on the basis of the data obtained at quite a few surveying points. The diffused regularity of the transient field, the characteristic of the field affected by roadway and boundary plane was analysised in detail. The results showed that diffused velocity of the transient field reduced and its attenuation slowed down, when magnetic field passing through the boundaryplane between the sheet conductive body and the earth; and as the iterative number increasing, a ring-contour shaped at the center of the sheet conductive body; the effect of laneway was obvious at early time and feeble at late time. The objectives are to provide interpretation guidelines for the whole-space TEM anomalies.

Key words: transient electromagnetic field, roadway, FDTD method, modeling