Early Analogue Modeling Experiments and Related Studies to Today's Problems of Geo-electromagnetic Exploration

As I learned it from extensive geo-electromagnetic analogue modeling experiments, some specific nonconventional interpretation parameters, in certain conditions, give more detailed information about the geometry of subsurface resistivity inhomogeneities than the routinely used parameters. In this article, I show several examples, and I present how these early results influenced our later research. An enhanced geometric sensitivity may be due to special array geometry (as we call it "null array"), or it may be due to a narrow and very special frequency range (i.e., the so-called "keyhole" range). Nonconventional but physically based interpretation parameters (like the Poynting vector) or higher order invariants of resistivity or impedance tensors may also give useful additional information about the shape of subsurface bodies. One should be very careful in their application because a large part of these nontraditional approaches are strongly constrained by measuring errors and geological noise.