A new resolution index for resistivity electrode arrays

Abstract

Historical arguments about the 'sensitivity' of an electrode array to different volume elements in the subsurface have been satisfied by the concept of signal contribution sections, although they address only homogeneous Earths. Similar arguments on the 'depth of investigation' of various electrode arrays have been put to rest by the concept of effective depth. The effective depth is a well-defined characteristic of the vertical response function of an electrode array obtained by integrating horizontal planes of the corresponding signal contribution section. Debate on the 'resolution' of various electrode arrays has not reached a firm conclusion. The ranking of arrays in order of resolving power varies according to the definition of resolution. A new resolution index is proposed here. It builds on the successful effective depth concept by introducing new concepts called effective thickness and extended depth. The index is quantified by formulating the cumulative vertical response function of a general electrode array. The dipole?dipole arrays are found to have the best vertical resolution, and the Schlumberger array is found to be better than the conventional Wenner array.