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Abstract The depth of investigation in any direct current resistivity method of surface geophysical prospecting is defined, following Evjen (1938), as that depth at which a thin horizontal (parallel to ground surface) layer of ground contributes the maximum amount to the total measured signal at the ground surface. Using the equivalence between static and stationary fields, we have found the following values for the absolute depths of investigation in homogeneous ground.
Roy et al. (Fri,) studied this question.