Two fundamental concepts-detective depth and detective range mostly used in apparent resistivity method have been studied theoretically.Some problems including deficiencits about these two concepts in electrical pro-specting have been discussed in this pager.In order to compare the under-ground condition of stations and study detective capability of stations,a sort of new definition of detective depth has been proposed,based on the theoritical formula of apparent resistivity in layered-medium.The detective depths in different structures and arrangements of current electr-ods have been quantitatively calculated under a unified standard.Besides,the relations between the theoritical positions of upper and lower in-terface of detective range in media and the parameters such as the mag-nitude of variation of resistivity in the top-Layer or deep-Layer,the distance of current electrods and the precision of instruments bave been discussed.The calculation indicates that the maximun detective depth of the lower interface in media can be about 1.5 times as much as the dis-tance between electrods AB in homogeneous media,using Symmetrical-Four-Pole-arrangement and instruments whose precision is 1.0.The approach of increasing detective range have been suggested theoretically.
This paper also discusses the difference and the relation between these two concepts as well the method of calulating detective depth in inhomo-geneous media in principle.