A Simple Apparent Resistivity Definition for Modified Central-Loop TEM System

Central-loop TEM technology can be used to survey the response of just central point. In practice, ones design modified central-loop TEM system to survey the response of several point around central location (within which the field is assumed to be uniform). However, there still exist some theoretical problems needed to be solved in obtaining TEM responses of this kind of modified system. In this paper, calculating and comparing the circle central-loop and modified circle-loop configuration of magnetic field responses at different non-center distances have been finished. The equations at non-center points are constructed using the technology of polynomial iteration. The polynomial coefficients are obtained adopting the method of least-squares iteration. Then, the improved calculation formula of the apparent resistivity at non-center points is constructed by adding an extra coefficient to the conventional formula, and this can make it better apply to TEM data collected at non-central locations of a circle-loop. Then the equivalent of circle and rectangular loop has been discussed; at last, the result due to circle loop has been introduced into square loop system and develop a new method to calculate the electromagnetic field response and apparent resistivity at non-central. An improved expression of apparent resistivity at non-center points is constructed and validated by a given model as well as coal water-filled area location, which shows that the constructed method is feasible.