Discussion on Method of Eliminating Large Loop Source TEM Border Effect

Abstract

Large loop source TEM method has played an important role in minerals and engineering exploration. But there is a strong border effect when one explains by central loop later-time apparent resistivity. In this paper, a method was used to calculate all-time apparent resistivity by magnetic dipoles composing loop. For 1D forward data, all-time apparent resistivity was computed and compared with later-time apparent resistivity. Conclusions have been drawn that all-time apparent resistivity has no border effect on homogeneous ground model; but for complex layered model, all-time apparent resistivity border effect is reflected in vicinity of false extreme point of apparent resistivity curve, and is much weaker than later-time apparent resistivity border effect. The conclusions are conducive to a correct understanding of using all-time apparent resistivity to eliminate border effect and guide correct interpretation of measurement data.