Reason and correction of low resistivity problem in mine transient electro-magnetic method

Mine transient electromagnetic method has a low resistivity problem for using minor transmitter and receiver loops,which leads to data interpretation difficulties and decreases detection depth. Firstly,this paper studied the varia- tion of secondary field with transmitter-receiver distance through numerical simulation and field test,and found that the simulant secondary field was almost unchanged with transmitter-receiver distance within 20 m while measured data de- creases linearly in logarithm coordinate system. Theoretical analysis shows that the mutual induced electromotive force is the main component of measured data,which leads to low resistivity problem. Furthermore,the paper proposed a re- sistivity correction method based on the different properties of secondary field and mutual induced electromotive force. The method eliminates the mutual induced electromotive force by using two measured data with different transmitter-re- ceiver distances. Finally,the proposed method was successfully used in a half-space field case and a whole-space field case to demonstrate its practical usefulness.