Anomaly body advance detection technology of down-hole transient electromagnetic

Down-hole transient electromagnetic method is a kind of detection technology, which laid the transmitting loop on the ground and received three component signal of magnetic induction intensity or attenuation voltage in borehole. Its observation system is placed in the borehole, which can effectively reduce the signal shielding and ground electromagnetic interference of the conductive overburden.It can obtain stronger abnormal response than the ground transient electromagnetic method as the receiver closer to the abnormal body. It is one of the most effective methods to detect deep buried geological bodies which can be considered for detect abnormal bodies beside in coal mine. According to the equivalent eddy current theory, the secondary field produced by the abnormal body of Down-hole transient electromagneticcan be expressed by the equivalent current loop. The three components Bx、By、Bz of the induced magnetic field intensity have certain directivity. The coordinates of the current loop center position can be roughly obtained by intersecting the composite vector Bxy and Bxz. So it canlocate the position of the abnormal body. There are errors while intersect Bxz in XZ plane directly. In this paper, a floating coefficient vector intersection algorithm is proposed. We can obtain the vector distribution characteristics by calculating the three components of magnetic induction Bx By and Bz of the horizontal circular current loop (current loop) in the XY and XZ planes, calculatethe ABS(By)/Bz value at feature points and constructthe coefficient library. The coordinate of the current loop center position in XZ plane can be calculated accurately after correctthe vertical component Bz and intersect Bx component. The results of theoretical model calculation and physical experiments show that the floating coefficient vector intersection algorithm can quickly and accurately locate the abnormal body center without prior information. It is an effective method for advanced detection.