Theory Research On The Transient Electromagnetic Sounding With Electric Dipole Of Shallow Detection

The transient electromagnetic method is one of the commonly used electromagnetic method in the geophysical exploration. In this paper,the author focus on the forward calculation of the transient electromagnetic method with electric dipoles which is less discussed nowadays. First, let the field theory deduces the homogeneous half-space and isotropic horizontal layered earth's vertical magnetic field, through the fast hankel transformation to realize frequency domain forward calculation, then through the G-S transformation to realize from the frequency domain to the time domain conversion. Through the iterative algorithm to obtained the apparent resistivity in the frequency domain. Since the turn-off effect produced by the turn-off current in the time domain, the author put forward with the calculation of the second field in the time domain with the turn-off effect, then through the all zone search algorithm to draw the all time apparent resistivity, so as to realize the turn-off current correction. Through calculation shows that for the multi-strata, the middle strata will be influenced by the close strata, but the curve that can reflect the basic underground electrical structures .