The Study And Application Of Transient Electromagnetic Sounding On The Theoretical Depth Of Investigation

This paper firstly introduces the principle、the history and trends for Transient Electromagnetic Method. It’s also introduced that the developing of depth of transient electromagnetic sounding, which reflects that it require further investigation. So the main idea of this paper is about the study of transient electromagnetic sounding.First, it is deduced the the central loop transient response calculation from Maxwell’s equations. Hankel transform and digital filtering method are introduced, which can solve the problems about bessel function. After compared the accuracy and computation time between 140 points improved fast Hankel transform and continued fraction, using improved Hankel transform to get the response of loop source frequency domain. It’s compared the accuracy between the digital filtering and the G-S transform, it’s decided to use digital filtering to get the conversion from frequency domain to the time domain. On the basis of the forward calculation method, it is make the forward procedure about central loop transient through Matlab. Using this program,it is simulated numbers of geo-electric models such as homogeneous half space model、two layers models and three layers models. And it’s also studied the characteristics for forward response in different sets of parameters.Second, based on the theory of theoretical depth of investigation, it is put forward the concept of using potential difference to discuss about theoretical depth of investigation for TEM. It is studied the factors that can influence the theoretical depth of investigation for TEM and calculated the theoretical depth of investigation in different parameters. It is summarized the influence rules on transmitter coil size and quantity、drive current and interference voltage to depth of transient electromagnetic sounding; The size of transmitter coil of TEM have a optimal value that makes the theoretical depth of investigation has a crest value; The greater of drive current, the greater theoretical depth of investigation, when reaching a certain degree, the depth of investigation is difficult to continue to increase; The more number of turns for transmitter coil, the greater theoretical depth of investigation, but when it reaches a certain number the the depth of investigation is also difficult to continue to increase.At last, it is introduced a practical example that use above conclusions apply into work design...