| Being a method of time-domain electrical magnetic surveying, the Transient Electromagnetic Method (TEM) that is used to observe and investigate the secondary field can greatly simplify investigation of anomaly of buried geologic bodies on condition that the primary field does not exist. It has some advantages, such as concise, precise, be rich in information and so on. On the other hand , people can not get the picture timely for guiding the job being done, because there is a large quantity of data and the processing is quite complex in latter time. The requirement to transient electromagnetic technology is becoming high with its continuous development. How to image fast becomes a hot direction of TEM.In this thesis, by introducing the transient electromagnetic method of detection, the characteristics of different receiver devices are discussed in application. Data-processing is discussing by taking the example of central-loop device in the process of TEM imaging. The main tasks of the thesis are presented as follows:①The condition of transmitter current wave decay in non-step in actual experiment is analyzed. The pretreatment method of"correction first, then calculation"is presented. Considering of W-TEM transmitter, the relationship between ramp turn-off and step turn-off transmitter current under central-loop device is discussed. Simulation testing to model is done combining with calibration method about turn-off effect from transmitter current. A simple method calibrating TEM response data, which can avoid the complicated mathematical treatment process and provide prerequisite for calculation resistivity ,is given under short decay turn-off current.②Conventional method of calculating resistivity in TEM response is analyzed. Two other fast improved methods of calculating resistivity, which are linear accelerated iterative algorithm and bisection pre-estimate method, are given. The former one is belonging to variable step-size iterative. Improved variable step-length numerical calculation is presented based on analysis of apparent resistivity methods commonly used. The latter one that suit the request in this thesis is bisection pre-estimate of numerical method, it also solves the problem of selecting initial value encountered in Newton's method. Simulation tests proved that it is valuable in engineering applications.③Artificial neural network (ANN) is used for the research in this thesis. Two methods based on independent variable and transient field parameters are given. Response curves of TEM are simulated by ANN. Input and output vectors and their impact on the training results are discussed. Choosing sample data, comparing the precise and convergent of different training algorithms, determining the number of hidden layer, at last, calculating resistivity using ANN is realization. The practicability of numerical calculation and ANN calculation algorithm are proved with theoretical models and field data experiments. Comparative study between them is also done.④Characteristic about transient response in other devices is analyzed. The method discussed in this thesis is extended. Variable parameters on the impact of engineering measurements and key issues in numerical calculation are discussed. Feasible suggestion about calculation is presented from the point of view in this thesis. |
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