The Study About ID Forward Modeling Of Large-fixed Loop TEM

The transient electromagnetic method is one of the Time domain electromagneticmethod, referred to the TEM, belonging to geophysical electrical prospecting.It is atime domain Artificial source electromagnetic exploration method based on theprinciple of electromagnetic induction. Useing the unground loop or groundingelectrode to observe the secondary field. Through analyzing,extracting and processingof the observed data, reach to the purpose of explaining the relevant physicalparameters of the underground minerals. Because the artificial source methods has theadvantaves of smaller random disturbances and larger launching magnetic moment andhigh resolution and depth of exploration, Now is widely used in energy,mineralresources,hydrology,engineering,environmental and so on.Firstly,It is reviewed the development of the transient electromagnetic method,andBriefly introducted the working principles, characteristics and the device type of thetransient electromagnetic method.And also introducted current development and thefuture trend at the processing and interpretation methods of the data in domesticand international.Secondly, the derivation process of forward formula and forward modeling of alarge-fixed loop TEM method was introduced in detail. Starting from the basictheoretical knowledge of the transient electromagnetic method, respectively, Theelectromagnetic field in frequency-domain and time-domain are derived in detail in thehomogeneous half space and the level of a large-fixed loop isotropic layered media.The electromagnetic field in frequency domain of was converted into time-domainelectromagnetic field expression by Hankel transform and the Gaver-Stehfest inverseLaplace transform. Finally, according to the transient electromagnetic field intime-domain solve the analytical expression of the early and late stages of the apparent resistivity.Because the early data of transient electromagnetic method which wascollected in the actual work are largely affected by turn-off effect, the late apparentresistivity is adopted in this paper. according to the forward numerical algorithm of thelarge-fixed loop, the one-dimensional forward was programmed by Matlab language toachieve the process of forward modeling.the characteristics of curve of the response oftransient electromagnetic and the apparent resistivity are analyzed andcompared,which are significance to guide the data processing and interpretation oftransient electromagnetic.Finally, on the aspect of data processing, on account of observation data of a large‐fixed loop a data processing software was designed and developed by C++language in the Microsoft Visual2008platform.the conversion of measured data was Completed to achieve attenuation curves of the single‐channel induced electromotive force and apparent resistivity and sectional drawing of the multi‐channel induced electromotive force and the apparent resistivity. That is beneficial to deduce the direction of attenuation of the induced electromotive force and the apparent resistivity of the subsurface geology and to Reflect the abnormal position and shape and trend of the geological body. To some extent complement the Qualitative interpretation of date of the large‐fixed loop.