The Research Of The Wide Band Spectrum Active Source And δ Function Electromagnetic Sounding In TEM Method

It is the strategic direction for the currently deep mine prospecting. And it is a new mission and challenge for our mine industry developing to setup the theory of the deep mine growing and research new technology of mine exploration. The prospecting for replaceable resource of crisis mines has become a strategic measure of mineral resource's guaranteeing the sustainable, rapid and harmonic development of China economy, and then a hotspot and frontier issue of prognosis, appraisal and prospecting for mineral resource. When carrying out the appraisal and prospecting for replaceable resource of crisis mines, we will have to cope with the situations of high-level mine exploration and exploitation, enormous accumulated raw data of geological exploration and mine exploitation, and mineral prospecting advancing on the third dimension of space, i.e. the depth and margin of the mine, which leads to the demand for establishing prospecting innovative systems and novel theories, techniques and methods of mineral resource appraisal suited for the prospecting in the depth, margin and outside of crisis mine.Time Domain Electromagnetic Sounding Method is a new method with high resolution and great depth of exploration. It is a very important part of the Geophysics Exploration.We often concern the type and intensity of the active source for TDEM in the application. We used to use the step wave for TDEM active source because of the simply calculating and a plenty of high frequency parts. But from the Spectrum of the Step Wave Active Source, we found the Spectrum energy is concentrated at the low frequency range (later time of Time Domain). The frequency value is less than 10Hz level, and Spectrum can not be controlled easily. For the early of Time Domain (corresponding to the high frequency range), it is very hard to obtain the high quality surveying data because of the coupling interference and the low Spectrum energy of Step Wave Active Source. And for the later time (corresponding to the low frequency range), although there is the high Spectrum energy for the Step Wave Active Source, it is proven that is the same hard to obtain the high quality surveying data because of the rapid declining characteristic of the Electromagnetic Wave.To the Time Domain Electromagnetic sounding Method, we should measure the induced second electromagnetic field after the active source stopping for avoiding the coupling interference. So some perfect active source can not be use because of without surveying intermission, and these sources have perfect Spectrum energy.It is very important to search a perfect active source for time domain electromagnetic sounding method. The author revealed a method by using 8 function active source of time domain. It can get the actual response of ground system, and the apparent resistivity can be ascertained during the all time range. As we know, the spectrum ofδfunction is a constant. And according to Fourier series, we often suppose to use the harmonic wave active source of frequency domain during the theoretic calculation of electromagnetic field. It is the same ofδfunction active source of time domain. For theδfunction, it almost doesn't have duration time and has enormous power. So it can sufficiently active for every frequency. We call this method as 8 function Electromagnetic sounding method.In this paper, the author deduced carefully the electromagnetic response of 8 function (harmonic wave), and defined the apparent resistivity for theδfunction electromagnetic sounding method. For the magnetism dipole and electricity dipole, the author calculated the electromagnetic field response and apparent resistivity of uniform half space. Comparing to the apparent resistivity of step wave active source method, we can find that the apparent resistivity ofδfunction electromagnetic sounding method is consistent with the actual resistivity of uniform half space.Through analyzing the Electromagnetic responses of the square wave for vary width; we found that the Electromagnetic responses could be approach to that of Step Wave active source for the big width of square wave. And for the other hand, the Electromagnetic response could be approach to the response of 8 function active source for the narrow width square wave active source. The square wave has triple characteristic of the Step wave, the Square wave and theδfunction active source. The author suppose to use vary width Square wave for approximate replacing theδfunction active source according to the different conditions.It often use the Square wave active source for the classical Electromagnetic sounding, but use the theory of Step wave to process the observed data and inversion of the ground section. By comparing the results of calculations, the author suggested to use the theory ofδfunction active source for process the observed data and inversion of the ground section.