【作者】 吴小平；

【导师】 何继善；

【作者基本信息】 中南大学 ， 地球探测与信息技术， 2010， 博士

【摘要】 拓展深部资源是当前矿产勘查的战略方向,进行深部成矿理论和勘查新技术研究,是促进我国矿业发展的新任务、新挑战。危机矿山可接替资源找矿已成为中国经济持续快速协调发展的矿产资源保障的战略措施,是当前矿产资源预测评价与找矿的热点和前缘问题。危机矿山可接替资源评价与找矿具有矿山勘探开发程度高、地质勘探与矿山生产原始资料积累充分、评价与找矿向深边部三度空间发展的特点,其要求建立适应于危机矿山深边部及外围找矿的找矿创新体系与评价新理论、新技术和新方法。时间域电磁测深方法是一种具有高分辨率、大探测深度的新方法,是地球物理勘探方法中的一个重要部分。时间域电磁法的实际应用中,通常与激励源的强度及种类有关。一般喜欢采用阶跃波信号来做激励源,表面看来,其高频成份丰富,计算相对而言要简单,但从阶跃波激励源的频谱可以看出,阶跃波的频谱能量主要集中在低频部分(时间域的晚期),谱值范围大部分集中在10Hz级次以下,而且其频谱没有办法实现人工控制。对于时间域的观测方法,过早期(对应于频率域的高频段),由于一次场的藕合干扰,加上电磁场的趋肤效应,再加上阶跃波高频部分的低能量的激励作用,因此,效果不会是最佳的；而在过晚期(对应于频率域的低频段),虽然阶跃波的激励成份主要集中于此,但由于电磁场的快速衰减特性,电磁响应分析表明效果也不是最佳的。寻找理想的激励源,对时间域方法非常重要。作者从分析激励源的频谱特征出发,提出了以时间域的δ函数激励源为基础的单脉冲电磁测深方法,它能在全频率范围内均匀激励,并可以获得准确的大地视电阻率随时间变化的规律。我们知道,δ函数的频谱为一恒定值,从而由傅立叶级数可知,时间域的δ函数可以表示为频率域的谐变波函数。事实上,我们在电磁场的理论计算中,常常假定为谐波激励源的情况,也就是时间域的6函数激励。对于时间域的δ函数激励来说,由于它没有持续时间,也就是没有一次场的存续时间,而它的激励能量又是足够的大,可以充分的对系统进行激励,我们定义这种方式为单脉冲电磁测深方法。作者在论文中详细推导了6函数激励源的时间域电磁相应,并定义了单脉冲电磁测深方法的视电阻率。从磁偶极子源和电偶极子源的实际激励方式出发,分别计算了均匀半空间的视电阻率和层状介质晚期视电阻率的值。通过与阶跃波激励源视电阻率图形的比较,发现单脉冲电磁测深方法的视电阻率更能反映大地的真实电阻率。通过对不同脉宽的方波激励源的电磁响应分析,发现激励方波的脉宽越宽,电磁响应越接近阶跃激励源激励的电磁场响应,而激励方波的脉宽越窄,电磁响应越接近单脉冲激励的电磁响应。方波信号激励源具有阶跃波、方波和单脉冲三重性。作者建议根据条件的不同选择不同宽度的方波激励源来近似单脉冲激励源进行单脉冲电磁测深方法。传统的时间域电磁测深方法大多采用方波的方式激励,而在资料处理和解释中又采用阶跃激励的理论。作者通过计算比较分析,发现这种处理方法在理论上就存在很大的不完备性。建议采用单脉冲电磁测深方法来处理和解释方波激励源的电磁响应更加合理实用。更多还原

【Abstract】 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.更多还原