中心回线瞬变电磁法（TEM）视电阻计算研究

【作者】 晏冲为；

【导师】 李文尧；

【作者基本信息】 昆明理工大学 ， 地球探测与信息技术， 2012， 硕士

【摘要】 瞬变电磁法(Transient electromagnetic methods)或者称为时间域电法(Time domain electromagnetic methods)中,视电阻率是形象表达地下电性结构的一种常用参数,全期视电阻率的计算对瞬变电磁信号的数据处理与推断解释显得尤为重要。国内很多学者对中心回线瞬变电磁法视电阻率计算作了研究,其中有白登海法,苏朱刘法,熊彬法,王华军法,陈清礼法等,但这些方法各有各的优缺点,在计算速度、计算精度及应用条件方面各有限制,本文通过对中心回线瞬变电磁法的研究提出了一种计算速度快、精度高、应用条件广的方法。本文通过对均匀半空间中归一化感应电动势核函数的研究,发现在(0,+∞)存在一个最大值点,设为max,其横坐标为1.61363,且在(0,1.61363)为单调递增,在(1.61363,+∞)为单调递减,基于核函数分段单调的特性,提出了通过两次二分法实现对z的求解,间接求解出视电阻率的值,对两个视电阻率的值的选取采用综合比较选取法。当z无解时,结合有解的视电阻率值通过三次Hermite插值的手段得到一条平滑的视电阻率曲线。同时可人为的设定二分法的精确度,进而反馈视电阻率计算的精度,对视电阻率的精度进行评价。理论和实践表明这是一种求解瞬变电磁法中心回线全期视电阻率系统而有效的方法,计算速度快,精度高。这一计算方法为LTEM-1型瞬变电磁仪全期视电阻率的计算与反演解释提供软件基础。本文还通过对均匀半空间中心回线装置瞬变电磁法核函数的研究,推导了中心回线瞬变电磁法观测二次电位误差对计算全期视电阻率的影响的准确表达式,发现在晚期测量的微小的二次电位的误差将比早期对视电阻率的计算的影响更大,并介绍了目前对早晚期信号采集与处理的方法技术,对瞬变电磁仪的开发与瞬变电磁信号的处理有所帮助。通过对均匀半空间中心回线装置瞬变电磁法表达式分析,可以为瞬变电磁法的反演提供理论正演数据、可以为瞬变电磁法的反演提供一定的方法,同时还可以为野外生产设计与室内数据筛选与剔除提供一定的参考。本文通过对均匀半空间中心回线装置瞬变电磁法正演的研究,编写了能返回各种工作装置和视电阻率理论正演二次电位衰减到自主设定的噪声影响程度高的准确时间的matlab程序,对工程设计、野外数据采集质量评价及室内资料处理都有一定的实用意义。观测二次电位的准确与否直接关系到瞬变电磁法反演解释的正确性,研究瞬变电磁法观测电位的影响因素有助于推动瞬变电磁法的发展；有利于高精度瞬变电磁仪的研制；有助于采集或处理得到可靠的数据,使推断解释结果接近客观实际,解决生产中的实际问题；有助于寻找更多的矿产资源；有利于更好的解决水文地质、工程地质、环境地质调查等领域的问题,为经济社会的发展作出更多的贡献。本文研究并总结了前人对影响观测二次电位的因素的部分研究成果,对观测二次电位的改正方法进行了研究。基于李文尧老师研发的LTEM-1型瞬变电磁仪的工作基础,总结了国内外瞬变电磁仪的研究现状,探讨了国内瞬电变磁仪存在的问题及解决的问题的研究方案及发展方向,并对中心回线瞬变电磁法视电阻率计算在LTEM-1中的应用作了简单介绍。更多还原

【Abstract】 The apparent resistivity is a common parameters of expressing the underground electrical structure vividly in Transient electromagnetic methods, the calculation of the all-time apparent resistivity is particularly important in data processing and the inference and interpretation of transient electromagnetic signals. Many domestic scholars studied on the calculating the apparent resistivity of central loop transient electromagnetic method, such as Bai Denghai method, Su Zhu Liu method, Xiong Bin method, Wang Huajun method, Chen Qingli method etc, but all these methods have their advantages and disadvantages in terms of the speed, the accuracy of calculating and the application conditions, this paper through the study on central loop transient electromagnetic method puts forward a method of calculating apparent resistivity which has fast calculating speed, high precision, wide application condition.This paper analyzed thoroughly the transient electromagnetic field analytic expression in homogeneous half space, discovered that the kernel function exists a maximum value at z=1.61363, and is monotone increasing in (0,1.61363) interval as well as monotone decreasing in (1.61363,+∞) interval. Accouding to the monotone features in (0,1.61363) and (1.61363,+∞) interval,we proposed bisection method to calculate full time domain apparent resistivity. The calculating speed of this method is quick, we can get the solution of z by no more than55times calculations in every channel,the precision of bisection method can be set by yourself, the precision of apparent resistivity is high and can be evaluated, the algorithm is stable. We can get a smooth curve of apparent resistivity by piecewise cubic Hermite interpolation when there is no solution.This paper also analyzed thoroughly the kernel function of the center loop transient electromagnetic method in homogeneous half space, deduced the expression of the influence secondary potential errors exerts upon calculating all-time apparent resistivity, discovered that the small secondary potential errors will have a greater impact on calculating all-time apparent resistivity in later time than in early time. And This paper introduced the current methods and techniques of improving the quality of data collection and data processing in early time and later time.This is beneficial to the development of transient electromagnetic apparatus and the data processing of transient electromagnetic signals.Analyzing the expression of the center loop transient electromagnetic method in homogeneous half space can provide the forward datas, the method of inversion and can select the correct datas or delete the wrong datas. This paper programmed with matlab to calculate the accurate time of secondary potential attenuating to the level affected by noise seriously. This work can provide a reference for engineering design evaluating the calculation of all-time apparent resistivity and deleting the data affected by noise seriously.The accuracy of the secondary potential is directly related to the correctness of the interpretation of transient electromagnetic inversion. Researching on the factors affecting the surveying of secondary potential can promote the development of the transient electromagnetic method,can conducive to the development of precision transient electromagnetic apparatus,can contribute to get reliable data by collecting or processing data and make the inference and interpretation close to the objective reality, can help us to prospect more mineral resources,can conducive to better solve problems in the fields of hydrogeology, engineering geology, environmental geology and can make more contribution to the economic and social development. This paper summarizes and discusses the previous part of the research results on the factors affecting the secondary potential and the correct of secondary potential.Basing on the research and development of LTEM-1apparatus that been developed by Liwenyao teacher, author summarized the status of transient electromagnetic apparatus and the problems of transient electromagnetic apparatus in China, put forward to the scheme of solving these problems and the direction of domestic transient electromagnetic apparatus in the future, and introduced briefly the application of the study of calculating apparent resistivity of central loop transient electromagnetic method in the research and development of LTEM-1apparatus.更多还原