大定源装置下瞬变电磁法视电阻率定义  

Definition of apparent resistivity for non-center vertical component of Large-loop TEM configuration

作　　者：戚志鹏[1] 李貅[1] 朱宏伟[1] 马炳镇[1] 张军[1] 吴琼[1] 

机构地区：[1]长安大学地质工程与测绘学院,西安710054

出　　处：《地球物理学进展》2011年第4期1350-1358,共9页Progress in Geophysics

基　　金：国家自然科学基金面上项目(41174108);国家自然科学基金项目(40774066)联合资助

摘　　要：对于应用较广的大回线源瞬变电磁装置,虽然得到了非中心点电磁响应式,但由于响应的复杂性,一直没有推导出不同场点视电阻率定义式,通常借用中心回线方式的视电阻率公式进行解释,必然会在观测区的边缘处出现异常.为提高瞬变电磁法的解释精度,将非中心点垂直分量转化为人们熟悉的电阻率参数,本文提出并建立了大定源装置情况下视电阻率定义.首先在频率域对回线内不同场点电磁响应进行计算,将计算出来的非中心点函数形态与中心点处垂直分量进行比较,认为两者具有相似的函数形态,因此,非中心点分量可以用与中心点垂直分量类似的多项式进行拟合,从而得到多项式形式的感应电动势表达式.根据中心点垂直分量视电阻率定义式,建立与中心回线方式相类似的与偏移距有关的视电阻率表达式.把回线内场点响应写成与中心回线方式多项式表达式相类似的多项式表达式,采用最小二乘法得到与偏移距有关的多项式各项系数,将求得的多项式系数代入形成不同偏移距情况下的视电阻率定义.根据推导的视电阻率表达式对模型计算数据进行解释,视电阻率曲线形态与地下模型电阻率变化一致,通过对实测数据视电阻率断面图对比可知瞬变电磁多分量解释提高了探测精度.研究成果具有很大的理论意义和实用价值.Although we can get the non-central electromagnetic response for the widely used large-loop TEM configuration, the definition of apparent resisitity in different point has not been formed due to the complexity of the electromagnetic response. Usually, in our interpretation we use the apparent resisitivity of the inqoop configuration. Obviously, abnormal phenomenon will appear in the edge of the observation zones. In order to improve the interpretation accuracy of the TEM method, we have proposed a new definition of apparent resistivity for large-loop TEM configuration. Firstly, we calculate the electromagnetic response of different field points inside the loop in frequency domain and compare the calculated non-central function form with the vertical component in the center of the loop. We find that they have similar function form. Therefore, the non-center vertical component can be fitted with the expression which was similar with the polynomial expression of center vertical component. With the polynomial expression, a new definition of apparent resisitity is proposed according to the vertical component, which is similar to the case of in-loop configuration and related to offset. Then, convert the response function inside the loop into multinomial expression similar to the function of in-loop configuration, and obtain each coefficient of polynomial expression by least squares fitting method. Lastly, substitute the coefficients into the new apparent resisitity expression in the situation of different offsets. With the new apparent resistivity expression, we can do interpretation with model computing data and measured data. By comparing the apparent resistivity sections, we have found that the TEM multi component interpretation not only improves detection precision but also has obvious reflection of low resistivity boundaries. This research has great theoretical significance and practical value.

关 键 词：大回线源 瞬变电磁 非中心垂直分量 视电阻率定义 曲线拟合 

分 类 号：P631[天文地球—地质矿产勘探]