大功率长偶极与环状电流源电磁波响应特征对比  

The contrast of response characteristics between large power long bipole and circle source

作　　者：许诚[1,2] 底青云[1] 付长民[1] 王妙月[1] 

机构地区：[1]中国科学院地质与地球物理研究所中国科学院工程地质力学重点实验室,北京100029 [2]中国科学院研究生院,北京100049

出　　处：《地球物理学报》2012年第6期2097-2104,共8页Chinese Journal of Geophysics

基　　金：国家公益性行业科研专项(201011079);国家自然科学青年科学基金项目(41004053);国家发改委重大科学工程项目联合资助

摘　　要：为了在深部第二成矿带找矿,需要进一步提高电磁法可控源的强度,因此,一种新的大功率固定发射源的电磁法正在孕育之中.该方法采用长偶极源或者环状电流源,为了提高发射源的强度,偶极长度L或者环状源半径R需要非常大.然而,电磁场信号的强度不仅仅依赖于发射源,当L或者R为数十公里时,接收点的位置远离发射源,电离层对电磁场的影响不可以忽略.电离层的影响既可能是增强信号,也可能是削弱信号,这依赖于不同类型源产生的电磁波.本文利用三维积分方程法对包含电离层、空气层、固体地球层(简称地-电离层模型)的线状和环状大功率电流源电磁波响应进行了三维数值模拟,对两种源的电磁波的响应特征进行了对比研究.研究表明虽然磁性源的发射效率高于电性源,但是由于发射源在波导区产生的直达波经电离层的反射波要产生相长相消干涉,波导区的场特征既和发射源的特征有关,也和电离层有关.对比研究发现对于x方向的水平长偶极源电离层对电磁场Ex和Hy的影响是使场的幅值增强,即波导场的Ex和Hy的衰减是减缓的.而对于水平环状电流源,电离层对水平方向的电磁场的影响是使场的幅值减弱,即波导场的Ex和Hy的衰减是增大的.为此,认为采用大功率固定源在波导场工作时应该采用线状电流源.In order to prospect in the deep second metallogenic belt, we have to increase the strength of source. So an EM method using fixed high power source comes into being. To increase the strength of source, the length of a bipole source, or the radius of a circle source （called magnetic source in this paper） should be much larger. However, the strength of electromagnetic signal does not depend only on transmitting source. When L or R is tens of kilometers and receiving point is far away from source, the influence of ionosphere canr t be ignored. The ionosphere may strengthen or decrease the signal, depending on the waves excited by different sources. We modeled electromagnetic wave response in a three-layer earth-ionosphere model with long bipole along cc direction and found that the ionosphere increases the amplitude of the E~ and Hy field, namely Exand Hy in the wave-guide field decay more slowly. But for the circle current source（magnetic source） , ionosphere makes the amplitude of the field weaker, namely Ex and Hy in the wave-guide field decays faster. For this reason, it is better to use long bipole source when working in the wave-guide field with a fixed large power source.

关 键 词：“地-电离层”模式 长偶极与环状电流源 大功率 电磁波场 

分 类 号：P631[天文地球—地质矿产勘探]