极低频电磁波技术电磁响应建模及电离层影响分析

THE ELECTROMAGNETIC RESPONSE MODELING OF THE ELF METHOD AND THE INFLUENCE OF THE IONOSPHERE

对极低频电磁波技术的理论进行讨论,首先根据研究对象和问题建立地质模型和相应的数学模型,然后根据电磁场理论选择了相适宜的计算方法,推导出水平长直导线接地源电离层、空气层和层状大地相互耦合频域电磁场响应的一般表达式。这些表达式将电磁响应和电离层的电导率等参数有机联系在一起,为极低频电磁波技术的正演计算以及极低频电磁波技术在资源探测应用中的可行性分析奠定基础。对理论地电模型的计算表明,由于电离层的存在使得电磁波在地面与电离层之间来回多次反射,从而改变了电磁响应曲线的形态。

The Extremely Low Frequency（ELF） method is a new artificial source electromagnetic detecting technique,which should be improved through forward modeling and data checking for the processing of the measured geophysical data.In this paper,the theory of the ELF method is systematically analyzed.First,in accordance with the studied objects and the problems,the geological structure model and its corresponding mathematical model are built.Then,on the basis of the electromagnetic theory and the selection of a suitable calculation method,the time-harmonic horizontal finitely long grounded wire is set on the crust surface,the mutual coupling of the ionosphere,the air layer and the layered earth are considered,and the general expressions for frequency-domain electromagnetic responses are deduced.These expressions connect electromagnetic response with all parameters such as the conductivity of the ionosphere,and provide theoretical foundation for forward modeling and the feasibility of the ELF method for resource exploration.The modeling indicates that the shape of the electromagnetic response curve is variable,and the electromagnetic waves are reflected back and forth between the ground and the ionosphere due to the existence of the ionosphere.