矩形大定源层状模型瞬变电磁响应计算

针对矩形大定源介绍了一种层状导电模型瞬变电磁响应的快速计算方法.其基本思想是，将大定源回线源用较少的有限大小方形回线叠加.在频率域，该叠加过程导出矩形大定源回线模型响应可以表示为一个标准的Hankel积分，叠加效应仅仅是相应Bessel函数的空间积分过程.瞬变电磁响应可以利用余弦变换由频率域响应获得.均匀半空间模型计算结果和解析解较为吻合，层状模型模拟结果符合物理规律，不同测点位置感应电动势的视电阻率具有很好的一致性.新方法误差只是来源于圆回线对小方形回线的等效误差.与均匀半空间解析结果比较，只用16个方形回线等效，相对误差就可以小于10^-3.

COMPUTATION OF TRANSIENT ELECTROMAGNETIC FIELD FROM A RECTANGULAR LOOP OVER STRATIFIED EARTHS

The paper introduces a new method for computing the transient electromagnetic (TEM) response from a large rectangular loop over a layered earth. In the method, the large loop is spanned by fictitious squares. The response from each square are then summed up as that of the large loop. In frequency domain, the superposition leads the vertical magnetic field to be expressed as a standard Hankel integral, whose integrand contains the addition of 0-order Bessel functions involving the distance from the center of each square to calculating point. Time-domain response can then be cosine transformed directly from the frequency domain result. The error of the method stems from the approximation of square loop by circular one, and comparing with analytical response of half space, relative error is less than 10~(-3) with only 16 squares used.