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将回线源电流密度加入时域麦克斯韦方程组的安培环路定理方程,可以实现任意发射波形的电磁响应三维正演.因为源电流密度参与迭代计算,所以称此法为有源有限差分法.本文采用非均匀网格的有源有限差分算法,对均匀半空间、K型和H型层状模型、三维低阻模型进行了正演计算,验证了算法的有效性和精度;对三维低阻体和高阻体进行正演,分析它们的响应特征规律;对不同脉宽的梯形波响应规律加以研究,并与阶跃波响应理论值进行对比,结果表明脉宽大小对梯形波响应早期影响不大,对响应晚期影响显著,脉宽越小,梯形波响应幅值衰减越快,结果越早偏离阶跃波响应的理论值.
By adding loop source current density to the Ampere loop theorem equation of Maxwell’s equations in time domain, the electromagnetic response of arbitrary emission waveforms can be realized in three-dimensional forward modeling, because the source current density is involved in the iterative calculation, this method is called active finite difference method. In this paper, the active finite difference algorithm of non-uniform grid is used to forward calculation of uniform half-space, K-type and H-type layered model and three-dimensional low resistance model to verify the effectiveness and accuracy of the algorithm. Body and high resistivity body forward to analyze their response characteristics of laws; different pulse width of the trapezoidal wave response law is studied and compared with the theoretical value of the step wave response, the results show that the pulse width of the early impact of trapezoidal wave response Not significant, the response to the late significant impact, the smaller the pulse width, the decay rate of the trapezoidal wave amplitude faster, the results earlier shift away from the theoretical value of the step wave response.