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在使用电偶极发射源的可控源电磁法(CSEM)勘探中,发射源的方位、长度、形状等对观测数据有重要的影响,然而现有的大部分三维数值模拟方法没有全面地将这些因素考虑进来,很多都只能应对非常简单的场源形态,例如单一方位的点电偶极子,这有可能显著降低模拟结果的准确性.本文实现了基于交错网格有限体积(FV)离散的海洋CSEM三维正演算法,能够模拟形态相对复杂的场源,包括任意方位的有限长直导线和弯曲导线发射源.该算法使用一次场/二次场方法,只需对二次场使用FV法求解,避免了场源的奇异性问题;一次场的计算为一维正演问题,使用准解析法求解,并且只要在计算一次场时考虑复杂的场源形态便可以实现同样场源的三维正演.通过与一维理论模型的解析解对比验证了三维程序的准确性,并针对三维理论模型进行了一系列正演测试,初步考察了场源形态对三维正演结果的影响.
In controllable source electromagnetism (CSEM) exploration using electric dipole sources, the orientation, length, shape, etc. of the source have an important influence on the observed data. However, most of the existing three-dimensional numerical simulation methods do not comprehensively describe Considering these factors, most of them can only deal with very simple field source patterns, such as a single azimuth dipole, which may significantly reduce the accuracy of the simulation results.In this paper, a method based on staggered grid finite volume (FV) The discrete oceanic CSEM 3D forward algorithm can simulate relatively complex field sources, including finite-length straight conductors and bent wire emitters of arbitrary azimuth. The algorithm uses a field / quadratic method that requires only the use of a secondary field FV method avoids the singularity problem of the field source. The calculation of the first field is a one-dimensional forward problem, which is solved by the quasi-analytic method, and the same field source can be realized by considering the complex field source form when calculating a field Dimensional forward modeling.Compared with the analytical solution of the one-dimensional theoretical model, the accuracy of the three-dimensional program was verified and a series of forward test was conducted for the three-dimensional theoretical model. Influence of 3D forward result.