基于振幅—相位张量分解的大地电磁电流型畸变校正

在大地电磁勘探中,当近地表三维电性不均匀异常体的几何尺寸远小于电磁波的趋肤深度时,阻抗张量会发生严重畸变。若不消除这种影响,反演得到的电性结构会偏离真实构造,进而影响后续的地质解释。传统的畸变校正方法大多假设区域构造为一维或二维,而实际区域构造一般都是三维。文中从阻抗张量的振幅—相位张量分解出发,基于不含畸变的振幅张量分解参数与相位张量分解参数最为相似这一特点,以对应分解参数差异之和建立目标函数,通过改进粒子群算法搜索畸变参数,将目标函数值作为粒子的适应度,实现区域构造为任意维性的大地电磁电流型畸变校正,提出了无需区域构造维性假设、适应性更广的大地电磁电流型畸变校正方法。最后,应用该方法对三维模型和实测数据进行计算,结果验证了该方法的有效性、正确性和实用性。

Magnetotelluric galvanic distortion correction based on amplitude-phase tensor decomposition

In terms of magnetotelluric (MT) exploration, when the geometric size of the near-surface three-dimensional abnormal body with inhomogeneous electrical property is much smaller than the skin depth of the electromagnetic wave, the impedance tensor will be seriously distorted. If this effect continues, the electrical structural model obtained by inversion will deviate from the true tectonic model, which will further affect the subsequent geological interpretation. Most of the traditional distortion correction methods assume that the regional structure is one-dimensional or two-dimensional, while the actual regional structure is generally three-dimensional. Therefore, this paper starts from the amplitude phase tensor decomposition of impedance tensor, uses the feature that the amplitude tensor decomposition parameters without distortion are highly similar to the phase tensor decomposition parameters, and establishes an objective function according to the sum of the corresponding decomposition parameter differences. Furthermore, the paper searches for the distortion parameters by improving the particle swarm algorithm and takes the objective function value as the fitness of the particles. As a result, the MT galvanic distortion correction in which the regional structure is arbitrary in dimensions is realized. In addition, the paper proposes an MT galvanic distortion correction method that requires no assumption of the dimension of regional structure and has wider adaptability. Finally, the method is applied to calculate the three-dimensional model and filed data, and the results verify the effectiveness, correctness, and practicability of the method.