大回线源瞬变电磁一维自适应反演方法及应用

The one-dimensional adaptive inversion method for large loop source TEM and its application

提出了一种适用于大回线源瞬变电磁法框内任意测点垂直Z分量的一维反演方法。该算法采用CMD正则化因子优化方案、光滑度函数和自然边界条件对反演过程进行了约束,减小了初值的依赖度,保证了反演过程的自主性和反演结果的稳定性;在反演过程中,在保证模型残差沿梯度下降的同时,对模型修正量的最大值进行了限制,使反演模型不易陷入局部极小,保证了反演结果全局的收敛性;同时反演的灵敏度矩阵采用牛顿法进行更新,减少了整个反演计算的工作量。最后通过五层的双低阻层模型、双高阻层模型和实测资料证明了该算法可靠。

A one-dimensional inversion method for the vertical Z component of any measuring point in the frame of the large loop source transient electromagnetic method is proposed in this paper. The algorithm uses the CMD regularization factor optimization scheme, smoothness function and natural boundary conditions to constrain the inversion process, reduce the initial value dependence, and ensure the autonomy of the inversion process and the stability of the inversion results. In the inversion process, while ensuring that the model residual decreases along the gradient, the maximum value of the model correction is limited, so that the inversion model is not easy to fall into the local minimum, which ensures the global convergence of the inversion results. The sensitivity matrix is updated by Newton's method, thus reducing the workload of the entire inversion calculation. Finally, the reliability of the algorithm is guaranteed by five-layer double low-resistance layer model, double high-resistance layer model and measured data.