Fast 3D nonlinear inversion method for airborne electromagnetic exploration

This paper presents an efficient three-dimensional nonlinear inversion method for airborne electromagnetic exploration. The stabilized biconjugate-gradient fast Fourier transform (BCGS-FFT) is used as the forward solver, and the distorted Born iterative method (DBIM) combined with the conjugate-gradient iterative solver is utilized in the inversion. Because of the usage of the FFT algorithm and the recursive matrix method combined with an interpolation technique to evaluate the layered media Greens functions rapidly, this method is highly efficient, and requires very low time and memory, O(NlogN) and O(N) respectively. Numerical examples for both 3D forward modeling and conductivity inversion are presented to show the accuracy and efficiency of the method.