Nonlinear multi-layer equivalent source continuation method in strong magnetic fields

Conventional total magnetic intensity (TMI) anomaly continuation typically approximate the difference between the measured total magnetic field and the main field modulus as the projection of the magnetic vector in the direction of the main field. However, in regions with high TMI anomaly amplitudes, using conventional linear approximation multi-layer equivalent source models results in significant continuation errors. This paper presents a nonlinear multi-layer equivalent source method for magnetic anomaly continuation, which utilizes an iterative technique. The technique begins by analyzing the physical significance of the magnetic anomaly modulus and subsequently constructs the model based on this interpretation. The iterative process is optimized using an adaptive conjugate gradient method. The findings demonstrate that, in high-amplitude areas, the differences in TMI anomaly modulus and approximate projections need to be taken into account. Moreover, the method proposed in this paper enhances continuation accuracy, with its accuracy advantage becoming more pronounced as the continuation distance increases.