Magnetic Field Downward Continuation Iterative Method Based on Low-pass Filter

Abstract

Abstract Magnetic field downward continuation is an important technique for expanding geomagnetic database, which can separate superimposed anomalies and enhance the resolution of local anomalies. However, the adaptability of the fixed filter operator of the existing downward continuation algorithm to the wavenumber domain frequency component of the observed data is not good enough, which leads to the poor applicability of the algorithm, resulting in poor applicability of the algorithm. The downward continuation iteration method based on a low-pass filter is proposed in this paper. First, the residual terms based on the remainder of the first and second vertical derivatives are constructed by using the stability of upward continuation; Secondly, the upward continuation low-pass filter operator, single parameter low-pass filter operator, and two-parameter low-pass filter operator are designed, and the effects of their filtering characteristics on the continuation stability are compared. At the same time, the cut-off frequency and order of the filter operator with parameters are optimized to update the iterative value. Simulation and experimental studies are carried out under different field source depths. Simulation results show that the convergence performance of this method is better when dealing with shallow source field, and the continuation accuracy is improved by 15%–25%. The stability and effectiveness of the magnetic field downward continuation method are verified by the measured data.