Pade approximation operator iterative method for potential field downward continuation

Abstract

Downward continuation (DWC) is an important method for potential field data processing that enhances the resolution of local anomalies. However, DWC is inherently unstable and can distort the true features of the potential field data. We derived different terms Pade approximation operators for the direct downward continuation operator in frequency domain, and proposed a Pade approximation operator iterative method for DWC. We analyzed the convergence of the proposed method, and then established a generalized difference ratio method to determine the optimal number of iterations. Test results on synthetic data showed that the proposed method can continue the potential field data downward to 20 grid units from the measured level. This method has higher accuracy compared to two other existing iterative methods. Additionally, the generalized difference ratio method could accurately determine an optimal number of iterations. According to theoretical analysis and the test, we demonstrated that the denominator of Pade approximation operator must be an even power function to ensure the stability of iterative process. We applied the proposed methods to a real data, the results showed that it can enhance the gravity anomalies generated by concealed orebody, and different approximation operators can achieve similar iterative results. When making the proposed method results continue upward to measured level, the obtained results have approximate distribution and amplitude with original anomaly.