Milne method for downward continuation of gravity field

Downward continuation of gravity field can highlight the anomaly of the local and shallow part of the earth, and can separate the anomaly feature from the overlying field. But downward continuation is usually unstable, with shallow downward continuation depth and inaccurate result. To this end, this paper presents a Milne formula method for downward continuation of gravity field by using gravity field and its first-order vertical derivatives, and based on Simpson quadrature formula. The method is applied to the synthetic model. The synthetic result and the error curve show that compared with the fast Fourier transform downward continuation method and the integral iteration downward continuation method, the new method's depth of downward continuation is larger, the relative error is smaller, and the result is stable and accurate to the model. The method is applied to the downward continuation of the measured airborne gravity data of Nechako basin in Canada. The downward continuation result of this method can restore the original data accurately. And the result can reflect the tendency of the original anomaly and enhance the local and tiny anomaly.