迭代法与FFT法位场向下延拓效果的比较

将水平观测面上的实测位场值，垂直投影至下部的延拓水平面上，作为该水平面上的位场初始值. 根据该水平面上的初始值，用快速傅里叶变换(FFT)的方法向上延拓计算观测面上的位场值. 用观测面上的实测值与计算值的差值，对延拓面上的位场值进行校正. 如此反复迭代，直至观测面上的实测值与计算值的差值小到可以忽略. 这种空间域的迭代法原理简单，不用解线性代数方程组，有较高的计算速度和良好的延拓效果. 本文用迭代法对模型数据和实际数据进行向下延拓，对比了迭代法与常规的FFT法在位场向下延拓中的效果，迭代法显著优于FFT法.

A comparison of effects between the iteration method and FFT for downward continuation of potential fields

The values of a potential field measured on a horizontal plane are projected on a lower horizontal plane to be continued as initial values of the field.With these initial values on the continuing horizontal plane,the potential field on the original plane is calculated using the Fast Fourier Transformation(FFT).A correction is then made in the potential field on the continuing plane based on the difference between the observed and calculated values of the potential field on the original plane.The process is iteratively repeated until the differences become negligible.The principle of this iteration method in space domain is very simple.It does not require solving algebraic equations and possesses a high computation speed with a reasonable accuracy.The downward continuations are made by the iteration method and the FFT for a model and practical data,respectively.The effect of the iteration method is much better than the FFT.