位场曲化平的插值-迭代法

将起伏曲面B上的位场向下延拓至曲面最低点的平面A的插值-迭代法步骤是：1）将曲面B上的场值放置在水平面A上具有相同水平坐标的点上，作为A上的初值；2）用若干水平面切割B，从A的初值，用快速傅里叶变换法(FFT)向上延拓出这些平面的场值，用插值的方法从这些平面的场值计算曲面B的场值；3）根据B上的实测值与计算值的差值，对A上的值进行加权改正；4）重复步骤2）和3），直到B上的差值小到可以忽略.这种插值-迭代法具有高的计算速度，比通常的FFT法延拓得更深，可以超过10倍点距.文中给出计算实例.

The interpolation-iteration method for potential field continuation from undulating surface to plane

The interpolation-iteration procedure of downward continuation from the undulating surface B to the horizontal plane A that below the lowest point of B is:(1) choose the initial potential field value at each point on the plane A as the observed one on the surface B at the point with the same horizontal coordinates;(2) intersect the surface B with several planes and obtain the field values on these planes by upward continuing the fields on A using the FFT technique,then the fields on the surface B can be interpolated from the fields on these planes;(3) the new field values on A are then obtained by adding the initial values and the weighted difference between the observed and the calculated field values on B;(4) repeat steps(2) and(3) until the difference becomes negligible.The interpolation-iterative continuation method possesses a higher computation speed and can stably downward continue data to a much deeper depth than using standard FFT techniques,up a depth equal to more than 10 times the grid interval.A test example for real survey data is given.