A hybrid migration method , named " fourier finite - difference migration " , is a post - stack depth migration scheme . the downward extrapolation operator is split into three operators : one operator is a phase - shift operator for a chosen constant background velocity , another operator is the well - known first - order correction term , and the third operator is a finite - difference operator for the varying of the velocity function . phase - shift downward extrapolation and finite - difference downward extrapolation preserves the advantage of phase - shift method and finite - difference method 傅立葉有限差分(簡稱ffd )偏移算法是一種疊后深度偏移算法,其向下延拓算子是一種混合算子,包括三項(xiàng):一項(xiàng)是處理常速的相移算子,一項(xiàng)是一階相移修正算子,最后一項(xiàng)是類似45度方程的有限差分算子,用來處理劇烈橫向變速。