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我们对速度横向适度变化的地区研究出一种偏移算法。该算法是相位移偏移算法的一个扩展。它利用一个变长度的空间变换。这个方法大大地减少所需的横向波数的数目去向下延拓数据,并且用一个简单的递归关系代替空间快速傅氏变换(FFT)。对某一个频率和位置x,一般只需10个横向波数就足够了,并且当速度结构v(x,z)在深度上是在几个厚度(△z)范围内变化,而横向速度梯度为1.9～1.0时,该偏移算法可产生精确的图象。
We have developed an offset algorithm for regions with moderately variable rates. The algorithm is an extension of the phase shift algorithm. It uses a variable-length spatial transform. This method greatly reduces the number of lateral wavenumbers needed to extend the data downwards and replaces the space fast Fourier transform (FFT) with a simple recursive relation. For a given frequency and position x, generally only 10 transverse wavenumbers are sufficient, and when the velocity structure v (x, z) varies in depth over several thicknesses (Δz) and the lateral velocity gradient is 1.9 ~ 1.0, the offset algorithm can produce accurate images.