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当平均速度随深度变化时,可以利用正常时差来区别基本反射和多次反射。正常时差的近似值是利用一个平均速度公式求得的,但是这种值通常都太大。误差的出现是受剖面层速度标准偏差与平均速度的比率所控制。射线轨迹法得出的正常时差值更符合于实际一些。地层倾角增大时,由共反射点法所得迭加道并不代表倾斜地层的同一地段。如果不同的反射带均在同一倾斜平面上,它们就可以同相相加,并装作反射时间如从平面上的一点得来。
When the average speed varies with depth, the normal time difference can be used to distinguish the basic and multiple reflections. The approximate value of normal time difference is obtained using an average speed formula, but this value is usually too large. The occurrence of errors is governed by the ratio of standard deviation of layer velocity to average velocity. The normal time difference obtained by the ray trace method is more in line with the actual number. When the dip of the strata is increased, the superimposed trace obtained by the common reflection point method does not represent the same section of the inclined stratum. If different reflection bands are on the same inclined plane, they can be added in-phase and fitted for a reflection time as if from a flat point.