采样长度（sampling length）是指矿产取样时，每个样品沿矿体厚度或矿化变化最大方向的实际长度。
若采样长度与回转速度不吻合，将会出现伪周期，使主值函数项中提取周期成分后的信号失实。
If sampling length doesn't adapt rotative velocity, the results of calculation by FFT or periodogram analysis will lead to pseudo-periods, which distorts the principal value function terms.
该方法是将采样波形取绝对值，定义数据窗长度为半个周期。
It changes the sampling waves into absolute values and set half period as data window length.
用该方法实现弹性波正演模拟只要算子半长度取到4—6，每波长取3个采样点即可获得精度很高的波场值。
The operator half length takes to 4-6 and each wave length takes 3 sampling, then the precise wave field can be obtained.
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