首波（head wave）产生于当入射角等于临界角时，透射线将沿着分界面以第二介质的速度滑行，形成首波。
研究结果表明，该区不同界面的首波和反射波具有不同的特征。
The result shows that the head waves and reflected waves from different interfaces in this region possess different characteristics.
用全波列记录，不仅可以确定首波的慢度，也可以确定后续波的慢度。
With full-waveform recording, it is possible to determine the slowness not only of the first arrival but also of later arrivals.
在慢速地层中偶极横波测井不能很好地压制纵波，致使横波首波的检测存在一定的难度。
Since P-Wave can not be suppressed in dipole shear wave log in slow formation, there are some difficulties in picking the first S-Wave arrival.
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