地声直达波干扰的速度域滤波

On Improving Accuracy of Acoustic Detection of Underground Objects

在浅地层地下物体的声波探测中，沿地表层传播的声直达波干扰是影响探测结果的主要因素之一．传统的频谱分析、解术积等方法很难将它与目标反射波分离。利用直达波与目标反射波视速度的差别，在速度域对其滤波，减小了直达波的干扰，提高了目标反射波的信噪比，解决了浅地层声波探测中反射波信号的提取问题。

Interference of acoustic direct wave coming from sound source makes accurate determination of underground conditions with acoustic waves difficult. We present now our researchresults on how to eliminate as much as possible the effect of such interference. The elimination of interference is expected to be achieved through making use of the difference betweenthe apparent velocity of direct wave and that of reflected wave. Eq. (6) can be used to compute 2- dimensional spectrum of acoustic wave in order to obtain f-k plane. With f-k plane established, we design filter using eqs. (if) and (12), whose parameters depend on the spacecoordinates of sound source, underground objects and receiving array.We achieved preliminary success with our method. We applied our method to determinethe depth of a Han dynasty tomb near Xi'an. Fig. 4(a) was obtained without using our filter;the reflected waves are hard to discern. Fig. 4(b) was obtained through processing with ourfilter ; the reflected waves of ChannelS 12 to 15 are easy to detect. We determined the depthof the tomb to be sin, which agrees with the actual depth discovered by excavation.