Extremely shallow underground imaging using optimum frequency range method.

Abstract

We propose a method of distinguishing a buried object using the optimum frequency response range corresponding to the vibration velocity. Air-borne sound and a scanning laser Doppler vibrometer are used for noncontact acoustic imaging in the extremely shallow underground. Flat speakers that have a sharp directivity are used as vibration sources. Plastic container, hollow steel can, unglazed pot, and stone are used as buried objects and they are buried in the sand about 2 cm deep. First, noise waves are used for the confirmation of the buried object’s frequency response range. The ground surface imaging result by scanning laser Doppler vibrometer is used to confirm the position of the buried objects. To confirm the frequency range, the difference of the vibration velocities is used. Next, burst waves are emitted again to make a clear image. The frequency of the burst waves is set near the frequency response range. Finally, the buried object’s frequency response range is checked again the same way. The clear image is made by using the optimum frequency. From the indoor experimental results, we confirmed the frequency response range of each buried objects and the effectiveness of our proposed method.