Study on the Characteristics of Sound Propagation in Shallow Underground by Air-Borne Sound

Recently, the importance of type-II dilatational waves generated by air-borne sound was recognized, because it is very useful in shallow underground imaging without making contact with the ground surface. To reconfirm the existence of this wave, the propagation time of air-borne sound in sand is measured using an acryl sand tank, condenser microphones and a loudspeaker. The experimental result shows the existence of this wave and the possibility of a non-contact method of shallow underground imaging.