Acoustic scattering experiments and characteristics of targets buried in sediment

We use weak form solution of 2D-FE model to calculate the far field of axis-symmetric target buried under the floor based on the variational principle. Assumed that the incident acoustic wave is perpendicular to the symmetry axis of a target, we give: when buried depth remains unchanged and grazing angle changed by 1° interval, difference of scattering sound pressure level compared with that of normal incident is derived. The expression is related to frequency and grazing angle. In addition, if the grazing angle is constant and the buried depth changed with 0.1 m interval, difference of scattering sound pressure level compared with that of shallow burial condition is also given. The experimental results show that the transmitting property of inner fillings and circumferential waves around the surface are suitable for the buried targets, the strongest echo is obtained when the grazing angle equals 90°. Resonance scattering characteristics of buried elastic targets show similarity to that in free space. In the case of oblique incidence, change law of difference of sound pressure level is verified when the sound wave incident at large grazing angle. The results of this work can provide a way for detecting deeper buried targets when broadband and high-frequency sound waves incident.