Enhanced backscattering in water by partially exposed cylinders at free surfaces associated with an acoustic Franz wave (L)

摘要

When a smooth curved object is lowered into water, the initial specular contribution to high frequency backscattering of sound is weak before the specular point on the object becomes illuminated by incident sound. The associated transition in reflection from a metallic cylinder viewed at grazing incidence was previously studied [Baik and Marston, IEEE J. Ocean. Eng. 33, 386–396 (2008)]. The present research involves analogous measurements of backscattering performed using short tone bursts facilitating improved temporal resolution of distinct mechanisms contributing to the backscattering. The measurements reveal the presence of a delayed contribution to the backscattering that evolves in time in a way consistent with a scattering contribution of an acoustic Franz wave. The wave appears to be partially reflected at the free surface after having been excited on the cylinder by the incident acoustic wave. For slightly exposed cylinders viewed at grazing incidence, the Franz wave mechanism dominated the observed backscattering.