Linear and parametric array transmission across a water–sand interface—Theory, experiment, and observation of beam displacement Available to Purchase

A series of measurements was made to investigate the effect of a water–sediment interface on the propagation of a bounded acoustic beam. The data obtained allowed mapping out of the sound‐pressure field in a homogeneous sand sample for 20‐kHz linear and parametric sources at several incident grazing angles. These results are compared with theoretical predictions calculated using the SAFARI model [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)]. The major results include: (1) absolute transmission levels and transmitted field structure; (2) demonstration that an attenuating liquid model of the sand sediment is adequate in theoretical modeling of the experiment and, as a by‐product, experimental testing of the SAFARI program; (3) the conditions under which one may determine the transmitted field structure due to a truncated parametric array source by use of an incident Gaussian beam and the characteristics of that beam; and (4) the beam displacement at and below critical angle. Regarding the issue of beam displacement, it is found that the angular spectrum of a narrow beam, not its parametric nature, is responsible for the beam displacement at the critical angle as measured here. It is also shown that, when examining beam displacement, care must be taken to establish how it will be determined.