A comparison of benchmark acoustic scattering solutions with tank experiments on buried and partially buried spheres

Abstract

Predicting the scattering response of objects near boundaries is of growing interest in underwater acoustics, especially when these objects are buried. Standard propagation models suggest that burial in fast attenuating ocean bottoms can seriously retard efforts to find such objects with high-frequency imaging sonar because of the need to operate at close range to overcome loss in the backscattered signal strength, resulting in low search rates. However, recent observations of anomalous sound transmission at shallow grazing angles as well as anomalous long-range detections of buried objects call into question standard assumptions made in regard to the modeling of sound transmission through the water/sediment interface. The present work investigates the breakdown of these assumptions for the scattering problem by comparing laboratory measurements conducted in the NRL Shallow Water Laboratory with predictions of exact scattering solutions for simple targets at various degrees of burial. Scattering data collected recently for a 60-cm-diam. spherical steel shell is used in the investigation. A discussion of the agreement between theory and measurements, features of special interest, and the consequences to our understanding of the acoustics of buried objects is given. [Work supported by ONR.]