Acoustic scattering from partially buried cylinders: measurement, validation and interpretation using physical acoustics and finite element models

When attempting to detect and classify objects in an ocean environment, it has been shown that the surrounding environment, specifically the target’s deployment within that environment, greatly affects the measured acoustic response. While sea trials go a long ways towards extending the development of better classification systems, they are costly and ultimately only investigate the target at a handful of burial depths and ranges. There exists a need for robust models that can predict the target response with the required level of fidelity to result in positive classification outcomes. To accomplish this, however, reliable measurements and efficient models go hand-in-hand, one validating the other or vice versa. A specific example of this is presented here by examining the acoustic scattering from a solid cylinder in an ocean environment, partially buried with its axis at an oblique angle relative to the sand sediment. Plots of the measured target strength versus frequency and aspect angle reveal a number of interesting acoustic phenomena, some of which are explained using physical acoustics models. To help validate these measurements and offer further insight into the physical mechanisms involved, results
from a numerical hybrid model are presented. This model, based on Finite Element and Helmholtz Kirchhoff Integral methods, has previously shown success in predicting the response of proud and partially buried targets with axes parallel to the sand sediment. To help validate the use of the hybrid model in this non-symmetric environment, a controlled tank experiment was conducted using a scaled version of the solid cylinder, mounted next to an air-water interface. The comparison between the hybrid model and tank measurements exposes potential areas where higher order re-scattering effects may become important, and is the topic of the following talk by M. J. J. Nijhof.