Non-negative intensity for target strength identification in marine ecosystem research

• Published in: Journal of Theoretical and Computational Acoustics
• Main Authors: Liu, Daipei, Marburg, Stefffen, Kessissoglou, Nicole
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: World Scientific 2022
• Subjects: Antarc*; Antarctic; Antarctic Krill
• Online Access: http://hdl.handle.net/1959.4/unsworks_77926; https://unsworks.unsw.edu.au/bitstreams/7045949b-8c5a-4f2e-b0a7-f0e0dbe5c419/download; https://doi.org/10.1142/S2591728521500237

We propose non-negative intensity (NNI) as an alternative intensity-based technique for target strength identification in marine ecosystem research. NNI identifies local surface regions of a body with positive-only sound power contributions. In this study, NNI is employed for sound scattering by fluid-loaded, fluid-filled elastic structures with weak scattering boundary conditions. Three numerical case studies are presented for which fully coupled fluid-structure interaction models based on the finite element method (FEM) and the boundary element method (BEM) are developed. To validate the three-way coupling between the structural and fluid domains, an elastic shell submerged in water and filled with different internal fluids is initially considered. Results for the scattered acoustic intensity obtained numerically are compared with analytical results from the literature. Models representing Antarctic krill of simple and complex geometry are developed. A 3×3 cylinder array representing a simplified aggregation of krill is also presented. Target strength is calculated using both the scattered intensity and NNI for different incident excitation angles. Results for NNI identify the surface regions of an individual organism or group of organisms with the greatest contribution to the scattered sound at the target strength locations.