Horizontal array beamforming in an azimuthally anisotropic internal wave field.

Area of Science:

• Acoustic propagation
• Ocean acoustics
• Wave phenomena

Background:

• Shallow water waveguides with summer thermoclines are complex acoustic environments.
• Internal wave fields, composed of diffuse and localized components, perturb acoustic propagation.
• Acoustic beamforming performance is sensitive to environmental variability.

Purpose of the Study:

• To numerically investigate the impact of evolving internal wave fields on acoustic beamforming in a shallow water waveguide.
• To analyze the effects of source-receiver orientation relative to internal wave structures.
• To understand the mechanisms causing beamforming degradation.

Main Methods:

• Numerical simulation of acoustic beamforming on a horizontal array.
• Modeling of a time-evolving internal wave field with isotropic and anisotropic components.
• Analysis of beamforming output as a function of time and source-receiver orientation.
• Modal decomposition and phase speed analysis of the acoustic field.

Main Results:

• Source-receiver orientation significantly affects beamforming; alignment parallel to solitary wave crests causes beam wander, fading, splitting, and coherence loss.
• Horizontal refraction and time-dependent modal excitation contribute to beamforming effects.
• Effects are substantially reduced when the source-receiver is not parallel to wave crests, indicating azimuthal selectivity.
• Acoustic propagation is predominantly adiabatic when aligned with wave crests/troughs.

Conclusions:

• Localized internal wave packets can selectively perturb acoustic fields, impacting beamforming.
• The orientation of the acoustic array relative to internal wave structures is critical for maintaining beamforming performance.
• Understanding these interactions is crucial for effective underwater acoustic communication and sensing.