Three-dimensional ambient noise modeling in a submarine canyon

Area of Science:

• Ocean Acoustics
• Underwater Noise Modeling

Background:

• Vertical noise coherence is crucial for understanding sound propagation in marine environments.
• Previous models often require complex computations for three-dimensional (3D) environments.

Purpose of the Study:

• To develop and validate a simplified quasi-analytical model for computing vertical noise coherence.
• To investigate the impact of bathymetry, specifically Gaussian canyons, on noise coherence.
• To compare different acoustic propagation models for noise coherence calculations.

Main Methods:

• Utilized a quasi-analytical 3D normal mode model for longitudinally invariant environments.
• Modified modal decomposition by excluding non-identical mode numbers to simplify calculations.
• Employed full 3D and Nx2D parabolic equation (PE) sound propagation models.
• Analyzed noise cross-spectral density and cross-modal amplitudes.

Main Results:

• A simplified normal mode model effectively computes vertical noise coherence.
• Gaussian canyon bathymetry can generate horizontally trapped modes.
• Parabolic equation models confirm the focusing effect of bathymetry on the noise field.
• Accounting for out-of-plane propagation increases absolute vertical noise coherence and shifts frequency zero-crossings.

Conclusions:

• The simplified normal mode model offers an efficient method for calculating vertical noise coherence.
• Bathymetry significantly influences underwater noise fields, particularly in canyon environments.
• Out-of-plane propagation is essential for accurate noise coherence predictions in complex ocean acoustics.