Normal modes in the ocean-sediment acoustic waveguide system at the New England Mud Patch

Area of Science:

• Ocean acoustics
• Geophysics
• Waveguide theory

Background:

• The New England Mud Patch (NEMP) features a mud layer over a sand-mud basement with an inverse-square sound speed profile.
• The ocean and sediment create a three-layer acoustic waveguide.

Purpose of the Study:

• Analyze the acoustic field within each layer of the NEMP waveguide.
• Investigate the modal solutions and characteristic equation for this specific acoustic environment.

Main Methods:

• Utilized spatial Fourier transforms over depth and horizontal range.
• Applied boundary conditions at the sea surface, seabed, and basement interface.
• Solved the transcendental characteristic equation for eigenvalues using the graphical bisection method.

Main Results:

• Identified eleven eigenvalues, each corresponding to a propagating normal mode.
• Demonstrated that the NEMP waveguide reduces to an inverted Pekeris waveguide in a limiting case.
• Showed the NEMP characteristic equation becomes identical to the Pekeris channel equation in this limit.

Conclusions:

• The study provides a detailed acoustic analysis of the NEMP waveguide.
• The findings confirm the waveguide's behavior and its relationship to the Pekeris channel.
• This research contributes to understanding acoustic propagation in complex marine environments.