Wave-wave interactions and deep ocean acoustics

Area of Science:

• Oceanography
• Acoustics
• Geophysics

Background:

• Deep ocean acoustics are influenced by surface processes, particularly non-linear surface wave interactions.
• The Longuet-Higgins mechanism is a key source of acoustic signals in the 0.1 to 10 Hz range.

Purpose of the Study:

• To derive the spectral matrix of pressure and vector velocity near the ocean bottom.
• To investigate the effects of an elastic half-space bottom on acoustic propagation.
• To test a weaker form of the standing wave approximation for deep ocean environments.

Main Methods:

• Derivation of the spectral matrix for pressure and vector velocity.
• Application of a weak standing wave approximation.
• Numerical calculations incorporating bottom effects.
• Comparison of theoretical predictions with observatory data.

Main Results:

• The spectral matrix ratios are universal constants in the absence of a bottom.
• A weaker standing wave approximation holds, independent of the surface wave spectrum but dependent on frequency and environment.
• Observed data from the Hawaii-2 Observatory show excellent agreement with the theory between 0.1 and 1 Hz.

Conclusions:

• The derived acoustic model accurately describes deep ocean sound propagation influenced by surface waves.
• The weak standing wave approximation provides a viable method for analyzing acoustic data in complex environments.
• Observatory data support the theoretical framework, highlighting the dominance of surface wave-generated noise in deep ocean acoustics.