Bottom attenuation estimation using sound intensity fluctuations due to mode coupling by nonlinear internal waves in...

Area of Science:

• Underwater acoustics
• Oceanography

Background:

• Shallow water environments present complex acoustic propagation challenges.
• Nonlinear internal waves (NIWs) significantly impact underwater sound fields.
• Previous studies have explored acoustic propagation in dynamic ocean conditions.

Purpose of the Study:

• To analyze low-frequency acoustic signal fluctuations in shallow water during the Shallow Water 2006 experiment.
• To investigate the effects of nonlinear internal waves (NIWs) on acoustic signal characteristics.
• To determine the potential for estimating bottom sediment attenuation from acoustic data.

Main Methods:

• Analysis of low-frequency (300 ± 30 Hz) acoustic signals recorded by a vertical line array.
• Examination of signal propagation in the presence of a nonlinear internal wave train.
• Spectral analysis of sound intensity fluctuations to identify mode coupling phenomena.

Main Results:

• Observed peaks in the sound intensity fluctuation spectrum indicate coupling of propagating acoustic modes.
• The angle between the NIW front and the acoustic track was approximately 10°.
• Analysis across different hydrophone depths provided insights into acoustic attenuation.

Conclusions:

• Nonlinear internal waves induce mode coupling in shallow water acoustics.
• Acoustic spectral analysis can be utilized to estimate attenuation in bottom sediments.
• The Shallow Water 2006 experiment provided valuable data for understanding acoustic-wave interactions.