Reverberation clutter induced by nonlinear internal waves in shallow water

Area of Science:

• Ocean Acoustics
• Environmental Acoustics
• Signal Processing

Background:

• Acoustic clutter and false alarms are significant challenges in active sonar operations, particularly in complex shallow-water environments.
• Reverberation signals, which are echoes from the environment, can mimic target echoes, leading to misinterpretations.

Purpose of the Study:

• To investigate the cause of target-like clutter observed in shallow-water active sonar reverberation.
• To determine if nonlinear internal waves can generate acoustic signatures that resemble actual targets.

Main Methods:

• Modeled a nonlinear internal wave using measured oceanographic data from the New Jersey shelf.
• Numerically simulated acoustic reverberation in the presence of the modeled internal wave.
• Analyzed the acoustic energy propagation, deflection, and backscattering characteristics.

Main Results:

• Nonlinear internal waves can cause target-like clutter in shallow-water reverberation signals.
• Acoustic energy is deflected by the internal wave into the seabed, resulting in strong, higher-angle backscatter.
• This clutter can be more than 10 dB above the mean reverberation level, creating a distinct target-like signature.

Conclusions:

• Nonlinear internal waves are a significant source of false alarms in active sonar due to the generated target-like clutter.
• Understanding these acoustic interactions is crucial for improving sonar performance and reducing false alarm rates in shallow-water environments.