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Observations and modeling of angular compression and vertical spatial coherence in sea surface forward scattering
1Applied Physics Laboratory and Department of Mechanical Engineering, University of Washington, 1013 NE 40th Street, Seattle, Washington 98105, USA. dahl@apl.washington.edu
The Journal of the Acoustical Society of America
|January 12, 2010
Summary
This study measured acoustic scattering from the sea surface, finding that downward sound refraction compresses the angular spread of scattered sound waves. This effect, termed angular compression, is quantified by a new parameter.
Area of Science:
- Ocean acoustics
- Wave scattering
- Underwater sound propagation
Background:
- Sea surface roughness significantly impacts acoustic signal coherence and angular spreading.
- Understanding these effects is crucial for sonar and underwater communication systems.
- Previous studies have explored scattering but often without considering sound speed profile effects.
Purpose of the Study:
- To measure and model the spatial coherence and angular spreading of forward-scattered acoustic signals from the sea surface.
- To investigate the influence of sea surface conditions and sound speed profiles on acoustic propagation.
- To quantify the phenomenon of angular compression caused by downward-refracting sound speed profiles.
Main Methods:
- Acoustic measurements using a vertical line array in 80m deep water off the New Jersey coast.
- Utilized a 14-20 kHz frequency range with a source at 40m depth and receiver array centered at 25m depth, 200m range.
- Analyzed data considering a downward-refracting sound speed profile and applying Snell's law for modeling.
Main Results:
- Measurements showed minimal influence of source-receiver bearing angle on spatial coherence and angular spreading.
- A downward-refracting sound speed profile was observed, significantly modifying the vertical angular spread.
- Observed and quantified 'angular compression,' where refraction reduces the angular variance of acoustic signals at the receiver.
Conclusions:
- Sea surface scattering effects on acoustic spatial coherence are measurable and modelable.
- Downward-refracting sound speed profiles lead to a reduction in angular spreading, termed angular compression.
- A new parameter is defined to quantify the angular compression effect, aiding in acoustic propagation modeling.
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