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Restless rays, steady wave fronts
1CIRES, University of Colorado and NOAA/Earth System Research Laboratory, DSRC, Mail Code R/PSD99, 325 Broadway, Boulder, Colorado 80305-3328, USA. Oleg.Godin@noaa.gov
The Journal of the Acoustical Society of America
|February 6, 2008
Summary
Acoustic wave fronts remain stable over long distances despite ocean turbulence, unlike the individual sound rays. This stability is explained by wave mechanics and Fermat's principle, offering insights into underwater acoustics.
Area of Science:
- Ocean acoustics
- Wave propagation physics
- Geophysical fluid dynamics
Background:
- Underwater acoustic fields are affected by ocean internal gravity waves.
- Previous observations showed acoustic wave fronts are more stable than rays.
- Sound propagation in perturbed ocean environments is complex.
Purpose of the Study:
- To provide a theoretical explanation for the observed wave front stability in underwater acoustics.
- To analyze the behavior of acoustic rays in a medium with weak sound-speed perturbations.
- To elucidate the relationship between wave front stability and ray scattering.
Main Methods:
- Analytical investigation of acoustic wave propagation.
- Numerical simulations of long-range sound propagation.
- Application of Fermat's principle and dimensional analysis.
Main Results:
- Acoustic wave fronts exhibit greater stability than individual rays in perturbed ocean environments.
- Ray endpoints scatter primarily along the unperturbed wave front at specific propagation ranges.
- The ratio of ray displacement along and across the wave front increases with range relative to perturbation correlation length.
Conclusions:
- Wave front stability in weakly perturbed media is a consequence of wave mechanics, not ray mechanics.
- Fermat's principle and dimensional considerations offer a physical explanation for wave front stability.
- Understanding wave front stability is crucial for accurate long-range underwater acoustic modeling.
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