Nonlinear Internal Gravity Waves (NIWs) significantly influence sound propagation in the ocean, particularly in shelfbreak areas. Variations in water depth and vertical stratification complicate acoustic transmission. To investigate these effects, Assistant Professor Tzu-Ting Chen and her research team integrated experimental data and simulations across multiple disciplines, including marine geology and geophysics (high-resolution bathymetry), underwater acoustics, and physical oceanography (NIWs). Their study analyzed sound propagation paths and intensities under the combined influence of shelfbreak and NIWs, with a particular focus on the oceanic whispering gallery effect—where sound waves follow curved paths and become “trapped,” similar to the architectural whispering gallery phenomenon.

The findings reveal that interactions between NIWs and the shelfbreak give rise to various acoustic phenomena, including horizontal refraction due to the sloping seabed, the horizontal Lloyd’s mirror effect, and three-dimensional sound ducting induced by internal waves. These effects were validated through acoustic experiment data collected in the South China Sea.

To further explore these phenomena, the research team employed a three-dimensional sound propagation model incorporating ray tracing and parabolic equation methods. This model predicts acoustic behavior under NIW and shelfbreak influences, offering key parameters to accurately forecast changes in sound propagation paths and intensities across different water masses.

This study underscores the significance of interdisciplinary integration across ocean acoustics, marine geology and geophysics, and physical oceanography. First, it enhances our understanding of internal waves in shelfbreak areas and their broad impact on horizontal sound propagation. Second, it highlights the importance of advanced three-dimensional acoustic models in refining experimental data interpretation, paving the way for improved acoustic observations and applications in ocean science.

This work was published in The Journal of the Acoustical Society of America:

Chen, T. T., Lin, Y. T., Chiu, L. Y. S., Siegmann, W. L. (2025). Observation and modeling of three-dimensional sound propagation along a nonlinear internal gravity wave at a shelfbreak. The Journal of the Acoustical Society of America, 157(2), 857-865. https://doi.org/10.1121/10.0035785

Figure 1 An illustration of the 3D sound duct formed by an NIW over a slope.