Publications by authors named "Sean P Walstead"
Article Synopsis
- The study examines how sound scattered from the ocean surface can be inverted to analyze wave shapes during different wind conditions: low wind, mixed wind and swell, and stormy weather.
- It addresses the issue of unrealistic wave profiles by imposing a slope constraint on the inverted waves, which leads to accurate modeling primarily under low wind conditions.
- The research also finds that while the power spectral density of surface waves levels off at higher frequencies, the inversion technique can still provide insights into high frequency ocean wave components, although it struggles to yield realistic results in high wind scenarios due to the influence of bubbles and scattering.
Article Synopsis
- * The scintillation index (SI), which measures the variance in sound arrival intensity, increases with wind speed up to a saturation point of 0.5 at 0.5 mm rms roughness; an adjusted SI (SI*) is proposed to better reflect these variations.
- * Modeling of forward scattering across frequencies (50-2000 kHz) aligns well with measured data, revealing that intensity saturation occurs at lower wind speeds for higher frequencies and indicating that arrival time fluctuations are related to surface wave conditions.
Article Synopsis
- - Surface wave shapes are reconstructed using underwater acoustic signals, transmitted at a frequency of 300 kHz, which reflect off paddle-generated gravity waves in a wave tank.
- - An inverse processing algorithm, utilizing a broadband scattering model based on Kirchhoff's diffraction formula, successfully reconstructs 50 wave shapes across a 2.10 m span, with the process relying on the same signals for initial geometry estimates.
- - Comparison with ground-truth measurements from a high-speed camera shows that the reconstructed surfaces are more accurate within specific regions called Fresnel zones, where the method achieves roughly a quarter-wavelength resolution and greater confidence is built through overlapping zones from multiple receivers.
Surface wave shapes are determined by analyzing underwater reflected acoustic signals. The acoustic signals (of nominal frequency 200 kHz) are forward scattered from the underside of surface waves that are generated in a wave tank and scaled to model smooth ocean swell. An inverse processing algorithm is designed and implemented to reconstruct the surface displacement profiles of the waves over one complete period.
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