Estimating Ocean Wind Wave Spectra by Means of Underwater Sound
NAVAL UNDERWATER SYSTEMS CENTER NEWPORT RI
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Measurements of the spectrum of ocean surface reradiated acoustic signals generated by an omnidirectional, sinusoidal source are used to estimate the ocean surface wave-height spectrum. Plane-wave physical optics theory is applied to a long-crested sea surface model to verify Marshs hypothesis that, for low sea states, the spectrum of acoustic waves reradiated by the rough moving sea surface consists of a specular component at the transmitted frequency and a scattered component which is the weighted surface wave-height spectrum. The approach employs theories by Parkins, Clay and Medwin, and Pierson. The weighting function applied to the surface spectrum depends on signal frequency, experimental geometry, and mean-square wave height. CW signals at 127 Hz and 1702 Hz were transmitted from fixed, omnidirectional sources to receivers 4.5 km and 41 km downrange. Additionally, wave height was monitored continuously by resistance wave staff. The time series records of sound pressure level and ocean wave height were analyzed for spectral content. Agreement between theory and experiment is good when the acoustic sideband levels are not more than 25 DB below the peak level of the specular component.
- Physical and Dynamic Oceanography