Modelling Wind Dependent Acoustic Transmission Loss due to Bubbles in Shallow Water
The acoustic transmission loss data from 1 to 8 kHz reported by Wille et al. (preceding paper) over a wide range of windspeeds in shallow water of 30 m depth exhibits a significant loss component which is attributed to bubbles. Indeed, the standard loss mechanisms, losses due to spreading, medium attenuation, bottom absorption and rough surface scattering are not sufficient to explain the data. Hence an absorbing layer of bubbles beneath the sea surface is additionally included into a stochastic ray-tracing routine to model the transmission loss. From the fitted attenuation coefficients a bubble density is estimated with a slope of -3.5 versus bubble radius which is in agreement with literature. In an intermediate range of windspeeds and waveheights the attenuation due to rough sea surface scattering is of equal importance to the transmission loss as the attenuation by bubbles, while at sufficiently high windspeeds the transmission loss is rather insensitive to the significant waveheight which is also observed in the measured data.
An extrapolation to 120 m waterdepth yields basically the same results, except for the insensitivity of the TL to waveheight at high windspeeds.
KeywordsTransmission Loss Bubble Radius Underwater Acoustics Bubble Density Bottom Absorption
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