Measurements of Wind Dependent Acoustic Transmission Loss in Shallow Water under Breaking Wave Conditions

Abstract

The enhancement of transmission loss induced by breaking waves in shallow water of 30 m depth, measured at a fixed 10 km-range under isothermal conditions rather depends on wind speed than on wave height. The attenuation coefficient, growing weakly at low wind speeds increases after a thresholdlike transition by the third to the fifth power of the wind speed, probably due to air bubble suspension. The transition wind speed around 10 m/s decreases with increasing frequency. The time lag between changing wind speed and attenuation is of the order of minutes. The loss differs at increasing and decreasing fetch. The close relation between wave height and attenuation at low sea states and predominating rough boundary scattering disappears at high sea states.