An airborne broadband acoustic method to measure the characteristics of a dynamically rough, air‐water interface.

Abstract

An acoustic method to measure the characteristics of a dynamically rough interface is presented. The theoretical foundation for this method has been adapted from outdoor sound propagation research whereby the boundary roughness is represented by an effective admittance. This model is used to calculate the excess attenuation of a broadband pulse emitted at near grazing incidence by a point source over a dynamically rough air‐water interface. The excess attenuation is compared to that measured with an array of microphones. The effects of the water surface pattern on the recorded excess attenuation spectrum and its relation to the spatial correlation function for the dynamically rough interface are then analyzed. A Newton–Raphson root finding method is used to determine the acoustic admittance from the measured excess attenuation data in the frequency range between 0 and 20 kHz. The relationship between the mean roughness height, its standard deviation, and the real and imaginary parts of the admittance are obtained.