Twinkling of underwater sound reflected by one realization from a Gaussian spectrum population of corrugated surfaces: Experiments and comparisons with a catastrophe theory approximation

xperimental and numerical investigations were carried out on sound in water reflected from a single realization of a population of Gaussian spectrum random rough surfaces. These investigations used ultrasound of various frequencies and pulse lengths to study a predicted scaling of intensity moments with frequency. The high-frequency scaling of the moments is a consequence of the caustics in the reflected wavefield. The resulting spatial fluctuations of the intensity are analogous to the scintillations or twinkling of light resulting from focusing and defocusing within the atmosphere.;The surface properties (rms height and correlation length) are such that the Kirchhoff approximation may be used to calculate the reflected wavefield. Relevant conceptual tools and results from the branch of mathematics known as catastrophe theory are used to classify the types of contributions one expects as well as providing the scattered pressure amplitude for a given caustic. Catastrophe theory also provides the scaling properties of the intensity moments.;The theoretical prediction that the second moment of intensity has a logarithmic dependence on the wave number is confirmed. The prediction that the third through the fifth moments depend upon the wave number in a manner as...