Physical Modeling of Underwater Acoustics

Abstract

With 17 FiguresIn the attempt to explain underwater acoustic phenomena and to exploit these phenomena in useful ways a number of techniques for analysis have been developed. These include, but are not limited to, mathematical analysis, numerical modeling, in situ empirical description, and physical modeling. All have made substantial contributions to our understanding of the WQy in which sound behaves in water. The purpose of this chapter is to review the methods and results of physical modeling and to discuss its role in underwater acoustic research. To do this an attempt will be made to define the technique and to set in perspective its rel~tionship to the other methods of analysis. Some attention will be paid to the use of small natural bodies of water, lakes and bays, for example, as model facilities. However, the main thrust of the discussion will be concerned with artificially constructed model tanks and particularly with the study of surface scattering in such facilities. Physical model research has been conducted for some time in a number of contexts. Unfortunately, until the present there has been little communication among various investigators on matters of technique. By discussing the development of physical model experimental methods and illustrating the degree of precision and flexibility possible in model tanks this chapter seeks to encourage and facilitate a more widespread and systematic employment of physical modeling in future underwater acoustic research. Background Information Definition and PurposePhysical modeling in this context refers to the empirical investigation of underwater acoustic phenomena in physical situations other than the ocean. This somewhat imprecise definition is intended to include acoustic experimentation in water tanks, lakes, bays and so forth; physical environments which, by virtue of their stability, convenience and flexibility, provide the experimenter with opportunities for precision, repeatability, and economy not normally available in ocean experimentation. Physical modeling is, in general, useful for two broad classes of application. The first, and probably more significant of these roles is in the validation of analyt-J. A. DeSanto (ed.), Ocean Acoustics

Scattering from a rough interface

“…Fourth, our multiple scatter result (curve d) works well for large roughness whereas the single scatter theories fail for one reason or another. We should also note that there is a great deal of scatter within these and other [Zornig, 1979] data, and the data results we chose roughly bracket this data scatter. For the specific case where the surface was constructed to agree with our theoretical assumption of a Gaussian distribution [Numrich, 1979]…”