Three-dimensional propagation effects: Modeling, observations, and suggested benchmark cases

Abstract

Over the past several years, many acoustic propagation models have been adapted to compute the influence of azimuthal coupling. These so-called three-dimensional (3-D) models should provide more accurate predictions of the acoustic field in 3-D variable environments than previous 2-D×N models. However, such advanced 3-D propagation models are generally slower than their 2-D×N predecessors. It is, therefore, important to understand the significance of the difference between 3-D and 2-D×N and when such effects should be considered. Furthermore, as of this date, no formal set of benchmark cases and solutions has been defined to test the accuracy of the various 3-D models currently being used. This paper will provide a general overview of 3-D propagation models and how they can be used to assess the significance of azimuthal coupling in ocean acoustics. Specific examples of such influences will be provided from a 3-D parabolic equation model and compared to results from the corresponding 2-D×N version. Of particular interest will be the pseudo-3-D effects predicted by 2-D×N calculations and the ability to distinguish true 3-D effects in experimental data. Finally, several environmental scenarios will be suggested as possible benchmark cases for future studies. [Work sponsored by ONR Code 321OA.]