An ocean acoustical ray-tracing tool based on Fermat's least time principle in real a environment

Abstract

Recently the Underwater Acoustics Modelling and Sonar Prediction - SeaRider tool was developed by the Portuguese Naval Academy. Based on Fermat's least-time principle, 2D and 3D models of propagation of acoustic rays in the ocean were developed. These models consist of an algebraic differential system of equations. In this work we considered additionally the possibility of calculating the trajectory, addressing the occurrence of acoustic ray reflections either on the water surface or on the ocean floor. The reflections in the boundaries were assumed specular and were modelled based on Snell's law. We also considered the possibility of calculating the trajectories, taking into account the actual data of the speed of sound in the ocean as well as the bathymetry of the bottom. For this purpose, the 2D and 3D ocean-acoustic ray tracing developed can use existing data bases (GEBCO, NOAA, WOD18 and TEOS-10), extracting information onthe topography and climatology to compute the acoustic ray trajectories in a real environment. This tool allows us, for example, to identify positions of ecosystems subjects to the effects of different sources of noise. The developed algorithms were submitted to several numerical simulations and compared with other ocean-acoustic modelling programs.