Introduction

Bellhop is a highly efficient ray tracing program, written in Fortran by Michael Porter as part of the Acoustic Toolbox (available at the website of the Ocean Acoustic Library). Bellhop is designed in order to perform two-dimensional acoustic ray tracing for a given sound speed profile $c(z)$ or a given sound speed field $c(r,z)$, in ocean waveguides with flat or variable absorbing boundaries. Output options include ray coordinates, travel time, amplitude, eigenrays, acoustic pressure or transmission loss (either coherent, incoherent or semi-coherent). The calculation of acoustic pressure is based on the theory of Gaussian beams [1,2], which can be applied using different approximations, namely:

• geometric beams (the default option) [3];
• beams with ray-centered coordinates;
• beams with Cartesian coordinates;
• Gaussian ray bundless approximation [4].

This description is intended to those working in Ocean Acoustics, interested in using Bellhop for particular applications. In the sections that will follow we are going to discuss briefly how to get and install the model, the equations that it solves, and to illustrate Bellhop capabilities through a set of examples.