Simulators and methods for simulating an acoustic field of an acoustic waveguide are provided. A sound speed profile of the acoustic waveguide is generated, where the acoustic waveguide has a region of a first fluid within a second fluid, and the first fluid has a different acoustic index of refraction than the second fluid. The sound speed profile and predetermined parameters of a sound source and a receiver are applied to a parabolic equation (PE) model of sound propagation in the acoustic waveguide. The acoustic field of the acoustic waveguide is determined from the PE model. The acoustic field includes an interference pattern from interference between an acoustic signal of the acoustic source and at least one signal refracted by the region of the second fluid.