Acoustic wavefront tracing in range-dependent ocean

It has been established experimentally and confirmed by numerical simulations that early arrivals of acoustic waves at long-range propagation in a deep ocean are stable and identifiable despite strong perturbations of the ray paths due to sound-speed fluctuations primarily induced by internal gravity waves. It is wavefronts rather than rays that are typically observed in underwater acoustic experiments. Wavefronts are much more stable with respect to environmental perturbations than individual rays, which form the wavefronts. The relative stability of the wavefronts takes place because scattering of the end points of rays resulting from weak environmental perturbations occurs primarily along wavefronts of the unperturbed wave with the same travel time [O. A. Godin, J. Acoust. Soc. Am. 122, 3353–3363 (2007)]. When wavefronts are much more stable than rays, the traditional approach, which relies on ray tracing to determine wavefronts' position, may be counterproductive and sometimes misleading, especially for highly structured environments such as the ocean with internal waves and “spice.” This paper presents an efficient numerical technique for modeling acoustic wavefronts and timefronts in range-dependent ocean without solving ray equations. The acoustic wavefront tracing code has been benchmarked using analytic solutions of the eikonal equation. [Work supported by ONR.]