A High-frequency Approximation Criterion for Deep-sea Sound Field

Abstract Ray theory is widely used in deep-sea sound propagation problems due to its clear physical meaning and concise expressions. The classical high-frequency approximation assumption ( f >10 c / H , where f is the sound frequency, c is the sound speed, and H is the water depth) is often used to determine whether the ray theory is applicable. However, although this classic criterion is simple, it may not be precise enough when dealing with very low frequency ( f <100 Hz) sound propagation problems. To overcome this problem, the curve-fitting goodness index is introduced to compare the differences between normal mode theory and ray theory in calculating distance, time delay, and group velocity. Then, an evaluation criterion was proposed. This criterion is more accurate than the classical one in judging the strong and weak frequency dependence of the sound field and is suitable for any environment. It can be approximated as a high-frequency limit for ray theory.