Dynamical space-time ray tracing and modified horizontal ray method

Abstract: The 'vertical modes and horizontal rays' method, commonly applied for simulating acoustic wave propagation in shallow water is advanced in this research. Our approach to this method involves the use of the so-called space-time rays, which are constructed by decomposing the time-dependent sound field into adiabatic vertical modes, the solutions to the Sturm-Liouville problem. The introduction of the time coordinate, while still considering it as an additional space coordinate instead of merely a parameter along the ray, allows us to describe the propagation of frequency-modulated signals in an effectively frequency-dispersive medium. The consideration of the extension of Hamiltonian ray-tracing methods (also used for the description of Gaussian beams and so-called quasiphotons) leads to a simple description of observable effects such as changes in modulation, time compression, differences between angles of phase and amplitude fronts, space-time caustics, etc., in dynamics - on the moving line or at some point of observation while having the general form of the source (for example, also a moving one).