Abstract:

An analysis of the effects of ocean internal waves on long-range propagation is presented from a geometrical-optics point of view, and the validity of this ray-based approach is discussed. It is concluded that in the presence of internal waves, the observed depth diffusion of energy in the late-arriving portion of the timefront is primarily a result of refraction (not diffraction) due to chaotic rays. It is found that internal waves can cause a single eigenray to break up into several microrays having upper turning points spread 10 km horizontally and 100 m vertically, affecting the resolution of ocean acoustic tomography. The validity of ray-based, semi-classical waveforms to represent received arrivals is evaluated by comparing waveforms generated with parabolic-equation simulations: The semi-classical waveforms reproduce the correct arrival time and temporal shape of almost all arrivals, even those that are made of dozens of microrays induced by internal waves. [Work supported by ONR.]