Does semiclassical ray theory work for megameter propagation?

Abstract

In the presence of internal waves, a very large number of rays connect any source to a distant receiver. The ray intensities vary by orders of magnitude, causing the scintillation index predicted by semiclassical ray theory to be very large. In this talk, possible diffractive effects at frequencies at or below 100 Hz are considered. One effect is caustics. A region where Airy functions must be used can be identified; if this region contains additional caustics, Airy functions do not suffice. This caustic region is identified and characterized from numerical ray-tracing simulations. The rays that are high intensity occur in narrow beams. The diffraction of these beams is estimated from the same numerical simulations. [Work supported by ONR.]