INVESTIGATION OF NEAR-AXIAL INTERFERENCE EFFECTS FOR PROPAGATION IN A DUCTED WAVEGUIDE

Abstract

The observed time-of-arrival patterns from a number of long-range ocean acoustic propagation experiments show early geometrical-like arrivals followed by a crescendo of energy that propagates along the sound channel axis and is not resolved into individual arrivals. To describe in a simple model case the interference of near-axial waves which results in forming the so-called axial wave and propose formulas for the axial wave in more general cases, the two-dimensional reference point source problem for the parabolic index of refraction squared is investigated. Using the method proposed by V. Buldyrev, the integral representation for the exact solution is transformed in such a way to extract ray summands corresponding to rays radiated from the source at angles less than a certain angle, the axial wave, and a term corresponding to the sum of all the rays having launch angles greater than the indicated angle. Numerical results for the axial wave and the last term are obtained for parameters corresponding to long-range ocean acoustic propagation experiments.