Evan K. Westwood
Appl. Res. Labs., P.O. Box 8029, Univ. of Texas at Austin, Austin, TX 78713-8029
A method for including the lateral (or head) wave in a normal-mode propagation model [E. K. Westwood et al., J. Acoust. Soc. Am. 95, 2908(A) (1994)] for acoustoelastic ocean environments has been developed. The method consists of replacing the original lower half-space with a thick layer having a constant sound speed but a small gradient in attenuation. Below the attenuating layer, the new lower half-space is given parameters such that there is no mismatch at the half-space interface. As a result, (1) the branch point corresponding to the critical angle in the half-space is moved upward in the complex k plane (where k is horizontal wave number), (2) the Pekeris branch line integral is also moved upward such that it becomes negligible, and (3) modes appear in the complex k plane between the old and new branch points. The cost of introducing the thick layer is not great because Airy function solutions are used in each layer. Removal of the Pekeris branch line integral, in conjunction with including the leaky modes, makes the mode solution represent the complete acoustic field. [Work supported by the ARL Internal Research and Development Program.]