## 5aUW4. Ray theory in mode models: Demonstration of high-frequency collective-mode interference effects.

### Session: Friday Morning, December 6

### Time: 8:40

**Author: Jason F. Manning**

**Location: Appl. Res. Labs., Univ. of Texas, Austin, TX 78713-8029**

**Author: Evan K. Westwood**

**Location: Appl. Res. Labs., Univ. of Texas, Austin, TX 78713-8029**

**Author: Eric Smith**

**Location: Appl. Res. Labs., Univ. of Texas, Austin, TX 78713-8029**

**Abstract:**

A number of acoustic reflection and refraction effects, normally associated
with ray theory, are used here as tests of a normal mode model in the
high-frequency limit, where the modes become dense in the complex wave-number
plane. The ray effects, which are associated with saddle points or branch line
integrals in the wave-number integration method, do not appear as
characteristics of any single mode in the modal solution. Rather, they emerge as
collective effects from the coherent addition of large numbers of modes. The
effects demonstrated include beam splitting at the Brewster angle for a
fluid--fluid interface and at the Rayleigh angle for a fluid--solid interface,
beam displacement near the critical angle for total reflection, and beam
spreading due to a fluid--solid lateral wave. Gaussian beams are modeled
efficiently using the ORCA normal mode model, by assigning complex values to the
source coordinates. This technique extends, in a full mode solution, methods
that have previously been implemented for Gaussian beams propagating in free
space [Deschamps, Electr. Lett. 7, 684 (1971)] and reflecting from single
interfaces [Ra et al., J. Appl. Math. 24, 396 (1973)]. [Work supported by the
U.S. Navy Office of Naval Research.]

ASA 132nd meeting - Hawaii, December 1996