### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 5pUW7. An efficient algorithm for calculating depth dependent modal phase
and for mode identification in normal-mode models based on the Airy equation.

**J. LeMond
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**
Robert A. Koch
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*Appl. Res. Labs., Univ. of Texas at Austin, Austin, TX 78713
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The underwater acoustic normal modes of multichannel environments may
exhibit closely spaced eigenvalues that require a fine horizontal wave-number
sample in models based on the Airy equation. Also, for broadband applications
the maximum frequency difference that permits accurate interpolation is limited
by the frequency difference of the modal depth functions. A straightforward and
numerically efficient algorithm to construct a monotonic depth-dependent phase
using the properties of the Airy functions is presented that significantly
reduces the computational burdens imposed by these constraints. The total phase
change of a mode across the depth of the waveguide gives the mode number,
modulo (pi), which is essential in adiabatic normal-mode calculations for range
variable environments because the acoustic field must be propagated from one
environment to the next mode by mode. [Work supported by the Advanced
Surveillance and Prediction System (ASAPS) Program of the Space and Naval
Warfare Systems Command (SPAWAR, PMW 181-14).]