### ASA 125th Meeting Ottawa 1993 May

## 2pUW4. Modeling global-scale three-dimensional sound propagation in the
ocean with the parabolic equation method.

**Michael D. Collins
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B. Edward McDonald
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W. A. Kuperman
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*Naval Res. Lab., Washington, DC 20375
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**Kevin D. Heaney
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*Planning Systems, Inc., McLean, VA 22102
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The parabolic equation (PE) method is efficient for solving
range-dependent sound propagation problems, including relatively small-scale
three-dimensional problems. Global-scale three-dimensional problems are well
beyond current computer resources because the size of the computational grid
increases with range. The adiabatic normal mode approximation, which ignores
the effects of mode coupling, is applied to reduce problems of this class to a
practical size. Each of the complex modal coefficients is a function of
longitude and latitude and is determined by solving a two-dimensional PE. The
wave number appearing in the PE, which is a function of longitude and latitude,
corresponds to the modal eigenvalue. An interesting description of global-scale
three-dimensional propagation can be obtained by solving this two-dimensional
problem for a small number of modes. This approach is orders of magnitude
faster than the three-dimensional PE even when all of the modes are considered.
This model should be applicable to analyzing results from global-scale
experiments such as the Perth to Bermuda transmissions [J. Acoust. Soc. Am. 71,
51--60 (1982)] and the Heard Island Feasibility Test [Baggeroer and Munk, Phys.
Today 45(9), 22--30 (1992)].