### ASA 124th Meeting New Orleans 1992 October

## 4aPA4. A phase screen approach to sound propagation through small-scale
turbulence.

**Xiao Di
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*Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677
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**Kenneth E. Gilbert
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*Penn State Univ., State College, PA 16804
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A Green's function method has recently been used to derive a fast
parabolic (PE) method for atmospheric sound propagation over a locally reacting
ground surface [K. E. Gilbert, X. Di, and C. You, J. Acoust. Soc. Am. 90,
2307(A) (1991)]. Because the algorithm can take range steps many wavelengths
long, it is approximately 100 times faster than existing PE algorithms that use
a Crank--Nicolson range step. In applying the fast PE method to propagation in
a turbulent atmosphere, however, one must somehow account for inhomogeneities
that are considerably smaller than the optimum range step of the PE. To avoid
losing the speed of the method by taking short-range steps, the use of
``integrated-turbulence'' phase screens has been investigated. On a given range
step, the phase screen method incorporates the integrated phase change due to
turbulence into a random phase factor that is applied at the end of the range
step. The objective is to use long range steps and still accurately account for
the effects of small-scale turbulence. Results from the phase screen approach
are compared to calculations based on a Crank--Nicolson method which accurately
accounts for small-scale turbulence by taking very short-range steps. A
theoretical and numerical analysis is given for the maximum range step one can
use with realistic models for atmospheric turbulence.