### ASA 126th Meeting Denver 1993 October 4-8

## 5aPA6. Comparisons of experimental measurements of sound propagation over
a hill and the polar parabolic equation method.

**Chulsso You
Henry E. Bass
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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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The polar parabolic equation (POPE) method, which introduces the boundary
fitting coordinates into the parabolic equation (PE) method, was developed to
solve for sound propagation over a curved surface and over irregular terrain
(hills) [X. Di et al., J. Acoust. Soc. Am. 92, 2431 (A) (1992)]. POPE can
include realistic sound-speed profiles and ground impedance. Predictions based
upon the POPE have been compared to measurements at the JAPE 91 (Joint Acoustic
Propagation Experiment) terrain masking experiment at White Sands Missile
Range, New Mexico during the period 27--28 July 1991. The sound sources were
hovering helicopters at the base of a hill and far away from the hill. In the
JAPE data, the relative sound pressure level decreases rapidly from the top of
the hill and becomes nearly constant along the base of the hill. This
characteristic feature is well predicted by the polar parabolic equation
calculations. POPE method appears to be an accurate means for predicting sound
propagation over realistic terrain.