The parabolic wave equation (PE) code of Rosenberg [J. Acoust. Soc. Am. 105, 144–153 (1999)] is used as a benchmark to study acoustic propagation in an ocean waveguide with a rough air/water interface. The PE results allow a close examination of the ability of a ray code [i.e., Gaussian RAy Bundle (GRAB)] to accurately estimate coherent field propagation using a coherent reflection coefficient derived from scattering theory. Comparison with PE implies that the Beckmann–Spizzichino model, as given within the GRAB software package, does not give accurate predictions of the coherent field at long ranges. Three other coherent reflection coefficient approximations are tested: the perturbation, the small slope, and the Kirchhoff approximations. The small slope approximation is the most accurate of the models tested. However, the Kirchhoff approximation is perhaps accurate enough for some purposes and would be simpler to implement as a module within GRAB.

1.
A. P.
Rosenberg
, “
A new rough surface parabolic equation program for computing low-frequency acoustic forward scattering from the ocean surface
,”
J. Acoust. Soc. Am.
105
,
144
153
(
1999
).
2.
H.
Weinberg
and
R. E.
Keenan
, “
Gaussian ray bundles for modeling high-frequency propagation loss under shallow-water conditions
,”
J. Acoust. Soc. Am.
100
,
1421
1431
(
1996
).
3.
M. D.
Collins
, “
A split-step Padé solution for the parabolic equation method
,”
J. Acoust. Soc. Am.
93
,
1736
1742
(
1993
).
4.
F. S. Henyey, D. Tang, S. A. Reynolds, and E. I. Thorsos, “Vertical modes with sediment absorption in general shallow water waveguides,” submitted to J. Acoust. Soc. Am.
5.
E. I.
Thorsos
, “
Acoustic scattering from a ‘Pierson-Moskowitz’ sea surface
,”
J. Acoust. Soc. Am.
88
,
335
349
(
1990
).
6.
E. I.
Thorsos
, “
The validity of the Kirchhoff approximation for rough surface scattering using a Gaussian roughness spectrum
,”
J. Acoust. Soc. Am.
83
,
78
92
(
1988
).
7.
E. I.
Thorsos
and
S. L.
Broschat
, “
An investigation of the small slope approximation for scattering from rough surfaces. Part I. Theory
,”
J. Acoust. Soc. Am.
97
,
2082
2093
(
1995
).
8.
S. L.
Broschat
and
E. I.
Thorsos
, “
An investigation of the small slope approximation for scattering from rough surfaces. Part II. Numerical studies
,”
J. Acoust. Soc. Am.
101
,
2615
2625
(
1997
).
9.
W. A.
Kuperman
, “
Coherent component of specular reflection and transmission at a randomly rough two-fluid interface
,”
J. Acoust. Soc. Am.
58
,
365
370
(
1975
).
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