A comparison of two acoustic parabolic equation transmission loss models for compatibility with the Wavenumber Technique in the determination of source depth.

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Author
Blanchard, Joe Lane, II
Date
1984-03Advisor
Coppens, A.B.
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Show full item recordAbstract
The Brock version of the Split-Step Fast Fourier
Transform (SSFFT) and the Jeager version of the Implicit
Finite Difference (IFD) acoustic parabolic equation models
are compared with a Lloyd mirror interference pattern in the
range domain. The SSFFT displays the inability to place the
transmission loss nulls at the correct ranges. It is also
unable to utilize bottom loss information correctly. The
IFD produced nulls at the correct ranges; however, it
inserted an unacceptable amount of noise except when small
{1 m) vertical grid steps were used and the pressure release
bottom was placed at extended depths. In shallow water
cases, the IFD is able to properly represent the pressure
information. Each model is explored in the wavenumter
domain by use of a "Waver.u mber Technique" (WT) model with
emphasis on source depth determination. The source depth
may be deterained by measuring the distance between the
equally spaced nulls in the wavenumber representation.
Neither acoustic model was able to provide accurate source
depth information when the null spacings were compared to a
known source-depth determination carve. Since the null
spacings were not uniformly spaced, this was tc be expected.
Some specific problem areas in the models were identified by
the use of the WT.
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