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

Abstract

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.