Effects on acoustics caused by ocean solitons, Part B: Acoustics

Abstract

Large amplitude internal solitary waves in the ocean can interfere with underwater acoustic signals. For certain acoustic parameters (source depth, receiver depth, and frequency) a redistribution of acoustical energy to higher-order acoustic modes can occur as the acoustic signal propagates through the solitary wave train. Depending on the ocean bottom composition, this can result in a significant loss in acoustical signal intensity. In order to simulate and understand this phenomena, it is necessary to generate a solitary wave train that is realistic and contains the spectral components that will interact with the acoustic signal. This requires a primitive equation nonhydrostatic ocean model. Part A [A.C. Warn-Varnas, S.A. Chin-Bing, D. King, J. Hawkins, K. Lamb, Effects on acoustics caused by ocean solitons: Part A. Oceanography, Nonlinear Anal., in press ( doi:10.1016/j.na.2009.02.104)] of this two-part article addressed that issue. In this work we use acoustic model simulations to demonstrate the mode linkage between the solitary wave train and the acoustic signal that can result in a large signal loss. Understanding the linkage allows for pre-examination of the solitary wave characteristics to determine if they could affect propagating acoustic signals. The procedure has the advantage that only a few computer runs are required from the ocean model and no lengthy computer runs are required from acoustic propagation models. Only a quick calculation of the acoustic mode eigenvalues is needed.