Effect of Inhomogeneous Sub-Bottom Layering on Broadband Acoustic Propagation

In this paper, the effects of range inhomogeneities in the seabed layering on low-frequency broadband sound propagation in a shallow-water ocean environment are examined. Acoustic measurements generated by an impulsive sound source were made on the New Jersey continental shelf over propagation paths where previous geophysical analyses provide information on the seabed layering structure. Additional information on the physical properties of the sediment layers, such as sound speed and attenuation, was obtained from previous analyses of continuous wave tow experiments. The seismic and the geophysical information, the inferred geoacoustic information for the sediment layers, and sparse water-column sound-speed measurements provide inputs for a finite element parabolic equation propagation model. For the three propagation paths considered in this study the seabed layering structure for two of the paths is range dependent and the other is approximately horizontally stratified. With this information modeled, time series are produced and are compared in the 35-265-Hz band to the measured received times series from impulsive sources deployed at ranges between about 70 and 350 water depths. Further, simulations of the received time series are performed for each of the three paths using modified sub-bottom layering structures for the purpose of quantifying the acoustic field effects associated with deviations of the seabed structure from horizontal stratification.