Finite element modelling of reverberation and transmission loss in shallow water waveguides with rough boundaries

TitleFinite element modelling of reverberation and transmission loss in shallow water waveguides with rough boundaries
Publication TypeJournal Article
Year of Publication2011
AuthorsIsakson, M. J., and Chotiros N. P.
JournalJournal of the Acoustical Society of America
Volume129
Pagination1273-1279
ISBN Number0001-4966
EndNote Rec Number8443
Abstract

A finite element model for the reverberation and propagation in a shallow water waveguide with a sandy bottom was calculated for five different environments at a centre frequency of 250Hz. The various environments included a rough water/sediment interface, a rough air/water interface, roughness at both interfaces and downward and upward refracting sound speed profiles with roughness at both interfaces. When compared to other models of reverberation such as ray theory, coupled modes, and parabolic equations, finite elements predicted higher levels of reverberation. At early times, this is due to the "fathometer" return, energy that is normally incident on the boundaries at zero range. At later times, the increased reverberation was due to high angle scattering paths between the two interfaces. Differences in reverberation levels among the environments indicated that scattered energy from the air/water interface is transmitted into the bottom at steep angles. This led to a large decrease in reverberation for a rough air/water interface relative to a rough water/sediment interface. Sound speed profile effects on reverberation were minimal at this frequency range. Calculations of the scintillation index of the different environments indicated that most of the reverberation was relatively Rayleigh-like with heavier tailed distributions at longer ranges. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3531810]