Geo-acoustic models for propagation modelling in shallow water

D.M.F. Chapman, D.D. Ellis

Abstract


Acoustic propagation in shallow water is viewed as a guided-wave phenomenon, with the sea surface and seabed forming the boundaries. At sub-kilohertz frequencies, the acoustic properties of the seabed to a depth of several wavelengths can have a strong effect on propagation. The computer modelling of propagation requires estimates of such parameters as sound speed, density, attenuation, and layer thicknesses, which are collectively called the geo-acoustic model of the seabed. Direct measurement of these quantities is difficult, and methods must be devised to infer these values from other experiments, often employing acoustic techniques. At DREA, the authors have adopted the approach of independently determining as many geo-acoustic parameters as possible, and adjusting the less precisely known parameters within reasonable limits to effect an agreement between theory and experiment. To this end, they have used sub bottom vertical reflection profiles to determine sediment types and thicknesses, large and small scale seismic refraction experiments to estimate sound speeds, and processing of sub-bottom reflection data to estimate volume attenuation. Examples of geo-acoustic models and comparisons with experiment are presented for shallow water sites on the Scotian Shelf and the southwestern approaches to the English Channel

Keywords


acoustic wave propagation; physics computing; seismic waves; underwater sound; geoacoustic models; acoustic propagation; guided wave phenomenon; subkilohertz frequencies; propagation modelling; shallow water; sea surface; seabed; computer modelling; sound speed; density; attenuation; layer thicknesses; sub bottom vertical reflection profiles; sediment types; seismic refraction experiments; Scotian Shelf; English Channel

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