Geoacoustic models for propagation modeling in shallow water

Abstract

Acoustic propagation in shallow water is viewed as a guided‐wave phenomenon, with the sea surface and seabed forming the boundaries. At subkilohertz frequencies, the acoustic properties of the seabed to a depth of several wavelengths can have a strong effect on propagation. The computer modeling of propagation requires estimates of such parameters as sound speed, density, attenuation, and layer thicknesses, which collectively are called the geoacoustic 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, we have adopted the approach of independently determining as many geoacoustic parameters as possible, and adjusting less precisely known parameters within reasonable limits to effect an agreement between theory and experiment. To this end, we have used sub‐bottom reflection profiles to determine sediment types and layer thicknesses, large and small scale seismic refraction experiments to estimate sound speeds, and processing of sub‐bottom vertical reflection data to estimate volume attenuation. Techniques used by other researchers will be reviewed. Examples of geoacoustic models and comparisons with experiment will be presented for shallow water sites on the Scotian Shelf and the southwestern approaches to the English Channel.