An experimental investigation of the contribution of sediment volume scattering to acoustic backscatter measured in the shallow waters of the Florida Strait

Abstract

Experiments were conducted in the Florida Strait region of the United States in July 1995 for the purpose of investigating the contribution of sediment volume scattering to measured backscatter levels at frequencies between 3.5 and 30 kHz. Each offive sites were analyzed for bottom backscatterrng level in both the radial and azimuthal directions. A relatively new volume scattering model was employed and the results compared with predictions made using a composite rough interface scattering model. Environmental parameters were established by a cross well tomographic measurement and used as input values for the modeling. Comparison of model predictions with the measured data showed that for grazing angles from the critical angle to approximately 60" volume scattering dominated, while for angles greater than approximately 60" surface roughness scattering consistently dominated. In geographic areas where the interface sound speed ratio exceeded one, roughness scattering controlled the backscatteredlevel for grazing angles less than the critical angle. Inversion of the measured backscatter data was performed using a genetic optimization algorithm developed around the volume scattering model. Inversion results were found to agree well with measured data and measured environmental parameters which describe the scattering volume. A second similar inversion was made to determine spectral properties of a two dimensional transform of the compressional velocity tomograms This inversion was based upon a power law representation ofthe spectral structure.