High-frequency bottom backscatter measurements in shallow water

Bottom backscatter measurements have been made at six shallow-water sites over the frequency range 20–85 kHz for bottom types including silt, sand, and gravel. Bottom samples were taken at all experimental sites, and some sites are well characterized in terms of seabed acoustic parameters and roughness. A slight frequency dependence was observed, and scattering strength was generally found to decrease as grazing angle decreased. Backscatter measurements in four azimuthal directions showed no measurable anisotropy for grazing angles between 10° and 40°. Spatial variability of backscatter strength was measured along two tracks approximately 35 and 75 km long.