Effects of the Sea-Bed on Acoustic Propagation.

Abstract

Abstract : The sea-bed is known to be the controlling factor in low-frequency shallow-water acoustics. In lossy sea-beds waterborne sound is attenuated both the compressional-wave attenuation in the bottom and by the coupling of sound into shear waves. The complicated frequency-dependent effect of the sea-bed on propagation has been studied theoretically, and it is found that bottom loss increases with decreasing frequency down to near the cut-off frequency of the ocean waveguide, at which frequency seismic propagation by interface waves on the sea floor becomes more important than acoustic propagation. It is also found that while propagation losses in the water column are strongly dependent on bottom type, a feature such as the optimum frequency of acoustic propagation in the water column is only slightly dependent on sea-bed properties. Broadband propagation data collected in different areas of the Mediterranean Sea and the eastern North Atlantic are shown to support these theoretical findings. (Author)