A detailed study of sound reflections from a layered ocean bottom

Abstract

The effect of layered sediments on sound reflection from the ocean bottom has been investigated theoretically and experimentally. Very detailed, systematic and computer-aided calculations of the reflection coefficient of a twolayer bottom are made, using well-known theory and varying the following parameters: (1) velocity and density contrasts; (2) layer thickness normalized with respect to wavelength; (3) absorption in the sediments (in db/wavelength); (4) shear wave velocity in the lower layer. Calculations are made both for a harmonic source and for a broadband source analysed within certain bands around the harmonic source frequency. A series of curves is obtained representing the two-layer effect for a range of parameters that encompasses typical ocean bottom values. It is shown that absorption in the upper layer is of great importance in sound reflection, especially beyond a critical angle, but that moderate shear wave velocities have little effect. An octave band analysis of experimentaldata -- using a broadband source -- tends to support this theoretical two-layer model.