Determination of the Acoustic Properties of the Sea Floor by Measuring the Angle Dependency of the Reflection Coefficient

Abstract

In shallow water rays which are reflected at low grazing angles at the sea floor are the principal contributors to the propagation of sound over long distances. The botton loss for low angle reflections affects the range of SONAR systems. It is impossible to measure the bottom loss directly under the interesting low grazing angles. We try to infer it from measurements of the angle dependency of the acoustic reflection coefficient of the sea floor. We developed a procedure to measure the relationship between the grazing angle and the reflection coefficient while the research ship is anchored. For a model of the boundary water-bottom, in which the sea floor is treated as a homogeneous half space the reflection coefficient is calculable by simple formulas. The parameters of the model are fitted to the measured values by an inversion program and used to calculate the reflection coefficient and consequently the bottom loss at the interesting low grazing angles.