Determination of sea bottom characteristics using acoustic field space dependence

Abstract
The effect of the layer structure of the elastic absorbing bottom on the space-frequency dependences of acoustic fields in shallow and deep seas in the frequency range 20-500 Hz is studied. The comparison of the experimental losses due to sound propagation in the deep-water part of the Atlantic Ocean at three frequencies and the results of numerical calculations by ray programs has shown that the experimental and calculated losses may agree satisfactory only if the layer bottom structure is taken into account. The numerical study in the frames of the approximation of adiabatic modes has shown that an absorbing layer of the geological bottom structure of the Barents Sea influences significantly the characteristics of sound fields and enriches the field mode spectrum. It is shown that the degree of this effect depends on the seasonal fluctuations of the sound velocity profile structure. The relation between the type of sediments which form bottom layers and frequency ranges, where the least losses due to propagation are observed, i.e. optimum propagation frequencies, is ascertained.