ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

1pAO15. Definition of geoacoustic characteristics of an elastic layered bottom using the spatial dependence of an acoustic field.

Margarita S. Fokina

Vladimir N. Fokin

Boris V. Kerzhakov

Inst. of Appl. Phys., Russian Acad. of Sci., 46, Ulyanov St., 603600, Nizhny Novgorod, Russia

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 that form bottom layers and frequency ranges, where the least losses due to propagation are observed, i.e., optimum propagation frequencies, is ascertained. [Work supported by RFFI project N 94-05-1725-a.]