LOW-FREQUENCY ARCTIC REVERBERATION .2. MODELING OF LONG-RANGE REVERBERATION AND COMPARISON WITH DATA

In the Arctic ocean, very low-frequency (10-50 Hz) reverberation retur ns from the ice and bottom both contribute to the total received rever beration and are not easily distinguishable in long-range reverberatio n data, except where there is a dominant bottom or ice feature. In thi s paper, a normal-mode model of scattering from surface and bottom pro tuberances is applied to model long-range reverberation data collected during the CEAREX 89 experiment in the Norwegian/Greenland Seas. Mode led reverberation spectrum levels at 23 Hz are compared with data to i nvestigate the relative contributions of the ice and bottom to the mea sured reverberation. The normal-mode model of boundary scattering is b ased on a generalization of recent work of Ingenito [F. Ingenito, J. A coust. Soc. Am. 82, 2051-2059 (1987)] treating scattering from a rigid sphere in a stratified waveguide. Adiabatic normal mode theory is use d to model the propagation to and back from the scatterer in a range-d ependent waveguide. Using the small-ka approximation for the scatterin g functions, where k is the wave number and a is the dimension of the boundary protuberance, the normal-mode calculations of the long-range reverberation levels are found to agree rather well with the CEAREX da ta for four different measurements involving different bottom bathymet ries and source depths. For a source at 91-m depth in the 3000-m-deep basin, it is found that the reverberation level for a receiver at 60 m is dominated by scattering from the ice except for reverberation asso ciated with certain identifiable bottom features. For the same environ ment but a deeper (244-m) source, reverberation levels from the ice an d bottom are more comparable. For a strongly range-dependent environme nt, returns from bottom features are clearly identifiable in the data.