MECHANISMS OF OCEAN ACOUSTIC ATTENUATION - SCATTERING BY INTERNAL SOLITONS, BY SEA-SURFACE WAVES, AND BY FISH

A recent paper by Zhou et al. [J. Acoust. Soc. Am. 90, 2042-2054 (1991)] presents evidence for an extra attenuation in shallow water, occurring over a limited frequency range, and hypothesizes that it is due to internal solitons. Three linked comments are made here. First, it is noted that the real sea is three dimensional, which increases the likelihood of soliton scattering being smeared in frequency, and leads to a connection with the contribution from surface-wave scattering. Second, a review is given of some early observations on shallow-water scattering by solitons, which resulted in fluctuation rather than attenuation. Third, there is the alternative hypothesis of absorption and scattering by fish, drawing on early and extensive observations of attenuation effects that were often limited in frequency. There is no absolute proof here for or against either hypothesis, and although internal wave scatter is accepted as a loss mechanism in general, the case seems stronger for fish in the present application.