New approach to scattering by random media and interfaces. II. Active underwater acoustic channels

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The general method of paper I above is systematically applied to the characterization of active underwater acoustic channels, in an isovelocity ocean. Expressions for the second-order statistics of the received scattered field are obtained, which, apart from a possible coherent term (k=0), exhibit a combination of the Poisson [or Faure-Olshevskii-Middleton (FOM) model] contribution (k=1), and the earlier continuum, or “classical” component (k=2). Unlike all earlier “classical” scatter theories, the dynamical effects of Doppler are explicitly obtained, from the ensemble of appropriate “Dopplerized” wave equations, e.g., Langevin equation. Random-path delays produce the expected random phase modulation, as do the various Dopplers, but unlike the former the latter have variances quadratic in time. Because of this, the scattering medium, even when stationary, progressively destroys the coherence of the injected signal. The continuum component (k=2) of the medium itself may be described by delay-spread and Doppler-spread “cells” which are now correlated (i.e., non WSSUS), unlike the Poisson term (k=1), which is WSSUS. Other channel features are considered, including conditions for validity of the FOM models, and the role of surface interactions. [Work supported by Naval Sea Systems Command.]