Signal coherence and coherence-induced effects on array output in multimode transmission channels

It is well known that the statistical effects of long-range signal propagation in random channels generally lead to considerable degradation of both the signal coherence and array output performances. In random-inhomogeneous underwater sound channels, these effects are of a primary importance if a large array is used for high-resolution operation in spatial domain. The key physical issue in such a scenario is known to be the range-dependent cross-modal coherence loss caused by multiple sound scattering by random channel inhomogeneities, both volume and windy surface ones. In this paper, we demonstrate numerically how and why the horizontal array output dramatically degrades if the received signal consists of a large number of partially-correlated or even uncorrelated normal modes. From the point of view of general statistical antenna theory, the results presented permit one to evaluate the coherence effects on large-array output performance, with application to multimode transmission channels.