Measurements were made of the fluctuations in amplitude and spatial coherence of acoustic wavefronts transmitted through the deep ocean at two frequencies concurrently, 114 and 400 Hz. The signals were generated by a ship-suspended souce at 1000-ft depth and received over two ranges, 130 and 145 nmi, on a string of five bottomed receivers laid horizontally on a deep-water slope at about 5000-ft depth. The receiver spacing varied from 500–2500 ft. Amplitude fluctuations were found to differ significantly at receiver separations of 500 ft and appeared unrelated at separations of 2000 ft or more. For multipath transmission, unlike single-path transmission, the relative phase fluctuations between given receiver pairs were not proportional to frequency, and phase coherence at a given receiver separation was generally less than for single-path transmission. Coherence at 145 nmi was almost as good as for single path, presumably because ray-tracing predicts a dominant path and because the phase measurements were averaged over 10 s, and thereby discriminated against frequency modulation effects by the sea surface. Thus frequency resolution and time resolution of the experiment are as important to the results as range, frequency, and receiver separation. Poorer coherence at 130 nmi is tentatively attributed to lack of a dominant arrival at 114 Hz, and near-surface refractions at both frequencies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.