Spatial and temporal coherence in a long range, upslope environment

Abstract

In an active acoustic test conducted off the USA Pacific Coast in November-December 1991, a low-frequency source, kept stationary over the deep basin, insonified from long range the coastal slope and shelf. An autonomous, bottom-mounted horizontal array was deployed at the transition from slope to shelf. The inter-hydrophone coherence along the array deteriorated with spacing, and the beam former output exhibited a corresponding degradation in array signal gain. The coherences were measured after matched filtering of the received hyperbolic frequency-modulated signals. The spatial coherence is in strong contrast with the good temporal coherences for subsequent tran smissions. The excellent measured temporal coherence is shown to have the potential to reduce the levels of direct arrivals and of reverberation