Abstract:

Realistic estimations of the deep-water acoustic coherence effects on the array gain for linear and quadratic beamformers, optimal ones included, were obtained for the North-West Pacific environments. An advanced technique was developed to calculate the signal coherence under the basic assumption that the long-range acoustic fluctuations are caused by internal waves in the summer channel or surface wind waves in the winter channel. Simulations were carried out both for horizontal and vertical arrays for the frequency of 250 Hz and ranges 500--1000 km. The following effects were shown to be the most essential points: (i) angular displacement and degradation of the plane-wave beampattern; (ii) large-array gain loss; (iii) coherence-induced gain ``gap'' between the optimal quadratic and linear beamformers; and (iv) gain dependence on the ambient modal noise. The optimal quadratic beamformer was shown to reduce the gain loss at a cost of increased processor complexity: The number of partial weight-sum channels is equal to the number of the largest signal eigenvalues. In some environments, a proper performance/complexity was realized using suboptimal beamformers which are, therefore, of particular interest for large-array applications. [Work supported by RFBR.]