Temporal coherence of acoustic signal transmissions in a fluctuating deep ocean

Temporal coherence of a propagating signal in the fluctuating ocean is an important property for many practical applications. In previous studies, it has been shown that the coherence time follows a - 3/2 power frequency dependence and a - 1/2 power range dependence for long-range deep-water propagations as well as for shallow water propagations. In this paper, the frequency and range dependences are studied for a relative near distance in the deep ocean based on the Monte Carlo simulations. The range is tens of kilometers and it cannot be regard as a long-range propagation. It is found in this paper that the - 3/2 power frequency dependence is still followed, while the simple - 1/2 power relationship is inadequate to show the range dependence in the near field of deep water. The signals mainly propagate through two different paths for tens of kilometers: the refracted path and the reflected paths. In different regions, the acoustic coherence times exhibit different dependences because the signals are dominated by different types of rays. The - 1/2 power range dependence still holds for the same kind of ray path.