Amplitude and Phase Structure of a Low-Frequency Hydroacoustic Field in the Deep Ocean

The paper investigates the sound-pressure and phase-gradient distribution in the deep sea along signal propagation paths in the near and far acoustic brightness fields, as well as in the shadow zone. It is shown that the field characteristics formed by leaky, trapped, and water modes differ significantly. It was found that in zones of interference maxima, the phase gradients are smooth and, by analogy with shallow water, can be described using the effective phase and group velocities. It is shown that the characteristics of the effective phase and group velocities for leaky and trapped modes with variations in distance, reception and emission depths, and sound pressure frequency are stable and determined by uniform invariant dependences on distance. Analytical relationships are proposed to describe these dependences. It was found that the values of the effective phase and group velocities in zones with dominant water modes are nearly equal to the average sound speed in water. Recommendations are given for applying the dependences of the effective phase and group velocities in direction-finding of noise sources.