Determination of Interference Invariants in a Deep-Water Waveguide by Amplitude and Phase Methods.

It is established that the interference invariant can be calculated not only by analyzing the frequency and spatial distribution of the intensity field but also by studying the phase-gradient field. It is found that the interference structure of the intensity field and the field of value inverse to the phase gradient (effective phase velocity) can be described by identical dependences, based on the use of invariant. It is shown that, in contrast to shallow water, which is characterized by relative stability of invariant values, the interference invariant in deep water changes significantly with variation in distance. In the shadow zone, with detectors and sources located at real depths (less than 400 m), the interference invariant can be described by an analytical dependence, which is in essence affected by only the water depth and distance; it is affected by neither sound frequency, nor source depth, nor detector depth and is only slightly affected by the characteristics of speed-of-sound vertical profile. Hence, the thus obtained analytical dependence can be referred to as invariant. [ABSTRACT FROM AUTHOR]