Interference Invariants in Hydroacoustic Field Maxima in Deep Water

Abstract

Chuprov’s interference invariant (II) well describes the properties of a sound field in shallow water. However, the question of how applicable Chuprov’s II concept is to deep water, where the patterns of sound field decay with distance are more complex has been insufficiently studied. Therefore, the authors studied the II properties in the near and far fields of acoustic illumination, as well as in the shadow zone. A new definition of the invariant was proposed and studied, and its characteristics were compared with Chuprov’s II as a function of distance, reception and emission depths, and summer or winter propagation conditions. The new invariant is called the phase-energy invariant (PEI), since orthogonal components of the phase gradient are used to describe the spatial sound energy distribution. The stability of the new invariant, its independence on different influencing factors, and its natural change with distance from zero to one are shown. It has been established that in winter conditions, at almost all distances, the PEI is equal to unity, and the II does not have stable values and varies jumpwise over a very wide range. In summer conditions, in the shadow zone, with increasing distance, the PEI increases, just like the II, from close to zero to one. In the near and far fields of acoustic illumination, the PEI is approximately equal to unity, and the II in these zones, both in summer and winter, is characterized by unlimited oscillations, caused by division by a value close to zero. It is shown that the definition of PEI is valid both in single-mode waveguides and in free unbounded space with a dispersive medium.