Effect of background internal waves and surface waves on phase fluctuations of the focused sound field in shallow water

Abstract

Phase variations of the low frequency sound field focused using the phase conjugation procedure are estimated in the focal spot in the presence of short-period (< 1 h) background internal waves and wind-driven surface waves. Numerical simulations of sound propagation in shallow water are performed with the normal-mode method. Mode coupling is taken into account. It is demonstrated that the phase fluctuations at frequencies of a few hundreds of hertz and at the range of several kilometers do not exceed ±π and can be easily measured with a typical acoustic noise field present. The fluctuations magnitude can be reduced about two times through the optimal choice of the modal structure. The applicability of phase methods for measuring the acoustic path length variation is discussed.