Horizontal refraction of low-frequency acoustic waves in the Barents Sea stationary acoustic track experiment

Abstract

In this paper, data from the Barents Sea stationary acoustic range experiment carried out in October 1983 are analyzed. The experiment used a tonal acoustic source at 100 Hz and a horizontal array that consisted of 48 hydrophones extending over 450 m, mounted on the bottom. From the measured phase difference between a reference signal and the signal received by the individual hydrophones, phase front fluctuations have been obtained. Continuous measurements of the sound-speed profile showed fluctuations of the thermocline boundary caused by long period (3.5 h) internal waves with 10-m amplitude. Simultaneously, acoustic measurements were made of the deviations from linearity of the phase front along the array. Using spatial Fourier analysis, it was seen that the variability of the phase front showed several scales. To explain the spatial phase fluctuations we used results from a horizontal refraction theory for shallow water and a theory of phase dislocation in a waveguide [Kravtsov et al., Sov. Phys. Acoust. 30, 45–47 (1984); Sov. Phys. Acoust. 35, 156–159 (1989)]. Calculations showed that long period phase fluctuations were produced by long period internal waves and short period fluctuations were produced by the interference of direct waves and waves reflected from the shore. It was also possible to account for some of the parameters of the internal waves and the reflected waves.