An experimental investigation of the horizontal refraction of low‐frequency acoustic waves in shallow water

Abstract

In shallow water, the measurement of horizontal refraction is a convenient method for the study of ocean mesoscale processes. In this paper, observations of horizontal refraction over a long, fixed acoustic track in shallow water are presented. A tonal signal at 100 Hz was transmitted from a near bottom source to a long, fixed receiving array 70‐km distant. The receiving array consisted of 48 hydrophones extending over 450 m horizontally. 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. Calculations showed that long period phase fluctuations were produced by long period interval 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.