Statistical properties of horizontal, vertical and omnidirectional underwater noise fields at low frequency

Abstract

Ambient noise was measured at a deep ocean site using 16-element vertical line array which was deployed near the axis of the sound channel. Noise samples were recorded for time periods from 30 s to 120 s, and for local wind speeds from 2 to 15 m/s. Beamformed data were used to study the statistical properties of horizontal components of the noise field at a frequency of 245 Hz. It is well known in underwater acoustics that the horizontal component is sensitive to distant shipping noise and the vertical component is sensitive to local surface noise. The results indicated that both components of the noise field were independent, stationary and normally distributed for wind speeds greater than 7 m/s. However, at lower wind speeds, the vertical component did not pass the Lilliefor's test for normality. This result suggests that the noise process for surface generated noise at low wind speeds is not normally distributed. The results for the analysis of omnidirectional noise data indicated that the noise in the 49-300 Hz band as independent, stationary and normal for periods of up to two minutes. >