Statistical properties of deep ocean noise.

Abstract

The various arrays sea test (VAST) was conducted in July 1989 in the northeast Pacific Ocean. A 3000-m-long, 200-element hydrophone array was suspended for an 11-day period from R/P FLIP, moored about halfway between San Diego and Hawaii (34N, 140W). Simultaneously, 12 neutrally buoyant, freely drifting Swallow floats equipped with both infrasonic hydrophones and three-component geophones were deployed at various depths 150 km off the California coast (35N, 122W). The statistical properties of deep ocean noise recorded by these sensor systems, both single element and beam level, are examined quantitatively under a variety of conditions, including wind-dominated (15–18 kt), distant air gun operations, and marine mammal vocalizations. Non-parametric statistical tests applied to narrow band complex time series of the data include the Wald–Wolfowitz run test for mutual independence of the data samples, the Kolmogorov–Smirnov two-sample test for stationarity, and the Kolmogorov–Smirnov one-sample test for Gaussianity. Results are presented over a broad range in frequencies and time scales and show that the noise field at times and in certain directions displays non-stationary and non-Gaussian properties. In a few cases, these statistical characteristics can be associated with specific physical processes. [Work supported by the Office of Naval Research.]