Abstract:
Sea noise was measured continually over a period of 1 year on experimental installations 40 miles south of Bermuda. One-hour stretches of data were recorded daily on four hydrophones, two on the seafloor and two suspended off bottom in 2420 fm s. Analysis of spectrum levels at six frequencies from 0.1 to 1.5 kHz included computation of means, standard deviations, distributions, and higher-order statistical moments. Spectral shape, levels, and variability closely resembled sea noise measured at shallower receivers throughout the western North Atlantic. The suspended very deep hydrophones were 2 to 3 dB noisier than those on the bottom; other statistical properties of both suspended and bottomed receivers were alike. The mean monthly noise migrated through an annual cycle of frequency-dependent change, from 7 dB at 0.1 kHz to 12 dB at 1.5 kHz. This seasonal trend progressed smoothly from winter high to midsummer low, though not at a constant rate. Monthly probability distributions changed form correspondingly, becoming skewed for months with a rapidly shifting mean and tightly peaked for seasons of relative climatic stability. [Work supported by NavElecs.]