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Depth dependence of noise resulting from ship traffic and wind 总被引：1，自引：0，他引：1
Under conditions of distantly generated noise, the noise level is found to decrease with depth in the mid-northeastern Pacific. These data show a decrease in noise level greater than 25 dB between critical depth and the ocean bottom. A result of this decrease is that locally wind-generated noise can be detected on near-bottom receivers for wind speeds less than 10 kn. It is shown that the noise level generated form local sources such as wind and nearby shipping is almost independent of receiver depth. The differences in spectra shape between the distant shipping noise and wind-generated noise and the low noise levels detected near the ocean bottom allow the measurement in the frequency band at 200-500 Hz of local wind noise level for wind speeds less than 10 kn 相似文献
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Photo-oxidation of dimethylsulphide in aqueous solution 总被引：2，自引：0，他引：2
Dimethylsulphide (DMS) is readily photo-oxygenated in the presence of micromolar amounts of photosensitizers such as methylene blue, rose bengal, anthroquinone and humic acid. Two moles of DMS are oxidized for every mole of molecular oxygen utilized consistent with dimethyl-sulphoxide being the oxidation product. Coastal seawater samples examined contained sufficient naturally occurring photosensitizer to photo-oxygenate DMS in sunlight with a first order rate constant of 2.4 × 10−5 s−1. This rate is rapid enough to imply that DMS is oxidized at approximately the same rate as it is lost to the atmosphere. 相似文献
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TenCate J.A. Muir T.G. Caiti A. Kristensen A. Manning J.F. Shooter J.A. Koch R.A. Michelozzi E. 《Oceanic Engineering, IEEE Journal of》1995,20(4):300-310
The problem of locating very low frequency sound sources in shallow water is made difficult by the interaction of propagating acoustic waves with the sea floor. Slow wave speeds and the attendant short wavelengths suggest that low frequency beamforming and source localization with sea floor geophones can be accomplished with relatively small arrays when compared with hydrophone arrays in the water column. To test the feasibility of this approach, experiments were carried out in the shallow water of the Malta Channel of the Straits of Sicily where the Scholte wave speed was some 10 to 20 times slower that the speed of sound in water. A linear array of ten vertically gimballed geophones was deployed and measurements were made on propagating seismic wave fields generated by explosive shots. The resulting directivities, beam patterns, and sidelobe characteristics are in excellent agreement with array theory, which suggests that coherent processing is a viable technique on which to base new applications for seismic arrays on the sea floor. Supporting materials on the geophysics of Scholte waves and calculations of the wave field at the site are presented 相似文献
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Gaul R.D. Knobles D.P. Shooter J.A. Wittenborn A.F. 《Oceanic Engineering, IEEE Journal of》2007,32(2):497-512
During the late 1960s and throughout the 1970s, the U.S. Navy conducted a series of ocean acoustic measurement exercises to support development of systems and techniques to detect nuclear submarines. The exercises and most of the technical documentation were classified. In 2003, a project was sponsored by the U.S. Office of Naval Research (ONR, Arlington, VA) to declassify documentation and demonstrate the capability to recover acoustic data recorded on magnetic tape. One of the exercises, known as CHURCH OPAL, was selected for demonstration of acoustic data recovery. The record on magnetic tape spanned a period of ten days in September 1975 from a vertical assembly of hydrophones at a site midway between Hawaii and California. This paper presents selected excerpts from a key report (Wittenborn, 1976) on ambient noise that previously was unpublished and unavailable for general distribution. The earlier work is augmented with more complete and detailed analyses of the recovered digital data using modern analytical techniques. Data acquired from the hydrophones below critical depth enabled isolation of ambient noise due to distant shipping and local wind. The frequency band of the acoustic analyses was 30-500 Hz. The wind component of the ambient noise was evaluated at frequencies lower than reported by Wenz (1962). 相似文献
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