Ambient noise spectral properties in the north area of Xisha
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Ambient noise spectral properties in the north area of Xisha DA Lianglong1, WANG Chao1*, HAN Mei1, ZHANG Lin1 1
Navy Submarine Academy, Naval Underwater Battlefield Environment Institution, Qingdao 266071, China
Received 28 April 2014; accepted 4 August 2014 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2014
Abstract Ambient noise is very important in the prediction system of a sonar performance, because it determines the detection ranges always in a passive sonar and usually in an active sonar. In the uncertainty issue for the sonar performance, it is necessary to know this factor’s statistical characteristics that are only obtained by data processing from the underwater ambient noise measurements. Broad-band ambient noise signals from 16 hydrophones were amplified and recorded for 2 min every 1 h. The results show that the ambient noise is essentially depth independent. The cross correlation of the ambient noise levels (1, 6 and 12 h average) with a wind speed is presented. It was found that the correlation is excellent on the upper frequency band and the noise levels correlate better with high wind speed than with low wind speed. Key words: ambient noise, cross correlation, wind speed Citation: Da Lianglong, Wang Chao, Han Mei, Zhang Lin. 2014. Ambient noise spectral properties in the north area of Xisha. Acta Oceanologica Sinica, 33(12): 206–211, doi: 10.1007/s13131-014-0569-4
1 Introduction The ambient noise of the sea has been measured and studied for over seven decades (Knudsen et al., 1948; Wenz, 1962; Wei et al., 2004; Walkinshaw, 2005; Gaul et al., 2007; McDonald et al., 2008). The results of the numerous studies have been published in the deep or shallow ocean over a wide frequency range and at many locations. Knudsen et al. (1948) concluded that in the absence of noise contributed by marine life or shipping, the ambient sea noise in the open ocean resulted primarily from the agitation of the sea surface by the action of local wind. A widely used set of average sea noise spectra with a wind speed or a sea state as a parameter was determined. Wenz (1962) presented results that generally were in agreement with those of Knudsen et al., which curves at frequencies above 500 Hz. However, at frequencies less than 500 Hz considerable differences exist among the reported results. Wenz (1962) suggested that many of these differences can be explained if the measured spectral are composites of the noise from three sources, turbulent pressure fluctuations in the water, bubbles and spray resulting from agitation of the sea surface by the wind, and distant ocean-ship traffic, and if the relative importance of these noise sources varies with time and area. For the vertical dependence of the noise field, most studies of the ambient noise were made at deep water in the past (Morris, 1978; Perrone, 1970; Marshall, 2005; Barclay, 2011), the reason is that the great depth variation of the ambient noise is easily observed. Perrone (1970) found that between 89 and 177 Hz the ambient noise level
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