珠江口低盐透镜现象的声传播特性分析
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摘要
低盐透镜现象是珠江口陆架海域常见的一种中尺度现象,它的出现会影响水下声传播环境。利用南海北部陆架区的CTD资料分析了低盐透镜的结构特征,基于简正波和射线模型,建立二维波导环境,设置不同声源条件,对低盐透镜环境的声传播特性进行了研究。结果表明:低盐透镜会在海水上层形成声道,距离15km处其传播损失较没有低盐透镜的情况小约15dB。虽然低盐透镜声道厚度通常较小,但是较大的盐度梯度可以保证声道对声能的有效传播。当频率高于截止频率的声源置于低盐透镜内,声道效应有助于声音的远距离传播。
Low salinity lens is a common mesoscale phenomenon in the continental shelf outside the Pearl River Estuary,and its appearance will affect the underwater acoustic waveguide.The structure characteristics of low salinity lenses were analyzed based on the CTD profiles in the northern shelf of the South China Sea.Based on the normal mode and ray model,the two-dimensional waveguide environment was established,the characteristics of sound transmission in the low salinity lenses environment were studied under different sound source conditions.The results show that the low salinity lens will become the acoustic channel in the upper layer of sea water,and the transmission loss at 15 km is about 15 dB less than that without low salinity lens.Although the channel thickness of low salinity lens is usually smaller than surface acoustic channel,the large salinity gradient can effectively trap energy in the acoustic channel.When the sound source whose frequency is higher than the cut-off frequency is placed in a low-salt lens,the acoustic channel can help the long-distance propagation of sound.
Low salinity lens is a common mesoscale phenomenon in the continental shelf outside the Pearl River Estuary,and its appearance will affect the underwater acoustic waveguide.The structure characteristics of low salinity lenses were analyzed based on the CTD profiles in the northern shelf of the South China Sea.Based on the normal mode and ray model,the two-dimensional waveguide environment was established,the characteristics of sound transmission in the low salinity lenses environment were studied under different sound source conditions.The results show that the low salinity lens will become the acoustic channel in the upper layer of sea water,and the transmission loss at 15 km is about 15 dB less than that without low salinity lens.Although the channel thickness of low salinity lens is usually smaller than surface acoustic channel,the large salinity gradient can effectively trap energy in the acoustic channel.When the sound source whose frequency is higher than the cut-off frequency is placed in a low-salt lens,the acoustic channel can help the long-distance propagation of sound.
引文
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[2]PULGAKOV N P,LOMAKIN P D.Acoustic characteristics of seawater in the area of the coastal discharge front off the Guinean shore[J].Physical Oceanography,1994,5(2):141-147.
[3]ZENG Li-li,LIU W T,XUE Hui-jie,et al.Freshening in the South China Sea during 2012revealed by Aquarius and in situ data[J].Journal of Geophysical Research Oceans,2014,119(12):8 296-8 314.
[4]LI Lei,LI Feng-qi,SU Jie,et al.Analysis on water masses in the South China Sea in summer and winter of 1988[J].Oceanologia et Limnologia Sinica,2002,33(4):393-401.李磊,李凤岐,苏洁,等.1998年夏、冬季南海水团分析[J].海洋与湖沼,2002,33(4):393-401.
[5]JING Chun-sheng,HUANG Jiang,GUO Xiao-gang.Low salinity lenses in the northeastern shelf of the South China Sea and their possible formation mechanism in summer,2002[J].Journal of Applied Oceanography,2013,32(2):148-155.靖春生,黄奖,郭小钢.2002年夏季南海东北部陆架海域的低盐透镜现象分析[J].应用海洋学学报,2013,32(2):148-155.
[6]YANG Yang,LI Rui-xiang,ZHU Peng-li,et al.Seasonal variation of the Pearl River diluted water and its dynamical cause[J].Marine Science Bulletin,2014,33(1):36-44.杨阳,李锐祥,朱鹏利,等.珠江冲淡水季节变化及动力成因[J].海洋通报,2014,33(1):36-44.
[7]KIM J,BOK T H,PAENG D G,et al.Acoustic channel formation and sound speed variation by low-salinity water in the Western Sea of Jeju during summer[J].The Journal of the Acoustical Society of Korea,2013,32(1):1-13.
[8]FAN Wei,LI Song-wen.Estimation and analysis of acoustic propagation loss in the water layer near sea surface[J].Technical Acoustic,2015,34(3):223-227.范威,李颂文.近海面水层中声传播损失估计和分析[J].声学技术,2015,34(3):223-227.
[9]ZHANG Xu,ZHANG Yong-gang,ZHANG jian-xue,et al.The effect of ocean mixed-layer structure on acoustic propagation in a surface duct environment[J].Acta Oceanologica Sinica,2012,34(1):79-89.张旭,张永刚,张健雪,等.海洋混合层结构对表面声道中声传播特性的影响分析[J].海洋学报,2012,34(1):79-89.
[10]DUAN Rui,YANG Kun-de,MA Yuan-liang.Investigation of long-range sound propagation in surface ducts[J].Chinese Physics B,2013,22(12):297-307.
[11]QU Ke,PIAO Sheng-chun,ZHOU Jian-bo,et al.Analysis of surface sound duct in the northern shelf of the South China Sea[J].Shock&Vibration,2018,2018:1-12.
[12]YANG Lei,WANG Dong-xiao,HUANG Jian,et al.Toward a mesoscale hydrological and marine meteorological observation network in the South China Sea[J].Bulletin of the American Meteorological Society,2015,96(7):1 117-1 135.
[13]ZENG Li-li,WANG Qiang,XIE Qiang,et al.Hydrographic field investigations in the Northern South China Sea by open cruises during 2004-2013[J].Science Bulletin,2015,60(6):607-615.
[14]ETTER P C.Recent advances in underwater acoustic modelling and simulation[J].Journal of Sound and Vibration,2001,240(2):351-183.