【作者】 张海青；

【导师】 王宁；

【作者基本信息】 中国海洋大学 ， 海洋信息探测与处理， 2008， 博士

【摘要】 内波做为一种季节性的中尺度海洋现象,它的活动是引起声场起伏不确定性的主要因素之一。浅海内波环境中的声传输起伏研究是近年海洋声学的研究热点之一。本文研究包括三部分:（一）研究温度数据时空统计特性、内波模态和内波谱提取方法;（二）研究浅海随机内波导致的声简正波传播时间起伏规律及其与局部温度观测数据统计规律的对应关系;（三）研究一类弱非线性内波导致的声信号幅度起伏机理。在第一部分,处理分析“2005黄海水声传播—起伏（AEYFI 05）实验”中获得的温度数据,提出了一种内波模态提取的方法。常规方法需预先知道浮力频率曲线,借助数值计算得到内波简正模态,经正交分解获取模态系数;而本方法只基于实验数据可以同时提取内波模态函数及其模态系数。第二部分研究“2005黄海水声传播—起伏（AEYFI 05）实验”温度时空相关特性及声传播时间统计特性。结果表明:一号声简正波的传播时间起伏谱可以清楚反映M2潮变化,包含相干结构:并且与跃层附近温度时间序列的功率谱在高频区域（f＞30cpd）呈近似同样ω^-α（α（?）1.7-1.8）的幂次衰减。应用简正波传播时间与声速起伏的对应微扰关系式,给出了上述对应关系的理论解释。最后在第三部分,研究一类非线性内波导致信号幅度起伏机理。实验数据处理发现:部分水听器在个别时段存在明显的“规则”强幅度起伏,这种起伏可解释为“上凸型”弱非线性内波恰好通过接受阵处引起的声场接收灵敏度起伏所导致。基于声简正波理论,给出了内波导致声场起伏特性的一般理论解释。更多还原

【Abstract】 Oceanic internal wave is considered to be one of the main reasons for acoustic field fluctuation. Recently, it more and more becomes one of study focuses of ocean acoustics in shallow water.Three parts have been studied in this paper. Firstly, extracting internal wave modes and their power spectra using temperature data is discussed. Secondly, the rule of sound normal mode travel-time fluctuation caused by shallow water random internal waves and its corresponding relationship with the statistical rule of local temperature data are studied. Thirdly, the fluctuation of sound signal amplitude caused by one kind of non-linear internal waves is analyzed.The data acquired from moored sensors of AEYFI 05, Acoustics Experiment of Yellow Sea Oceanic Front and Internal Waves, are processed in first part A method of extracting internal waves’ modes is given. In conventional ways, buoyancy frequency must be known and the internal waves’ normal modes are gotten by numerical computing, then the modes’ coefficients are determined by orthogonal decomposition. But in this part, internal waves’ mode functions and mode coefficients are extracting from experimental data at the same time.Both of the temperature temporal-spatial and the sound travel-time statistical characteristics are analyzed in second part. Results indicate that the change of M2 tide and coherent-structure are clearly reflected in the frequency spectrum of the 1^st Normal Mode travel-time fluctuation. This spectrum is qualitatively similar to the spectrum of temperature time sequence near thermocline, two spectra present power lawω^-α（α（?）1.7-1.8） attenuation in the range over 30cpd. The relation equations between Normal Mode propagation travel-time and sound-speed fluctuation are used to explain the qualitatively relationship between two spectra.The fluctuation of sound signal amplitude caused by one kind of non-linear internal waves is analyzed in third part. Strong and "regular" sound signal amplitude fluctuations can be discovered in part of hydrophones. This phenomenon can be explained by the theory of sound field receiving sensitivity fluctuation caused by an "up-flange" weak non-linear internal waves passing receiving vertical array. Based on Normal Mode theory, the explanation of sound field fluctuation characteristic caused by internal waves is given.更多还原