【作者】 张晓云；

【导师】 李秀坤；

【作者基本信息】 哈尔滨工程大学 ， 水声工程， 2008， 硕士

【摘要】 提取目标回波的时域相关特征和频域功率谱特征是水下目标特征提取中最基本的方法,但在功率谱估计中,各频率分量间的相位信息难以体现出来,且功率谱和自相关函数仅能对均值已知的高斯过程进行完整的描述。而高阶统计量是针对二阶统计量(功率谱和相关函数)的各种局限性提出的,它是研究信号非高斯和非线性的有效工具。本文尝试将高阶统计量理论应用到水下目标特征提取中,分析目标回波的非高斯和非线性特征。本文主要研究了高阶统计量中的双谱、双相干谱、1.5维谱和2.5维谱理论。双谱是阶数为3的谱,描述了信号在双频率域的能量分布;双相干谱可以检测信号偏离高斯性和相位耦合的程度;复信号的1.5维谱和2.5维谱可以分别检测信号中的二次相位耦合和三次相位耦合关系。本文对典型信号如CW脉冲信号、带限高斯噪声和由单元散射模型得出的混响信号进行了功率谱、双谱和双相干谱的仿真研究,还对复信号的1.5维谱和2.5维谱进行了大量的仿真研究,仿真结果与理论表达式一致。另外,本文还分析了在高斯噪声、单边指数色噪声和瑞利分布色噪声背景影响下,1.5维谱和2.5维谱在相位耦合中的应用,仿真表明1.5维谱和2.5维谱不仅能抑制对称分布的噪声,而且能抑制非对称分布的噪声。在本文最后,利用双谱、双相干谱处理了大量实验数据,进行了基于双谱和双相干谱的特征提取和压缩。在基于双相干谱的特征空间里,目标回波和混响呈现了良好的类间可分性,而基于双谱的特征向量提取被证明是一个较差的特征向量。最后分析了实验数据中半掩埋雷的回波中不同分段的1.5维谱和2.5维谱,证明雷壳回波和其周围底部混响具有不同的非线性相位耦合性。更多还原

【Abstract】 Autocorrelation in time domain and power spectrum in frequency domain are basic methods in feature extraction of underwater acoustic targets echoes. But the phase information in each frequency component cannot be contained in power spectral estimation, and power spectrum and autocorrelation only perfectly describe a Gaussian process which has a known mean. Higher-order Statistic (HOS) is proposed due to many limitations of 2-order statistic (power spectrum and autocorrelation). HOS is an efficient analysis tool in analyzing non-Gaussian signal and nonlinear signal. Extracting features and analyzing the non-Gaussian and nonlinear of mine echoes is the main contribution in this paper.The bispectrum, bicoherence, 1.5-dimension spectrum and 2.5-dimension spectrum are applied in this paper. Bispectrum and bicoherence are a third-order spectrum. Bispectrum describe the energy location of the signal in bi-frequencies and the non-Gaussian and the phase-coupling can be characterized by means of bicoherence. The 1.5-dimension spectrum and 2.5-dimension spectrum of complex signals can detect separately 2-order and 3-order phase coupling relations. The typical signals, such as CW pulse signal, band-limited Gaussian noise and reverberation from Unit-scatter Model, are be researched by means of power spectrum, bispectrum and bicoherence. A number of simulations are done based on 1.5-dimension spectrum and 2.5-dimension spectrum. Besides, the 2-order and 3-order nonlinear phase coupling phenomenon are researched in Gaussian noise, Exponential distribution noise and Rayleigh distribution noise environment by 1.5-dimension spectrum and 2.5-dimension spectrum, which are demonstrated not only to suppress symmetry distribution noise but also non-symmetry distribution noise.In the end of this paper, a large number of experiment data sets are tested applying bispectrum and bicoherence. Feature extraction and optimization are done based on bispectrum and bicoherence. The reverberation and the target echoes have good class separability in bicoherence feature space. But the feature based on bispectrum is proved a bad feature vector. Lastly, the different subsections of semis-buried steel mine shell echoes are analyzed by means of 1.5-dimension spectrum and 2.5-dimension spectrum. Consequently, the mine subsection echoes has different nonlinear phase coupling degree comparing other subsections echoes. These other subsections echoes are reverberations from the bottom zones around mine shell.更多还原