水下多声源激光相干探测信号的解调技术研究

发布时间：2018-04-02 13:18

本文选题：水下声源　切入点：激光干涉　出处：《哈尔滨工业大学》2017年硕士论文

【摘要】：水下目标探测在海洋防务和海洋工程领域备受关注。实现水下声场的探测是突破水下目标识别、定位、跟踪等难题的基础。目前用于水下目标探测的方法众多,其中“激光-声”联合探测属于一种前沿基础研究方法,作者所在实验室从2008年开始便致力于“激光-声”联合探测水下声目标的研究,并取得了一系列的阶段性成果。但是关于探测信号频谱混叠情况下的多声源准确探测一直是技术瓶颈。因为当水下存在多个声源,且各声源频率接近时,激光相干探测信号的频谱将混叠在一起,无法直观的判断出声源的个数,也无法利用传统的方法直接获取水下各声源发声频率。本文的研究目的就是解调出水下多个频率接近的声源发声频率。围绕这一主题,本文主要从以下几个方面展开研究:建立了水下多声源频率解调的理论模型,并进行了仿真验证。分析水下目标辐射噪声的特性、噪声在水介质中传播时的衰减特性以及噪声传至水表面形成水表面声波的原理。着重探讨水下存在多个声源,且探测信号频谱混叠在一起时的频率解调方法,提出一种基于Hilbert变换的水下多声源频率解调方法,推导出水下多声源探测信号经处理后的具体数学表达式,并仿真验证解调方法的正确性和可行性。研究实测水下多源声信号频率提取的频率解调实现。根据理论模型的推导和实际探测实验的分析,以MATLAB为平台,研究实测信号的解调算法实现。结合五点三次平滑滤波方法对探测信号进行预处理,使得自然水表面波动引起的频带对信号解调的影响降到最低。借助小波包分解与重构的方法将有用信号频带从干涉信号中剥离出来。通过对信号Hilbert变换及模值计算和平滑滤波等处理使得原来混叠在一起的多个频带得以分离,最后通过频带中心值搜索计算获取水下多个声源的发声频率。设计并在光学暗室下搭建一套水下多声源解调系统。根据本课题探测信号的特征,结合实际探测技术要求,设计一套水下多声源解调系统,根据实际探测需求对一些关键器件进行分析和选择。在光学暗室下搭建实验系统并进行调试,使之能达到探测要求。为验证本文提出的解调方法的可行性和准确性,利用搭建的激光相干探测系统进行发声频率在1kHz-10kHz之间的多个频率组合的水下目标探测,并进行水下声信号频率信息的探测效率评估。实验结果表明本文所提出的信号方法能很好地实现水下复杂声信号频率信息的检测,为水下声信号处理提供了新的思路。
[Abstract]:Underwater target detection has attracted much attention in the field of marine defense and marine engineering.The detection of underwater acoustic field is the basis to break through the difficult problems of underwater target identification, positioning and tracking.At present, there are many methods used in underwater target detection, among which "laser-acoustic" joint detection is a kind of advanced basic research method. Since 2008, the author has devoted himself to the research of "laser-acoustic" joint detection of underwater acoustic target.And has obtained a series of stage achievement.Nor can the traditional method be used to directly obtain the sound frequency of underwater sound sources.The purpose of this paper is to demodulate the sound frequency of multiple underwater sound sources.Focusing on this topic, this paper mainly studies the following aspects: the theoretical model of underwater multi-source frequency demodulation is established, and the simulation is carried out.The characteristics of underwater target radiated noise, the attenuation characteristics of noise propagating in water medium and the principle of acoustic wave formation on water surface are analyzed.In this paper, the frequency demodulation method when there are many sound sources under water and the spectrum of detection signals are aliasing together is discussed. A frequency demodulation method based on Hilbert transform for underwater multi-sound sources is proposed.The mathematical expression of the underwater multi-source detection signal is deduced, and the correctness and feasibility of the demodulation method are verified by simulation.In this paper, the frequency demodulation of underwater multi-source acoustic signal is studied.According to the derivation of the theoretical model and the analysis of the actual detection experiment, the demodulation algorithm of the measured signal is studied on the platform of MATLAB.The detection signal is pretreated with 5.3 times smoothing filtering method, which minimizes the influence of frequency band caused by natural water surface fluctuation on signal demodulation.The useful signal band is separated from the interference signal by wavelet packet decomposition and reconstruction.The signal Hilbert transform, modulus calculation and smoothing filtering are used to separate the original overlapping frequency bands. Finally, the sound frequency of multiple underwater sound sources is obtained by searching the center value of the frequency band.A underwater multi-source demodulation system is designed and built under the optical darkroom.According to the characteristics of the detection signal and the requirements of the actual detection technology, a set of underwater multi-source demodulation system is designed, and some key devices are analyzed and selected according to the actual detection requirements.The experimental system is built and debugged under the optical darkroom to meet the detection requirements.In order to verify the feasibility and accuracy of the demodulation method proposed in this paper, a laser coherent detection system is used to detect underwater targets with multiple frequency combinations of sound frequency in 1kHz-10kHz.The detection efficiency of underwater acoustic signal frequency information is evaluated.The experimental results show that the proposed method can detect the frequency information of underwater complex acoustic signals and provide a new idea for underwater acoustic signal processing.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB56

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