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1、烟台大学 硕士学位论文 水下声场激光相干探测的实验研究 姓名：刘伟 申请学位级别：硕士 专业：理学；光学 指导教师：张骏 2011-03 II 摘 要 水下声信号的探测具有十分重要的意义和广阔的应用前景， 直到八十年代末 期， 西方发达国家对于水下声场的探测还局限在利用放置于水下的探头的探测技 术上。早期水下目标间的无线通信主要使用声波作为通信手段。 由于水-空气交界面的限制，实现水下目标和水上平台通信的传统方法需要 将水上平台的传感器浸入水中，从而限制了通信的灵活性。另外，单纯采用激光 直接实现对水下目标通信的方法由于激光对水体的穿透能力有限， 限制了它的应 用范围。近几年来，非接触式激光探
2、测由于具有准确和快速的特点，逐步取代了 传统的探测方法，成为研究的热点。国内科研人员早期对水表面强度理论作了研 究并开展了相应的实验研究。 提出了水表面微波振动对入射激光的强度调制和水 表面横向微波理论，数值计算的结果表明，二维水表面横向微波具有和一维情况 类似的结果，可以对入射到表面的激光束进行调制，为水下声信号检测奠定了理 论基础。 近年来， Antonelli Lynn T.和她的同事们通过一套可以模拟速度可变的水 流和空气流的水池试验系统对激光声纳探测声的可行性进行了测试， 可以检测到 水下声场频率和声压级。 本文在前期研究的基础上，设计了一套光纤激光相干探测的实验装置，利用 从水表面
3、获取的带有水下振源信息的光与参考光进行相干， 从干涉信号中解调出 水下声源的振动特征。 本文首先介绍了激光干涉法探测水下声信号的应用背景及其发展情况。其 次，分别引用了国内外关于水表面横向微波一维模型的理论证明，为之后的实验 过程奠定了理论基础。然后建立了一套基于光纤光路并以 632.8 nm 激光器作为 光源的水下声场探测系统。展开了应用干涉法探测水下声信号的实验研究。分析 数据时，我们采用了快速傅里叶变换的信号处理方法，能够准确的分析出信号的 频率信息。另外，我们对信号采用了时频变换分析，分析出了信号随时间变化的 特征。 实验结果表明：该套装置能够准确的探测出水下声信号。相对于强度探测，
4、相干探测的方法无论在信号的强度还是探测的范围上都有不同程度的提高。 关键词：光纤激光；相干探测；水下声信号；频谱分析；时-频分析 I Abstract Detection of underwater acoustic signals is very important and has broad application prospects, not until the late 1980s,the detection of underwater acoustic signals for western developed countries is restricted to the techn
5、ology of utilizing the probe underwater. In early stages, wireless communication between targets in the water mainly used sound waves as means of communication. Because of restriction of water-air Interface, in order to realize communication between targets underwater and above water platform by tra
6、ditional methods we should put sensor into water, which limits the flexibility of communication. In addition, because of the penetrate ability to water of laser is limited, the scope of application would be restricted if we contact with targets merely with laser directly. In recent years, the non-co
7、ntact laser detection gradually replaces traditional methods and become the hot spot of research because of its accuracy and rapidity. In early stages, domestic researchers did some research on water surface intensity theory and carried out corresponding experimental research. They proposed theory o
8、f intensity modulation of water surface microwave vibration for incident laser and theory of water surface transverse micro wave, the results of numerical computation show that two dimensional water surface transverse micro wave have the same results for conditions of one dimension, the incident las
9、er beam was modulated and lay theory foundation for underwater acoustic signal detection. In recent years, Antonelli Lynn T. and her colleagues tested the feasibility of detecting underwater acoustic signals through a set of tank experimental system which could simulate water and air flow whose velo
10、city can be changed, which could detect the acoustic frequency and sound pressure under water. This article designed a set of optical fiber laser coherent detection system based on the initial research, which can bring about light acquired from water surface which bring the information of underwater
11、 acoustic signals and the reference light to be coherent, and demodulate underwater acoustic signals from the coherent signals. This article first introduced the application background and development situation of detection of underwater acoustic signals with method of laser coherent. Secondly, it q
12、uoted theoretic proof both at home and abroad about water surface transverse micro wave one dimension model, which lay theory foundation for later experiments. Then we designed a set of underwater acoustic signals detective system II which used laser as the optical source, based on optical fiber pat
13、h whose wavelength was 632.8 nm and carried out the experimental research of detecting underwater acoustic signals with coherent method. When anglicizing the data, we used digital possessing method of FFT, which can pick up the frequency information from signals accurately. In addition, we applied t
14、ime-frequency joint analysis to the signals and got the feature signals changing with time. Results of the experiments proved that this system could detect underwater acoustic signals accurately. Compared to intensity detection, coherent detection method improved to some distant both at scope and in
15、tensity of the signals. Key words: optical fiber laser; coherent interferometry; underwater acoustic signal; Spectrum analysis; time-frequency analysis 烟台大学硕士学位论文 烟台大学硕士学位论文 1 1 绪论 1.1 研究背景和意义 位于海洋中的舰艇是战时威胁我方水面舰只执行特种任务时最主要的敌人， 如何准确、实时地探测并发现敌方水面舰船，高效地执行反潜任务就成为了当前 一个重大而富有意义的课题。 传统的水下目标与空中或水面平台之间的通信必须将
16、传感器等探测设备浸入 到水下，从而限制了通信的灵活性和应用性。因次，发展非接触式1的遥感探测方 法就十分具有现实意义。由于光对水体的穿透能力有限，而声波相对于电磁波在 水中的衰减2要小很多。根据相关文献分析，水下声源在水表面激起的横向微波的 振动频率3就等同于声源本身的振动频率4-5。因此目前应用比较广泛的方法是在 水下使用声波通信，在水和空气的交界面采用光波通信。而这些理论研究的分析 就为水下声信号的光探测方法奠定了理论基础。 在研究初期，研究人员往往采用纯强度探测的方法进行实验。所谓的强度调 制，即将激光光束投射到所要探测的水面，此时激光光束将被反射至散射屏，同 时接受单元将探测到散射光，根据上文提到过的理论模型，水下声信号将对水表 面微波进行强度调制，那么就可以在将探测到的散射光进行解调之后得到水下声 场的振动频率，也即探测到水下的声源。 然而，纯强度探测也存在它的不足，它的缺点是探测的精度不是很高，而其 探测范围仅仅局限于低频信号，对于 200 Hz 以上的中高频信号并不敏感。主要原 因是：根据表面微波理论，随着声源频率的提高，表面微波波长逐渐变短。并且
