【作者】 刘娜；

【导师】 杨苏辉；

【作者基本信息】 北京理工大学 ， 电子科学与技术， 2017， 硕士

【摘要】 射频强度调制激光雷达是以射频强度调制激光作为载波进行测距测速和成像的新型激光雷达,兼具激光雷达的空间分辨率高、成本低、体积小、机动灵活和微波雷达抗干扰能力强、信号处理技术成熟等优势,在目标识别、测绘、水下目标探测、海洋资源考察等领域具有广泛的应用前景。本文结合射频强度调制激光雷达的应用背景深入研究了双频激光信号抗大气湍流干扰的特性以及射频强度调制绿光在水中的传输特性。论文主要内容包括:阐述了本论文的研究背景和意义,对射频强度调制激光雷达的光源—双频激光器以及射频强度调制激光雷达系统的国内外发展情况进行了文献综述,并着重总结和分析了射频强度调制激光技术在水下探测中的应用及发展。深入研究了双频激光信号抗大气湍流干扰的特性,建立了双频激光信号通过大气湍流干扰后位相变化的理论模型。采用功率谱反演法设计了用于模拟大气湍流装置的随机相位屏,搭建了Mach-Zehnder干涉仪,以双频信号为光源,利用空间光调制器实现对双频激光束的随机相位扰动,模拟不同强度下的大气湍流,并利用干涉条纹对比度的变化来表征大气湍流对双频激光位相造成的扰动。改变双频激光的参数进行实验,利用Matlab进行图像处理干涉图样,并对结果进行分析。研究结果表明,在较强的大气湍流条件下,双频激光信号的调制深度对其抗干扰能力有着较大的影响,调制深度越深,其抗大气湍流干扰能力越强。对射频强度调制绿光的抗水中散射的特性进行了研究,建立了基于蒙特卡洛方法的光子水下传输模型,进而推导出载波调制水下探测激光雷达的仿真模型。模拟了余弦调制高斯脉冲信号水下探测的情况,改变载波调制激光雷达系统中的脉冲宽度、调制频率和调制深度等参数进行模拟,分析其对探测结果的影响。模拟结果表明,在调制深度和调制频率一定时,脉冲宽度影响目标回波信号的展宽和信噪比,存在最佳脉冲范围是10～40ns。在调制深度和脉冲宽度一定时,调制频率同时影响探测精度和信噪比,因此需要折中选择。在调制频率和脉冲宽度一定的情况下,调制深度增加,目标回波信号的信噪比增大。本文的研究对射频强度调制激光雷达系统的设计和应用具有一定的参考价值。更多还原

【Abstract】 Lidar-radar uses RF intensity modulated laser as a carrier in velocimetry,ranging and imaging.It combines the advantages of high resolution,low cost,small volume,flexibility of lidar and anti-turbulence ability,mature signal processing technology of microwave radar.Lidar-radar has wide applications in the fields of target identification,surveying and mapping,underwater target detection and marine resource investigation.In this paper,based on the applications of lidar-radar,the characteristics of anti-atmospheric turbulence interference of dual-frequency laser signals and the transmission characteristics of RF intensity modulated green light in water are studied.The main contents are listed as follows:The background and significance of this paper is presented.The developments and applications of lidar-radar and the light source: dual-frequency lasers are summarized.The application and development of lidar-radar in underwater detection are summarized and analyzed.A theoretical model is deduced to find out the coherence changes of dual-frequency laser after atmospheric turbulence.The power spectrum inversion method is used to design a random phase screen for simulating atmospheric turbulence.An Mach-Zehnder interferometer is built to study the influence of atmospheric turbulence on the phase of the modulated beam.A spatial light modulator taking the random phase screen as its input signal is used to simulate the atmospheric turbulence disturbance.The contrasts of the interfering fringes are used to quantitate the phase changes of the dual-frequency signal.The interference patterns obtained in the experiment were processed with Matlab software.The dependence of phase changes of the modulated signal to the modulation index at different atmospheric strengths are studied theoretically and experimentally.The experimental results are in agreement with the theoretic model.It is shown that when the atmospheric turbulence is strong,the higher the modulation index of the dual-frequency laser signal,the stronger the ability to resist atmospheric turbulence disturbance.An underwater transmission model for photons based on Monte Carlo method is presented.An Gaussian pulse modulated by cosine signal is used as input signal.The effects of parameters such as pulse width,modulation frequency and modulation index on the detection results are discussed.The simulation results show that the pulse width has the optimum range 10～40 ns when the modulation index and frequency remain constant.There is an optimized modulation frequency when both the SNR and ranging resolution are concerned.In case when the modulation frequency and pulse width keep unchanged,the higher the modulation depth,the higher the signal-to-noise ratio of the target echo signal can be obtained.更多还原