粗糙目标对光外差探测信号的退相干效应

发布时间：2018-08-10 17:11

【摘要】：光外差探测是公认的具有量子探测极限本领的相干探测体制,可以实现对回波信号振幅、频率和相位携带信息的全息探测,在微弱信号探测方面,具有直接探测不可比拟的优点,广泛应用于激光雷达、相干光通信、遥感、工业超精密测量以及激光多普勒测振、测距和测速等众多领域。然而,光外差探测实现条件非常苛刻,除了波前匹配、波矢匹配、模式匹配外,实际应用中,目标表面的粗糙特性也会严重影响回波外差探测效率。本文针对这一问题主要展开以下研究。1.对于光波来说,实际目标基本上都是粗糙的,目标表面粗糙程度的量化,对于定量分析粗糙目标对光外差探测的影响至关重要。通过蒙特卡罗方法,建立高斯型一维、二维随机粗糙面模型,以高度起伏均方根代表粗糙表面的“纵向”变化,以相关长度代表粗糙表面的“横向”变化,对实际粗糙目标表面形貌进行仿真,研究目标表面粗糙程度与这两个参数之间的关系,为粗糙目标光外差性能理论分析奠定基础。2.以蒙特卡罗方法建立的高斯随机粗糙面模型作为目标,对光外差探测系统中信号光回波波前进行一维和二维仿真,对粗糙目标光外差探测中,信号光和本振光波前匹配恶化的现象进行说明。最后,使用波前分析仪,对光外差系统中光源波前、本振光波前、光滑目标信号光波前和粗糙目标信号光波前进行测量,实际测量结果与仿真结果一致,验证信号光波前受粗糙目标表面调制,畸变严重。3.为了深入研究粗糙目标表面引起的“退相干”效应,通过蒙特卡罗方法建立的高斯随机粗糙面目标,对目标回波信号的探测过程进行仿真,研究目标表面粗糙对中频信号的影响,给出归一化中频电流在探测器光敏面上的一维和二维分布。此外,设计了粗糙面和光滑面两组光外差探测实验,验证目标粗糙对中频电流严重的“退相干”效应。实验结果充分说明了理论分析结论。4.由于不同目标,表面粗糙程度不同,对信号光波前的调制效应也不同,实际的“退相干”效应也不同。针对这一问题,通过粗糙面的蒙特卡罗模型,研究了目标回波光外差信号与目标粗糙程度参数——均方根高度及相关长度的相互关联。通过对大量不同粗糙程度目标光外差信号的数值仿真,给出了光外差信号与均方根高度及相关长度的定量关系曲线。最后,使用粗糙度比较样块作为目标,设计光外差实验,验证了仿真曲线。5.粗糙目标表面凹凸不平导致光外差信号随机起伏,如何准确设置探测阈值,正确判决是否存在信号成为难题。传统目标回波光外差探测使用高斯分布等简单模型来描述,这常常导致判决误差。提出一种准确获得光外差信号概率密度曲线的方法,利用多项式对实际目标测量数据进行拟合,给出较准确的概率分布曲线。通过对某装甲车表面样块多组测量数据的统计分析显示,利用多项式拟合来确定判决阈值,比起用简单的高斯分布来确定阈值,可以获得更高的检测概率和更低的误警概率。研究表明:对实测中频信号的统计直方图进行多项式拟合的方法,有利于精确设置探测阈值,可以使检测概率提高6.02%,误警概率降低7.7%。6.目标振动特性是目标识别和激光雷达探测系统设计的关键技术,也是光外差探测技术的一个重要应用。在理论分析目标振动特性测量原理的基础上,设计了一套激光多普勒振动特性测量系统,并且成功应用于实验室内音箱振动测量和室外汽车振动特性测量,得到相应的振动谱,这套系统也可以应用于其他振动目标(如飞机、坦克、舰船等)特性的测量,对精确打击军事目标和精确制导有重要意义,为激光多普勒探测的实用和推广奠定了基础。本文工作深入分析了粗糙目标光外差探测技术及其实际应用。研究了目标表面粗糙程度对光外差探测信号的影响,给出不同粗糙程度目标导致的退相干效应变化曲线,并设计实验验证了理论分析结果。还提出了一种提高探测阈值精度的方法,以装甲车实测中频信号进行说明,证明这种方法可以有效提高检测概率。此外,在外场环境下,使用光外差探测技术成功测量了汽车振动谱。文中所取得的阶段性成果为系统设计提供定量参考,也为探测系统性能评估仿真提供依据。
[Abstract]:Optical heterodyne detection is widely used in laser radar, coherent optical communication, remote sensing and industrial ultra-precision measurement because it can detect the amplitude, frequency and phase of the echo signal. In addition to wavefront matching, wavefront vector matching and pattern matching, the roughness of the target surface will also seriously affect the efficiency of echo heterodyne detection in practical applications. This paper focuses on this problem. 1. For light In terms of wave, the actual target is roughness basically, and the quantification of the roughness of the target surface is very important to quantitatively analyze the influence of the rough target on optical heterodyne detection. The length represents the "transverse" change of the rough surface. The surface topography of the actual rough target is simulated. The relationship between the roughness of the target surface and the two parameters is studied, which lays a foundation for the theoretical analysis of optical heterodyne performance of the rough target. 2. The Gaussian random rough surface model established by Monte Carlo method is used as the target to detect optical heterodyne. One-dimensional and two-dimensional simulation of signal light echo forward in the measurement system is carried out to illustrate the worsening matching between signal light and local oscillator in optical heterodyne detection of rough targets.Finally, the wavefront analyzer is used to analyze the light source wavefront, local oscillator wavefront, smooth target signal wavefront and rough target signal wavefront in optical heterodyne system. Measurements show that the wavefront of the signal is modulated by the rough surface of the target, and the distortion is serious. 3. In order to study the decoherence effect caused by the rough surface of the target, the detection process of the target echo signal is simulated by Monte Carlo method. The influence of surface roughness on IF signal is given, and the one-dimensional and two-dimensional distribution of normalized IF current on the photosensitive surface of the detector is given. In addition, two groups of optical heterodyne detection experiments are designed to verify the serious "decoherence" effect of target roughness on IF current. The experimental results fully illustrate the theoretical analysis conclusion. In order to solve this problem, the correlation between the optical heterodyne signal of target echo and the roughness parameter of target, the height of root mean square and the correlation length, is studied by Monte Carlo model of rough surface. The quantitative relationship curves between optical heterodyne signal and root mean square height and relative length are given by numerical simulation of a large number of optical heterodyne signals of different roughness degree targets.Finally, the optical heterodyne experiment is designed with the roughness comparison sample as the target to verify the simulation curves.5. The rough surface of the target causes random fluctuation of optical heterodyne signal. How to set the detection threshold accurately and decide whether there is a signal is difficult. Traditional target echo optical heterodyne detection is described by simple models such as Gaussian distribution, which often leads to decision error. A method to obtain the probability density curve of optical heterodyne signal accurately is proposed. The actual target measurement data is simulated by polynomial. Through the statistical analysis of several groups of measured data of an armored vehicle surface sample, it is shown that the decision threshold can be determined by polynomial fitting, and higher detection probability and lower false alarm probability can be obtained than by using simple Gaussian distribution to determine the threshold. Statistical histogram polynomial fitting method is advantageous to setting detection threshold accurately, which can increase detection probability by 6.02% and reduce false alarm probability by 7.7%. 6. Target vibration characteristic is the key technology of target recognition and lidar detection system design, and is also an important application of optical heterodyne detection technology. On the basis of the principle of property measurement, a laser Doppler vibration characteristic measurement system is designed and successfully applied to the vibration measurement of the loudspeaker in the laboratory and the vehicle in the outdoor. The corresponding vibration spectrum is obtained. This system can also be applied to the measurement of the characteristics of other vibration targets (such as aircraft, tanks, ships, etc.) to hit accurately. Attacking military targets and precise guidance is of great significance, which lays a foundation for the application and popularization of laser Doppler detection. In this paper, the optical heterodyne detection technology for rough targets and its practical application are deeply analyzed. The influence of the roughness of the target surface on the optical heterodyne detection signal is studied, and the decoherence caused by the targets with different roughness is given. A method to improve the accuracy of detection threshold is also proposed, which is illustrated by the measured IF signals of armored vehicles. It is proved that this method can effectively improve the detection probability. The phased results provide a quantitative reference for the design of the system and a basis for the performance evaluation and Simulation of the detection system.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN24

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