光电调制反馈激光多普勒测速仪研究

本文介绍一种新型激光多普勒测速仪——光电调制反馈激光多普勒测速仪(简称OEMF-LDA)。该仪器突破了传统LDA系统构成的模式,采用变频光学频移技术和光电混合反馈技术,将光路和电路连接成闭环负反馈跟踪环路,提高了信噪比,降低了成本。文中结合实验,讨论了OEMF-LDA的静态及动态特性,并在系统的结构及性能等方面与传统LDA作了比较。     

颠簸摇摆引起的车辆测速误差分析

分析了车辆颠簸摇摆时单光束测速系统的测量误差,提出了一种基于Janus配置的激光测速系统。该系统由两个单光束系统组成,安装于车辆底部,分别向车头和车尾方向以相同的倾角发射同频激光束,测量各自散射回波的多普勒频移,根据两多普勒频移和发射倾角得到摇摆角的值,进而求得车辆运行速度。理论分析和仿真结果表明:单光束系统的测速精度受光束的发射倾角、车辆摇摆角以及车辆垂直方向的速度影响较大;Janus系统对车辆的颠簸摇摆不敏感,可得到较高的测速精度,颠簸起伏速度为0.3m/s,当摇摆角为16°时,误差小于0.5%。     

参考光束型激光多普勒测速仪的误差分析

阐述了参考光束型激光多普勒测速仪的基本原理,从理论上分析了原理公式近似、高斯光束干涉、激光线宽、探测器孔径、有限渡越时间、信号处理算法、空气折射率变化及角度测量等诸多因素对激光多普勒测速仪测量结果造成的误差,研究并给出了每一种影响因素所引起误差的理论公式,在每一种影响因素中具体讨论了各种光学参数对测量误差的影响并对部分参数进行实验研究。理论分析和实验表明:在实验中需要选择线宽较窄的激光器及孔径较小的光电探测器,而在选择光束光斑半径和信号光中心光线的方向与粒子运动方向的夹角时,既要考虑激光的质量和多普勒信号的强度,同时也需要考虑原理公式近似、探测器孔径的尺寸、有限渡越时间及高斯光束干涉等多种因素对测量结果的影响。     

相位调制激光多普勒频移测量方法的改进

本文对现有相位调制激光多普勒频移测量方法进行了改进,通过定义新的鉴频参量来同时利用相位调制信号直流和交流分量中的有用信息进行多普勒频移测量.由于相位调制信号直流分量中包含着调制信号光的Fabry-Perot干涉仪光强透过率,所以这一改进本质上是将基于Fabry-Perot干涉仪的边缘技术激光多普勒频移测量方法的优势引入到相位调制测量方法中,以提高其自身的性能.理论上证明改进后的相位调制激光多普勒频移测量方法无需对信号光的光强进行测量,所以可以进一步简化探测系统的结构和较少噪声混入的通道.另外,通过对改进前后鉴频和测量灵敏度曲线进行对比,还证明了其具有更高的测量灵敏度和动态范围.实验上对硬目标反射的频移可控信号光进行测量,不但证明了理论的正确性,而且证明了改进后的相位调制激光多普勒频移测量方法,测量动态范围提高约1倍,测量标准偏差降低约35%.     

基于不同散射机制特征的海杂波时变多普勒谱模型

海杂波的多普勒谱建模对采用多普勒处理技术的雷达进行有效的海杂波抑制和目标检测具有重要的意义.本文分别考虑Bragg,白冠和破碎波三种散射机制对应的多普勒谱分量的特征,对三种谱分量的频移和展宽进行分离,并引入附加速度频移量,提出了基于不同散射机制特征的雷达海杂波时变多普勒谱模型.该模型假设谱强度为受观测时间区间影响的随机变量,能够同时适用于平均多普勒谱与短时多普勒谱建模.通过分别对黄海海域实测的岸基P,S波段海杂波平均多普勒谱与短时多普勒谱建模测试,结果表明该模型相对传统模型的建模精度更高,尤其体现在短时谱的观测时间较长和平均谱形式较为复杂的情况下,建模误差显著减小.     

一种结合两类相位调制激光多普勒频移测量的方法

提出了一种新的激光多普勒频移测量方法,该方法以相位调制拍频信号振幅和相位作为自变量定义新函数,并以该函数作为多普勒频移鉴频参量,将两类相位调制激光多普勒频移测量方法结合.理论上将该方法的鉴频曲线、灵敏度曲线以及误差曲线等与两类相位调制方法的相应曲线进行比较,发现该方法不但继承了相位调制拍频信号振幅方法的工作方式,能够对小频移量进行测量,而且吸收了相位调制拍频信号相位方法的测量能力,具有更高的测量灵敏度和动态范围.通过实验对硬目标反射的频移可控信号光进行测量,证明了理论的正确性,而且通过调整平移参数,可以使该方法的测量动态范围提高约26.8%,更适合对高多普勒频移量进行测量.     

激光多普勒自主测速仪天线安装误差对测速精度的影响

为了减小激光多普勒自主测速仪天线安装误差引起的测速误差,以多普勒频移原理为基础,通过旋转矩阵的复合变换推导出测速误差与安装误差间的函数关系,分析了三个安装误差角对三维测速精度的影响,并对旋转矩阵采用Bursa模型线性化后在整体最小二乘准则下给出安装误差角的最优估计,从而实现测速误差的补偿。仿真结果表明:测速误差随速度的增大而增大,影响纵向、横向测速精度的主要因素是偏航角,影响垂向测速精度的主要因素是纵倾角,补偿后三维测速误差显著减小。     

公路超速检测激光测速仪研究（英文）

为了减少公路违章超速现象的发生,使交通安全监测体制更完善,设计并研制了一种可远距离工作的便携式激光多普勒测速系统.阐述了激光多普勒测速的基本原理和光束变换的实现方法,并利用双透镜类望远系统的结构搭建了用于公路超速检测的激光测速仪.理论分析与路边测试试验表明:该激光多普勒测速系统具有长工作距离和大景深的特点,并且可以较高精度获得车辆的行进速度.相比于传统激光测速仪,便携式激光多普勒测速系统提升了中心工作距离并增大了景深.新激光测速仪的中心工作距离为10m,景深为±1m,测速精度可以达到0.1%.     

基于激光多普勒技术扭振测量的研究

提出一种基于激光多普勒技术和光学外差原理对高速回转机械进行扭振测量的新方法,分析了工作原理,推导出光路部分的数学模型,并通过实验分别验证了测量方法的可行性和准确性。高相干激光投射到转轴同一个截面上2点,反射光的多普勒频移正比于转轴转速,通过光学配置,使前后两个时刻的多普勒频移光信号在光探测器上发生光学混频,光电流拍差正比于转轴在两个时刻的速度差,控制两个时刻时间差很小,直接得到角加速度。与其他激光多普勒扭振测量方法相比,该方法直接测量转动角加速度,在保证测量精度的前提下,提高了扭转振动测量的实时性,极大地扩展了扭振测量的动态范围,对大型回转机械运行状态监测和故障诊断具有重要意义。     

基于TMS320VC5402的激光多普勒测速系统

介绍了激光多普勒测量技术的原理和差动后向散射测量方式以及数字信号处理式激光多普勒测速仪的设计方案.其中包括基于TMS320VC5402的多普勒信号采集卡硬件电路和软件设计.运用该测速仪对固体表面运动速度进行测量.对采集到的多普勒信号进行高通滤波处理,以提高信噪比,运用傅里叶变换处理数据,计算出运动目标的速度并与实际速度进行了比较.结果表明该系统用于固体表面速度的测量切实可行,精度可达到2%.     

Two-dimensional laser Doppler velocimeter using polarized beams and 90° phase shift for discrimination of velocity direction

A laser Doppler velocimeter (LDV) for two-dimensional velocity measurement using a simple optical configuration without any optical modulator is proposed. The structure using polarized beams and the 90° phase shift of the reference beam is used to discriminate the direction of velocity. The analytical relation among beat frequencies and velocity components is derived and the characteristics of the proposed LDV are simulated. The simulation results indicate that the direction of velocity can be discriminated by the proposed LDV as well as the magnitudes of the components of the velocity.     

油中悬浮粒子激光多普勒测速瞬时速度的分析

二维频移激光多普勒测量油中悬浮粒子速度时,根据悬浮粒子通过针孔光阑时存在的四种不同情况,对原有激光多普勒测量悬浮粒子瞬时速度的方法进行了改进,提出一种悬浮粒子瞬时速度分析处理方法,利用该方法,对水平方管内的油中悬浮粒子的瞬时速度进行了测量分析。结果表明:改进方法获取的悬浮粒子瞬时速度的稳定性较好,能够表征在一组粒子通过激光多普勒的针孔光阑的时间段内粒子组随着时间的变化趋势,提高了频移激光多普勒采样数据的利用效率,有利于进一步准确表征悬浮粒子在油液中二维瞬时速度的分布特征和运动轨迹,为激光多普勒实验测量中悬浮粒子瞬时速度的表征提供理论支撑。     

Solid state and fibre optic laser doppler velocimeters

Laser Doppler velocimetry (LDV) has become established as an important technique for the measurement of velocities of macroscopic objects and fluids: the dynamic range is large (～10^-6-10⁵ ms^-1) and the measurement is absolute and non-invasive. However, the size and cost of LDV has restricted its use in some areas. This paper presents two separate approaches to reduce these problems: we describe a compact LDV system incorporating a solid state laser diode and also an investigation of the feasibility of a fibre optic LDV system in which the conventional optical components are replaced by fibre optics.The experimental arrangement used for the solid state LDV system was of the Doppler difference type; i.e. a system of parallel interference fringes is focused in the measurement volume, so that a particle passing through this volume produces a scattered light signal which is intensity modulated. In its simplest form, the technique cannot determine the direction of motion of the particle, but this difficulty may be overcome by causing the fringes to ‘move’ within the measurement volume with known velocity. In the present experiments, the laser output frequency was modulated by modulating its drive current; since the path lengths of the two beams interfering in the measurement volume were unequal, fringe motion was achieved.The fibre optic LDV experiment was also of the Doppler difference type, and it was demonstrated that the necessary stabilised interference fringe system could be projected using a fibre optic system. An electronic servo was devised to compensate for the random differential thermal drifts in the fibres which would otherwise have produced unacceptable drifts in the fringe pattern.     

Research on laser Doppler velocimeter for vehicle self-contained inertial navigation system

An idea of using laser Doppler velocimeter (LDV) to measure the velocity for the vehicle inertial navigation system was put forward. The principle of measuring its own velocity with laser Doppler technique was elaborated and reference-beam LDV was designed. Then Doppler signal was processed by tracking filter, frequency spectrum refinement and frequency spectrum correction algorithm. The result of theory and experiment showed that the reference-beam LDV solved the problem that dual-beam LDV cannot be used for measuring when the system was out of focus. Doppler signal was tracked so that signal-to-noise ratio was improved, and the accuracy of the system was enhanced by the technology of frequency spectrum refinement and correction. The measurement mean error was less than 1.5% in velocity range of 0-30 m/s.     

Automatic laser frequency stabilization to iodine absorption line

The measurement accuracy of a Doppler lidar and other laser spectra research is very sensitive to the frequency drift of the laser transmitter. Because currently used frequency locking methods usually involve complicated optics and are sensitive to the working conditions, we present a simple and robust locking method—locking the laser to iodine absorption lines with a software-based PID controller. The locking strategy was successfully applied to three kinds of cw single-frequency Nd: YAG lasers with different tuning actuators. The disadvantage of a slow tuning response is eliminated by using a parameter-adjustable PID algorithm. The frequency stability is better than 200 kHz for 3 h which, to our knowledge is one of the best long-period locking result achieved for this kind of laser.     

The development of an optical Doppler technique for measuring flow velocities

For a generalized scheme of LDV, the expressions describing the light intensity distribution in a photo-receiver plane with regard to the size of the scattering particles have been calculated using Fourier optics.The LDV signal should be considered as a narrow-band stochastic process representing the sum of random phase radio frequency pulses arising from each light scattering particle. Then the expected error of the mean velocity measurement is equal to half the reciprocal of the number of interference fringes squared and the input signal-to-noise ratio is equal to the square root of the product of Doppler frequency, fringe number and averaging time.The device developed by the authors includes d.c. optical signal compensation. The device is described and the results of its use are given.     

An international review of laser Doppler vibrometry: Making light work of vibration measurement

In 1964, just a few years after the invention of the laser, a fluid velocity measurement based on the frequency shift of scattered light was made and the laser Doppler technique was born. This comprehensive review paper charts advances in the development and applications of laser Doppler vibrometry (LDV) since those first pioneering experiments. Consideration is first given to the challenges that continue to be posed by laser speckle. Scanning LDV is introduced and its significant influence in the field of experimental modal analysis described. Applications in structural health monitoring and MEMS serve to demonstrate LDV's applicability on structures of all sizes. Rotor vibrations and hearing are explored as examples of the classic applications. Applications in acoustics recognise the versatility of LDV as demonstrated by visualisation of sound fields. The paper concludes with thoughts on future developments, using examples of new multi-component and multi-channel instruments.     

Experimental study on minimum resolvable velocity for heterodyne laser Doppler vibrometry

A high spatial resolution,high velocity resolution all-fiber laser Doppler vibrometry(LDV) based on heterodyne detection for vibration measurements is reported.A linewidth of 1-kHz single-mode continuous fiber laser,polarization-preserving fiber,and a telescope with 30-mm aperture are used in this LDV.With the inphase-quadrature circuit and the digital differentiating discriminator,a high velocity resolution of 96.9 nm/s and a high displacement resolution of 2.5 pm are obtained simultaneously with a glass a...     

A novel optical method in micro drop deformation measurements

A novel method was developed to determine the deformation of a micro drop on a substrate. The principle of the method is based on the scattering of parallel fringes pattern from the deformed droplet. Because only a very few components are needed together with a conventional laser Doppler anemometry (LDA) transmitting unit, the newly developed method is very easy to be implemented. Within the geometrical optics approach, it is possible to reconstruct the profile of a non-spherical micro drop from the scattered interference fringes. The spatial frequency of the fringes was analyzed using fast Fourier transform (FFT). The validation experiments for this method in the determination of micro drop deformation which is affected by gravity, capillary force and surface tension were performed and the results are agreed well with the theoretical analysis.     

Application of Hilbert–Huang transform to laser Doppler velocimeter

A new method based on Hilbert–Huang transform is proposed to analyze the laser Doppler signal with a large acceleration. The Doppler signal is decomposed into several Intrinsic Mode Functions (IMFs) via empirical mode decomposition (EMD). And the Hilbert transform is used to compute the instantaneous frequency. The vehicle velocity parameter is estimated by taking linear fitting on the instantaneous frequency of the relevant IMF. The simulation results show that the HHT-based method is quite useful for the LDV that offers velocity parameter to the vehicle self-contained navigation system when the vehicle moves at a large acceleration.