移动式多普勒激光雷达光束扫描及风场反演技术研究

移动式多普勒激光雷达在外场实验过程中,考虑到工作平台的随机性,测量坐标系很可能不再是地面参考坐标系,这为三维矢量风场的反演带来困难。提出采用三维空间坐标旋转变换的方法建立了测量坐标系与地面参考坐标系的一般关系式,并进一步导出了反演三维风场的普遍公式。此外,在光束扫描过程中,由于二维扫描仪加工精度等的限制,光束存在一定的定向误差。采用Monte-Carlo模拟方法定量研究了光束指向偏差引起的风场测量误差,结果表明,当水平风速为100m/s时,1°的光束定向误差引起的水平风速大小误差为0.712m/s,方向误差为0.704°,与理论计算结果一致。理论分析结果还表明:当水平风速为100m/s时,1°的光束最大定向偏差引起的水平风速大小的最大偏差为1.16m/s,方向最大偏差为1°。     

Ultraviolet Rayleigh Lidar for Wind and Temperature Measurements

A new method of simultaneous remote sensing of atmospheric wind and temperature by a ultraviolet Rayleigh lidar is described. This technique uses two narrowband filters located at either side of the wings of the Rayleigh backscatter spectrum to analyze Rayleigh backscattering signals. These filters are selected to be greatly sensitive to both velocity and temperature. By measuring the ratio and the sum of the two normalized filtered signals, the line-of-sight wind velocity and temperature profiles can be retrieved. A lidar system is proposed for the wind velocity and temperature measurements in the middle atmosphere, and the simulation results show that the accuracies of velocity and temperature are about 1 m/s and 2 K at the height of 30 km, respectively. The influence of aerosol component has been estimated for clear weather conditions, and with an uncertainty of aerosol component of 15% the errors are about 0.1 m/s and 2 K above the troposphere, respectively.     

瑞利散射多普勒激光雷达风场反演方法

介绍了瑞利散射多普勒激光雷达的风场探测原理和系统结构. 给出了Fabry-Perot(FP)标准具透过率曲线的校准方法. 指出对透过率采用Lorentz或Voigt拟合会产生较大误差,特别是采用Lorentz拟合最大将引起8%的误差. 提出了采用非线性最小二乘法拟合标准具的透过率函数,该方法可以有效消除拟合误差,提高风速测量精度. 考虑到温度不确定度在风场反演过程中的主导影响,提出了同时反演风速和大气温度的非线性迭代算法. 风场反演仿真试验结果表明:在不考虑米散射信号的影响下,该反演算法与传统的反演方法相 关键词： 激光雷达 瑞利散射 多普勒 风     

Mie-Rayleigh Doppler Wind Lidar with Two Double-edge Interferometers

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Accuracy Analysis of the Fabry–Perot Etalon Based Doppler Wind Lidar

A direct detection Doppler wind lidar with the dual Fabry–Perot technique has been built in Hefei, China, and the system is described in this paper. A dual, air-spaced Fabry–Perot etalon is designed as the frequency discriminator and the transmission characteristics are measured with a stabilized cw laser and a pulse laser. The experimental data are found to be in agreement with the designed parameters. The Doppler shift is measured by taking the ratio of the transmitted intensities from the dual etalon. Analysis of the accuracy of Doppler measurement is made by considering the factors of the number of iterations in converting the measured ratio to the Doppler shift, the laser intensity fluctuation and the signal-to-noise ratio. In the sufficient signal-to-noise ratio the velocity accuracy of the Doppler lidar system is estimated to be better than 0.5 m/s.     

Mie-Rayleigh Doppler Wind Lidar with Two Double-edge Interferometers

The Mie-Rayleigh direct detection Doppler lidar (DDDL) with two double-edge etalons is presented. Fabry-Perot (F-P) etalon is used as the spectral analyzer for Doppler measurement formthe aerosol and molecule backscattered signals. The aerosol and molecular backscattering signals are separated by a polarization isolator with less signal decrement, so this system has about same accuracy as individual Rayleigh Doppler lidar or Mie Doppler lidar system. The simulation on a proposed ground-based DDDL at 532 nm shows that the velocity error is less than 2 m/s below 8 km for a 100 m vertical resolution by Mie channel and 2m/s up to 20 km by Rayleigh channel, respectively.     

光谱稳定性对直接探测多普勒测风激光雷达的影响研究

从种子注入固体激光器的不稳定和多普勒频移检测干涉仪的光谱漂移出发,模拟和分析其对基于双边缘探测技术的直接探测多普勒激光雷达风速测量准确度的影响. 模拟结果显示,在5 min积分时间的30 000个脉冲内,如果达到风速准确度1 m/s,要求激光器出现多纵模的脉冲不能超过总脉冲个数的0.06％.在干涉仪光谱稳定方面,使用两级温控可以将干涉仪温度控制在±0.002℃,对应风速误差为±0.226 m/s.同时提出通过监视种子注入过程中的脉冲建立时间和干涉仪温度,可以在数据反演时,消除激光频率跳动和干涉仪光谱漂移对风速测量准确度的影响.     

角度调谐的多普勒激光雷达硬目标转速测量

利用角度调谐方法确定直接探测多普勒测风激光雷达的初始工作点,角度调节精度可达10 μrad.在此工作点处使用频率稳定性为10-7,单纵模出现概率大于98%的Nd:YAG激光器,通过偏振分光光路测得参考信号与回波信号.配合目标准确放置到准直镜的焦距上,分别测量了配合目标静止,正转和反转时的参考信号与回波信号.利用配合目标静止时测得参考信号与回波信号的关系可得参考信号的角度矫正因子为1.1949,使用该矫正因子测得硬目标在正转和反转时转速与真实转速之间的误差小于0.5 m/s.     

基于周期图最大似然算法的相干激光测风多普勒频率估计

采用径向风速的估计不确定度和探测概率作为评价指标,研究了周期图最大似然(PML)算法的多普勒频率估计性能.基于大气分层激光回波模型,分别以PML和周期图最大值法(PM)对回波信号进行处理,验证了PML算法在相干激光测风中的可行性;分析比较不同信噪比条件下PML算法的风速估计不确定度与探测概率.仿真结果表明,在发射脉冲宽度为400ns、采样点数为128时,PML算法适合在中等信噪比条件下使用,且风速估计的不确定度整体小于PM算法的,在信噪比为-13dB时径向风速的估计不确定度为0.75m/s,探测概率在90%以上,该研究为后续的外场试验提供了指导.     

Mobile Rayleigh Doppler wind lidar based on double-edge technique

<正>We describe a mobile molecular Doppler wind lidar(DWL) based on double-edge technique for wind measurement of altitudes ranging from 10 to 40 km.A triple Fabry-Perot etalon is employed as a frequency discriminator to determine the Doppler shift proportional to the wind velocity.The lidar operates at 355 nm with a 45-cm-aperture telescope and a matching azimuth-over-elevation scanner that provides full hemispherical pointing.To guarantee wind accuracy,a single servo loop is used to monitor the outgoing laser frequency to remove inaccuracies due to the frequency drift of the laser or the etalon.The standard deviation of the outgoing laser frequency drift is 6.18 MHz and the corresponding velocity error is 1.11 m/s.The wind profiles measured by the DWL are in good agreement with the results of the wind profile radar(WPR).Evaluation is achieved by comparing at altitudes from 2 to 8 km.The relative error of horizontal wind speed is from 0.8 to 1.8 m/s in the compared ranges.The wind accuracy is less than 6 m/s at 40 km and 3 m/s at 10 km.     

全光纤M-Z干涉仪的高灵敏度与大动态范围多普勒激光雷达风场探测技术

多普勒测风激光雷达是大气风场探测的重要手段之一。通过检测风速导致的大气后向散射谱的多普勒频移从而实现风速的探测。由于受鉴频器本身特性的影响,高灵敏度与大动态范围的探测一直是大气风场探测的难点。提出采用双光纤Mach-Zehnder干涉仪(FMZI)作为多普勒激光雷达的鉴频器件,设计两路不同动态范围及风速探测灵敏度的FMZI鉴频器同时对大气回波信号进行鉴频。采用小光程差(13.7 cm)、大动态范围(±100 m·s-1)鉴频光路FMZI-2对风速区间进行定位,大光程差(74.8 cm)、高探测灵敏度(2.62%/(m·s-1))的鉴频光路FMZI-1进行风速精细探测,从而实现大动态范围高灵敏度的风场探测。利用标准大气模型对不同参数条件下的系统灵敏度、系统探测的信噪比及风速误差进行仿真分析。结果表明,该系统可以实现±100 m·s-1大动态范围内风速误差小于1 m·s-1的大气风场探测,为大动态范围高灵敏度测风激光雷达的发展进行了有益的探索。     

Differential Discrimination Technique for Incoherent Doppler Lidar to Measure Atmospheric Wind and Backscatter Ratio

A new incoherent Doppler lidar scheme is proposed using a high resolution Mach-Zehnder interferometer discriminator with sinusoidal transmission functions. A two-channel differential discrimination technique is developed which provides high sensitive velocity measurement. The aerosol and molecular backscatter signals can be separately measured and the backscatter ratio obtained. Principle of the measurement is described and the characteristics of this technique are analyzed and compared. Numerical calculation for a moderate size 1.064 μ lidar shows that an accuracy better than 1 m/s for the velocity measurement and 18% for the backscatter ratio measurement can be obtained up to a height of 10 km by a 500 shot average.     

基于菲佐干涉仪测风激光雷达的误差分析

详细分析了基于菲佐(Fizeau)干涉仪测风激光雷达利用条纹重心法反演风速时的方法误差和系统噪声引起的测量误差。提出了方法误差的修正方法,推导出了测量误差理论公式。并用蒙特卡罗方法模拟了低对流层的回波信号,并对其进行条纹重心法风速反演。结果表明:方法误差和气溶胶与分子后向散射比有关,噪声引起的测量误差与信号强度和气溶胶与分子后向散射比有关。在0~5 km,高度采用条纹技术测量的风速误差小于1 m/s。     

机载激光雷达风切变探测性能分析

介绍了用于风切变测量的激光雷达外差探测系统，阐述了其工作原理，根据CO2雷达系统与Ho：YAG雷达系统相关参数进行信噪比模拟和风速误差对比，模拟结果表明波长为2．1μm的Ho：YAG雷达和波长为10．6μm CO2雷达都适合机载低空风切变探测。通过对比表明Ho：YAG雷达的性能更为优良，误差更小，探测距离更远。     

基于大气分层的激光测风雷达回波模型

从相干激光测风雷达原理入手,论述了激光雷达回波特性和多普勒效应在测风雷达中的应用。基于大气分层模型,考虑到激光束的传播及其与大气之间的相互作用,建立了激光测风雷达回波模型,模拟回波信号在大气中的传输过程,为激光测风雷达回波信号的模拟提供了理论基础。     

条纹技术测风激光雷达研究

使用单纵模355 nm激光作为发射光源,Fizeau干涉仪作为光谱鉴别设备,对条纹技术测风激光雷达进行了研究.对激光器频率抖动和Fizeau干涉仪光谱进行了分析,建立了条纹技术激光雷达系统,使用Fizeau干涉仪扫描的方法对系统进行了风速标定.利用研制的激光雷达系统对引入的参考光信号和大气后向散射信号进行同时测量,得到1.5 km以内的大气风速剖面.     

新型双通道Mach-Zehnder干涉仪多普勒测风激光雷达鉴频系统研究及仿真

Mach-Zehnder(M-Z)干涉仪可作为鉴频器件应用于多普勒测风激光雷达系统中.鉴于一般M-Z干涉仪的稳定性差,不易于调节的缺点,提出一种基于双棱镜结构的新型双通道M-Z干涉仪作为多普勒测风激光雷达鉴频器件.在进行探测原理分析的基础上,利用光学设计软件对其鉴频系统结构进行了参量优化设计和系统仿真.通过设定实验参量并进行光线追迹模拟仿真实验结果,应用反演理论获得了风速值.利用多普勒频移公式计算获得理论风速并与仿真结果进行了对比,结果表明反演仿真风速与理论风速值基本吻合,标准差为0.46m/s.此新型双通道M-Z干涉仪可以作为鉴频器件应用于多普勒测风激光雷达系统中,在光路的调节及提高系统稳定性上具有优势.     

Correction of temperature influence on the wind retrieval from a mobile Rayleigh Doppler lidar

A mobile Rayleigh Doppler lidar based on double-edge technique is implemented for simultaneously observing wind and temperature at heights of 15 km-60 km away from ground.Before the inversion of the Doppler shift due to wind,the Rayleigh response function should be calculated,which is a convolution of the laser spectrum,Rayleigh backscattering function,and the transmission function of the Fabry-Perot interferometer used as the frequency discriminator in the lidar.An analysis of the influence of the temperature on the accuracy of the Une-of-sight winds shows that real-time temperature profiles are needed because the bandwidth of the Rayleigh backscattering function is temperature-dependent.An integration method is employed in the inversion of the temperature,where the convergence of this method and the high signal-to-noise ratio below 60 km ensure the accuracy and precision of the temperature profiles inverted.Then,real-time and on-site temperature profiles are applied to correct the wind instead of using temperature profiles from a numerical prediction system or atmosphere model.The corrected wind profiles show satisfactory agreement with the wind profiles acquired from radiosondes,proving the reliability of the method.