基于双法布里-珀罗干涉仪多纵模米散射多普勒激光雷达技术

Multi-longitudinal-mode Mie scattering Doppler lidar technology based on dual Fabry-Perot interferometer

提出了基于双法布里-珀罗干涉仪(FPI)的多纵模米散射多普勒激光雷达技术,分析了探测原理,并导出了径向风速和后向散射比测量误差公式。该技术要求多纵模激光源的纵模间隔与双FPI的自由谱间距相匹配,并将各纵模的中心频率锁定在双FPI周期性频谱曲线的交叉点附近。详细分析了频率匹配误差引起的风速测量误差。在低风速区域,由频率匹配误差造成的风速测量误差增加的百分数EV随匹配误差的增大而迅速增大;频率匹配误差不变时,EV随风速增大而缓慢减小;当频率匹配误差小于10 MHz时,EV将小于5%。设定合理的大气模式和系统参数,对基于双FPI的多纵模米散射多普勒激光雷达的探测性能进行了仿真分析。结果表明:在0~10 km高度、0~50 m/s的径向风速范围内,当距离分辨率为30 m、时间分辨率为30 s、激光发射天顶角为30°时,系统白天和晚间的径向风速测量精度分别优于1.50 m/s和1.02 m/s;在无云条件下,系统白天和晚间的后向散射比相对测量精度分别优于6.57%和4.53%。

Objective Doppler lidar is one of the most powerful tools for the remote sensing of the three-dimensional wind field in the atmosphere at present.It is widely used in wind power generation,weather forecast,aviation safety,atmospheric science research and other fields.The traditional coherent detection or direct detection Doppler lidar requires a single-longitudinal-mode laser source with narrow linewidth,resulting in the shortcomings of the existing Doppler lidar system such as high cost,poor environmental adaptability,low laser energy utilization,which seriously restricts their industrialization and the airborne and spaceborne applications.Therefore,it is of great significance and scientific value to explore and study the technology of multi-longitudinal-mode(MLM)Doppler lidar using MLM laser as the emission source.For this purpose,the MLM Mie Doppler lidar technology based on dual Fabry-Perot interferometer(FPI)is proposed and studied.Methods The detection principle of MLM Mie Doppler lidar based on dual FPI is analyzed(Fig.1).The theoretical formulas of radial wind speed and backscatter ratio measurement errors are derived,and the matching relationship between the longitudinal mode interval of the MLM laser source and the free spectral spacing of the dual FPI is analyzed,as well as the wind speed measurement error caused by the mismatch between the two.The lidar system structure(Fig.7)and parameters(Tab.1)are designed,and the detection performance of the designed lidar system is simulated using the 1976 USA atmospheric model and simulated cumulus clouds.Results and Discussions The frequency matching condition between the longitudinal mode interval of the MLM laser source and the free spectral spacing of the dual FPI is that the former is an integral multiple of the latter.When the frequency matching condition is satisfied,the MLM wind measurement is equivalent to the superposition of each single-longitudinal-mode(SLM)wind measurement.In the low wind speed region,the percentage of the wind speed measurement error EV caused by the frequency matching error increases rapidly with the increase of the matching error;When the frequency matching error remains unchanged,EV decreases slowly with the increase of wind speed;When the frequency matching error is less than 10 MHz,EV will be less than 5%(Fig.6).The simulation results of lidar detection performance show that,in the range of 0-10 km altitude and 0-50 m/s radial wind speed,when the range resolution is 30 m,the time resolution is 30 s and the zenith angle of laser emission is 30°,the radial wind speed measurement accuracy of the lidar system is better than 1.50 m/s and 1.02 m/s in daytime and nighttime respectively;Under cloudless conditions,the relative measurement accuracy of the backscatter ratio in daytime and nighttime is better than 6.57%and 4.53%,respectively(Fig.9).Conclusions A Mie Doppler lidar technology based on multimode laser and dual FPI is proposed and studied.This technology requires that the longitudinal mode interval of the laser source should match the free spectral spacing of the dual FPI,and the center frequency of each longitudinal mode should be locked near the intersection of the dual FPI periodic spectrum curves.When the frequency matching condition is satisfied,the MLM wind measurement is equivalent to the superposition of each SLM wind measurement.The frequency matching error will increase the wind speed measurement error,but as long as the frequency matching error is controlled below 10 MHz,the impact of the matching error on the wind speed measurement accuracy is less than 5%,which can be easily achieved through system calibration.The simulation results show that the Doppler lidar system based on this technology has high detection accuracy of wind speed and backscatter ratio in all weather.These conclusions fully demonstrate the feasibility of this technology.