全光纤相干多普勒激光雷达非线性最小二乘风速反演方法及实验研究

Study of All-Fiber Coherent Doppler Lidar Wind Profile Nonlinear Least Square Retrieval Method and Validation Experiment

研制了一套人眼安全的全光纤相干多普勒激光测风雷达系统。系统采用1550 nm全光纤单频保偏激光器作为激光发射光源,激光器单脉冲能量0.2 m J,重复频率10 k Hz,脉冲半高全宽400 ns,线宽小于1 MHz。激光雷达接收望远镜和扫描器口径100 mm,采用速度方位显示(VAD)扫描模式对不同方位的视线风速进行测量,使用平衡探测器接收回波相干信号,通过1 G/s的模拟数字(AD)采集卡对相干探测信号进行采集,在现场可编程门阵列(FPGA)数字信号处理器中进行1024点快速傅里叶变换(FFT)得到不同距离门回波信号功率谱信息。对于获得的各方位视线风速,研究采用非线性最小二乘法对激光雷达测量的风速剖面矢量进行反演。激光雷达与风廓线雷达测量的风速进行了对比,两者测量的水平风速,风向和竖直风速相关系数分别为0.988,0.941和0.966。

An eye-safe all-fiber coherent Doppler wind lidar system is developed. The system employs an all-fiber single-frequency polarization-maintaining laser as emission light at 1550 nm. The laser has pulse energy of 0.2 m J,repetition frequency of 10 k Hz and pulse full width half maximum of 400 ns, and the linewidth is less than 1 MHz.The aperture of the receiver-telescope and scanner of lidar is 100 mm. The system is operated in velocity azimuth display（VAD） scanning mode for wind speeds measurement at different azimuths. The mixing echo signal is received by balanced detector and sampled by 1 G/s analog to digital（AD） acquisition card, then 1024 points fast Fourier transform（FFT） and spectrum accumulation of echo signal at every range gate are implemented in the field programmable gate array（FPGA） signal processor. For the line of sight wind speeds at each azimuth, the nonlinear least square method is used to retrieve three-dimensional wind field vector measured by lidar. The wind speed measured by lidar is compared with that of wind profile radar. Correlation coefficients of horizontal wind speed,wind direction and vertical wind speed of them are 0.988, 0.941 and 0.966.