Key Technology Research Of Coherent Dopplerwind Lidar Based On Image-reject Homodyne Technology And Wind Data Analysis

Doppler lidar is one of the important remote sensing equipments for wind detection in clear air.It has the characteristics of high precision,high spatial and temporal resolution.At present,on the market most of continuous coherent Doppler lidars use homodyne coherent detection technique and heterodyne coherent detection technique to obtain atmospheric velocity speed and direction in the radial direction of the radar.In this thesis,the continuous all fiber Doppler wind lidar developed based on image-reject homodyne technology and using Integrated 90°Optical Hybrid Receiver is introduced.The IQ cross signal has been got through the phase control of the local or backsccatering signal,and using the image-reject homodyne technology,the radial wind is detected.Compared with the doppler lidar using homodyne and heterodyne technique,this lidar has the advantages of higher signal to noise,stronger data storage,lower ADC sample rate at the same speed range and so on.The radial wind detecting experiment was carried out with the prototype of the all polarization maintaining fiber image-reject homodyne continuous coherent Doppler lidar.The results showed that this lidar system has a high detection accuracy,the radial wind direction is entirely consistent with the anemometer and the wind speed bias and standard deviation are-0.03m/s and 0.63m/s seperately.At the same time,the detailed analysis of the wind speed measurement ability among the homodyne cohenrenct technique,heterodyne technique,and image-reject homodyne technique is presented.In order to improve the data quality of Doppler lidar,and give full play of its benefits in meteorological forecasting,the wind profiles deteceted by the vehicle doppler lidar of MOC(meteorological observation center)were compared with the profiles by the numerical prediction and L band radar separately,the results showed that the lidar wind data is credible,but the high frequency random error is existed as the higher sensitivity of the lidar.In order to filter the high frequency random error in the wind data,the filter of the Chebyshev polynomial is used to get the low-pass components,and large-scale wind information is better revealed and can be used in large-scale NWP models for improving the assimilation effect.The wind profiles deteceted from 27^th-28^th September 2008 by the vehicle Doppler lidar were compared with the NWP wind profiles,all the data includes 35 groups wind profiles(20192 pairs of wind speed and direction),the correlation coefficient of the wind speed is 0.778,the system difference is-0.015m/s,and the standard deviations is 4.25m/s.From 21^th March-18^th April 2011,the wind profiles detected by the vehicle Doppler lidar in Beijing compared with the L band radar profiles,all the data includes 50 groups wind profiles(30240 pairs of wind speed and direction),the correlation coefficients of the wind speed and direction are 0.82 and 0.94 separately,the system differences are 0.586m/s and5.96°separately,and the standard deviations are 5.38m/s and 37.86°separately.The all result show that the wind data detected by the Doppler lidar is credible.With the high-pass signals filtered out by the Chebyshev polynomials,the 50 pairs of lidar wind profiles and radiosonde system were compared.As a result,the average correlation coefficient of wind speed and direction improved by 0.05 and 0.04 respectively,while the standard deviation was reduced by 0.52 m/s and 12.01°respectively.