Research On Signal Processing Method Of Coherent Laser Wind Radar

Atmospheric wind fields are closely related to people's lives.Accurate measurement of atmospheric wind fields has an inestimable effect on airport wind shear detection,weather forecasting,wind energy utilization,and aerospace guidance.Coherent wind lidar has become the principal method for measuring atmospheric wind field because of its outstanding detection capability under clear weather,high temporal resolution and high spatial resolution brought by laser characteristics.In this paper,key technologies such as Doppler frequency correction,wind speed inversion data quality control and signal accumulation method in the signal processing of coherent wind lidar are studied.Firstly,the method of combining theoretical analysis,software simulation and experimental verification is used to study the algorithm of frequency correction using spectrum amplitude.Several representative frequency correction methods,such as energy center of gravity method,triangle method,double-spectral line interpolation method and tri-spectral line interpolation method,have been analyzed and compared.It shows that the energy center of gravity method is more suitable for the experimental conditions and is selected for further optimization.As a result,the accuracy of wind speed measurement was improved by an order of magnitude;By analyzing the error sources and principles of wind speed inversion,the corresponding wind speed inversion data quality control method was proposed based on the signal-to-noise ratio,wind speed residual error,the number of data points in the scan interval,and the data validity rate;Finally,the signal-to-noise ratio enhancement method based on signal accumulation is studied,and it is found that the time-domain signal is firstly coherently accumulated and then the fast Fourier transform is used to achieve the best signal-to-noise ratio enhancement effect.But when measuring the soft target area,the phase of the received time-domain signal will change continuously with the position of the area.At this time,directly accumulating time-domain signals will have the opposite effect of overwhelming the useless signals.Therefore,the method of selecting the time-domain signal first to perform the fast Fourier transform and then performing the coherent accumulation is more suitable for the measurement of soft targets.This article also provides two schemes that combine the principle of orthogonal mixed frequency to achieve signal coherent accumulation,and use Simulink system simulation to verify its feasibility.A coherent wind lidar system based on continuous wave mode was built in the laboratory,and the speed measurement was calibrated by a turntable controlled by a servo motor.The measured speed was corrected by frequency correction method.It proves that frequency correction has obvious effect on the improvement of wind speed measurement accuracy.