| Wind is formed by the movement of the Earth’s atmosphere as a gradient of horizontal pressure.In atmospheric science and aircraft safety,wind detection is an important index.Among all kinds of wind speed detection methods,Doppler wind measurement Lidar has become the main research direction of wind speed detection due to its advantages of high detection accuracy,long distance and high spatial and temporal resolution.Doppler lidar acquires wind speed by acquiring Doppler frequency shift.However,there are some problems in the detection process,such as the influence of external environment,weak echo light and difficult to extract,and low signal-to-noise ratio of the system detection.To address these issues,in order to improve the signal to noise ratio of wind speed detections,combining the signal processing method of wavelet transform and the principle of Doppler wind measurement,this paper designs the wind measurement lidar system,which realizes the accurate and stable detection of wind speed and meets the actual engineering requirements.An analysis of the interaction principle between the laser and the atmosphere,and an investigation of the lidar equation.According to the Doppler wind measurement principle and the Machzender interferometer frequency discrimination principle,the combination of meter scatter and atmospheric molecular scatter characteristics allows analysis of the optimal optical path difference of the interferometer,which improves detection accuracy and provides a theoretical foundation for Doppler wind measurement lidar system design and research.The detection method of the system is studied,and the overall design method of Doppler wind measurement lidar system composed of optical transceiver system,frequency discrimination system,signal acquisition system and control system is proposed.In order to analyze the influence of different wavelength lasing on the scattered signals,and the wavelength of the laser is measured to be 532 nm.In order to realize the structure miniaturization and zero blind area receiving echo signals,A paraboloid reflector was used as a telescope to receive atmospheric scattered light,and the structure of the telescope was designed.SOLIDWORKS software was used to model the mirror tube of the telescope,and the integrated structure design of laser and mirror was realized.The signal acquisition system is designed,the design of photodetector is completed,the weak signal of atmospheric scattered light is amplified,and the filter circuit of the power supply is designed to reduce the impact on the photoelectric conversion signal.Multisim software is used to simulate and analyze the amplitude-frequency characteristics of the filter within the filter circuit,and its performance is verified,and the working principle of the data acquisition module is expounded.Once the hardware design,FPGA logic design,and control software design are finished,and the data statistics,real-time calculation and efficient storage are realized.The calibration and experimental system model of the key parameters of the frequency discrimination system was established,the arm length difference was determined to be99.9mm and the central wavelength was determined to be 532.09318 nm,and the Doppler wind detection lidar system based on Machzender frequency discriminator was built.This completes the simulation analysis of wavelet transform denoising,FIR filter denoising,and sliding-average filter denoising.To denoise the echo signal,we adopt the wavelet transform denoising approach.We can see that the SNR of the semi-soft threshold method is higher than that of the soft and hard threshold methods,SNR=4.9335.Root mean square error(RMSE)decreased,RMSE=0.6762.The laser radar is used to obtain the echo signal,so as to calculate and invert the wind speed and calculate the wind speed measurement error.The experimental results show that when the detection distance is 200m～600m,the radial wind speed measurement error of the system is 0.01m/s～0.05m/s,which meets the detection requirements. |
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