Application Of Pulse Coding Technique In Coherent Lidar

Coherent lidar has the characteristics of high accuracy,high temporal and spatial resolution.The principle of coherent Doppler wind lidar is based on aerosol Doppler shift.With the detection distance increases,the signal-to-noise ratio of the system will drop rapidly,and the Doppler shift estimation in the low signal-to-noise ratio area will be biased.The purpose of this paper is to demonstrate a coherent wind lidar based on pulse coding technique.The pulse coding technique can improve the signal-to-noise ratio of the system without sacrificing the detection range resolution,and improve the weak signal estimation ability in the low signal-to-noise ratio region.This article mainly carried out the following work:1.Review the development of coherent Doppler wind lidar technology at home and abroad,and introduce the research status of pulse coding technology.2.The Doppler effect of the laser is introduced,which is the basis of wind lidar.Based on the system structure of a Doppler coherent wind lidar,its constituent modules are described in detail.Based on the principle of coherent lidar detection,the mathematical expression of the optical heterodyned current signal of the coherent lidar is deduced.Combined with the system noise power,the carrier-to-noise ratio is obtained.The parameters such as the local oscillator power and the telescope truncation ratio are optimized.3.Signal processing algorithm of coherent lidar is introduced.The precise Cramer-Rao bound of the signal estimation error is deduced.Combined with the probability density distribution of the Doppler shift,the merits of the signal estimation algorithm can be evaluated.Based on the atmospheric layer slicing model,a coherent lidar time-domain simulation signal is generated.Based on the measured data of 1.5?m coherent Doppler wind lidar,the signal estimation algorithm is used to obtain the information of atmospheric wind velocity.4.The generation principle of Simplex code and Golay code is introduced separately,and the improvement of the signal to noise ratio of the system by different coding techniques is theoretically analyzed.Based on the decoding principle and the coherent lidar time-domain simulation signal,the system wind velocity based on the pulse coding technology is obtained.Simulation results show that when the time resolution is 1s and the distance resolution is 60m,the wind velocity error is less than 3m/s in the range of 0-5.3km when the coded pulse is used as the detection pulse of the coherent lidar.In the same measurement time,compared with the traditional pulse coherent lidar,the detection distance increased by 2.5 km.