Development Of Picometer Bandwidth Filter For Wind Observation With Rayleigh Wind Lidar

The middle and upper atmosphere is a very important and applicative region which has attracted much attention of space science researchers.It is necessary to get the spatial and temporal distribution of wind field in this region during the whole day to understand kinematics and dynamics of atmosphere.The direct-detect wind lidar is the most effective tool that would measure three-dimensional wind field with high accuracy,high temporal and spatial resolution in the global region continuously compared with the other wind remote sensors.Affected by the strong sky background noise,the detection altitude has limited severely by working during the daytime.In ordor to solve the above-mentioned problems,this topic carried out the research of ultra-narrow bandwidth filter to achieve the purpose of continuous measurement of the middle and upper atmospheric wind fields during daytime based on the well-developed direct-detect Rayleigh Doppler wind lidar in our group.By the investigation of the narrow-band filter technique worked with lidar system abroad,this filter technique is proposed to use the interference filter(IF)and the Fabry-Perot interferometer(FPI)to compress the system bandwidth based on the design parameters of double-edge discriminator of 70 km wind lidar.Then through the optimization of the parameters of each optical device of the ultra-narrow bandwidth filter,we choose 0.15nm as the bandwidth of IF,8.39pm as the bandwidth and 150.02pm as the free spectral range(FSR)of the FPI,respectively.By receiving the atmospheric backscattering signals during daytime,the background noise is reduced to 4.89%and the detection altitude is increased from 22 km to 33 km with the accumulation time 15 min compared with the results of IF.At the same time,we found that there are still strong background noises in the two edge channels.In order to further compress the system bandwidth,a new idea that combining an IF and two FPIs of different resolution to compress the bandwidth of lidar system is proposed.By comparing with the received atmospheric backscattering signals with IF,the background noise is reduced to about 2.3‰ and the detection altitude is increased to 55 km.Finally,we carried out the experiment of wind observation in July and August,2019 in Xinjiang.The experimental results showed that the measurement results of the east-west wind speed of lidar are in good agreement with the results of radiosonde during the daytime with 30 min accumulation time from morning to afternoon.So with the ultra-narrow bandwidth filter,the Rayleigh wind lidar achieved the purpose of wind measurement during daytime and the results demonstrate the feasibility of ultra-narrow bandwidth filter working in Rayleigh wind lidar.The above works provide a technical reference for the development of the middle-and upper-atmosphere wind lidar worked during all daytime.