| Mie scattering lidar is a kind of lidar system that accurately measures aerosol by receiving the backscatter light of particles.Traditional Mie scattering lidar systems mostly use Newtonian receiving system and Cassegrain-type receiving system.The transmitting unit and receiving unit usually adopt an off-axis design,which separat the light source from the receiving system.There is no doubt that the structure is relatively complex.And the short-range scattered signal can not be received.So this design will produce a large detection distance blind zone.Moreover,the echo signal is easily affected by noise,resulting in a low SNR of the detection echo,which will increase the difficulty of subsequent algorithms.In view of these problems,the purpose of this paper is to streamline structure of the system,make a recduction of the detection blind spot and improve the measuring accuracy.A coaxial Mie scattering lidar aerosol detection system was designed to analyze the space-time distribution of regional aerosol particles.The main work of this paper is as follows:1.Analysing the reasons for the blind zone of the traditional Mie scattering lidar structure design,and the design concept of using a 90° off-axis parabolic mirror as the backscattered light receiving unit is proposed.The system adopts the transceiver coaxial mode,which makes the system structure more compact.The APD photoelectric detector module is designed independently for photoelectric conversion.A photoelectric balance detector and a power filter are significantly designed to reduce the dark current noise and improve the SNR.2.Based on the parameters of the lidar system and corresponding atmospheric parameters,a numerical simulation of the system SNR is conduct.This study mainly discussing the influence of laser pulse energy,radar receiving aperture and pulse accumulation number on the echo SNR.Increasing the transmitted laser pulse energy,increasing the radar receiving aperture,and increasing the pulse accumulation number can all improve the echo SNR.Among them,the increase of radar receiving caliber is the most obvious to the increase of echo SNR.3.Based on the system structure,a movable Mie scattering lidar experimental platform was built.And the preliminary detection of atmospheric aerosols was carried out,which show that increasing the emission laser pulse energy had little effect on the detection distance.The system can reach a detection distance of 10 km.In comparison to the direct probe approach,the SNR of the balanced probe method is improved by a factor of 2.7,and the spatial resolution of the system reaches 120 m.4.Based on Matlab software,wavelet denoising is carried out to improve the inversion accuracy.Then,using wavelet denoising data to invert aerosol extinction coefficient,the coefficient contours of different heights and moments in a certain region are obtained.Finally,the horizontal atmospheric visibility at different times in the atmosphere was calculated using aerosol level extinction data.The correlation between the calculated data and the data provided by the Local Weather Bureau is high,and the system is reliable in the measurement of horizontal visibility. |
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