Development Of Mie Scattering Lidar And Inversion For Return Signal

Atmospheric aerosol such as dust, fog and cloud play an extremely important role in the atmosphere, and have a strong influence on the Earth's local meteorology and global climatology. Because most of aerosols are below 2 to 3km in the troposphere, and can exist in much long time, the atmosphere will be polluted by it. With the increasing of aerosol density, the visibility of atmosphere will fall down. So, it has bad influence to traffic. The forming of aerosols is not only from nature but also man-made factors such as the emission of chimney and car. As an effective means for measuring aerosols, Mie scattering lidar is used to detect the characteristic of aerosols. So the man-made pollution could be effectively controlled.The optical parameters of atmospheric aerosol such as backscatter coefficient and extinction coefficient can be gotten by Mie lidar. The extinction coefficient is related to directly optical depth, transmission coefficient and visibility of atmosphere. So, it is important to processing the return signal for getting extinction coefficient. Among algorithms for Lidar signal inversion, Slope method and Klett's analytical inversion algorithm are representative. Slope method is customarily used for inversion of atmospheric optical parameters in the case of homogeneous atmospheres. In fact, the real atmosphere usually is inhomogeneous, so Klett's analytical inversion algorithm was used for inversing atmospheric optical parameters in inhomogeneous atmosphere.In this work, firstly, the experiment set-up is developed, which consists of laser transmitter, signal receiver and data processing system for lidar. Much lidar work only at night to avoid interferes of sky radiation. So there are three measurements taken in the set-up for eliminating the background interferes. One is a narrow band filter is used by day, one is a small pinhole matching the laser emission and receiving field angle strictly, another is averaging for samples of Lidar returns. The lidar system can work by day.Secondly, on the basis of Klett's analytical inversion algorithm, two creative ideas are developed. One is estimating extinction efficient boundary values with least square fitting for return signals of Lidar. In the algorithm, the boundary value of extinction is calculated by fitting Lidar return signal in cloudless weather. But for cloudy weather, first, the measured region is divided into cloudy and cloudless section. Then it is assumed that the cloudless region is homogenous circumstance, and the boundary value of extinction is calculated by fitting Lidar return signal except for the cloudy region. The other is correcting near field laser Lidar returns by conic fitting and slope method. With the two new methods and Klett's analytical inversion algorithm, good results of inverting Lidar returns in Chengdu are gotten.