Study On The System And Observation Of Scanning LIDAR

Dust, smoke, clouds and aerosol particles whose optical properties and spatial distribution are important to researches of weather forecast and atmospheric environment are mainly distributed in the troposphere. LIDAR is a product of the combination between laser technology and radar technology. LIDAR has high space-time resolution and measurement accuracy; besides, laser can produce effective interaction with aerosol particles, small cloud particles. Thus, LIDAR becomes one of the important means of observing the distribution of atmospheric aerosol optical properties. At present, most LIDAR’s observe with fixed direction or pointing vertically, the sampling to cloud and aerosol is limited.In this paper, a scanning LIDAR for aerosol and cloud observation is developed. The system uses a small solid-state Nd:YAG laser which is carried on the receiving telescope, the single pulse energy is 20μJ in frequency multiplication operation, and the pulse repetition frequency is 11 KHz to make the system to get high SNR of time unit. The telescope with diameter of 76 millimeters is fixed to the 3D scanning platform, and it can scan easily. The fiber of 200μm core diameter is used to translate backscattering signal that has be received by the telescope to receiving system. Then after collimation and light filtering, the backscattering signal will be translated to PMT. VB code is written to control the direction of the telescope, so the system can work at different scanning model to detect the cloud and aerosol of all direction. The measurement capability of that scanning LIDAR has been verified through the comparison with RRML LIDAR.On this basis, the horizontal atmospheric aerosol, atmospheric aerosol profile and the stack emission of Nanjing Beijiao chemical factory is observed. And we use Slope method, Fernald method and the combined method of Slope and Fernald for data inversion. Then, we will get the horizontal visibility, the atmospheric extinction coefficient and the plume extinction coefficient, and we also can get three-dimensional distribution of aerosol emissions around the plume. The data analysis show that, the scanning LIDAR can detect the horizontal visibility, the atmospheric aerosol of three-dimensional space, can automated acquire the direction of pollution source and pollution situation, can realize the real time monitoring of relative concentration, space diffusion regional and space change law of extinction coefficient of pollutants emission. The scanning LIDAR is an effective tool for monitoring environment. The scanning LIDAR is also used to detect the cloud distribution with three observation methods as vertical observation, sector-scanning and volume-scanning. We use differential enhanced method, single point integration method and transmittance method to get cloud height, cloud cover and cloud optical thickness. Then, we can analyze the spatial distribution of cloud optical property comprehensively. We have compared the scanning LIDAR data with RRML LIDAR. Data shows that, scanning LIDAR can accurately describe the spatial distribution of cloud height, cloud cover and cloud optical thickness. Comparing with the traditional LIDAR, the scanning LIDAR has much more advantage on the cloud detection.