探测气溶胶-水汽的拉曼-米散射激光雷达系统

设计和构建了发射波长为355 nm和532 nm的户外型全天时激光雷达系统，用于探测大气气溶胶和水汽。运用355 nm和532 nm的米散射、532 nm的偏振、氮气和水汽分子的拉曼激光雷达技术，用于对边界层结构、对流层气溶胶和云光学特性及其形态、水汽混合比进行连续探测研究。该系统结构紧凑，运输方便，具备远程操作、数据传输、一键式启动等功能。利用该系统对大气气溶胶和水汽进行探测，探测结果表明：在大气气溶胶的探测过程中，在重污染条件下混合层高度较干净天低，在0.5 km以下，而干净天在1 km左右；通过对消光系数、Angstrom指数和退偏振比分析可知，重污染条件下，底层大气气溶胶以球形粗粒子污染物为主，干净天底层大气气溶胶以球形细粒子污染物为主；在云层中，Angstrom指数明显减小，且出现负值，说明云粒子半径较大。在水汽探测过程中，采用自标定方法获得系统的标定常数为121，与已标定的激光雷达系统对比，误差在±0.3 g/kg以内；连续探测结果表明可对夜晚5 km及白天混合层以内进行探测。该系统满足产品化的需求，可广泛运用于大气环境的监测领域中。

Raman-Mie scattering lidar system for detection of aerosol and water vapor in the atmosphere

  Objective   With the development of society and economy, environmental problems are becoming more and more serious. The environmental protection and meteorological departments pay more and more attention to obtaining atmospheric parameters (such as aerosol, water vapor, temperature, etc.). The accuracy of weather forecast can be improved by continuously detecting atmospheric aerosols and water vapor. It is of great scientific significance to study the characteristics and diffusion mechanism of atmospheric pollution aerosols, the formation of clouds, rainfall and so on. As an active remote sensing tool, lidar has better temporal and spatial resolution and continuity than traditional atmospheric detection methods, and plays an important role in the measurement of atmospheric parameters. With the development of lidar technology, the development of lidar is towards miniaturization, production and simplification. In order to meet the requirement of environmental protection department to know the atmospheric parameters in time, an outdoor all-weather atmospheric aerosol-water vapor lidar has been developed by the key laboratory of atmospheric optics of the Anhui Institute of Optics and Fine Mechanics to long-term detection of aerosols and Chinese Academy of Sciences.  Methods   All-weather outdoor lidar system with emission wavelengths of 355 nm and 532 nm is designed and established for detecting atmospheric aerosols and water vapor. Adopting the existing mature technology of Mie-scattering of 355 nm and 532 nm, polarization of 532 nm, Raman lidar remote sensing of nitrogen and water vapor molecules, the lidar system is used for automatic continuous detection of planetary boundary layer, tropospheric aerosol particle and cloud particle optical characteristics and their morphology, water vapor mixture ratio. The lidar structure is compact and convenient for transportation with remote operation, data transmission, one-touch button functions.  Results and Discussions   The system is used to detect atmospheric aerosols and water vapor, the detection results show that the mixed-layer depth is lower under heavy pollution conditions than that of the clean weather conditions. The mixed-layer depth is below 0.5 km in the heavy pollution days, while in clean days are around 1 km. Through the analysis of extinction coefficient, Angstrom index and depolarization ratio, it can be seen that the bottom atmospheric aerosol is dominated by spherical coarse particle pollutants under heavy pollution conditions, and spherical fine particle pollutants under clean weather conditions. In the cloud layer, the Angstrom index is significantly reduced to a negative value, indicating that the cloud particle radius is large. In the process of water vapor detection, the system calibration constant obtained by the self-calibration method is 121. Compared with the calibrated lidar system, the error is within ±0.3 g/kg for the water vapor mixing ratio. The continuous detection results show that the water vapor content within 5 km at night and the mixed-layer during the day can be detected.  Conclusions   Unlike the traditional atmospheric aerosol and water vapor lidar, the system has the functions of 355 nm and 532 nm wavelength Mie-scattering detector, 532 nm depolarization detector, and Raman detector for nitrogen and water vapor molecules. The two-wavelength Mie-scattering detection function can detect the structure of atmospheric boundary layer, the extinction characteristics of aerosol and cloud, and the distribution of coarse and fine particles. The 532 nm depolarization detection function can reflect the shape characteristics of aerosol and cloud particles, and can recognize spherical particles (water cloud, pollution aerosol and haze) and non-spherical particles (sand dust and ice crystal cloud). The Raman detection function of nitrogen and water vapor molecules can obtain the spatial-temporal distribution characteristics of water vapor mixing ratio. The following detection unit of the system adopts a high-stability integrated structure, and the shelter is equipped with the constant temperature function of dust-proof and water-proof, so it can be directly detected in the open air for a long time, it is useful for statistical analysis of physical parameters such as local aerosol particles, cloud particles and water vapor, and has been used in research fields such as atmospheric environmental monitoring and science.