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.