How does LIDAR work? What are its characteristics? What are its application fields and prospects

The principle of LIDAR is based on the physical processes of scattering, absorption, extinction and scintillation of laser light by the atmosphere, and the inversion of atmospheric parameters, such as aerosol optical parameters, atmospheric temperature, wind contours, and the spatial and temporal distribution of water vapor and atmospheric trace gases through the reception of backward-scattered signals. LIDAR is a product of the combination of traditional radar technology and modern laser technology. Its working principle is similar to that of microwave radar or radio radar, i.e., a signal is emitted by the transmitting system, which interacts with the target, and the returned signal is collected and processed by the receiving system to obtain the required target information. Unlike ordinary radar, the emission signal of LIDAR is a laser, which has a much shorter wavelength compared with the radio waves and even millimeter waves and microwaves emitted by ordinary radar, which makes LIDAR more sensitive to tiny aerosol particles and atmospheric molecules, and is suitable for atmospheric detection. In addition, most of the ordinary radar received for the hard target of the reflected signal, and for atmospheric detection of the signals received by LIDAR With the development of laser technology, optical processing technology, optoelectronic detection technology and data acquisition technology, LIDAR in the detection distance, detection accuracy, spatial and temporal resolution, automatic and continuous observation, etc. shows excellent detection capabilities. The development trend of LiDAR:

(1) Functional diversification

With the development of LiDAR, its measurement range has been developed from the initial detection of atmospheric aerosol distribution by using the meter scattering signal to the detection of temperature, wind field, gas composition and other fields. By utilizing multi-channel detection, a single lidar system can be realized to simultaneously detect a variety of atmospheric parameters such as water vapor mixing ratio and aerosol parameters [31]. Multi-wavelength lidar can measure the extinction coefficient and backward scattering coefficient of aerosols at multiple wavelengths, and then inversely perform the complex refractive index and particle spectral distribution of aerosols [32].

(2) Diversification of platforms

Long-term observation of ground-based single-point stationary lidar is very necessary, and it is valuable for studying and statistically analyzing the pattern of change of some important atmospheric components. But the LiDAR mounted on a variety of mobile platform, more can play the role of LiDAR. Vehicle-mounted lidar, with a high degree of mobility, transfer observation site more convenient [33], easy to respond to the detection needs of unexpected events. Airborne lidar can carry out a large range of mobile observation, and easy to conduct experimental detection of clouds [34]. Shipborne lidars can observe over the oceans, and they play an important role in some regional and even global atmospheric radiation and atmospheric environment studies, as well as multi-instrument comparison experiments [35]. Star-borne lidars are capable of active remote sensing of important atmospheric parameters on a global scale. The meter scattering aerosol lidar, carbon dioxide differential absorption lidar, and Doppler wind measurement lidar will be applied to global satellite remote sensing observations in the near future [36].

(3) Network observation

With the need for international cooperation in atmospheric radiation and environmental science research, the establishment of LIDAR observation network is necessary. Through the unification of measurement and data processing methods and standards, long-term observation. To study the characteristics of long-term changes in aerosols and the distribution of different types of aerosols within a region, as well as the paths and mechanisms of aerosol transport and the changes in their physical and chemical properties during transport. Some international collaborative research programs, such as the Network for Global Observation of Stratospheric Change (NDSC) [37] and the Aerosol Characterization Experiment (ACE-I, II) [38, 39], use multiple lidar deployment networks to observe the spatial distribution of some important atmospheric constituents. The European Lidar Observation Network (EARLINET) [40] includes 21 ground-based Lidar stations in different European countries; the Asian Lidar Observation Network (AD-Net) [41] carries out joint observations of the optical properties of sand and dust aerosols and their long-range transport processes in the Asian continent; and the Latin American Lidar Network (LALINET) [42] carries out cooperative observations of important atmospheric constituents in the tropics and the lower latitudes of the Southern Hemisphere. atmospheric constituents in the tropics and at low latitudes in the southern hemisphere.

(4) Commercialization

Lidar is able to monitor the spatial and temporal distribution of a variety of important atmospheric constituents and covariates, with a long measurement distance, high spatial and temporal resolution, low detection costs, and continuous automatic observation, with other detection methods can not be replaced, in the meteorological observation, atmospheric environment monitoring and wind field measurements and other civilian fields are increasingly important, so its application of The market is broad. At present, single-wavelength meter scattering lidar, differential absorption lidar for detecting polluted gases, and wind measurement lidar have been successfully commercialized. For example, the U.S. SESI company developed a series of micropulse lidar, Germany ELIGHT company developed a vehicle-mounted pollution measurement lidar, France LEOSPHERE company introduced Windcube wind measurement lidar, and the United States ORCA and Canada OPTECH company developed a series of lidar products. In China, in recent years, the Chinese Academy of Sciences, Anhui Institute of Optical Machinery developed vehicle-mounted pollution measurement LIDAR AML-1, micropulse LIDAR MPL-A1 and portable polarization - meter scattering LIDAR PML, etc., have begun to shift from the laboratory research stage to the commercialization of product development and development.