Objective  The chemical industry occupies an important position in the national economy. However, it is also facing challenges such as environmental pollution, carbon dioxide emission, resource consumption and safety risks. Therefore, it is particularly important to develop remote sensing technology that can monitor pollutant discharge, dangerous gas leakage, wind and rain and other meteorological elements in chemical parks with high sensitivity, high stability, wide range and continuous day and night monitoring. In recent years, 1.5 μm lidar has been regarded as an important detection means for the detection of atmospheric environment and atmospheric parameters due to its advantages of human eye safety, continuous day and night observation, high spatial and temporal resolution, all-fiber integration, low power consumption and high stability. At present, differential absorption lidar (DIAL) has been used to detect the concentration distribution and flux emission of various greenhouse gases and dangerous gases, while coherent wind lidar (CDWL) is also widely used to detect atmospheric multiple parameters such as wind field, aerosol and precipitation. Lidar has gradually become one of the important means of safety and environmental protection monitoring in chemical parks. For this purpose, atmospheric multi-parameter detection lidar is applied in the field of safety and environmental protection in chemical industry park.

  Methods  For simultaneous detection of aerosols, gases, and wind fields, we built an atmospheric multi-parameter lidar system integrating direct detection module and coherent detection module (Fig.1 and Tab.1). The outgoing light source uses a tunable external cavity semiconductor laser (ECDL) as the detection light source (On wavelength laser) and a fiber laser as the reference light source (Off wavelength laser). the ECDL's outgoing frequency is locked by the optical frequency comb. The receiving system consists of two parts: direct detection module and coherent detection module. In direct detection module, the signal is detected by a large area superconducting nanowire single photon detector (SNSPD). Gas detection requires high sensitivity, and SNSPD provides a higher signal-to-noise ratio than coherent detection techniques. In coherent detection module, the backscattered signal is coupled with the local oscillator light and detected by a balanced detector. In this system, direct detection module uses differential absorption technology of molecular spectrum for gas detection, and coherent detection module uses range correction echo signal, doppler frequency shift, turbulent kinetic energy dissipation rate (TKEDR), the velocity gradient of wind profiles and power spectrum deep analysis technology for pollutant, wind, rain, turbulence and wind shear.

  Results and Discussions  Firstly, by combining the detection results of range correction echo signal PR² and wind vector, the atmospheric multi-parameter lidar can be used for the early warning and monitoring of pollutant emission tracing and diffusion. The stability of monitoring and the accuracy of tracing are verified by experiments (Fig.2-3). Then, the accuracy and stability of carbon dioxide monitoring by the atmospheric multi-parameter lidar were verified through long-term and large-scale monitoring experiments on CO₂ distribution in chemical industry park (Fig.4-6). Finally, in view of the simultaneous detection of wind and rain by CDWL, the atmospheric multi-parameter lidar is applied to the fine meteorological support of the chemical industry park, and the meteorological observation capability of the atmospheric multi-parameter lidar is verified by observation experiments. (Fig.7).

  Conclusion and Prospect   A set of atmospheric multi-parameter lidar integrated with direct detection and coherent detection is applied to the safety and environmental protection of chemical parks. In general, the atmospheric multi-parameter lidar has a good application prospect in the field of safety and environmental protection in the chemical industry park, which can accurately and stably achieve tracing of pollutant emissions, monitoring gases, and refined meteorological support. The application of atmospheric multi-parameter lidar in chemical industry park can effectively improve the level of environmental protection and optimize the ability of safety management, and realize the sustainable development of chemical industry park. Due to the use of scanning light sources, it is theoretically possible to achieve the detection of a variety of gases. (Tab.2) In the future, we will use atmospheric multi-parameter lidar to detect a variety of dangerous gases in the chemical park, and plan to integrate polarization detection capabilities on atmospheric multi-parameter lidar to enhance pollutant and gas classification capabilities.