Simulation And Experimental Study Of Mid-infrared Differential Absorption Lidar To Measure Polluted Gas

As an important means of pollution gas monitoring,differential absorption lidar(DIAL)has many advantages,such as wide detection range,high detection sensitivity,no need of on-site sampling and so on.A series of gas detection laser equipment has been developed in ultraviolet,visible and near-infrared bands,which can realize the daily monitoring of CH₄,O₃,SO₂ and NO₂.In order to further research the mid infrared band laser gas detection technology,the feasibility of mid infrared band gas detection technology is discussed by combining theoretical detection and experimental detection.Starting from the lidar echo equation,this paper analyzes the parameters that affect the echo signal.Through the parameterization of meteorological elements,gas,noise and lidar system,we defined the parameters affecting the differential absorption lidar signal.The lidar echo signal with specific parameters was simulated and analyzed.The concentration inversion effect at different distances was calculated according to the intensity signal-to-noise ratio of the echo signal.It is proved theoretically that the mid infrared differential absorption technology can realize the effective determination of gas.A 2.5?m?4?m all solid-state high repetition rate mid infrared path integral DIAL was developed.The wavelength can be changed by replacing PPLN crystal and adjusting temperature.Taking NO₂ and SO₂ as researching objects,we carried out the gas cell experiment and the open field gas emission experiment.The correlation coefficient between the measured concentration and the real concentration in the gas cell experiment is higher than 98%.The open field gas detection experiment shows that the lidar system can record the real-time gas concentration changes on the whole path.The detection results show that the system has certain advantages in time resolution,which can be used to monitor the chemical gas concentration around the factory and complete the efficient early warning task.In the later stage of this study,we will continue to develop the lidar system,and make full use of the characteristics of the long-range adjustment of the wavelength to realize the effective determination of many kinds of chemical gases.