Numerical Simulation And Experimental Study Of The Mid-infrared DIAL

The rapid development of economy is usually accompanied by the development of environmental problems. Air pollution is an important part of environmental pollution. There are many kinds of air pollutants and the main sources are industrial production, heating, transportation, etc., among which the industrial emissions accounted for the largest proportion. Detection with high spatiotemporal resolution,high detection precision and fast response speed can be down by differential absorption lidar. It is a new advanced technology with wide range of application in recent years in the field of environmental monitoring. In this paper, based on the research and development of the mid infrared differential absorption lidar, the system function and the inversion algorithm are simulated and analyzed.On the basis of the principle of differential detection, in this paper, the absorption characteristics of three types of trace gases (sulfur dioxide, nitrogen dioxide and nitric oxide) were simulated through line-by-line integral algorithm utilizing the HITRAN2012 database. The influence of the temperature, pressure, and other interfering gases were analyzed. This study proposes suitable sets of wavelength for the detection of polluted gases by mid-infrared differential absorption lidar. The structure, components, main parameters and working flow of the mid-infrared differential absorption lidar system were introduced. The process of retrieving the concentration is derived and simulated, including the establishment of the simulation model and the signal processing method.In this paper, to validate the ability to disregard the interference, it is assumed that there is interference that exists in the same way in natural atmospheric components, while the measured gases exist in the designed concentration. The cumulative average combined multiple autocorrelation detection method of concentration inversion algorithm is improved. The simulation model results show that the nitrogen dioxide concentration inversion results within 1 km of the analog detection error is about 0.1 mg/m3, so as to the inversion precision was effectively improved,to further improve the technology of laser radar signal processing.Based on the results of numerical simulation on echo signal and spectrum, the simulation GUI of the mid infrared differential absorption lidar system is designed,including the signal acquisition and the absorption simulation. The interface is friendly, easy to operate, and the results show good. In the end, the gas absorption cell was measured twice and the measured absorption spectrum is consistent with the simulated one, which verifies the correctness of our analysis on the spectrum. In order to verify the detection ability of the experimental system, the surface of a corner reflector and its stainless steel surface are detected as the hard targets. The results show that the system has strong ability currently to detect echo signal of hard targets.