Differential absorption lidar (DIAL) is an effective instrument for detecting nitrogen dioxide (NO2) in the atmosphere. Under the condition of heavily polluted weather, aerosol has a serious influence on the concentration inversion of NO2. In this paper, using both echoes of SO2 and NO2 at weak absorption wavelengths (301.50 nm and 446.60 nm) in differential absorption lidar, the aerosol extinction coefficient and backscattering coefficient are calculated by recursive inversion algorithm. It is also used to correction the concentration distribution of NO2 on the detective path. The experimental results show that the standard deviation of NO2 concentration distribution using the correction algorithm is less than 10μg/m3 , and the fluctuation range is less than that of direct inversion. This concentration inversion algorithm overcomes the uncertainty caused by the assumption of the boundary value at the reference point when using the single-wavelength Klett or Fernald backward integration method to invert the aerosol extinction coefficient in heavily polluted weather, and has higher accuracy.
Using SolidWorks software, the finite element modal analysis of a vehicle-borne pollution monitoring lidar cabin is carried out. The lidar cabin for the integrated lidar can ensure that the lidar system has good maneuverability and can effectively monitor the emission of air pollution. Since lidar is an integrated system of optics, mechanism, electricity and calculation, the performance of the cabin is directly related to the safety of the equipment and the lidar to work properly. Firstly, the cubic structure is modeled to simulate the cubic structure. Then, the model of the cabin model is analyzed by using the simulation plug-in, and the first 10 modes and natural frequencies are analyzed and recorded. The calculation results show that the cabin is dominated by bending vibration, and the amplitude area is concentrated in the opening of some windows and doors on each board. Therefore, we should increase the number of reinforcement bars or the strength of the skeleton in the vicinity of the door and window. At the same time, to avoid the resonance and ensure the precision of the optical elements and the electrical components and avoid structural damage of the cabin, the incentive frequency should be keep away from the natural frequency of the cabin. The vehicle-borne lidar system has been put into operation, and the analysis results have direct meaning to the transport of the cabin and the normal work.
Lidar instruments are efficient detectors of air pollutants such as nitrogen dioxide (NO2). However, the measurement errors are not negligible due to the influence of the aerosol in the atmosphere. We present a novel lidar for measuring tropospheric NO2 vertical profiles. For improving the received powers, the emitter unit consists of two pulsed pump laser – dye laser combination, and use three wavelengths of 448.10nm, 447.20nm and 446.60 nm corresponding to the strong, medium and weak absorption of NO2 respectively. The effects of aerosol on tropospheric NO2 measurements by three - wavelength (448.10 -447.20 -446.60 nm) dual differential absorption lidar (dual-DIAL) and conventional two - wave length (448.10- 446.60nm) differential absorption lidar (DIAL) are theoretical analyzed, and their system err are computer simulated. Experimental results show that the three - wavelength dual - DIAL method is more effective to reduce the effects of aerosol than the two - wavelength DIAL method, and its system error is no more than 4% without correcting the aerosol effect.
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