差分吸收NO_2激光雷达波长漂移和能量波动对浓度反演的影响

为评估差分吸收二氧化氮激光雷达中激光器的稳定性对反演浓度的影响,以NO_2的吸收谱和激光雷达方程为基础,分析了波长漂移和能量波动对距离分辨差分吸收激光雷达浓度反演带来的相对误差。采用两台Nd:YAG激光器的354.7nm波长分别泵浦两台染料激光器的方式,产生差分吸收探测所需的两个波长λon(448.10nm)和λoff(446.80nm),搭建探测大气NO_2实验系统,并就波长漂移和能量波动对NO_2浓度反演影响进行了实验验证。实验结果表明:在没有稳频条件下,当λon和λoff波长漂移≤0.005nm时,引起的浓度相对误差为≤3%;能量波动对反演浓度没有影响,但能量降低减小探测距离,当能量下降≤5%时,探测距离≤100m,实验结果与理论计算基本一致。最后,开展了大气NO_2浓度实验观测,获得实验期间水平及垂直高度0.5~3km内NO_2浓度的分布廓线,系统稳定可靠。本方法为实用化NO_2差分吸收激光雷达的设计及应用提供了理论依据及技术支持。

Effects of wavelength shift and energy fluctuation on inversion of NO2 differential absorption lidar

To evaluate the effect of the stability of the laser on the inversion of the NO₂ distribution in differential absorption based on the NO₂ absorption spectrum and the lidar equation. The relative errors caused by wavelength shift and energy fluctuation in the range resolved differential absorption lidar were analyzed. Two Nd:YAG lasers are used to pump into two dye lasers to produce two wavelengths, λ_on (448.1 nm) and λ_off (446.6 nm), respectively. In the absence of frequency and power stability conditions, the influence of the change of NO₂ absorption cross section caused by wavelength drift on the inversion concentration was analyzed. When the two wavelengths' drift is less than 0.005 nm, the total relative error of inversion concentration due to λ_on and λ_off wavelength drift is less than 3%, and λ_on drift is the main factor. Then the influence of energy fluctuation on the inversion concentration is analyzed. The results show that the energy fluctuation has no effect on the inversion concentration, but the energy reduction will increase the statistical error. When the energy fluctuates in a range of 5% or less, detection range decreases about 100 meters. Lastly, the vertical or horizontal NO₂ profiles were measured at range of 0.5 km to 3.0 km. This method provides theoretical basis and technical support for the design and application of practical NO₂ differential absorption lidar.