地基CO2廓线探测差分吸收激光雷达

研制了一台利用气溶胶散射信号的CO₂廓线探测差分吸收激光雷达. 系统利用染料激光器实现波长调制, 采用双光路气体吸收池, 结合Voigt拟合方法实现了脉冲红外激光的高精度定标. 针对输出激光带宽较宽的问题, 采取仿真实验评估了影响, 并设计了基于吸收池的订正因子获取方案. 进而, 开展了水平、垂直和连续观测实验, 通过与地面CO₂分析仪测量值的对比, 证明了系统具备优越的精密性和精确性. 实验表明, 该样机能够俘获CO₂浓度随高程和时间变化而产生的变化.

A ground-based differential absorption lidar for atmospheric vertical CO2 profiling

A differential absorption lidar (CO₂-VDIAL), which is designed for vertical CO₂ profile retrieving by using aerosol-scattered signals, is demonstrated in this paper. To our knowledge, it is the first time that a dye laser has been utilized to realize the wavelength modulation for a CO₂-DIAL/IPDA system. Such a design scheme greatly reduces both the threshold and the cost to develop a CO₂-DIAL. However, two key problems emerge in this system, i.e., wavelength stability and broad bandwidth. By adopting the CO₂-VDIAL, a dual-path gas cell, and the Voigt fitting procedure, the accurate wavelength calibration of infrared pulse laser is achieved. Experimental results show that the error of wavelength calibration can be suppressed under 0.1 pm. And a wavelength stability of ～2 pm is then achieved. For tackling the error introduced by using the laser of a broad bandwidth, simulated experiments are carried out to estimate its influence. On that basis, we propose a method to calculate the correction coefficient and demonstrate the process via experiments by using a gas cell. It is demonstrated that the bandwidth of the output infrared laser is around 600-700 MHz. Hence, the broad bandwidth correction is an indispensable step for this CO₂-VDIAL. Finally, horizontal, vertical and continuous detections are carried out to verify the precision and the accuracy of our CO₂-VDIAL. The slope method is used to retrieve the X_CO2 in the above experiments. In the horizontal detections, an R₂ of 0.999 is achieved, suggesting that the precision of the system is excellent. By comparison with the in-situ measurements, a difference is found to be lower than 4 ppm. Consequently, it is concluded that the CO₂-VDIAL is capable of providing retrievals with the high precision and accuracy. Moreover, the X_CO2 decreases with increasing altitude according to the vertical detection experiment in the midnight on June 19^{m th} 2015 at an urban site, demonstrating that the CO₂-VDIAL is capable of providing retrievals of ranged-resolved. Finally, temporal characteristic of X_CO2 can be also revealed by the CO₂-VDIAL in light of continuous detections. The CO₂-VDIAL has already been assembled in a container which is due to be transported to Huainai for further verifications in late 2015. Once we finish the performance optimization, the CO₂-VDIAL will be installed in Tibet for long period observation.