光学 精密工程, 2020, 28 (9): 1881, 网络出版: 2020-12-28
球载CRDS高灵敏度甲烷测量系统的研制
Development of highly sensitive balloon-borne methane measurement system based on cavity ringdown spectroscopy
光谱学 腔衰荡光谱技术 痕量气体 实时测量 spectroscopy cavity ringdown spectroscopy isotopes aburdance highly sensitivity real time detection
摘要
为了分析青藏高原地区甲烷浓度的垂直分布, 本文采用腔衰荡光谱技术(CRDS)设计了一套高灵敏度的球载甲烷浓度实时测量系统, 该测量系统在基于DSP的单板电路上实现腔模锁定、衰荡信号采集、光谱扫描、数据存储等功能并在DSP上实时处理衰荡信号、光谱信号和浓度等数据。本文首先介绍了CRDS测量原理与采用的光谱处理算法, 通过固定高斯线宽的方式改进光谱拟合算法, 使得浓度计算结果得到明显提升。然后, 分析了电路系统采集的衰荡信号与光谱信号, 采集的衰荡信号信噪比达62 dB, 并在实验室使用标准气体进行了标定试验, 标准气体的测量值标准差σ最大为2.2×10-9, 测量值的均方值RMS和标准气体标称值之间的校正可决系数为0.998 7。最后, 系统进行了实际试验, 在西藏鲁朗地区成功实现了从海拔3 340 m到海拔6 000 m的上升和下降过程中甲烷浓度的测量。该系统可以通过改变激光波长与光腔反射镜测量其他大气痕量气体, 进一步改进与优化的系统可以应用到大气同位素丰度的测量中。
Abstract
This paper presents the design for a highly sensitive balloon-borne measurement system based on cavity ringdown spectroscopy (CRDS) in order to analyze the vertical distribution of methane above the Tibetan Plateau. The proposed measurement system uses a digital signal processing (DSP) board to lock the cavity mode, acquire the cavity ringdown signal, scan the laser wavelength, and store data. Calculation of the decay rate, spectral curve fitting, and concentration calculations are all performed via DSP. First, the principle of CRDS and the spectrum calculation algorithm are introduced, including details on the improvement of calculation results by using a fixed Gaussian linewidth for fitting the spectral curve. Second, the cavity ringdown signal and spectral curve of the measurement system were analyzed, yielding a signal-to-noise ratio of approximately 62 dB for the cavity ringdown signal. The measurement system was calibrated in the laboratory by measuring standard gases; the maximum standard deviation of the measured values was 2.2×10-9, and the adjusted R-square between nominal values and the RMS of the measured values was 0.998 7. Finally, a field test was conducted in Lulang, Tibet. The instrument was carried by a tethered balloon, and methane concentrations at altitudes between 3 340 m and 6 000 m above sea level were successfully measured. Different trace gases can be measured by replacing the super mirrors in the optical cavity and using lasers with appropriate wavelengths, while the measurement system can be refined further to measure the abundances of certain isotopes.
袁峰, 高晶, 姚路, 陈兵, 何亚柏, 胡迈, 许振宇, 阚瑞峰. 球载CRDS高灵敏度甲烷测量系统的研制[J]. 光学 精密工程, 2020, 28(9): 1881. YUAN Feng, GAO Jing, YAO Lu, CHEN Bing, HE Ya-bai, HU Mai, XU Zhen-yu, KAN Rui-feng. Development of highly sensitive balloon-borne methane measurement system based on cavity ringdown spectroscopy[J]. Optics and Precision Engineering, 2020, 28(9): 1881.