球载TDLAS的对流层CO_2浓度廓线探测

Measurements of CO_2 Concentration Profile in Troposphere Based on Balloon-Borne TDLAS System

大气中CO2主要的源和汇都集中在对流层,精确地获取对流层CO2浓度廓线分布,对研究CO2的垂直输送和全球气候演变具有重要意义。基于可调谐半导体激光吸收光谱(tunable diode laser absorption spectroscopy,TDLAS)高分辨、高灵敏度和快速响应等特点,研制了采用直接吸收技术的小型化CO2探测系统,选取位于2 004.02nm处的R(16),ν1+ν3吸收谱线,避免了附近H2O分子的吸收干扰,对CO2浓度廓线进行了球载测量,获取了10km以下对流层中CO2的分子数密度分布。受限于球载测量环境,系统采用紧凑型设计,在单块电路板上实现激光器驱动、弱信号调理,光谱数据采集及浓度计算等功能,受嵌入式微处理器的运算能力和硬件资源限制,对浓度反演算法进行了优化,避免冗余计算,降低了算法耗时。和采用波长调制技术的TDLAS传统仪器相比,借助光程20m的开放式Herriott多次反射池,采用直接吸收技术,避免了浓度标定步骤,提高了对测量环境的适应性,通用性的硬件和软件结构可适用于测量不同气体,只需更换激光器和调整算法关键参数。小型化的设计思想降低功耗,减小体积,兼顾了响应速度和测量精度,室温条件下功耗小于1.5 W,单板体积120mm×100mm×25mm,1.5s时间响应下的测量精度为±0.6×10-6,经验证,该系统可在对流层内实现CO215m垂直空间分辨的高精度检测,是一种可行的气体廓线球载探测手段。

The main source and sink of CO2 in the atmosphere are concentrated in the troposphere .It is of great significance to the study of CO2 flux and global climate change to obtain the accurate tropospheric CO2 concentration profile .For the character‐istics of high resolution ,high sensitivity and fast response of tunable diode laser absorption spectroscopy （TDLAS） ,a compact balloon‐borne system based on direct absorption was developed to detect the CO2 concentration profiles by use of the 2 004.02 nm ,R（16） ,ν1 ＋ν3 line without the interfere of H2 O absorption and the CO2 density of the number of molecules below 10 km in the troposphere was obtained .Due to the balloon‐borne environment ,a compact design of one single board integrated with laser driver ,signal conditioning ,spectra acquiring and concentration retrieving was developed .Limited by the working capability and hardware resources of embedded micro‐processor ,the spectra processing algorithm was optimized to reduce the time‐cost .Com‐pared with the traditional TDLAS sensors with WMS technique ,this system was designed based on the direct absorption tech‐nique by means of an open‐path Herriott cell with 20 m optical‐path ,which avoided the process of standardization and enhanced the environmental adaptation .The universal design of hardware and software platform achieved diverse gas measuring by chan‐ging the laser and adjusting some key parameters in algorithm .The concept of compact design helped to reduce the system’s power and volume and balanced the response speed and measure precision .The power consumes below 1.5 W in room tempera‐ture and the volume of the single board is 120 mm × 100 mm × 25 mm ,and the measurement accuracy is ± 0.6 × 10^-6 at 1.5 s re‐sponse time .It has been proved that the system can realize high precision detection of CO2 profile at 15 m vertical resolution in troposphere and TDLAS is an available method for balloon‐borne detection .