研制了一套基于可调谐半导体激光吸收光谱(TDLAS)技术的开放式长光程甲烷(CH4)浓度实时监测系统, 系统采用波长调制和二次谐波探测相结合, 并利用光强归一化的方法消除光强波动对测量结果产生的影响, 实验证明采用消除光强波动的方法后使测量结果的误差小于2%。然后利用该系统在往返750 m的光程上, 对合肥市董铺岛进行了为期1周的大气CH4浓度测量, 测量结果表明董铺岛CH4浓度有明显的日变化趋势, 白天浓度低, 夜间浓度高, 日平均浓度(1.8～3.4)×10-6, 日最小值(1.8～2.2)×10-6, 日最大值(3.0～3.4)×10-6。通过分析, 可实现1～2 km范围的空气中CH4浓度的实时在线监测, 为生态系统的区域排放通量监测提供了有效的方法, 也为卫星遥感提供了可行的地面校准方法。

A long open-path tunable diode laser absorption spectroscopy (TDLAS) system based on wavelength modulation and second harmonic detection is developed. The method of normalized light intensity is adopted to eliminate the influences on the measurement by light intensity, and the measurement error is less than 2%. Then by using this system ambient methane is monitored at Dongpu island of Hefei with 750 m-optical-path. The measurement result is analyzed and the diurnal variation of atmospheric CH4 concentration has a very clear cycle in the Dongpu island. The general characteristics of diurnal variation are the lowest value in the daytime and the highest value at night, with the average concentration range of (1.8～3.4)×10-6, the highest concentration of (3.0～3.4)×10-6, and the lowest concentration of (1.8～2.2)×10-6. Experimental analysis shows that the system can achieve large region on-line monitoring of methane concentration with the distance of about 1～2 km and supply effective method to the monitoring of area emission flux of ecosystem and feasible ground calibration means to the satellite remote sensing.