傅里叶变换红外（FTIR）光谱技术可用来测量宽带红外光谱，能同时分析大气中的多种成分。描述了利用开放光路FTIR光谱技术测量环境大气中水汽的稳定同位素的新方法。以分析采集的中红外光谱为基础，在外场实验中，应用开放光程FTIR系统连续测量环境大气中水汽的稳定同位素H216O和HD16O，并得到大气中的氘同位素比值δD。对该测量系统，H216O和HD16O的测量误差分别约为0.25%和1.60%，氘同位素比值δD的测量精度约为1.32‰。详细分析了其中5天的数据，研究了环境大气中水汽的稳定同位素H216O、HD16O 以及同位素比值δD随时间的变化规律。并采用Keeling图分析方法，研究了地表蒸散的氘同位素特征。外场实验的结果证明了所提的测量方法和开放光程FTIR系统相结合长期测量环境大气中稳定同位素的能力。

Fourier transform infrared (FTIR) spectrometry can be used to measure broadband infrared spectra, and it can analyze various gases in the air simultaneously. A new method of measuring stable isotopes in atmospheric water vapor by open-path FTIR spectrometry is described. An open-path FTIR system is utilized to continuously measure the stable isotopes of water vapor in ambient air in a field experiment, which is based on the analysis of collected mid-infrared spectrum. The deuterium isotope ratios δD are also obtained. The measurement error of this system is about 0.25% and 1.60% for H216O and HD16O respectively, and the measurement precision is about 1.32‰ for δD. A detailed analysis of five-day data is presented to explore the variation of H216O, HD16O and δD with time. Furthermore, Keeling plot method is employed to study the deuterium isotopic signature of evapotranspiration. The results of the field experiment show the ability of this proposed measuring method combined with the open-path FTIR system for long-term measurement of the stable isotopes in the air.