Water vapor isotopic abundance measurement in Tibetan Plateau based on portable laser heterodyne radiometer

Tibet Plateau is known as the third pole of the world, the environmental changing in this area profoundly impacts on east Asian or even global climate. HDO is the stable isotope of water vapor and is the ideal tracer of water cycle, which has been applied to atmospheric circulation and climatic studies. For monitoring the water vapor isotopic abundance in Tibetan Plateau and providing reliable information for environmental and climatic studies, a portable laser heterodyne radiometer was operated at Golmud (Qinghai Province) in summer 2019. The radiometer adopted a narrow linewidth 3.66 μm DFB laser as the local oscillator and performed high resolution(~0.009 cm^-1) and high signal-to-noise ratio(~160). Furthermore, the absorption spectra of atmospheric HDO and H₂O were obtained and the retrieval algorithm of water vapor isotopic abundance was discussed. The optimal estimation method based on LBLRTM was chosen for retrieving, the ratio of HDO/H₂O at Golmud is 185±7×10^-6 during the observation, the value is less than the Vienna Standard Mean Ocean Water (VSMO, 311.5×10^-6) but larger than Standard Light Antarctic Precipitation (SLAP, 178.2×10^-6).