Remote sensing of H2O and HDO column based on Fourier Transform Infrared spectroscopy

Abstract

The phase transition of water vapour is typically accompanied by a change in the water vapour isotopes. The dynamics, transpiration, and condensation of water vapour in the atmosphere can also be revealed by measuring water vapour isotopes in the atmosphere. This information is crucial for understanding the water cycle in the atmosphere. Fourier Transform Infrared (FTIR) spectroscopy is widely used to monitor atmospheric trace gases. This study is based on near-infrared solar absorption spectra collected by portable Fourier Transform Infrared spectrometer (FTS) to observe the column concentration results of H2O and HDO. And the column isotope ratio δD is calculated by H2O and HDO results. The fitted root-mean-square errors (RMSE) of the spectral retrieval window of H2O and HDO were 0.107% and 0.175%, respectively. And the mean retrieval error for H2O and HDO was (0.59 ± 0.21) % and (0.94 ± 0.20) %, respectively. The calculated error of δD was 0.0035‰, which shows a high level of observational accuracy. The time series of δD obtained from September 2016 to December 2017 with a varied in the range of -5.69‰ to -369.19‰. And the lowest δD observed in January with a mean value of (-249.63 ± 32.35) ‰ and the highest δD observed in July with a mean value of (-38.61 ± 2.43) ‰, the time series show a clear seasonal variation. The observations demonstrate the capability of the FTIR spectrometer to observe the stable isotope and isotope ratio δD of atmospheric water vapour with accuracy and precision.