Ground-based remote sensing of HDO/H2O ratio profiles: introduction and validation of an innovative retrieval approach

[摘要] We propose an innovative approach for analysing ground-based FTIRspectra which allows us to detect variabilities of lower andmiddle/upper tropospheric HDO/H₂O ratios. We showthat the proposed method is superior to common approaches. Weestimate that lower tropospheric HDO/H₂O ratios canbe detected with a noise to signal ratio of 15% andmiddle/upper tropospheric ratios with a noise to signal ratio of50%. The method requires the inversion to be performed ona logarithmic scale and to introduce an inter-species constraint.While common methods calculate the isotope ratio posterior to anindependent, optimal estimation of the HDO and H₂Oprofile, the proposed approach is an optimal estimator for the ratioitself. We apply the innovative approach to spectra measuredcontinuously during 15 months and present, for the first time, anannual cycle of tropospheric HDO/H₂O ratio profilesas detected by ground-based measurements. Outliers in the detectedmiddle/upper tropospheric ratios are interpreted by backwardtrajectories.

[学科分类] 大气科学