A new approach to HDO/H2O ratio profile retrieval in the atmosphere from TANSO-FTS/GOSAT-2 spectrum data by using TIR and SWIR spectral ranges simultaneously: method and software

Global monitoring of isotopic composition of water vapor in the atmosphere provides information regarding atmospheric hydgrological cycle in the Earth’s climate system. The observed HDO to H₂O ratio (δD) in atmospheric water vapor gives information on origin and history of air masses in the atmosphere.

In this study we present a method, software tool and some results on δD ratio retrieval from spectra, measured simultaneously in the thermal (TIR) and short wave infrared (SWIR) spectral ranges. The TANSO-FTS high spectral resolution spectrometer on board GOSAT-2 satellite is unique to perform simultaneous measurements in TIR and SWIR spectral bands. A method of simultaneous using of these both bands can improve vertical resolution of δD retrieved profile.

We applied conventional optimal estimation method to solve inverse problem. The output data of atmospheric general circulation model ECHAM5-wiso were used as a statistical ensemble of HDO and H2O a priori profiles. The averaging kernels, a posteriori covariance matrices and degrees of freedom are calculated. The retrieval algorithm is implemented using original FIRE-ARMS software and VLIDORT radiation transfer model.

This study is supported by the Russian Science Foundation grant No. 18-11-00024.