Intercomparison of XH2O Data from the GOSAT TANSO-FTS (TIR and SWIR) and Ground-Based FTS Measurements: Impact of the Spatial Variability of XH2O on the Intercomparison.

Spatial and temporal variability of atmospheric water vapor (H₂O) is extremely high, and therefore it is difficult to accurately evaluate the measurement precision of H₂O data by a simple comparison between the data derived from two different instruments. We determined the measurement precisions of column-averaged dry-air mole fractions of H₂O (XH₂O) retrieved independently from spectral radiances in the thermal infrared (TIR) and the short-wavelength infrared (SWIR) regions measured using a Thermal And Near-infrared Sensor for carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT), by an intercomparison between the two TANSO-FTS XH₂O data products and the ground-based FTS XH₂O data. Furthermore, the spatial variability of XH₂O was also estimated in the intercomparison process. Mutually coincident XH₂O data above land for the period ranging from April 2009 to May 2014 were intercompared with different spatial coincidence criteria. We found that the precisions of the TANSO-FTS TIR and TANSO-FTS SWIR XH₂O were 7.3%-7.7% and 3.5%-4.5%, respectively, and that the spatial variability of XH₂O was 6.7% within a radius of 50 km and 18.5% within a radius of 200 km. These results demonstrate that, in order to accurately evaluate the measurement precision of XH₂O, it is necessary to set more rigorous spatial coincidence criteria or to take into account the spatial variability of XH₂O as derived in the present study. [ABSTRACT FROM AUTHOR]