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ABSTRACT
A Fourier Transform Infrared (FTIR) spectrometer has been operational since March 2014, at National Remote Sensing Centre (NRSC), Shadnagar, which is a suburban site of central India. Direct solar radiation spectra recorded by the FTIR during clear sky days at a high spectral resolution of 0.01 cm‒1 were analysed using the line-by-line radiative transfer algorithm (LBLRTA) to retrieve the initial results of column-averaged concentrations of methane (XCH4) and nitrous oxide (XN2O) in the atmosphere. Error residuals between the measured and estimated atmospheric transmissions are in the range of 0.40–0.80% for CH4 and 0.20–0.50% for N2O, respectively. The maximum (minimum) XCH4 and XN2O were, respectively, 1.88 ± 0.04 ppm (1.67 ± 0.02 ppm) and 316.15 ± 5.85 ppb (278.92 ± 4.02 ppb). Columnar concentrations of CH4 and N2O retrieved from the Infrared Atmospheric Sounding Interferometer (IASI) were compared against retrieved XCH4 and XN2O using the ground FTIR. The observed differences between the two data sets lie between −0.06 ppm and +0.10 ppm for CH4 and between +32 ppb and ‒10 ppb for N2O.
Acknowledgements
The authors sincerely thank colleagues of Atmospheric and Climate Sciences Group (ACSG) of Earth and Climate Science Area (ECSA) for their immense support in collecting the data. We would like to acknowledge Dr J. Hannigan, NCAR, Boulder, CO, and Dr Frank Hase, project manager Collaborative Carbon Column Observing Network (COCCON), for sharing the climatology data and their valuable suggestions. The authors express sincere gratitude to NDAAC/TCCON website (http://www.ndsc.ncep.noaa.gov/). The authors greatly acknowledge the editor, technical editor, and anonymous referees for their valuable suggestions/comments to improve this manuscript.
Disclosure statement
No potential conflict of interest was reported by the authors.