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CH4, CO, and H2O spectroscopy for the Sentinel-5 Precursor mission: an...

Galli, A., A. Butz, R. A. Scheepmaker, O. Hasekamp, J. Landgraf, P. Tol, D. Wunch, N. M. Deutscher, G. Toon, P. Wennberg, D. W. T. Griffith, and I. Aben (2012), CH4, CO, and H2O spectroscopy for the Sentinel-5 Precursor mission: an assessment with the Total Carbon Column Observing Network measurements, Atmos. Meas. Tech., 5, 1387-1398, doi:10.5194/amt-5-1387-2012.

The TROPOspheric Monitoring Instrument (TROPOMI) will be part of ESA’s Sentinel-5 Precursor (S5P) satellite platform scheduled for launch in 2015. TROPOMI will monitor methane and carbon monoxide concentrations in the Earth’s atmosphere by measuring spectra of back-scattered sunlight in the short-wave infrared (SWIR).

S5P will be the first satellite mission to rely uniquely on the spectral window at 4190–4340 cm−1 (2.3 µm) to retrieve CH4 and CO. In this study, we investigated if the absorption features of the three relevant molecules CH4 , CO, and H2 O are adequately known. To this end, we retrieved total columns of CH4 , CO, and H2 O from absorption spectra measured by two ground-based Fourier transform spectrometers that are part of the Total Carbon Column Observing Network (TCCON). The retrieval results from the 4190– 4340 cm−1 range at the TROPOMI resolution (0.45 cm−1 ) were then compared to the CH4 results obtained from the 6000 cm−1 region, and the CO results obtained from the 4190–4340 cm−1 region at the higher TCCON resolution (0.02 cm−1 ).

For TROPOMI-like settings, we were able to reproduce the CH4 columns to an accuracy of 0.3 % apart from a constant bias of 1 %. The CO retrieval accuracy was, through interference, systematically influenced by the shortcomings of the CH4 and H2 O spectroscopy. In contrast to CH4 , the CO column error also varied significantly with atmospheric H2 O content. Unaddressed, this would introduce seasonal and latitudinal biases to the CO columns retrieved from TROPOMI measurements. We therefore recommend further effort from the spectroscopic community to be directed at the H2 O and CH4 spectroscopy in the 4190–4340 cm−1 region.

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