Mapping spectroscopic uncertainties into prospective methane retrieval errors from Sentinel-5 and its precursor
- 1IMK-ASF, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
- 2Netherlands Institute for Space Research (SRON), Utrecht, the Netherlands
- 3Laboratoire Interuniversitaire des Systèmes Atmosphériques, CNRS-UMR 7583, Université Paris Est Créteil, Université Paris Diderot, Institut Pierre-Simon Laplace, France
- 4Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR6303 CNRS-Univ. Bourgogne Franche-Comté, 9 Av. A. Savary, BP 47870, Dijon, France
- 5Space Research and Planetary Sciences, Physics Institute, University of Bern, Bern, Switzerland
- 6Center for Atmospheric Chemistry, Faculty of Science, Medicine & Health, University of Wollongong, Wollongong, Australia
Abstract. Sentinel-5 (S5) and its precursor (S5P) are future European satellite missions aiming at global monitoring of methane (CH4) column-average dry air mole fractions (XCH4). The spectrometers to be deployed onboard the satellites record spectra of sunlight backscattered from the Earth's surface and atmosphere. In particular, they exploit CH4 absorption in the shortwave infrared spectral range around 1.65 μm (S5 only) and 2.35 μm (both S5 and S5P) wavelength. Given an accuracy goal of better than 2 % for XCH4 to be delivered on regional scales, assessment and reduction of potential sources of systematic error such as spectroscopic uncertainties is crucial. Here, we investigate how spectroscopic errors propagate into retrieval errors on the global scale. To this end, absorption spectra of a ground-based Fourier transform spectrometer (FTS) operating at very high spectral resolution serve as estimate for the quality of the spectroscopic parameters. Feeding the FTS fitting residuals as a perturbation into a global ensemble of simulated S5- and S5P-like spectra at relatively low spectral resolution, XCH4 retrieval errors exceed 0.6 % in large parts of the world and show systematic correlations on regional scales, calling for improved spectroscopic parameters.