amt-10-4135-2017.pdf (9.54 MB)
Global height-resolved methane retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp
journal contributionposted on 2018-01-05, 14:14 authored by Richard Siddans, Diane Knappett, Brian Kerridge, Alison Waterfall, Jane Hurley, Barry Latter, Hartmut Boesch, Robert Parker
This paper describes the global height-resolved methane (CH4) retrieval scheme for the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp, developed at the Rutherford Appleton Laboratory (RAL). The scheme precisely fits measured spectra in the 7.9 micron region to allow information to be retrieved on two independent layers centred in the upper and lower troposphere. It also uses nitrous oxide (N2O) spectral features in the same spectral interval to directly retrieve effective cloud parameters to mitigate errors in retrieved methane due to residual cloud and other geophysical variables. The scheme has been applied to analyse IASI measurements between 2007 and 2015. Results are compared to model fields from the MACC greenhouse gas inversion and independent measurements from satellite (GOSAT), airborne (HIPPO) and ground (TCCON) sensors. The estimated error on methane mixing ratio in the lower- and upper-tropospheric layers ranges from 20 to 100 and from 30 to 40 ppbv, respectively, and error on the derived column-average ranges from 20 to 40 ppbv. Vertical sensitivity extends through the lower troposphere, though it decreases near to the surface. Systematic differences with the other datasets are typically < 10 ppbv regionally and < 5 ppbv globally. In the Southern Hemisphere, a bias of around 20 ppbv is found with respect to MACC, which is not explained by vertical sensitivity or found in comparison of IASI to TCCON. Comparisons to HIPPO and MACC support the assertion that two layers can be independently retrieved and provide confirmation that the estimated random errors on the column- and layer-averaged amounts are realistic. The data have been made publically available via the Centre for Environmental Data Analysis (CEDA) data archive (Siddans, 2016).
This work has been funded by the UK Natural Environment Research Council (NERC) through the National Centre for Earth Observation (NCEO) and the strategic programme “Greenhouse Gases UK and Global Emissions” (GAUGE). Work has also been partly funded by a EUMETSAT study (contract no. EUM/CO/14/4600001315/RM). Robert Parker and Hartmut Boesch are funded by NCEO and ESA GHG-CCI; Robert Parker is also funded by an ESA Living Planet Fellowship. We thank the Japanese Aerospace Exploration Agency, National Institute for Environmental Studies and the Ministry of Environment for the GOSAT data and their continuous support as part of the Joint Research Agreement. This research used the ALICE High Performance Computing Facility at the University of Leicester.
CitationAtmospheric Measurement Techniques , 2017, 10 (11), pp. 4135-4164 (30)
Author affiliation/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
- VoR (Version of Record)
Published inAtmospheric Measurement Techniques
PublisherEuropean Geosciences Union (EGU), Copernicus Publications