Inverse modelling of CH<sub>4</sub> emissions for 2010–2011 using different satellite retrieval products from GOSAT and SCIAMACHY
At the beginning of 2009 new space-borne observations of dry-air column-averaged mole fractions of atmospheric methane (XCH<sub>4</sub>) became available from the Thermal And Near infrared Sensor for carbon Observations–Fourier Transform Spectrometer (TANSO-FTS) instrument on board the G...
| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/113/2015/acp-15-113-2015.pdf |
| Summary: | At the beginning of 2009 new space-borne observations of dry-air column-averaged mole
fractions of atmospheric methane (XCH<sub>4</sub>) became available from the Thermal
And Near infrared Sensor for carbon Observations–Fourier Transform
Spectrometer (TANSO-FTS) instrument on board the Greenhouse Gases Observing
SATellite (GOSAT). Until April 2012 concurrent {methane (CH<sub>4</sub>) retrievals} were
provided by the SCanning Imaging Absorption spectroMeter for Atmospheric
CartograpHY (SCIAMACHY) instrument on board the ENVironmental SATellite (ENVISAT). The GOSAT and SCIAMACHY
XCH<sub>4</sub> retrievals can be compared during the period of overlap. We estimate
monthly average CH<sub>4</sub> emissions between January 2010 and December 2011,
using the TM5-4DVAR inverse modelling system. In addition to satellite data,
high-accuracy measurements from the Cooperative Air Sampling Network of the
National Oceanic and Atmospheric Administration Earth System Research
Laboratory (NOAA ESRL) are used, providing strong constraints on the remote
surface atmosphere. We discuss five inversion scenarios that make use of
different GOSAT and SCIAMACHY XCH<sub>4</sub> retrieval products, including two sets
of GOSAT proxy retrievals processed independently by the Netherlands
Institute for Space Research (SRON)/Karlsruhe Institute of Technology (KIT),
and the University of Leicester (UL), and the RemoTeC "Full-Physics" (FP)
XCH<sub>4</sub> retrievals available from SRON/KIT. The GOSAT-based inversions show
significant reductions in the root mean square (rms) difference between
retrieved and modelled XCH<sub>4</sub>, and require much smaller bias corrections
compared to the inversion using SCIAMACHY retrievals, reflecting the higher
precision and relative accuracy of the GOSAT XCH<sub>4</sub>. Despite the large
differences between the GOSAT and SCIAMACHY retrievals, 2-year average
emission maps show overall good agreement among all satellite-based
inversions, with consistent flux adjustment patterns, particularly across
equatorial Africa and North America. Over North America, the satellite
inversions result in a significant redistribution of CH<sub>4</sub> emissions from
North-East to South-Central United States. This result is consistent with recent
independent studies suggesting a systematic underestimation of CH<sub>4</sub>
emissions from North American fossil fuel sources in bottom-up inventories,
likely related to natural gas production facilities.
Furthermore, all four satellite inversions yield lower CH<sub>4</sub> fluxes across
the Congo basin compared to the NOAA-only scenario, but higher emissions
across tropical East Africa. The GOSAT and SCIAMACHY inversions show
similar performance when validated against independent shipboard and aircraft
observations, and XCH<sub>4</sub> retrievals available from the Total Carbon Column
Observing Network (TCCON). |
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| ISSN: | 1680-7316 1680-7324 |