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Carbon dioxide (CO2) and methane (CH4) are the two most important anthropogenic greenhouse gases (GHGs) and a focus of international research activities related to a better understanding of the carbon cycle (see, for example, the Global Carbon Project (GCP)).
Within the GHG-CCI project we focus on satellite data. Satellite observations combined with modelling can add important missing global information on regional CO2 and CH4 (surface) sources and sinks required for better climate prediction. The ESA project GHG-CCI aims at delivering the high quality satellite retrievals needed for this application. GHG-CCI is one of several projects of ESA's Climate Change Initiative (CCI), which will deliver various Essential Climate Variables (ECVs). The GHG-CCI project started 1. Sept. 2010.
The GHG-CCI core ECV data products, generated with ECV Core Algorithms (ECAs), are column-averaged mole fractions of CO2 and CH4 retrieved from SCIAMACHY on ENVISAT and TANSO on GOSAT.
Other satellite instruments will be used to provide constraints for upper layers such as IASI, MIPAS and ACE-FTS. The corresponding retrieval algorithms are referred to as Additional Constraints Algorithms (ACAs) within the GHG-CCI project.
Important aspects also covered by GHG-CCI are calibration, validation and user assessments. 
Two satellite instruments exist (or existed until recently) performing radiance measurements which are sensitive to near-surface CO2 and CH4 concentration changes: SCIAMACHY on ENVISAT (2002 - 2012) and TANSO on GOSAT (launched in 2009). Both sensors enable the retrieval of near-surface sensitive column-averaged dry air mole fractions of CO2 and CH4, i.e., XCO2 (in ppm) and XCH4 (ppb). These data products are the core data products generated within GHG-CCI with ECC Core Algorithms (ECAs).
Using measurements from the first years of SCIAMACHY it had already been demonstrated prior to the start of this project that regional methane emissions can be well constrained via inverse modelling approaches. Within GHG-CCI this methane time series has been extended. For SCIAMACHY XCO2 first surface flux inversions have been carried out within GHG-CCI. Note that the XCO2 user requirements are more stringent compared to XCH4. Within GHG-CCI SCIAMACHY XCH4 and XCO2 retrieval algorithms are being further improved to improve the quality of the SCIAMACHY greenhouse gas data products.
GOSAT had been launched shortly before this project started and only initial data products were available at that point in time. Operational GOSAT data products are generated at JAXA and NIES in Japan. GOSAT data products are also generated outside Japan, most notably in the USA by NASA (ACOS team). With GHG-CCI European GOSAT retrieval efforts have been significantly strengthened and first high-quality global multi-year data sets have been generated. Improving the quality of these XCO2 and XCH4 time series and extending it is a major focus of GHG-CCI.
More details are given in various documents which have been generated so far and in the Quarterly Reports given here:
Apr - Jun 2018: Quarterly Report No 31
Jan - Mar 2018: Quarterly Report No 30
Oct - Dec 2017: Quarterly Report No 29
Jul - Sept 2017: Quarterly Report No 28
Apr - Jun 2017: Quarterly Report No 27
Jan - Mar 2017: Quarterly Report No 26
Oct - Dez 2016: Quarterly Report No 25
Jul - Sept 2016: Quarterly Report No 24
Apr - Jun 2016: Quarterly Report No 23
Jan- Mar 2016: Quarterly Report No 22
Oct - Dec 2015: Quarterly Report No 21
Jul - Sep 2015: Quarterly Report No 20
Apr - Jun 2015: Quarterly Report No 19
Jan - Mar 2015: Quarterly Report No 18
Oct - Dec 2014: Quarterly Report No 17
Jul - Sep 2014: Quarterly Report No 16
Apr - Jun 2014: Quarterly Report No 15
Jan - Mar 2014: Quarterly Report No 14
Oct - Dec 2013: Quarterly Report No 13
Jul - Sep 2013: Quarterly Report No 12
Apr - Jun 2013: Quarterly Report No 11
Jan - Mar 2013: Quarterly Report No 10
Oct - Dec 2012: Quarterly Report No 9
Jul - Sep 2012: Quarterly Report No 8
Apr - Jun 2012: Mid-Term / Quarterly Report No 7
May 2012: Achievements Report
Jan - Mar 2012: Quarterly Report No 6
Oct - Dec 2011: Quarterly Report No 5
Jul - Sep 2011: Quarterly Report No 4
Apr - Jun 2011: Quarterly Report No 3
Jan - Mar 2011: Quarterly Report No 2
Oct - Dec 2010: Quarterly Report No 1
December 2011: GHG-CCI Science Leader Michael Buchwitz has presented a GHG-CCI project overview and status at the AGU Fall Meeting in San Francisco in Dec. 2011. The presentation can be obtained from here: pdf, ppt.
Prior to the official start of the GHG-CCI project the GHG-CCI Science Leader Michael Buchwitz has presented an overview about the planned activities at the ESA Living Planet Symposium in 2010 in Bergen, Norway. The presentation can be obtained from here: pdf. Here a video of the presentation: flv. View the entire CCI session if you wish.