A multi-year methane inversion using SCIAMACHY, accounting for systematic errors using TCCON measurements

This study investigates the use of total column CH4 (XCH4) retrievals from the SCIAMACHY satellite in- strument for quantifying large-scale emissions of methane. A unique data set from SCIAMACHY is available span- ning almost a decade of measurements, covering a period when the global CH4 growth rate showed a marked transition from stable to increasing mixing ratios. The TM5 4DVAR in- verse modelling system has been used to infer CH4 emissions from a combination of satellite and surface measurements for the period 2003–2010. In contrast to earlier inverse mod- elling studies, the SCIAMACHY retrievals have been cor- rected for systematic errors using the TCCON network of ground-based Fourier transform spectrometers. The aim is to further investigate the role of bias correction of satellite data in inversions. Methods for bias correction are discussed, and the sensitivity of the optimized emissions to alternative bias correction functions is quantified. It is found that the use of SCIAMACHY retrievals in TM5 4DVAR increases the esti- mated inter-annual variability of large-scale fluxes by 22 % compared with the use of only surface observations. The dif- ference in global methane emissions between 2-year periods before and after July 2006 is estimated at 27–35 Tg yr−1. The use of SCIAMACHY retrievals causes a shift in the emis- sions from the extra-tropics to the tropics of 50±25 Tg yr−1. The large uncertainty in this value arises from the uncertainty in the bias correction functions. Using measurements from the HIPPO and BARCA aircraft campaigns, we show that systematic errors in the SCIAMACHY measurements are a main factor limiting the performance of the inversions. To further constrain tropical emissions of methane using current and future satellite missions, extended validation capabilities in the tropics are of critical importance.

HOUWELING Sander;  KROL M.;  BERGAMASCHI Peter;  FRANKENBERG Christian;  DLUGOKENCKY Edward;  MORINO I;  NOTHOLT Justus;  SHERLOCK V.;  WUNCH D.;  BECK Veronika;  GERBIG Christoph;  CHEN Huilin;  KORT Eric;  ROECKMANN Thomas;  ABEN I.; 

2014-06-16

COPERNICUS GESELLSCHAFT MBH

JRC84400

1680-7316,   

http://www.atmos-chem-phys.net/14/3991/2014/acp-14-3991-2014.pdf,    https://publications.jrc.ec.europa.eu/repository/handle/JRC84400,   

10.5194/acp-14-3991-2014,