Global height-resolved methane retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp

This paper describes the global height-resolved methane (CH 4 ) retrieval scheme for the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp, developed at the Rutherford Appleton Laboratory (RAL). The scheme is novel in: (a) precisely fitting 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 and (b) making specific use of nitrous oxide (N 2 O) 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 scheme is shown to be capable of retrieving column average methane with random errors of ~20–40 ppbv on individual soundings. Systematic differences with the other datasets are typically http://dx.doi.org/10.5285/B6A84C73-89F3-48EC-AEE3-592FEF634E9B ).