Retrieval of sea surface temperature and trace gas column averaged from GOSAT, IASI-A, and IASI-B over the Arctic Ocean in summer 2010 and 2013

Abstract : The Arctic Ocean is a very important region of the globe in which the effect of climate change can be detected over short time periods. We have used the possibility provided by the three infrared sounders TANSO-FTS on the GOSAT platform, IASI-A, and IASI-B on the MetOp platforms to retrieve the sea surface temperature (Tsurf) and the column averaged mixing ratio of several trace gases (CO₂, CH₄, N₂O, O₃) for pairs of nearly coinciding footprints (IFOVs) at small time separations (typically for IASI ~46 min and ~54 min depending on which satellite has first observed the corresponding scene). A strict filtering based on the AVHRR cloud fraction and the radiance analysis within the GOSAT and IASI footprints lead to a large number of quasi-coinciding IFOVs for which a 1D-var inversion (Tsurf and XCO₂ as the main parameters in the state vector, plus scaling factors for the profiles of H₂O and O₃) has been performed. As an example, we used during retrieval the atmospheric window between 940 and 980 cm^-1 (CO₂ laser band) for which the sensitivity to the surface is maximum. The statistics of the comparison between IASI-A and IASI-B retrievals is presented and compared to the corresponding Eumetsat L2 products. The months of July and August for the years 2010 and 2013 have been considered since in these Arctic summer conditions the ice pack coverage is reduced. The differences between these two consecutive years is discussed and a comparison with 2010 (for which only IASI-A was in orbit) is confirming that IASI can indeed be used for climate change studies.