Cross-Calibration of Water Vapor Absorption Bands from International Geostationary Satellites for Consistency with IASI

A geostationary (GEO) satellite may view about one third of the Earth’s surface with its full disk. The constellation of the international GEO satellites almost have a global coverage (except the polar region), which makes them ideal for climate studies. In the past 20+ years, GEO Imagers with water vapor absorption InfraRed (IR) bands have been observing the Earth’s atmosphere, providing useful information about upper tropospheric humidity (UTH), especially the diurnal variation of UTH. However, due to the differences of spectral response functions (SRFs) and observation angles in GEO satellites, these observations are not consistent for generating climate data records (CDR). In this study, a methodology has been developed to cross-calibrate the water vapor radiances from the international GEO satellites to generate a consistent CDR. All other GEO Imager water vapor radiances are re-calibrated to GOES-15 Imager 6.5 µm nadir view radiances. A cloud mask scheme is implemented in post-processing to remove high clouds. The validation is carried out both qualitatively and quantitatively. The self-consistency test examines the discontinuity between two adjacent satellites, for example, a successful cross-calibration should remove such discontinuities. Quantitatively, IASI radiances from Metop-A/B are convolved with the SRF of GOES-15 Imager 6.5 µm, and compared with the re-calibrated radiances from all GEO satellites. The results from a three-year (2015 – 2017) comparison will be shown for seven GEO Imager sensors: GOES-13/-15, SEVIRI-8/-10, Himawari-8 AHI, MTSAT-2, and GOES-16 ABI. Also, the impact of viewing angle on generating consistent GEO water vapor band radiance CDR will be investigated.