Impact of Assimilating Surface Sensitive IASI and CrIS Radiance Observations over Land in the NASA GEOS

Abstract Satellite infrared radiances contain a wealth of information on Earth’s environment including its atmosphere and different surface properties. The potential of infrared (IR) radiances to further improve the quality of the data assimilation remains significant, especially for surface-sensitive IR measurements. Assimilating surface-sensitive radiances over land is indeed still challenging for IR radiances. Currently, very few IR radiances are assimilated over land in the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System (GEOS). A large number of IR radiances are rejected by the surface sensitivity check process as well as the cloud detection mechanism. This study presents an initial effort aimed at assimilating IR radiances over land in the NASA GEOS in clear-sky conditions. To facilitate this assimilation, the land surface temperature (LST) is first retrieved using IR radiances from the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS) at selected channels, to use it as a surface boundary parameter for the assimilation of the rest of the channels. This paper provides a full assessment of the quality of this LST by comparing it and its spatiotemporal variability to the LST predicted by the GEOS model. The impacts on the quality of the resultant analysis and subsequent forecast will also be discussed. The developed methodology is relevant to other infrared sensors and could be used to prepare for the assimilation over land of next-generation hyperspectral sensors such as IASI Next Generation (IASI-NG on board MetOp Second Generation) and Infrared Sounder (IRS).