Assimilation of surface-sensitive infrared radiances over land: Estimation of land surface temperature and emissivity


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Whilst the assimilation of radiances from infrared sounding spectrometers such as the Infrared Atmospheric Sounding Interferometer (IASI) and the Atmospheric Infrared Sounder (AIRS) over the sea is well established, observations over land have, until recently, only been assimilated at wavelengths insensitive to the surface. This was due to uncertainties in the infrared emissivity and skin temperature of the land. A method is described for analyzing the land surface emissivity spectrum in terms of its principal components in order to allow the assimilation of land-sensitive IASI channels and the results of the implementation of this scheme in an operational numerical weather prediction (NWP) system are presented. The use of additional IASI data over land resulted in small improvements in global NWP skill, mainly affecting near-surface temperature and mid-tropospheric water vapour fields.