Evaluation of the AIRS Near Real Time channel selection for numerical weather prediction application

Année de publication

2003

The Atmospheric Infrared Sounder (AIRS) on board the National <br>Aeronautics and Space Administration (NASA) Earth Observing System (EOS)<br> Aqua satellite provides 2378 channels for each field of view of the <br>instrument. As it is neither feasible nor efficient to assimilate all <br>the channels in a numerical weather-prediction system, a policy of <br>channel selection has to be designed in this context. This paper <br>attempts to assess the optimality of the selection of the AIRS radiance <br>channels that are made available to the scientific community in near <br>real time (hereafter called AIRS NRT) by the National Oceanic and <br>Atmospheric Administration (NOAA) National Environmental Satellite Data <br>and Information Service. This assessment is done by comparing this <br>channel selection with a method preserving the information content of <br>the instrument, the so-called global' method. It turns out that <br>although the selected channels are different and the information content<br> as measured by the entropy reduction (ER) and the degrees of freedom <br>for signal (DFS) is slightly smaller for the AIRS NRT channel set than <br>for the global' set, both channel selections give similar results in <br>terms of analysis error for temperature, humidity and ozone. The <br>robustness of the results is then evaluated by varying the range of <br>input parameters to the channel-selection scheme, in particular the <br>atmospheric training dataset on which the channel selection is based, <br>and the background-error covariance matrix. It is found that the <br>performance of the global' channel selection is sensitive to the <br>training dataset, while the AIRS NRT channel selection remains robust, <br>even, to some extent, for the retrieval of key analysis-error <br>structures. Altogether, the manually selected' AIRS NRT channels <br>provide a good compromise between robustness and quality. <br>Copyright © <br>2003 Royal Meteorological Society.</div>

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