Selection of IASI channels for use in numerical weather prediction

The Infrared Atmospheric Sounding Interferometer (IASI) is an infrared Fourier-transform spectrometer that has been flying on the MetOp satellite series since October 2006. It measures the radiance emitted from the Earth in 8461 channels, covering the spectral interval 645-2760 cm(-1) at a resolution of 0.5 cm(-1) (apodized). The high volume of data resulting from IASI presents many challenges, particularly in the areas of data transmission, storage and assimilation. The simplest methods for reducing the data volume are spatial sampling and channel selection. In this paper, the issue of channel selection is discussed, and a selection of 300 channels suitable for transmission to numerical-weather-prediction centres is examined; the primary aim is the improvement of the temperature, humidity, ozone and carbon-dioxide state vectors. The channel-selection method takes account of redundancy, the effects of interfering species, and robustness against the choice of assumed background-error covariance, and atmospheric state. Copyright (c) 2007 Royal Meteorological Society.