In order to improve the processing of partly cloudy pixels, the IASI instrument includes a built-in imager to enable accurate collocation between IASI and METOP companion instrument AVHRR and also some stand-alone mean for cloud analysis. The field-of-view of the imager coincides with that of the IASI sounding unit (3.3333 deg by 3.3333 deg). The field-of-view is covered by a raster of 64 by 64 imager pixels.
The imager has a single spectral channel ranging from 10.3 to 12.5 µm. The radiometric performance is characterised by NEDT of 0.5 K at 280 K and calibration accuracy of better than 1 K at 280 K. The positioning error of imager pixels with respect to the pixels of the sounding unit is less than 0.05 deg.