To achieve global coverage, the IASI instrument observes the Earth until an angle of 48.3 degrees on either side of the satellite track. Scene scanning is stepped, with field motion compensation. For each view, the instrument analyses an atmospheric cell of about 3.3 degrees x 3.3 degrees, or 50 km x 50 km at nadir. Each cell is analysed simultaneously by a 2 x 2 array of detectors.
This geometrical arrangement, combined with the step-by-step scanning mode, gives IASI a field of view that is compatible with the other instruments on the platform. The pixel diameter of 12 kilometres is a trade-off between radiometric performance and statistics indicating the likelihood of acquiring valid measurements, depending on cloud cover.