The animation shows the Infrared Atmospheric Sounding Interferometer (IASI) scanning mirror directing emitted infrared radiation from one swath into the uncovered interferometer. One swath covers 30 scan positions towards the Earth and two calibration views. One calibration view is into deep space and the other is via an internal blackbody. Each scan starts on the left with respect to the flight direction of the satellite. The animation sequence concludes with the interferometer housed in the MetOp satellite showing the incident radiation being directed through the long split opening to make observations through the atmosphere, the calibration process then quickly takes place.