As the MetOp satellite orbits the Earth, the MHS instrument continuously scans down through the atmosphere across the track of the flight path. During each scan cycle the instrument provides data (for each of its five channels) for 90 individual Earth scenes, each with a footprint of about 16 kilometres in diameter at nadir. Each cycle takes 2.67 seconds, but the scan cycle is optimised to maximise the time available monitoring the Earth, which equates to more than 60% of the scan duration.