Fig 1.3.1.2.1.1: GOME at the start of a scan.
The dark red line represents the instantaneous field of view.

In the dayside section of its orbit the ERS2 satellite is travelling north to south. Its ground speed is approximately 7 km/s.

The GOME instrument has an instantaneous field of view (IFV) of 2 x 40 km. An azimuth scan mirror can move this field of view across the track by ±31°, giving a maximum scan width at ground level of 960 km.

Note

The Earth is also rotating relative to the orbit of the satellite. This lateral motion has been ignored in the diagram, because even at the equator, when it is at its fastest, the offset it causes within the timescale of the diagram is only a few km towards the west.

Note also that for clarity of explanation the diagram uses different scales for the x-axis (20 km per division) and y-axis (10 km per division).