SEVIRI: geared to top performances
The MSG mission
with both its radiometric and imaging functions demands also high spatial resolution
and short repeat cycle, together with very low noise.
The radiometric characteristics
of the SEVIRI instrument have been defined to provide improved image quality compared
to the current Meteosat imager.
The instrument collects a flux determined by the radiance of the current target,
which is distributed to each detector.
This flux includes parasitic radiation from stray light (affecting all channels)
and from the instrument self-thermal emission (also called background, affecting
only the IR channels).
The signal offset, including the instrument background and the detection dark signal,
is measured at each line scan during the deep space viewing and removed from the
detector output signal (DCR function).
The absolute radiometric accuracy
of the VNIR channels is based on a vicarious calibration process, by observation
of landmarks with well-known radiative properties, at different periods of the year.
IR radiometric calibration
A sophisticated methodology has been implemented on board the MSG satellites
in order to achieve an accurate calibration of the IR channels.
Radiometric performances
The noise is the parameter that drove the overall SEVIRI sizing, with detectors
and pre-amplifiers being the main contributors. The radiometric performances need
to be referred to such noise.
Geometric performances
The imaging area is defined as the square circumscribing the Earth's disc as
seen from the satellite. The geometric performances quoted in terms of location and
resolution apply to that area.
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