ANNEX III : Definition of SEVIRI channels and characteristics of MSG
MSG is a spin-stabilised satellite in geostationary orbit, as its predecessor Meteosat. Its main
payload will be the Spinning Enhanced Visible and Infrared Imager (SEVIRI) providing earth
observation of the earth in 12 spectral channels.
SEVIRI has eight channels in the thermal infrared (IR), three Visible and Near InfraRed (VNIR)
channels in the solar spectrum, and a high resolution visible (HRV) channel.
Channel Centre Nominal spectral Dynamic range Radiometric Noise
wavelength Bandwidth (µm),
(µm) integrated energy (%)
HRV between 0.5- Broadband channel 0 – 459 W/m2 µm S/N > 4.3 for target of 1%
0.9 µm similar to Meteosat (scaled at centre of max dynamic range
VIS 0.6 0.635 0.56 - 0.71 0 – 533 W/m2 µm S/N > 10.1 for target of 1%
98% of max dynamic range
VIS 0.8 0.81 0.74 - 0.88 0 – 357 W/m2 µm S/N > 7.28 for target of 1%
99% of max dynamic range
IR 1.6 1.64 1.50 - 1.78 0 – 75 W/m2 µm S/N > 3 for target of 1% of
99% max dynamic range
IR 3.9 3.92 3.48 - 4.36 0 – 335 K 0.35 K @ 300 K
WV 6.2 6.25 5.35 - 7.15 0 – 300 K 0.75 K @ 250 K
WV 7.3 7.35 6.85 - 7.85 0 – 300 K 0.75 K @ 250 K
IR 8.7 8.70 8.30 - 9.10 0 – 300 K 0.28 K @ 300 K
IR 9.7 9.66 9.38 - 9.94 0 – 310 K 1.50 K @ 255 K
IR 10.8 10.8 9.80 - 11.80 0 – 335 K 0.25 K @ 300 K
IR 12.0 12.0 11.00 - 13.00 0 – 335 K 0.37 K @ 300 K
IR 13.4 13.40 12.40 - 14.40 0 – 300 K 1.80 K @ 270 K
Table 1: Spectral channels of MSG. Spectral bandwidth refer to percentage of total integrated energy received in this
band, except for the HRV channel that is defined merely as a successor of Meteosat.
These spectral channels build upon the heritage of other satellites as outlined below:
0.6 and 0.8 µm: Known from the Advanced Very High Resolution Radiometer (AVHRR). They
are essential for cloud detection, cloud tracking, scene identification, aerosol observation,
1.6 µm: Some recent heritage from the Along Track Scanning Radiometer (ATSR).
Discriminates between snow and cloud, ice and water clouds, and provides aerosol
3.9 µm: Known from AVHRR. Primarily supports low cloud and fog detection. In addition, it will
support measurement of land and sea surface temperature at night. In order to improve signal-
to-noise ratio, the channel on MSG is broader and has been shifted towards higher
6.2 and 7.3 µm: Continues the mission of the Meteosat broadband water vapour channel for
observing water vapour and winds, but is split into two channels peaking at different levels in
the troposphere. Height allocation of semitransparent clouds will also be supported.
8.7 µm: Known from the High resolution Infra Red Sounder (HIRS) instrument on the polar
orbiting NOAA satellites. The channel will deliver quantitative information of thin cirrus clouds
and support the discrimination between ice and water clouds
9.7 µm: Total Ozone channel. As an experimental channel, it will be used for tracking of ozone
patterns that should be representative for wind motion in the lower stratosphere. Its radiances
are considered as an essential input to future Numerical Weather Prediction (NWP).
10.8 and 12.0 µm: Well-known split window channels from AVHRR, essential to measure earth
surface and cloud top temperatures. Detection of cirrus and inference of total precipitable water
vapour over sea.
13.4 µm: CO2 absorption channel known from former GOES VAS instrument. It will improve
height determination of transmissive cirrus clouds. In cloud free areas, it will provide
temperature information from the lower troposphere for static instability assessment.
Figure 1: Contribution functions of SEVIRI IR channels based on spectral response curves of the Engineering Model.
The imaging area of SEVIRI will be the same as for Meteosat. The sampling distance in N-S
and in E-W direction will be 3 km for the VNIR channels and 1 km for the broadband visible
channel (HRV), referring to a location at the nominal subsatellite point at zero degrees
longitude over the equator. Fields of view are 4.8x4.8 km for the VNIR channels and 2.67x2.0
km for the HRV channel.
The scan area of the HRV channel will be restricted in the E-W direction by scanning only half
the nominal scan line of the other channels. For the northern quarter of the image area, the
scan line will in the nominal case be centred. For the lower part, the observations area can be
adjusted in the E-W direction by ground command, as shown in the example below.
All Channels except HRV HRV (nominal and alternative coverage)
Figure 1: Nominal Earth coverage of MSG Image Channels
All Channels except HRV HRV (nominal and alternative coverage)
Figure 2: Nominal Earth coverage of MSG Image Channels
The nominal repeat cycle of SEVIRI for scanning full disk images is 15 minutes. Shorter repeat
cycles will be possible by scanning a reduced number of scan lines.
Level 1.0 data
Level 1.0 data are the samples observed by SEVIRI and transmitted to ground in digital form in
10 bits per pixel. SEVIRI Level 1.0 data will be archived and will be processed by the IMPF into
Level 1.5 data.
Level 1.5 data
Level 1.5 data is the primary product of the MSG system and is derived from Level 1.0 image
data by radiometric and geometric processing by the IMPF of the MSG Ground Segment.
Level 1.5 data will be disseminated in near real time through the HRIT and LRIT schemes, and
will be archived.
Radiometric processing includes linearisation and equalisation of detector data. Signal
contribution from straylight in the solar channels is also removed.
Calibration coefficients for the IR channels are derived in real-time based on the black body
information of each detector, accounting for the contribution of the front optics. This contribution
is modelled using temperature measurements at relevant locations within the SEVIRI
instrument. The target value for absolute radiometric accuracy is 1K.
Calibration coefficients for the solar channels are derived regularly through a vicarious
calibration scheme based on selected and well characterised ground targets. The target value
for absolute radiometric accuracy is 5%.
Geometric rectification and quality assessment
In a single step, the radiometrically corrected image is geometrically corrected, remapped into
a standard geostationary projection, and the registration between channels is performed.
Space image data (in the corners of the images) are masked out.
The channel registration to a common reference grid is expected to be with an accuracy of 600
m at SSP for the HRV and VNIR channels. The IR channels will be registered within 750 m at
SSP. The registration of the HRV, VNIR and IR channels is ensured via the geometric
accuracy. The quality control of the geolocation process will be based on the extraction of
landmarks. The processing scheme is designed so that the quantisation error from
linearisation, equalisation and re-sampling processes should affect the image radiometric
quality by no more than 0.5 digital count RMS. Basic geometric quality figures are given in
Table 2 below.
Geometric quality criterion RMS
Absolute accuracy < 3 km SSP
Relative accuracy (image to image) < 1.2 km SSP
Relative accuracy within an image (500 pixels) < 3 km SSP
Relative accuracy within an image (16 pixels) < 0.75 km SSP
Table 2: Geometric quality accuracy of the level 1.5 image data at the Sub-Satellite Point.
The resulting Level 1.5 image is a data set with 37123712 pixels per channel except for the
HRV channel which has a size of 111365568 (NSEW). All channels are coded in 10 bits per
pixel. All pixels are geolocated on a common grid in the geostationary projection. The
geostationary projection used for the level 1.5 image is defined with sub-satellite point (SSP) at
zero degree longitude and latitude. This SSP has the image coordinates at (1856, 1856) for
non-HRV channels and (5566, 5566) for HRV.
The origin has image coordinates at (1, 1).
Level 1.5 image data description
Level 1.5 image data will be transmitted to external users or to the MPEF in the MSG ground
segment as the basic input data for the derivation of meteorological products.
In order to allow full interpretation, validation, calibration, reprocessing and further processing,
Level 1.5 data will contain header and trailer blocks with the following information:
Status information of level 1.0 image acquisition;
The satellite, Sun and celestial bodies position at the time of image acquisition;
Status information on the radiometric and geometric processing;
The radiometric image quality for both level 1.0 and 1.5;
The geometric image quality of level 1.5;
Information related to the calibration schemes applied.
Detailed information on MSG image data contents, characteristics and data formats can be
found in the document MSG/ICD/105 Level 1.5 Data Format Description that is available for
download from the site
Illustration of MSG image sampling
Due to the nature of the scanning mechanism and the curvature of the Earth, the sub-satellite
point sampling distance increases as the satellite viewing angle increases. Figure 3 shows the
East-West sampling distance over of the MSG disk for a satellite nominal position of 0 degree
longitude. This distance remains in the range of 4 km over most part of Europe and Africa. The
corresponding South-North sampling distance is shown on Figure 4. In this case, the sampling
distance remains almost unchanged along the Equator. Figure 5 shows the pixel area
normalised by the sub-satellite point pixel area.
Figure 3: MSG East-West sampling distance in km. The result is shown in an equidistant cylindrical projection.
Figure 4: MSG South-North sampling distance in km. The result is shown in an equidistant cylindrical projection.
Figure 5: MSG normalised pixel area. The result is shown in an equidistant cylindrical projection.