Different calibration methods (temperature/radiance tables) have been used for the Meteosat satellite series, Meteosat First Generation (MFG) and Meteosat Second Generation (MSG), to convert the radiances into brightness temperatures.
Calibration of the Level 1.5 Images comprises a number of steps:
Meteosat IR / WV Channel Calibration Methods
(equalisation and linearisation)
SEVIRI Solar Channel Calibration Coefficients for Meteosat-8 and Meteosat-9:
Initial calibration is performed, pre-launch, on the SEVIRI instrument of each detector of the 12 channels — in terms of spectral, polarisation and radiometric characterisation, spatial frequency response and spatial sampling. These responses are non-linear and may change over the lifetime of the instrument. It is these changes that must be corrected for after launch, when producing images from the system.
Spectral responses are derived for all 12 channels of the SEVIRI instrument.
Spectral responses for Meteosat Second Generation (MSG) (ZIP, 226 KB). Note: SEVIRI PFM is onboard Meteosat-8, SEVIRI FM2 is onboard Meteosat-9, SEVIRI FM3 is onboard MSG-3, and SEVIRI FM4 is onboard MSG-4.
In the MSG-MPEF the conversion from the observed radiances of the 'cold' channels (IR3.9, IR6.2, IR7.3, IR8.7, IR9.7, IR10.8, IR12.0, IR13.4) to equivalent black-body temperatures (so-called brightness temperatures) is done with the help of an analytical relation between these two quantities.
Information previously provided to the User community describes the process used to convert MSG radiances to temperatures. Recent analysis has revealed that an inaccuracy arises when this conversion formula is applied to the spectral black-body radiance provided by the Level 1.5 images, that is significant enough to justify the modification of the MSG Ground Segment to generate Level 1.5 Image Products, in terms of effective black-body radiance rather than spectral black-body radiance.
Information on how the MSG level 1.5 image product in effective radiance can be interpreted in terms of equivalent brightness temperatures (EBBT) can be found in the document Effective Radiance and Brightness Temperature Relation for Meteosat-8 and -9 (PDF, 918 KB), in the form of tables relating EBBT to effective radiance (ZIP, 382 KB) in this zipped Excel sheet.
After launch a number of characteristics of the instrument will be measured to check for changes in instrument response due to launch and a different operating environment. These include measuring the noise and medium-term drifts and an assessment of the Level 1.5 Image quality using an independent tool, the Image Quality Ground Segment Equipment (IQGSE).
Calibration of the 'cold' channels (IR3.9, IR6.2, IR7.3, IR8.7, IR9.7, IR10.8, IR12.0, IR13.4) is performed several times a day. An on-board black-body source is placed in the optical path of the instrument, at two different known temperatures. The response of the instrument at these two temperatures is then fed into a mathematical model, representing the instrument optics, which gives the required scaling and offset needed to be applied to the instrument output in order to determine the corresponding radiance for any output.
However the on-board black body can not be used for the 'solar' or 'warm' channels (HRV, VIS0.6, VIS0.8, IR1.6). For these channels, on-ground vicarious calibration is used. Data from outside the MSG system, from other satellites or from calibration campaigns, about known stable sites on the Earth and meteorological conditions, are used, along with a Radiation Transfer Model (RTM), to predict the response of the instrument. These predicted responses are compared to the actual response and, again, offsets and scaling required for the instrument output are calculated.
For each scan of the instrument, three lines of Level 1.0 image are collected (nine for the HRV channel), one for each detector. Each of these detectors may have different responses and offsets which, if left uncorrected, would cause a visible striping of the image. Furthermore, the detector response is not necessarily naturally linear.
Hence, on-ground processing is performed, by the Image Processing Facility (IMPF), to
The image is then geometrically corrected to a standard projection.