The SEVIRI Instrument

The SEVIRI is a 50 cm diameter aperture, line by line scanning radiometer, which provides image data in four Visible and Near InfraRed (VNIR) channels and eight InfraRed (IR) channels. The VNIR channels include the High-Resolution Visible (HRV) channel, which contains 9 broadband detection elements to scan the Earth with a 1 km sampling distance at SSP. All the other channels (including the IR channels) are designed with 3 narrow band detection elements per channel, to scan the Earth with a 3 km sampling distance. The full Earth disc image is obtained after 1250 scan line steps (south – north direction) of 9 km SSP per line step. The satellite spin of 100 rpm allows to complete (east – west direction) a full image in about 12.5 min. A flip-flop mechanism is activated to put the on-board black body in the optical path for the instrument calibration. The black body is removed after about 2 seconds from the calibration position. After that, the scan mirror moves back to its initial position. The Earth observation is resumed (after retrace during ~2 min) leading to an overall repeat cycle of maximum 15 minutes. The instrument functional architecture is based on four main assemblies: the Telescope and Scan Assembly (TSA) including the Calibration Unit and the Refocusing Mechanism, the Focal Plane & Cooler Assembly (FPCA), the Electrical Unit Assembly (EUA) consisting of the Functional Control Unit (FCU), the Detection Electronics (DE) including the Main Detection Unit (MDU), the Preamplifier Unit (PU) and the Detectors. This paper will present the instrument design including a description of the SEVIRI hardware elements together with a summary of the flight unit performances.