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lSEVIRI to Help Nowcasting Meteorology

Successfully launched aboard the European Space Agency/European Meteorological Satellite's (EUMETSAT) Meteosat Second Generation (MSG)-1 satellite on 28 August 2002, the Astrium-sourced Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) payload is set to radically upgrade the accuracy of nowcasting short-term weather forecasting for Europe, Africa and the Atlantic and Indian Oceans. Located at 0° longitude 22,300 miles above the Gulf of Guinea, the SEVIRI instrument is designed to transmit a 12 spectral channel Earth image every 15 minutes. The availability of such imagery is billed as facilitating comprehensive observation of a range of parameters including cloud, land and sea surface temperatures and the composition of particular air masses. Equally, the availability of near real-time imagery is expected to upgrade the accuracy of extreme weather reporting.

Technically, SEVIRI is a combined scan/telescope assembly that weighs 260 kg and incorporates a movable mirror that is positioned in front of its telescope and performs a linear scan of the Earth's surface from north to south. The telescope collects radiation for a focal plane array that divides it into 12 channels of 0.4 to 1.6 mm visible light (four channels including one high resolution) and 3.9 to 13.4 mm IR. The processed data is recorded and passed to a functional control unit that acts as the sensor's interface with the satellite's transmission system. A ground-based, Astrium-sourced image processing facility acts as the link between the space-based sensor and the end user. SEVIRI offers a resolution of 1 km in the visible sector of the spectrum and 3 km in the IR sector and against water vapour. SEVIRI incorporates a total of 42 detectors and has a power consumption requirement of 150 W.

Alongside SEVIRI, the Anglo-European Astrium joint venture is responsible for a range of operational and planned satellite meteorological instrumentation packages that include the Advanced Microwave Sounding Unit (AMSU)-B, the Humidity Sounder for Brazil (HSB), the Advanced Scatterometer (ASCAT), the Microwave Humidity Sounder (MHS) and the Atmospheric Laser Doppler Instrument (ALADIN). Of these, AMSU-B is operational aboard the US's National Oceanographic and Atmospheric Administration's NOAA-M satellite (launched on 24 June 2002) and is used to image cloud cover and precipitation cells together with data gathering on water vapour content in cloud masses. The HSB device is installed aboard the US National Aeronautics and Space Administration's Aqua vehicle and measures the vertical distribution of water vapour in the atmosphere as a means of predicting atmospheric stability.

For its part, ASCAT is a radar instrument that is designed to measure open ocean wind speed and direction together with the distribution of snow and ice on land and sea surfaces. The MHS is intended to establish atmospheric humidity profiles and cloud and precipitation parameters. As currently planned, ASCAT and MHS are to be installed aboard three Metop weather satellites that the ESA plans to have in polar orbit by 2005. The remaining instrument - ALADIN - is planned for use aboard the ESA's Aeolus spacecraft that is scheduled to be in service by 2007. Here, the device will undertake extremely precise wind strength and direction measurements using harmless laser pulses and analysis of laser light reflected by atmospheric cells. Alongside MSG-1, SEVIRI is to be fitted aboard the forthcoming MSG-2 and -3 vehicles.

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