Monitoring weather and climate from space

SEVIRI

The Meteosat Second Generation (MSG) satellites (from Meteosat-8 onwards) produce SEVIRI image data in the form of both High and Low Rate SEVIRI image data. These real-time data are processed to Level 1.5, i.e. are corrected for radiometric and geometric non-linearity, before onward distribution to the user. The data are accompanied by the appropriate ancillary information that allows the user to calculate the geographical position and radiance of any pixel.

'Nominal Coverage': includes the whole of Europe, all of Africa and locations at which the elevation to the satellite is greater than or equal to 10°. The various channels provide measurements with a resolution of 3 km at the sub-satellite point. The High Resolution Visible (HRV) channel provides measurements with a resolution of 1 km.

Figure 1 MSG Telecommunications coverage area

Figure 1 MSG Telecommunications coverage area

The service, which commenced operations in January 2004, is due to continue until at least 2018.

All SEVIRI image data is available on.

Changes to MSG Level 1.5 Image Product Radiance Definition

Please note: 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 blackbody 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 blackbody radiance rather than spectral blackbody radiance.

A description of a more accurate conversion to brightness temperature, the planned changes to the Level 1.5 Image Product radiance definition, as well as the steps that the User community may take to prepare for the change to effective radiance are described in the document (PDF, 197 KB).

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 in the form of tables relating EBBT to effective radiance. The same information is also contained in a zipped Excel sheet .

A new Header flag has been established in the SEVIRI level 1.5 Header, which will be used to indicate the spectral/effective radiance. The (PDF, 2092 KB) has been updated accordingly. For a brief summary, please see .

A Simple Conversion from Effective Radiance back to Spectral Radiance for MSG Images is described (PDF, 40 KB).

Service Description

High Rate SEVIRI - the features of the High Rate SEVIRI image data service are as follows:

  • Data in 15-min repeat cycles
  • Lossless compression in the form of WaveLet Transform - the WaveLet Transform Decompression software is available under licence from EUMETSAT. To apply for a licence see Useful Programs and Tools.
  • Full spatial resolution in 12 spectral channels
  • Data available on EUMETCast

SEVIRI Spectral Channels - SEVIRI data consist of geographical arrays of various sizes of image pixels, each pixel containing 10 data bits, representing the received radiation from the earth and its atmosphere in the following 12 spectral channels:

  • Visible band centred on 0.6μm -
  • Visible band centred on 0.8μm -
  • Near-infrared band centred on 1.6μm -
  • Infrared band centred on 3.9μm -
  • Water Vapour band centred on 6.2μm -
  • Water Vapour band centred on 7.3μm -
  • Infrared band centred on 8.7μm -
  • Ozone band centred on 9.7μm -
  • Infrared band centred on 10.8μm -
  • Infrared band centred on 12.0μm -
  • Carbon Dioxide band centred on 13.4μm -
  • Broadband high-resolution visible band -

An illustration of the fine detail visible with the HRV channel can be seen in (AVI, 10.4 MB), consisting of HRV images covering Italy on 13 August 2005, from 06.45 to 17.45 UTC. The low-level clouds over the Po valley in the morning are visible, as well as convection along the Appennines in the afternoon, producing cirrus anvils.

High Resolution Visible (HRV) -The SEVIRI HRV channel supports a mode of operation known as Alternative HRV Scanning Mode Operations. In this mode it is possible to introduce a horizontal split into the HRV image, and separately specify the E-W offset of the HRV image window above and below the split. From the start of Meteosat-8 routine operations until 31 August 2005, the HRV scanning mode was fixed as follows:

    Split position: Line 914
    E-W offset for lower window: Chosen to east-justify the image
    E-W position for upper window: Chosen to optimise the coverage of the European region

From 31 August 2005 onwards, the lower window shifts to follow the daily illumination.The configuration is as follows:

  1. Between 00:00 and 14:00 UT the lower HRV window is east-justified so as to optimise the coverage of the Indian Ocean region.
  2. Between 14:00 and 17:00 UTC the lower HRV window moves every hour, on the hour incrementally westwards, until in becomes west-justified.
  3. Between 17:00 and 00:00 UTC the lower HRV window is west-justified to optimise the coverage of the Atlantic Ocean.

An illustration of the above HRV sequence can be seen inof the HRV lower window configuration from 22 June 2005, 00:00-24:00 UTC.

SEVIRI Spectral Bands & Channels

The following documents describe the technical details:

Low Rate SEVIRI - the features of the Low Rate SEVIRI image data are as follows:

  • Data in 30-min repeat cycles
  • Lossy JPEG compression
  • Full spatial resolution in 5 spectral channels:
    • Channel 1 (VIS 0.6)
    • Channel 3 (IR 1.6)
    • Channel 4 (IR 3.9)
    • Channel 5 (WV 6.2)
    • Channel 9 (IR 10.8)
  • Data available on EUMETCast, FTP over the Internet and Direct Dissemination (Direct Dissemination from the Meteosat-9 satellite onwards)

SEVIRI Repeat Cycles

Each repeat cycle nominally consists of 8 segments of image data, except for the HRV channel, which has 24 segments. Each segment has 464 lines of image data. A repeat cycle prologue file precedes the delivery of the image segments and a repeat cycle epilogue file follows after the delivery of the segments and contains final quality information for the image. The image segments are numbered and a fixed relationship between the image segment number and the line offset is established. The image segment numbering direction follows the radiometer scan direction.

For further information on SEVIRI format, repeat cycles and other technical information,consult the Mission Specific Implementation Plan and the Level 1.5 Format Description, see .

For examples of the use of the SEVIRI image data, view the set of PowerPoint slides that make up the .

MSG Level 1.5 Quality Indicators

The MSG Level 1.5 Image Product contains numerous image quality indicators. These indicators provide information on the completeness, geometric quality, radiometric quality, and timeliness of the Level 1.5 Image Product, as well as information on the quality and completeness of the Level 1.0 Image from which the Level 1.5 Image Product was derived.

EUMETSAT has produced a technical note to provide the user with an overview of the image quality information that is available in the Level 1.5 Image Product, . This technical note should be read together with the ,which provides detailed information on the quality indicators.

Service Monitoring

The end-to-end monitoring of the SEVIRI Image Data Services is provided by EUMETSAT. To view the scheduled outages and service news on any unplanned outages, see the .

Service Registration

To access the SEVIRI image data, users are requested to register with the User Service Helpdesk, see . SEVIRI data other than the 6-hourly transmissions is restricted and subject to the signing of a licence agreement. For access to SEVIRI data via EUMETCast, in the first instance users will need to complete the EUMETCast registration form.

 
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