Meteosat satellites are spin-stabilised with instruments designed to provide permanent visible and infrared imaging of the Earth.
When operating in geostationary orbit, 36,000 km above the equator, the satellites spins counter-clockwise at 100 rpm around their longitudinal axis, which is aligned with the Earth's rotational axis.
Meteosat Second Generation spacecraft
The MSG body is a cylindrical-shaped solar drum, 3.2 m in diameter and 2.4 m high.
The satellite itself is built in a modular way around three main sub-assemblies:
- Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument in the central compartment.
- GERB scanning radiometer in the central compartment.
- Mission Communication Payload (MCP), including antennas and transponders, in the upper compartment.
- The platform support sub-systems, in the lower compartment.
|Orbit time||Repeat cycle||Mass in Orbit||Imager Mass||Imager Ground Sampling Distance||Power capability|
|24 hour (geostationary)||15-mins (full disc)
Rapid Scan 5-mins (Europe)
|1,200 kg||260 kg||1 km Ch 12 (HRV)
3 km Ch 1–11 (VIS, IR, WV)
|600 W average|
For its initial boost into geostationary orbit, as well as for station keeping, the satellite uses a bi-propellant system. This includes small thrusters, which are also used for alttitude control. The MSG solar array, built from eight curved panels, is wrapped around the satellite body.
The MSG payload is designed in accordance with the MSG Mission objectives, in order to accomplish the following functions:
- Permanent visible and infrared imaging of the Earth's disc, with a baseline repeat cycle of 15 minutes.
- High-resolution visible HRV imaging of half of the Earth's disc.
- Transmission of raw data, and other information, from the satellite to the PGS.
- Transmission of Data Collection Platforms (DCP) information, via the satellite, to the PGS.
- Accommodation of a scientific payload.
- Geostationary Search and Rescue (GEOSAR).
Detailed information on the MSG instruments is provided below. See also the Animation on Meteosat instruments
Spinning Enhanced Visible and Infrared Imager (SEVIRI)
The MSG system provides accurate weather monitoring data through its primary instrument — the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) — which has the capacity to observe the Earth in 12 spectral channels.
SEVIRI has twelve spectral channels, as opposed to three on the previous system. These provide more precise data throughout the atmosphere, giving improved quality to the starting conditions for Numerical Weather Prediction models.
Eight of the channels are in the thermal infrared, providing, among other information, permanent data about the temperatures of clouds, land and sea surfaces. One of the channels is called the High Resolution Visible (HRV) channel, and has a sampling distance at nadir of 1 km, as opposed to the 3 km resolution of the other visible channels.
Using channels that absorb ozone, water vapour and carbon dioxide, MSG satellites allows meteorologists to analyse the characteristics of atmospheric air masses and reconstruct a three-dimensional view of the atmosphere.
The improved horizontal image resolution for the visible light spectral channel (1 km as opposed to 2.5 km) also helps weather forecasters in detecting and predicting the onset or end of severe weather.
For details on the data ad products available from SEVIRI see our 0 Degree Service page.
Geostationary Earth Radiation Budget (GERB)
The Geostationary Earth Radiation Budget (GERB) instrument is a visible-infrared radiometer for Earth radiation budget studies. It makes accurate measurements of the short wave (SW) and long wave (LW) components of the radiation budget at the top of the atmosphere. GERB provides valuable data on reflected solar radiation and thermal radiation emitted by the Earth and atmosphere.
A GERB International Science Team (GIST) had been established and tasked to, among other things, define the science requirements, products and processing algorithms, and to implement science and validation activities.
The consortium that developed and is responsible for operating the GERB system includes the Rutherford Appleton Laboratory (RAL), UK; Imperial College of Science, Technology and Medicine (ICSTM), UK; Met Office Hadley Centre, UK; Leicester University, UK; Koninklijk Meteorologisch Instituut van België (KMI); Advanced Mechanical and Optical Systems (AMOS), Belgium, and SELEX Galileo, Italy.
The GERB instrument has two broadband channels — one covering the solar spectrum (0.32 to 4.0 µm), the other covering a wider portion of the electromagnetic spectrum (0.32 to 30 µm). Together these channels are used to derive the thermal radiation emitted by the Earth in the spectral range 4.0 to 30 µm.The GERB broadband channels span the 12 much narrower channels measured by the MSG’s other instrument — the Spinning Enhanced Visible and Infrared Imager (SEVIRI). GERB fills in the gaps in the thermal radiation spectrum missed by the SEVIRI channels, but measures the thermal radiation at a coarser spatial resolution.
Data are calibrated on board, in order to support the retrieval of radiative fluxes of reflected solar radiation and emitted thermal radiation at the top of the atmosphere, with an accuracy of 1%. The radiation budget represents the balance between incoming energy from the Sun and outgoing thermal (long-wave) and reflected (short-wave) energy from the Earth. Back on the ground, RMI scientists use the finer spatial resolution of the SEVIRI data to improve the spatial resolution of the GERB images.
Search and Rescue transponder
The transponder or Search and Rescue signal repeater (SARR), allows a continuous monitoring of the earth disc and immediate alerting of distress signals.
As part of the Cospas-Sarsat programme it relays distress signals from 406 MHz beacons within the MSG coverage zone in Europe, Africa and the Atlantic Ocean.
The signals are sent to Geostationary Earth Orbit Local User Terminals (GEOLUTs) and eventually passed on to Rescue Coordination Centres (RCC) for quick organisation of rescue activities.
Geostationary satellites, such os MSG, continually view large areas of the Earth and can provide near instantaneous alerting from a 406-MHz beacon. However, they cannot determine a beacon's location using Doppler shift processing ideally, a LEOSAR or Sarsat satellite (a specially-equipped polar-orbiting satellite) will fly over the the beacon within the next hour and calculate the beacon's location.
Mission Communication Payload (MCP) Subsystem
MCP contains all antennas and transponders necessary to meet the demanding communication needs of the MSG mission. This includes the acquisition and transmission of SEVIRI and GERB raw data, the delivery of House Keeping Telemetry (HKTM)and the relay of messages from Data Collection Platforms (DCPs) and Search and Rescue (S&R) beacons.
Telemetry, Tracking and Command (TT&C) Subsystem
The TT&C S/S provides the MSG spacecraft with the capability for receiving and demodulating telecommands, transmitting status and data in the form of spacecraft telemetry, and transponding ranging signals from and to the MSG Ground Stations.
The spectral response of an instrument is a measure of the instrument's response to radiation at specific wavelengths. Spectral response characterisation is the most crucial aspect of satellite calibration. The responses are non-linear and may change over the lifetime over an instrument, making it necessary to correct for these changes when producing images from the system.
The accuracy of pre-launch spectral response characterisation, and how well the on-orbit changes are understood, directly affects calibration accuracy and the quality of the data products. Even within the same satellite series, spectral response varies by instrument and even by detector on the same instrument. Spectral responses are derived for all 12 channels of the SEVIRI instrument.
Spectral responses for MSG (ZIP, 300 KB)
Note: SEVIRI PFM is onboard Meteosat-8, SEVIRI PFM2 is onboard Meteosat-9, SEVIRI FM3 is onboard MSG-3, and SEVIRI FM4 is onboard MSG-4.