Meteosat Second Generation
Meteosat Second Generation (MSG) Spacecraft
The first generation Meteosat series (Meteosat-1 to -7) of EUMETSAT is gradually being replaced by a second generation series (MSG) with a launch of the first satellite MSG-1 on Aug. 28, 2002, to be followed by three more satellites, ensuring operational continuity in GEO for at least 16 years. MSG-1 became Meteosat-8 on Jan. 29, 2004 when the mission was declared “operational” (i.e., commencement of routine operations after the end of the commissioning phase).
Note: Prior to launch, the satellite series is referred to as MSG. EUMETSAT assigns a new name, namely “Meteosat-x” after launch and after on-orbit commissioning starting with the commencement of routine operational services
The MSG program definition started in 1993, the phase C/D began in 1995. The program is funded by the European Space Agency (ESA) and the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) according to the following share of responsibilities:
• ESA is responsible for designing and developing the first of the four satellites in the MSG program (the fourth S/C of the MSG series was approved in 2003).
• EUMETSAT has overall responsibility for defining the end-user requirements, developing the ground segment and procuring the launchers. EUMETSAT is also the operator of the MSG system. EUMETSAT is contributing about 30% of the development costs for MSG-1 and fully financing the three subsequent flight units (MSG-2, MSG-3, and MSG-4).
Figure 1: Artist's rendition of the MeteoSat-8 satellite (image credit: EUMETSAT)
The MSG program is planned as a two-satellite operational service, like the first-generation Meteosat system, where one satellite is available in orbit as a spare. The MSG system provides the user community with continuity of services from the first-generation Meteosat system, but with significantly enhanced services and products. MSG is designed to support nowcasting, very short and short range forecasting, numerical weather forecasting and climate applications over Europe and Africa, with the following mission objectives:
• Multispectral imaging of the cloud systems, the Earth surface and radiance emitted by the atmosphere, with improved radiometric, spectral, spatial and temporal resolution as compared to the first generation Meteosat
• Extraction of meteorological and geophysical fields from the satellite image data for the support of general meteorological, climatological and environmental activities
• Data collection of data from data collection platforms (DCP)
• Dissemination of the satellite image data and meteorological information upon processing to the user community in a timely manner for the support of nowcasting and very short range forecasting
• Support to secondary payloads of scientific or pre-operational nature (GERB) and Search & Rescue (called GEOSAR) in supporting operations which are not directly relevant to the MSG program
• Support to the primary missions (e.g. archiving of data generated by the system MSG, for successful operation of the system etc.).
The MSG satellites are being built by a European industrial consortium led by Alcatel Space Industries (ASI) of France. MSG satellites are spin-stabilized (cylindrical in shape, similar to the first generation S/C series) with a rotation speed of 100 rpm. The S/C body is a cylindrical-shaped solar drum, 3.2 m in diameter and 3.7 m in height (2.4 m body height) with stepped cylinder. The major subsystems of the platform are: AOCS (Attitude and Orbit Control Subsystem), EPS (Electrical Power Subsystem), UPS (Unified Propulsion Subsystem), and DHSS (Data Handling Subsystem). 1) 2) 3) 4) 5)
• AOCS: Attitude is measured by means of Earth sensors and sun sensors. AND (Active Nutation Damping) is used during GTO; there is no AND in the GEO phase. In addition, AOCS provides synchronization signals to keep the SEVIRI, GERB, and the electronically de-spun antenna Earth-pointing.
• EPS (Electrical Power Subsystem): Solar power of 600 W EOL is provided to the S/C bus 28 V power bus. Two NiCd batteries provide 1200 Wh for ecliptic operations support. The solar array is composed of 8 body mounted panels, based on CFRP (Carbon Fiber Reinforced Panel) substrate. The solar network utilizes 7854 Silicon High Eta cells delivering a beginning of life power of 740 W. 6)
• UPS: A bi-propellant unified propulsion system of two 400 N apogee engines are used for a 3-burn insertion from GTO into GEO. Four tanks hold up to 976 kg of propellant. About 810 kg are used for the GEO insertion of MSG.
• DHSS: The system consists of three units: CDMU (Central Data Management Unit) and two RTUs (Remote Terminal Units). CDMU and RTUs are interconnected via the serial standard OBDH (On-Board Data Handling) data bus of ESA.
The software design of the S/C provides a high level of onboard autonomy, the main requirement being spacecraft survival after a single onboard failure during 24 hours without ground intervention. This implies an elaborate FDIR (Failure Detection, Isolation and Recovery) capability, allowing to detect any malfunction and perform the necessary recovery/reconfiguration action autonomously. It also implies a high level of robustness against failure of the CDMU proper, which requires the autonomous switch-over of the processor unit and a restart with context saving of the onboard software. Special emphasis was also put on the possibility to easily modify the monitoring parameters and thresholds and the corrective actions triggered by the monitoring, without having to resort to software patches. Instead, specific telecommands were introduced for the modification of these parameters.
The satellite itself is built in a modular way around three main sub-assemblies: The SEVIRI instrument is located in the central compartment; the communication payload, including antennas and transponders, are positioned in the upper compartment; while the platform support subsystems are located in the lower compartment. The S/C design life is seven years. Total S/C mass = 2040 kg, power = 600 W (EOL).
Launch: MSG-1 was launched on Aug. 28, 2002. Ariane-5 launch from Kourou along with the Eutelsat communications satellite Atlantic Bird 1.
Orbit: Geostationary orbit at 3.5º W longitude (held to within 1º by thrusters) over the equator.
Launch: MSG-2 was launched on Dec. 22, 2005 to provide a two-satellite operational system [two satellites are simultaneously in orbit (one operating and one in cold redundancy) to assure availability].
Application: Operational meteorology and climate monitoring. The Meteosat program is part of WWW (World Weather Watch) satellite network of WMO (World Meteorological Organization), the largest and most important technical and research program of WMO. Besides improving weather forecasting, all fields of human endeavor which depend upon meteorological phenomena (agriculture, oceanography, hydrology, air traffic, civil engineering ...) profit by the Meteosat imagery.
Table 1: Overview of some MSG spacecraft parameters
Launch: The MSG-3 spacecraft (~2000 kg) was launched on July 5, 2012 on Ariane-5 ECA from Kourou along with EchoStar-XVII (6100 kg), a broadband Ka-band S/C for the American operator Hughes Network Systems. The objective of MSG-3 is to replace the ageing Meteosat-8 and secure continuity of the operational services from the geostationary orbit. 7)
Figure 2: The MSG spacecraft in orbit with the main payload SEVIRI (image credit: ESA)
Figure 3: Blowup of the MSG structure showing the main components of the S/C and its payload (image credit: EUMETSAT)
Mission status of MSG spacecraft series:
• On April 9, 2013, Meteosat-9 took over the rapid scanning imagery service (RSS) from Meteosat-8. This completes the reassignment of roles of the three Meteosat Second Generation (MSG) satellites following the launch of Meteosat-10 on July 5, 2012. 8)
- After being replaced in January by Meteosat-10 as the prime operational satellite supplying full disk images of Europe and Africa, Meteosat-9 now provides the RSS, delivering more frequent images every five minutes over Europe only. The two-satellite system continues the services previously delivered by Meteosat-8 and -9 in support of weather forecasters in one of their most challenging tasks, nowcasting, which involves detecting and monitoring rapidly developing high impact weather like thunderstorms or fog and issuing related warnings up to 12 hours ahead (Ref. 8).
• March 28, 2013: Ten years ago EUMETSAT revolutionized the way users can access satellite data, with the introduction of EUMETCast. EUMETCast is a data dissemination system which allows users to access numerous data streams via regular, ‘off-the-shelf’ satellite TV equipment and a PC. Every day more than 100 GB of data, from 37 data providers, are disseminated to the EUMETSAT users worldwide. 9)
Figure 4: The bandwidth evolution on EUMETCast Europe since the start of the DVB service (image credit: EUMETSAT)
For EUMETCast’s users ( > 3,000 in 2013), the system is ideal because it enables them to access various types of data via one station. It also offers:
- Secure delivery — multicast to a specific user, or group of users
- Handling of many file formats and both high and low volumes
- Quick delivery
- Worldwide coverage through the GEONETCast partnership. 10)
• January 21, 2013: Meteosat-10 has replaced Meteosat-9 as EUMETSAT’s prime operational geostationary weather satellite after being moved to 0º. 11)
• On Dec. 12, 2012, the MSG-3 satellite was declared ready to support the Meteosat operational services and renamed to Meteosat-10. This was done after the successful completion of in-orbit testing. 12)
In the next two months, Meteosat-10 and Meteosat-9 will deliver full Earth scan image and meteorological products in parallel, with Meteosat-10 scheduled to become the prime operational satellite on January 21, 2013 after moving to 0º. Parallel dissemination will allow users to prepare themselves before Meteosat-10 takes over.
• Oct. 23, 2012: EUMETSAT has started trial dissemination of MSG-3 image data and meteorological products to national meteorological services in the organisation’s Member and Cooperating States and to the ECMWF (European Centre for Medium-Range Weather Forecasts). 13)
• August 28, 2012: Tenth anniversary of MSG-1 (alias MeteoSat-8 ) on orbit. When the first MSG-1 satellite, namely MeteoSat-8, was launched on 28 August 2002, it heralded a new era of discovery for meteorologists. It became fully operational at 0º longitude at the equator on 19 January 2004 and, in addition to providing weather information in much more detail, it provided information on phenomena which had never been considered before. 14)
• On August 7, 2012, the SEVIRI instrument on MSG-3 (alias MeteoSat-10), launched on July 5, 2012, captured its first full disk image of the Earth. ESA was responsible for the initial operations after launch (the so-called launch and early orbit phase) of MSG-3 and handed over the satellite to EUMETSAT on 16 July, 2012. 15)
Figure 5: First full disk image of the SEVIRI instrument on MSG-3 (MeteoSat-10) captured on Aug. 7, 2012 (image credit: EUMETSAT)
• July 16, 2012: Following the successful launch of the MSG-3 satellite on July 5, 2013 aboard an Ariane 5 from Europe’s Spaceport in French Guiana, and after 11 days of LEOP (Launch and Early Orbit Phase) by ESA/ESOC, EUMETSAT took control of the MSG-3 operations. 16) 17)
• In 2011, Meteosat-9 (MSG-2) is EUMETSAT's nominal operational satellite at 0º longitude, performing the full-disc mission (one image every 15 minutes on 12 spectral channels). Meteosat-8 serves as its back-up. Satellite and payload performances remain excellent.
- In 2011, the Meteosat-8 (MSG-1, backup) spacecraft and instruments are in good health. The last north/south stationkeeping maneuver was made at the end of October 2010, after which the satellite inclination will drift at a rate of about one degree/year. Provided there are no serious failures, at least six additional years of mission are possible (from a design life of seven years). Nevertheless, preparations for reorbiting operations at the end of its life have started. 18)
• Meteosat-8 (backup) and Meteosat-9 (primary service provision) are operating nominally in 2010. 19)
- The Meteor-8 spacecraft is in good health with instruments performing flawlessly. It is providing the Rapid Scan Service (RSS), complementing the 15-minute High Resolution Image data generated by the operational Meteosat-9.
- Meteosat-9 is Eumetsat’s nominal (primary) operational satellite at 0º longitude, with Meteosat-8 as its backup. Satellite and instruments performance are excellent.
• On 25 May 2009, Eumetsat extended the coverage of the AHRPT (Advanced High Resolution Picture Transmission) system on Eumetsat's Metop-A polar-orbiting satellite. The improved service provides additional coverage over the Gulf of Mexico and Indian Ocean regions. 20)
• On May 22, 2007, Meteosat-8 experienced an orbit change which was not the result of a commanded maneuver by EUMETSAT. The incident was initially detected by the Image Processing System as a change of satellite state; this orbit change event included a decrease in spin rate, a change in attitude, some nutation, a temperature change on thrusters and fuel lines, and a small drop in solar array power. A possible cause is that the spacecraft was likely hit by a micro-meteorite or space junk.
Investigations have shown that the propulsion subsystem, the thermal control subsystem, and to a lesser extent the electrical power subsystem have been affected by this incident. In particular, one of the nominal thrusters used for east-west station keeping maneuvers seems affected, possibly damaged. The redundant thruster for the same function has been tested and seems to be performing well. As the redundant branch of thrusters can be safely used, and as a new thermal configuration can be developed, there should be no impact on Meteosat-8's ability to serve as the in-orbit backup satellite, and to provide the Rapid Scanning service.
• On Jan. 3, 2006, control of the second Meteosat Second Generation (MSG-2) satellite has been passed from ESA/ESOC to EUMETSAT so that commissioning operations could start. MSG-2 became operational in July 2006 and was renamed at this point to MeteoSat-9.
• MSG-1 was declared operational on January 9, 2004 and renamed to Meteosat-8. In January 2004, at the end of the commissioning phase for MSG-1, it had been concluded that nearly all MSG mission objectives were met, and that the imaging performances are excellent, in many cases much better than the specifications. Moreover, image acquisition and the image rectification are still being achieved during the eclipses, or during the east-west maneuvers, leading to a very high mission availability. In particular: 21) 22)
- Image radiometric performance: All radiometric performances were met with significant margins.
- Image geometric performance: In all cases, including during eclipses and east-west maneuvers, the geometric performances of the rectified images are met with significant margins. In nominal cases, most of the geometric performances are met with a factor 2 to 3 better than the specification.
• MSG-1 commissioning got under way on Sept. 25, 2002. Then on Oct. 17, 2002, SSPA-C (Solid State Power Amplifier-C) failed just before switching on the SEVIRI instrument. It was to be used to re-broadcast the data that had been processed by the EUMETSAT control center.
Operational conditions of the satellite were nominal but the failure led to an automatic payload switch-off. All attempts to restart the SSPA failed and commissioning was suspended. A new satellite configuration was applied, and commissioning activities resumed on November 26, 2002.
In order to disseminate MSG-1 data, engineers extended EUMETCast, a multicast distribution system using commercial communications satellites. In this new approach, files are distributed using the DVB (Digital Video Broadcast) standard in the Ku-band for Europe via the Eutelsat Hot Bird-6 spacecraft, located at 13º East, and in the C-band for Africa via Eutelsat Atlantic Bird-3, located at 5º West (see EUMETCast heading at end of file).
• During the launch of MSG-1 in 2002 many unexpected issues were encountered that drastically affected the confidence in determining the satellite’s attitude and ultimately caused an extension to the originally foreseen timeline. Although MSG-1 was successfully delivered into the required orbit and handover attitude, ESOC’s Flight Dynamics Division had to considerably revise its attitude determination algorithms to account for the unforeseen spacecraft dynamics.
MSG-2 was therefore an opportunity to test the improvements made to the flight dynamics operational software and see whether the better understanding of the spacecraft’s dynamics would allow the operational timeline to be maintained. 23)
Figure 6: EUMETSAT space segment (image credit: EUMETSAT) 27)
Figure 7: Comparison of first and second generation Meteosat spacecraft (image credit: EUMETSAT)
Sensor complement: (SEVIRI, GERB, GEOS&R, DCS)
SEVIRI (Spinning Enhanced Visible and Infrared Imager):
SEVIRI is the principal onboard instrument, an imaging radiometer for imaging and sounding (12 channel instrument as defined in Table 3). The instrument was designed and built by EADS Astrium SAS, France. Its operating principle is based on collecting radiation from a target area and focusing it on detectors sensitive to 12 different bands of the electromagnetic spectrum by means of a telescope. This is followed by the electronic processing of the signals provided by the detectors. Channels VIS 0.6 µm, VIS 0.8 µm, IR 1.6 µm and HRV (High Resolution Visible) are referred to as “warm”, while channels IR 3.9 to IR 13.4 µm are referred to as “cold.” The cylindrical instrument has a diameter of about 1 m and a height of 2.1 m along the spin axis of the satellite. Instrument mass = 270 kg, power = 123 W. The instrument functional architecture is based on four main assemblies: 28) 29) 30) 31) 32) 33)
Background: SEVIRI is a new generation of geostationary orbit imaging instrument for meteorological applications succeeding the MVIRI instrument on the FGM (First Generation MeteoSat) spacecraft. SEVIRI studies started at the end of the 1980s. The development phase started in 1994. The first flight model was delivered in 1999 after less than 5 years of development and extensive testing. SEVIRI was then integrated into the MSG-1 spacecraft.
Figure 8: Illustration of TSA (Telescope and Scan Assembly) and FPCA of SEVIRI (image credit: EADS-Astrium)
Figure 9: Sun angle evolution with respect to SEVIRI (image credit: EADS Astrium)
• TSA (Telescope and Scan Assembly) including the calibration unit and the refocusing mechanism. TSA employes a three-mirror telescope of compact design. The primary mirror is concave aspherical with a diameter of 510 mm. The secondary mirror is concave aspherical of 200 mm diameter. The tertiary mirror is convex a-spherical of 60 mm diameter. The total length of the telescope structure is 1.3 m. All mirrors are light-weighted and manufactured from Zerodur (Schott Glas, Mainz, Germany). The rotating scan mirror assembly uses a linear spindle drive with a stepping motor, providing continuous bi-directional image scanning.
- Scan assembly. North to south scan of the Earth: scan capability of 22º in N-S direction and 18º in E-W direction. At each satellite revolution, three image lines are acquired (9 lines for the High Resolution Visible channel) for a total of about 1250 lines in a repeat cycle of 15 minutes. Each nominal raw image consists of 3750 lines, each one containing about 3834 pixels except for HRV channel for which a nominal raw image consists of 3750 lines with 5751 pixels per line.
- REM (Refocusing Mechanism) permits for in-orbit focus adjustments. REM operates by moving the M2/M3 mirror assembly along the instrument's south-north axis.
- CALU (Calibration Unit) permits calibration of the IR channels by inserting a CRS (Blackbody Calibration Reference) source into the optical beam at the focal point of the primary mirror. A flip-flop type mechanism is employed based on a DC voice coil motor. A refocusing mechanism is included in the SEVIRI telescope to correct, on an occasional basis, for potential defocus after launch and during lifetime. It consists of a stepper motor, a transmission gear box and a roller screw to provide the translation. 34)
Figure 10: The optical layout scheme of SEVIRI (image credit: ESA)
Figure 11: Illustration of scan assembly (image credit: ESA)
• FPCA (Focal Plane and Cooler Assembly). FPCA is a passive two-stage cooler providing an 85 K environment for the IR channels. The PCA (Passive Cooler Assembly) is a two-stage passive cooling device, composed of the radiator and the sunshield, which provide the IR detectors with a cryogenic environment. The sunshield is used to avoid direct solar radiation onto the first and second stages of the radiator.
• EUA (Electrical Unit Assembly), consists of FCU (Functional Control Unit), DE (Detection Electronics) including the MDU (Main Detection Unit), the PU (Preamplifier Unit) and the detectors. EUA controls SEVIRI and processes its data. The DE consists of the detectors and the front-end electronics.
Figure 12: The cold IR optical bench of SEVIRI (image credit: ESA)
Figure 13: Illustration of FPCA the SEVIRI instrument (image credit: ESA)
The overall SEVIRI design is based on a compact telescope and scan assembly, allowing the implementation of a large passive cooler which improves IR detector performances by lowering their operating temperature. The imaging SEVIRI radiometer is equipped with a patented three-mirror (3M) telescope of compact design (focal length of 5367 mm) which allows the insertion of a small black body for full-pupil calibration. The primary mirror (M1) is a concave circular ellipsoid (centered on the satellite axis). M1 is a 500 mm diameter mirror with a baffled central hole of 90 mm diameter. It is followed by a magnifying two-mirror assembly including the secondary mirror (M2) , which is a concave ellipsoid centered on the satellite axis, and the tertiary mirror (M3) which is a convex spherical mirror. The M2/M3 assembly is a compact ”light-tight” configuration allowing easy alignment. 35)
The main innovation of SEVIRI is the presence of 12 spectral channels geometrically co-registered and acquired simultaneously. The 12 channel detectors are positioned at the focal plane using a total of 42 detectors. Each channel has an array of 3 detector elements, with the exception of the HRV channel which has 9 detectors. The eight IR channels have HgCdTe detectors, they are passively cooled. The VIS channels feature photo-voltaic silicon diodes while the NIR channels have InGaAs photovoltaic diodes.
Data quantization is done inside the MDU (Main Detection Unit) by a 12 bit ADC, for an effective 10 bit resolution at the electronic outputs, after digital dynamic offset and fine gain correction. Auxiliary data are added to the detector data for image processing on ground.
Table 3: Channel definitions of the SEVIRI instrument
The Earth's radiation enters the instrument at every revolution through a 50 cm x 80 cm aperture. The nominal repeat cycle of 15 minutes was the driver in selecting the number of detectors per channel and the spin rate (100 rpm). Twelve minutes are allocated to the imaging phase, leaving three minutes for calibration, retrace and stabilization. The 1 km sampling at SSP of the HRV channel is achieved by using 9 broadband detection elements. The other channels are sampled at 3 km SSP by using 3 narrow-band detection elements per channel.
Spatial resolutions: SEVIRI observes the Earth-atmosphere system with a spatial sampling distance of 3 km at SSP in 11 channels while the HRV channel covers half the full disk with a 1 km spatial sampling at SSP. The actual IFOV of the channels is about 4.8 km (11 channels) and 1.67 km (HRV), respectively, at SSP. The detector sizes are:
- 5,625 pixels x 11,250 pixels for the 1 km sampling channel (HRV)
- 3,750 pixels x 3,750 pixels for the 3 km sampling channels
SEVIRI imaging is performed by combining S/C spin and rotation (stepping) of the scan mirror (optomechanical instrument). The images are taken from east to west. The E-W scan is achieved through the rotation of the S/C with a nominal spin rate of 100 revolutions/min. The spin axis is nominally oriented parallel to the north-south axis of the Earth. The scan from south to north is achieved through the scan mirror covering the Earth's disk with about 1250 scan lines; this provides 3750 image lines for channels 1-11 since three detectors are used for the imaging. A nominal repeat cycle is a full-disk imaging of about 12 minutes, followed by the calibration of the thermal IR channels with an onboard blackbody that is inserted into the optical path of the instrument. Then the scan mirror returns to the initial scanning position.
Figure 14: Imaging scheme of SEVIRI (image credit: ESA)
Table 4: Some SEVIRI imaging parameters
Table 5: Projected data rates of the SEVIRI instrument
SEVIRI employs the classical calibration approach using deep space as cold source and a known onboard source as a warm reference. The onboard blackbody temperature is used to determine the correction factor accounting for the different levels of background flux. The deep-space view is performed via the full optical path by commanding the acquisition of a sufficient number of samples during that part of the S/C revolution, when neither the Earth nor the sun (or moon) is in the FOV of SEVIRI. 36)
Table 6: Comparison of radiometer parameters of Meteosat and MSG missions
GERB (Geostationary Earth Radiation Budget):
GERB is an AO (Announcement of Opportunity) instrument, and provided on a national funding basis by a consortium led by the UK (NERC, RAL, IC), Belgium (OSTC, IRMB) and Italy (ASI). RAL of UK provides overall instrument management, systems engineering and other services (consortium lead). PI: J. Harries, Imperial College London (ICL). 37) 38) 39) 40) 41) 42) 43) 44) 45) 46)
GERB is an absolute radiometer of high measurement accuracy with the objective to monitor the Earth's radiation budget (global climate change, food production and natural disaster prediction) measuring at the top of the atmosphere (continuous temporal sampling), in particular the reflected shortwave and the emitted longwave regions of the spectrum, essential for the understanding of the Earth's climate balance.
The instrument is composed of two main elements, the IOU (Instrument Optical Unit) and the IEU (Instrument Electronics Unit), featuring the following basic design:
• Three-mirror anastigmatic system (TMA) + one rotating and one flat folding mirror
• Wide-band linear detector array (256 thermoelectric elements)
• Continuously rotating scan mechanism
• Channel separation via quartz filter
• Blackbody for thermal calibration
• Solar diffuser for shortwave calibration
• Passive thermal design
• Structure based on solid optical bench
Table 7: GERB instrument performance parameters
Figure 15: Scan geometry of the GERB instrument (image credit: ICL)
The IOU measures 450 mm x 200 mm x 200 mm and contains the imaging optics, detector system, de-spin mirror and driving mechanism, the quartz filter mechanism, the on-board blackbody and the short wavelength calibration monitor.
The IEU receives detector data, formats it and passes it on to the spacecraft data-handling system. It also provides regulated power to all the subsystems, thermal control of the IOU, command and data interfaces and instrument health monitoring and control.
At the core of the GERB instrument is a broadband, three mirror telescope housed in the IOU. This views the Earth with a black wideband detector array, providing measurements of the Earth's output radiation in a total band, and a shortwave band. Shortwave measurements are accomplished by using a quartz filter to block the wavelengths beyond 4 µm. The longwave band is obtained by subtraction. GERB removes the effect of S/C spin (100 rpm) by means of a rotating mirror, this increases the length of available exposure time per spin [use of a de-scanning mirror for staring at appropriate targets, continuously rotating at 50 rpm in the opposite direction the the satellite's rotation at 100 rpm, thus freezing the view of the Earth for a period of 40 ms].
Figure 16: Photo of the scan mirror and telescope (image credit: ICL)
Figure 17: Layout of the IOU (Instrument Optical Unit), image credit: RAL
The detector consists of a 256-element blackened linear thermoelectric array, mounted in the N-S direction. This arrangement provides an image column per S/C rotation; a complete image is obtained by successive measurements of columns. Every 15 minutes a complete dataset of both, solar and total spectral band, is obtained for the entire area visible from geostationary orbit. The great advantage of GERB is its ability to sample a large region of the globe with high time resolution. GERB instrument data provides close synergies with other instruments such as CERES, ScaRaB, and with SEVIRI on MSG (observations from both geostationary and polar-orbiting satellites). 47)
ASIC (Application Specific Integrated Circuit) development for GERB detector: The SNR and timing requirements make it impossible to multiplex the detector pixel outputs. Also the low level of the detector output signals mean that at least part of the electronics chain needs to be in close proximity to the detector. Consequently, an ASIC solution was selected for the processing of the detector output pixels. The FPA design resulted in a complex composite focal plane structure making use of silicon and ceramic substrates and the integration of discrete semiconductor die. 48)
Figure 18: Schematic view of the GERB detector system (image credit: University of Leicester)
Figure 19: The GERB FPA unit with the four integrated ASICs (image credit: University of Leicester)
Figure 20: Illustration of the IOU inside the calibration tank for pre-flight calibration (image credit: RAL)
Instrument calibration: Extensive pre-calibrations were provided on the ground. In-flight calibration is provided by a blackbody source and a solar transmission diffuser. For zero reference space views are used. An image is obtained by measuring the signal difference between views of the on-board blackbody and the Earth-view at every rotation of the satellite using the thermoelectric detector. Possible degradation of the shortwave spectral response can be corrected by means of occasional comparisons with an onboard solar-illuminated integrating sphere. 49) 50) 51)
GERB-1 is the first ever Earth radiation budget/solar constant instrument in GEO. The analysis of simultaneous GERB and SEVIRI products provides the basis for new process studies. The first GERB image was received Nov. 28, 2002.
Table 8: Comparison of some LEO and GEO observation parameters 52)
Figure 21: Photo of the GERB IOU instrument with thermal blanket (image credit: ICL)
Figure 22: Overview of GERB data flow (image credit: ICL)
GEOS&R (Geostationary Search and Rescue):
GEOS&R is a communications payload within the S&RSAT/COSPAS system. Provision of transparent relay function for search and rescue operations (a 406 MHz transponder is carried by the MSG satellites). 53)
Figure 23: GEOS&R payload functional diagram (image credit: COSPAS/SARSAT)
DCS (Data Collection System):
DCS is an on-board collection system. The current data rate of 100 bit/s for each DCP (Data Collection Platform) in the ground segment will continue to be supported by MSG operations. MSG supports a significantly increased number of simultaneously relayed messaging channels.
Table 9: Some DCS performance characteristics of the MSG satellites
Table 10: Service comparison of 1st and 2nd generation Meteosat S/C 54)
MSG Ground Segment:
The MSG ground segment is composed of:
• MCC (Mission Control Center) located at ESOC in Darmstadt, Germany
• PGS (Primary Ground Station) located in Usingen, Germany
• BRGS (Backup and Ranging Ground Station) located in Maspalomas, Gran Canary Island, Spain
• An application ground segment, which extracts meteorological and geophysical products from the calibrated and geolocated image data generated by MCC, and performs data management functions. The application ground segment is composed of MPEF (Meteorological Product Extraction Facility) and U-MARF (Unified Meteorological Archive and Retrieval Facility), both are located at EUMETSAT HQ in Darmstadt, and a distributed network of SAFs (Satellite Application Facilities). There are five SAFs using MSG data, they are:
- SAF on Ocean and Sea Ice hosted by France
- SAF on support to Nowcasting & VSRF hosted by Spain
- SAF on Climate Monitoring (CM) hosted by Germany. Within the CM-SAF consortium six meteorological services [Deutscher Wetterdienst (DWD), Finnish Meteorological Institute (FMI), Konijklik Netherland Meteorological Institute (KNMI), Meteoswiss, the Royal Meteorological Institute of Belgium (RMIB), and the Swedish Meteorological and Hydrological Institute (SMHI)] jointly develop, implement, and validate satellite based climate monitoring products. DWD is the operations leading entity and responsible for the overall coordination and execution of the activities of the SAF on Climate Monitoring. 55)
- SAF on Numerical Weather Prediction hosted by the United Kingdom
- SAF on Land Surface Analysis hosted by Portugal
• User Ground Segment. This comprises all MSG user stations. These are receive-only systems, operated by the users, which make use of either LRIT (Low Rate Information Transmission) or HRIT (High Rate Information Transmission) from the MSG satellites.
MSG Communication Services and Data Distribution
The MSG communication subsystem provides an all digital data transmission capability. The communication payload consists of three subsystems, namely the antenna subsystem, the transponder subsystem (including the S&R transponder), and the TT&C subsystem. 56) 57)
Table 11: Summary of MSG communication-link characteristics
Table 12: Specification of some MSG antenna parameters
Figure 24: Schematic overview of the MCP (Mission Communication Payload), image credit: Alcatel Espace
Figure 25: The MSG system configuration (image credit: ESA, EUMETSAT) 58)
Figure 26: Overview of MSG ground segment (image credit: EUMETSAT) 59)
HRIT/LRIT Dissemination Service:
A primary objective of the Meteosat service is to deliver image data for nowcasting within a few minutes of the end of acquisition of each image, therefore the timeliness of data delivery is an issue of utmost importance.
Two dissemination channels are defined within the MSG system to broadcast data to end-users via (Low Rate and High Rate Information Transmission (LRIT/HRIT) schemes. Both channels multiplex image data from the SEVIRI and foreign satellites together with meteorological products and DCP data (link), within the limits of the defined packetized data rate. The limited channel capacity requires the use of data compression in order to maximize the amount of information to be transmitted. 60) 61)
• The HRIT data stream has a capacity of 1 Mbit/s which allows the reception of the disseminated level 1.5 data in quasi real-time and full spatial and temporal resolution. It is segmented, encrypted and JPEG-compressed for the purpose of transmission. The compression is lossless for all channels and lossy for the HRV (High Resolution Visible) channel.
• The LRIT data stream capacity is 128 kbit/s. The images are all compressed in a lossy manner (by about a factor of 8) in full spatial resolution with the image data rounded to 8 bits representation. The current baseline is that only every second image is disseminated.
Table 13: Physical link parameters of the HRIT/LRIT service
Table 14: MSG generic data products
EUMETCast (EUMETSAT's Multicast Distribution System)
EUMETCast is EUMETSAT's data distribution service transmitted via EutelSat's HotBird-6 satellite in GEO located at 13º E longitude. The service was initiated at the end of April 2003 utilizing data file distribution via DVB-S (Digital Video Broadcast-Satellite) to a wide audience located within the geographical coverage zone which includes most of Europe and all EUMETSAT Member States and Cooperating States.
The extension of the system includes coverage over the African continent (trials started in August 2003). The overall trial period of EUMETCast, designed to fully test the system infrastructure, ended in late 2003, and the service became fully operational as the primary 0º longitude service in late January 2004 with the satellite having then been drifted from its commissioning location (10º W). 62) 63) 64)
The following EUMETCast services are available:
• Meteosat-8 (former MSG-1) routine Meteosat-8 operational services. This consists of: full HRIT data - 12 channel SEVIRI data every ¼ hour. Full LRIT data - 5 channel reduced SEVIRI data ¼ hourly + foreign satellite relays - GOES-E, GOES-W, [GOMS]/Meteosat-5 Indian Ocean and GMS/MTSAT/GOES (temporary replacement).
• EUMETSAT ATOVS (Advanced TOVS - a NOAA/NESDIS processing system) Retransmission Service (EARS)
• Rapid Scanning Service (RSS)
The EUMETCast system is based on a client/server system architecture. The server site is implemented at the EUMETCast uplink site (Usingen, Germany) and the client side installed on the individual EUMETCast reception stations. The DVB multicast distribution mechanism is provided by the telecommunication network providers. Data/product files are transferred via a dedicated communications line from EUMETSAT to the uplink facility. These files are encoded and transmitted to a geostationary communications satellite for broadcast to user receiving stations. Each receiving station decodes the signal and recreates the data/products according to a defined directory and file name structure.
The system uses a DVB/MPEG-2 based transport for carrying IP datagrams. It uses a set of broadcast satellite forward channels, but does not use the return channel. The forward links are provided by a set of geostationary, digital telecommunications satellites.
The geographic coverage of a DVB is determined by the characteristics of the spacecraft and its associated antenna beams. In the current operational configuration, EUMETCast reception is available in:
• European service in Ku-band via HotBird-6 (starting from November 2002)
• African service in C-band via AtlanticBird-2 (from November 2003, available in demonstration mode from August 2003, full service provision from Aug. 2005 onwards)
• American service in C-band via NewSkies-806
Reception station requirements: A typical EUMETCast reception station consists of a standard PC with DVB card inserted and a satellite offset antenna fitted with a digital universal V/H LNB. In addition, users require the multicast client software. As EUMETCast operates a tq®-TELLICAST server, the tq®-TELLICAST client software is mandatory and a licence is required for each user station. The tq®-TELLICAST client software used with EUMETCast must be purchased directly from EUMETSAT, all other components of the reception station are commercially available.
Figure 27: Overview of the EUMETCast system (image credit: EUMETSAT)
Background: EUMETSAT was forced to abandon its conventional meteorological data dissemination service when the MeteoSat-8 weather satellite rebroadcast function (i.e. its ability to retransmit data once it has been pre-processed on the ground) malfunctioned in orbit on Oct. 17, 2002 (just 6 weeks after launch). In particular, the SSPA-C (Solid State Power Amplifier-C) failed which was to be used to re-broadcast the data that had been processed by the EUMETSAT control center. 65)
Scrambling to find a quick operational retransmission solution, EUMETSAT decided to lease a small amount of commercial telecommunication satellite capacity to retransmit the data in Ku-band to its customers via the HotBird-6 of EutelSat. However, EUMETCast required also that users purchased new satellite reception equipment and pay for the transmission fee.
The switch to a commercial service provider permitted EUMETSAT to send larger amounts of data at faster rates to a much larger user community. EUMETSAT and the EU later extended the EUMETCast service by funding data reception equipment in Africa, using C-band capacity leased aboard the AtlanticBird-3 satellite of EutelSat.
In addition, EUMETSAT has leased capacity on the NewSkies-806 satellite of SES, also in C-band, to provide data services to portions of South America (the regions that are covered by the Meteosat observations).
As of 2006, about 1800 EUMETCast PC-based stations have been installed worldwide, so that MSG imagery from MSG (Meteosat Second Generation) satellites are available in less than 5 minutes from sensing time to end users.
The following environmental data streams and products are delivered via EUMETCast in 2006:
• Meteosat first generation image data
• Meteosat second generation image data
• GOES East & West image data
• MTSAT image data
• DCP & MDD in-situ and forecast data
• EUMETSAT meteorological products
• Land and OSI SAF products
• NOAA POES regional products
• DWDSAT products from DWD
• SPOT VEGETATION products from VITO
• Basic Meteorological Data (BMD) for WMO RA VI
• Metop Global Data Service
• NOAA POES Global Area Coverage
• Metop Regional Data Service
• GRAS and Ozone SAF products
The current EUMETCast system is seen as an emerging prototype candidate of a future GEONETCast service, a global system in its definition phase at GEOSS (Global Earth Observation System of Systems). An important step into the direction of a unified Earth observation approach was done at the GEO (Group on Earth Observations) summit in Tokyo, Japan, on April 25, 2004 when GEOSS (Global Earth Observation System of Systems) was created. GEOSS is an international framework to develop a 10?year implementation plan (for the period 2005?2015), a comprehensive, coordinated and sustained system that will help to better understand Earth systems, including weather, climate, oceans, water cycle, geology, ecosystems, agriculture and biodiversity, energy, disasters, etc. Representatives of 47 countries and more than a dozen international organizations [UN (UNEP, FAO, UNESCO), ESA, EUMETSAT, EC, ECMWF, ISCU, WMO, IGOS?P, CEOS, WCRP, etc.] were present at the ad hoc GEO (Group on Earth Observations) summit, signing the document (the finalization of a draft implementation plan).
The 10?year GEOSS program implementation plan was formally approved/adopted by government delegates at the 3rd Earth Observation Summit on February 16, 2005 in Brussels, Belgium. Nearly 60 nations and about 40 international organizations are working to establish the emerging network of Earth observation systems.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.