The decision of the European meteorological community to enter the field of space meteorology dates back to the early 1970s. The legal arrangements between eight European Space Agency (ESA) Member States to develop Meteosat-1 were made in 1972, and they were followed by a protocol signed in 1975 that enabled ESA to operate this satellite for Europe's meteorological services.
Meteosat-1 was launched in November 1977. Placed in geostationary orbit at 0 degrees longitude, it provided a permanent field of view over most of Europe, the whole of Africa, the Middle East and the eastern half of South America - in total over 100 countries. Meteosat-2 was launched in June 1981 to replace Meteosat-1.
During the eight years until 1985, ESA's initial Meteosat system fulfilled its mission to the complete satisfaction of meteorologists and scientists working in climatology and atmospheric physics.
However, ESA's satellite programs focus on exploring new space applications. Financing and running the operational systems that result from ESA experimental programs has to be done by specialised operators, and for this reason, an intergovernmental European conference in 1981 sought ways of financing an operational Meteosat programme. A dedicated organization, Eumetsat, the convention on which came into force on 19 June 1986, was set up for this purpose. ESA's responsibilities within the Meteosat Operational Programme include the construction and launch of the satellites, their orbital operations, the processing of the images and the generation of meteorological products on behalf of Eumetsat which owns and finances the operational spacecraft.
The last of the ESA owned Meteosat satellite, Meteosat-3, built from spare parts left over from the initial programme, was launched on 15 June 1988. The first operational satellite, Meteosat-4, was launched on 6 March 1989, the second, Meteosat-5, on 1 March 1991 and the third, Meteosat-6, on 20 November 1993 (2).
* The numbers between brackets are the numbers of the related images on the "ESA Meteosat Collection No. 1" Photo-CD in their order of projection. The Photo-CD is available from the ESA Meteosat Exploitation Project against pre-payment of DM 20.-.
The two major components of the Meteosat system are two or more satellites in orbit and the ground segment.
The operational Meteosat satellites are located at 0 degrees longitude at 36000 km above the equator. Only one spacecraft, the primary satellite, is active, while the reserve satellite(s) are located nearby in standby mode. However, the spacecraft can be moved above any point over the equator. In 1991 it was possible, for example, to shift one of three Meteosat satellites in orbit (Meteosat-3) westwards over the Americas. From its new position, it supplies data to NOAA, the US weather service, which had only one satellite left in geostationary orbit.
All Meteosat satellites (3) are composed of a main cylindrical body, on top of which a drum-shaped section and two cylinders are stacked concentrically. They are 2.1 metres in diameter and 3.195 metres long, and weigh 320 kg in orbit including 39 kg of consumable propellant used for orbital maneuvers. The satellite spins at 100 rev/min around its main axis, which is aligned parallel to the Earth's north-south axis.
The principal payload of the satellite is a multi spectral radiometer. This instrument provides the basic data of the Meteosat system, which are images of the full Earth disk in three spectral bands:
|1 - 0.5-0.9 micron (visible light band) (4):||The Visible light channel measures the solar radiation reflected from the Earth's surface, i.e. sea, land and clouds. In a visible image the oceans are dark, the land is grey and the cloud tops are white.|
|2 - 5.7-7.1 micron (infrared water vapour absorption band) (5):||The Water Vapour channel measures the thermal radiation emitted, principally, by atmospheric water vapour in the middle troposphere. The dark areas on the image show regions of relatively high radiative temperature and hence low humidity. Conversely the brighter areas correspond to regions of high humidity.|
|3 - 10.5-12.5 micron (thermal infrared window band) (6):||The Infrared channel measures the thermal radiation emitted from surfaces. The dark areas in the image represent warm areas such as land, oceans and low clouds. The white areas are cold and correspond to regions of high clouds.|
The infrared and water vapour images are composed of 2500 lines of 2500 picture elements each, while the composed image in visible light has 5000 lines of 5000 picture elements giving spatial resolutions of 5 km and 2.5 km, respectively.
A set of three Earth Images is generated every 30 minutes. The onboard communications system transmits these raw images from the satellite to an ESA ground station in Germany, whence they are relayed to the nearby ESA Operations Centre (ESOC). From there the spacecraft and its payload are controlled, the images processed and meteorological products derived.
Meteosat is equipped with power amplifiers and antennae which allow processed Earth images and other meteorological information (weather charts, and images from other meteorological satellites) to be transmitted, mainly from ESOC, via the satellite to the user reception stations.
Finally, Meteosat has a total of 66 telecommunications channels to receive environmental data from automatic or semi-automatic Data Collection Platforms, relaying them to ESOC in Darmstadt.
In ESOC the responsibility for the Meteosat Operational Programme has been entrusted to the Meteosat Exploitation Project (MEP).
The Meteosat ground segment can be split into two parts: the Meteosat Ground Facilities needed to carry out the missions, and over 2000 user stations of three different types.
The Meteosat Ground Facilities consist of five elements, the first three of which are located at ESOC, the fourth at Michelstadt, 40 km from ESOC in the Odenwald, and the fifth at Wallops on the east coast of the United States.
The Meteosat Operations Control Centre (7) at ESOC oversees the performance and operations of the satellites and ensures that the missions are performed correctly; the Meteosat Ground Computer Systems carries out data processing for spacecraft control and image correction and oversees the data collection and distribution missions; the Meteorological Information Extraction Centre (8) supplies meteorological information such as wind fields, sea surface temperature charts, cloud system analyses etc... from the processed images.
The Data Acquisition, Telecommand and Tracking Station (9) near Michelstadt, with its impressive 15 and 13.5 metre antennae, (10 & 11) acquires from the satellite raw images, housekeeping data and messages from the Data Collection Platforms. It transmits to the satellite telecommands and meteorological data or images for dissemination to the user stations.
There are two different types of user station (12): Primary Data User Stations, which receive high-resolution Earth images in digital format, are mainly located at the European meteorological offices or at sites of important meteorological data users. Secondary User Stations, which are conceptually simpler and thus cheaper and which receive images, data and charts in an analog format, are now widely used throughout Europe as well as in Africa and the parts of Asia that are within Meteosat's field of view (13). A consumer electronics company is even offering a secondary station for use in conjunction with a TV set.
The nearly 1000 Data Collection Platforms take measurements of the local environment and transmit the data to the satellite. They can be installed in extremely varied locations on the ground, on buoys, ships or aircraft.
Meteorological Data Distribution (MDD) Stations receive weather charts and bulletins from the satellite in digital format.
The Meteosat mission is completed by an ESA sponsored archive of all images, image-related data and meteorological products since 1977. Users can request retrieval of individual images from this archive and receive them as digital data on magnetic tape or on photographic film. Recently, a collection of 2300 images at 460 lines resolution (one IR image per day over the period 1986 - 1991, plus the catalogue of the full archive) has been made available in digital format on a single CD-ROM. The present PhotoCD underlines again the permanent policy of the European Space Agency to provide students and scientists with easy access to European satellites data.
For the orbital control of Meteosat-3 at its temporary position over the Americas, where it is out of sight of the Odenwald ground station in Germany,a dedicated ground station has been set up by ESA on the US east coast at Wallops, state of Virginia. This station is connected via commercial satellite telecommunications links with the ESA Meteosat facilities in Darmstadt in order to receive and transmit images, telemetry data and telecommands (14). The raw images from Meteosat-3 are actually processed at ESOC and digital high-resolution images transmitted back to the US weather service, NOAA, for use in conjunction with daily weather forecasts for the United States. Meteosat-3 plays an important role during the annual hurricane season, as it is able to observe in real time the creation and movement of tropical storms that have their origins in the eastern Atlantic. As a consequence, loss of life was minimized during two natural disasters that hit the US recently - Hurricane Andrew on 14 August 1992 and the blizzard of 12/13 March 1993 - thanks to timely warnings issued on the basis of Meteosat imagery.
Meteosat-3 has been put free of charge at the disposal of the United States of America by the European Space Agency for this joint mission named XADC(eXtended Atlantic Data Coverage). The United States only reimburse ESA for the operations costs.
With one satellite operating at 0 degree Longitude (Meteosat-5) and one satellite operating at 75 degrees West Longitude (Meteosat-3) the Meteosat system operated by the European Space Agency covers more than 50% of the globe (15 & 16).
The European Meteosat satellites are part of a global meteorological geostationary monitoring system which includes the American GOES and the Japanese GMS satellites (17).
Although Meteosat images are received at several thousand sites, their primary users are the meteorological services of the Eumetsat Member States, of the USA, and of many other countries in the world. Meteosat data play a pivotal role in weather forecasting, and have contributed significantly to improvements in this area over the past 10 years.
Thirty years ago, weather forecasts were limited to about 24 hours ahead and to areas a few hundred kilometres across. Meteorologists used barometric charts and other measurements to make an "educated guess" based upon linear approximations, knowledge of atmospheric processes and experience. Only with the advent of powerful computers in the early 1970s was it possible to extend forecasting to 72 or more hours ahead and to large geographical areas.
Today, in numerical weather prediction models, meteorologists have wrapped a finely spaced three-dimensional grid over the Earth's surface and its atmosphere. Over 100000 daily measurements taken at 21000 sites are the basis for numerical forecasts making use of the world's most powerful computers. But these forecasts still require "fine-tuning" by meteorologists, a task for which data from satellites such as Meteosat are needed as they provide a real-time image of the weather systems, in particular the position of weather fronts. Without such fine-tuning, the accuracy of short- and medium-range forecasts would be significantly below the present standard. Computer-generated weather forecasts are usually provided at 12-hour intervals, but the capability of Meteosat to follow the actual development of the weather in real time helps forecasters to make very precise short-term and regional forecasts. For example, the movement of a weather front bringing rain or the development of thunderstorm clouds over a specific region can be forecast with reasonable certainty for a few hours ahead. A recent survey of meteorological services confirmed this: forecasters estimate that 21 % of the improvements in six-hour forecasts over the past 10 years have been achieved thanks to Meteosat imagery (18).
As accurate and timely weather forecasting becomes ever more important, specialized forecasting services are emerging that make extensive use of the Meteosat system.
There are many examples of production businesses or services that benefit from the Meteosat system. Although it is difficult to calculate their exact cash value, an independent group of meteorologists, economists and consultants has recently made a comprehensive study of these benefits, covering all relevant economic sectors and all ESA Member States.
The study's objective was to give answers to the following questions: what improvements have been made in weather forecasting over the last decade and how much has Meteosat contributed to these? What is the cash value of weather forecasts in general, and of the Meteosat contribution in particular? On the basis of a large survey carried out in the United Kingdom, complemented by the establishment of a comprehensive database of economic and climate data covering all ESA Member States, the group was able to paint a detailed picture of how every single ESA Member State profits from the Meteosat system.
Not surprisingly, the majority of the benefits arises from economies of resources (90%). However, in certain areas the group also observed increases in sales or production thanks to better weather forecasts (10%). These Meteosat-induced benefits total an annual 130MECU - more than twice what ESA is currently spending on Meteosat manufacturing and operations each year.
It is equally interesting to compare the average annual ESA spending on the 10-year Meteosat Operational Programme with the annual benefits: here the ratio is 52MECU average annual expenditure to 130MECU in annual benefits, corresponding to a return factor of more than 2.5 for the ESA Member States' economies alone. As Meteosat imagery is used in many developing countries and by the US weather service, the figure for the benefits on a global scale must be considerably higher. There are four areas of economic activity that benefit more than others from weather forecasts and Meteosat (19):
Construction: bad weather has a direct impact on many types of civil construction work. Moreover, certain critical operations such as pouring concrete require fair weather conditions over a guaranteed period of time. By using weather forecasts to plan the use of resources more carefully and to schedule critical operations, construction companies can substantially reduce their costs. The cash value of Meteosat's contribution to weather forecasting amounts to 40MECU a year on the companies' balance sheets.
Transport: All types of transport - land, air and maritime - are obviously in some way dependent on the weather. Timely knowledge of impending bad weather enables roads to be cleared of ice and snow, reducing accidents and loss of life while minimizing environmental damage caused by salt and de-icing chemicals. Long distance routes for aircraft and ships are now adjusted in real-time as weather fronts develop. In Europe, where aircraft must stay within narrow air corridors, knowledge of wind speed and direction allows efficient fuelling. North Sea helicopters and supply vessels can optimise their scheduling to avoid the worst weather conditions and reduce the risk of aborted missions. The cash value of Meteosat's contribution in the transport sector amounts to 36MECU a year, reflecting reduced insurance claims and fuel bills.
Agriculture: fields have to be sprayed regularly with pesticides and herbicides during the growing season. These are costly operations, the success of which can be jeopardized by rainfall washing chemical products from the plants. The cash value of Meteosat's benefit to farmers amounts to 31MECU a year, not including reduced contamination of ground water because less chemical products are washed off the plants.
Energy production: weather forecasts play an important role for gas and electricity companies in establishing forward demand. As the pressure in gas pipelines has to be increased in anticipation of increasing demand, precise assessments minimise the need to liquefy and store unused gas. Power stations update their forward planning at half-hourly intervals taking into account weather forecasts. Experts estimate that today's power generation capacity would have to be increased by 2 to 3% if there were no weather forecasts. The cash value of Meteosat's contribution is worth 11MECU in reduced provision of capacity by energy utilities.
Finally, there is a benefit in Meteosat for everyone which is not measurable: the "value" of public weather forecasts in television, radio and newspapers. Today this service allows everybody to plan his life a little bit more carefully: skiing, sailing, walking, cycling, climbing, outdoor games, domestic gardeners and decorators, holiday makers ... indeed everybody who decides what clothes to wear uses weather forecasts! Although it is basically provided free of charge, a survey showed that each European would be willing to pay on average an annual 30ECU for it - a striking demonstration of the cash value of public services.
The Meteosat programme was started over 20 years ago. Although the six spacecraft that will have been launched by the end of 1993 allow services to the meteorological community to be continued until well beyond 1995, ESA and Eumetsat are already preparing for the future of Europe's weather satellites.
The last spacecraft in the initial Meteosat-series will be Meteosat-7, to be launched in 1997. It will be followed, in 2000, by MSG-1, the first Meteosat-Second-Generation satellite, which will provide more frequent images at higher resolution, will employ more spectral channels and exhibit increased telecommunications capabilities.
By that date, ESA will also launch its first meteorological satellite into a polar orbit, METOP-1, complementing the measurements provided by the US NOAA series.
As from the end of 1995, Eumetsat will take over from ESA responsibility for operating the Meteosat satellites, using a new operations centre and a new network of ground facilities. Following a financial contribution to MSG-1 and METOP-1, it is intended that Eumetsat will completely fund and operate subsequent MSG and Metop satellites.
When the European Space Agency was set up in 1975, it was the political will of its founders that ESA's research and development programs should lead to a strong, independent European space sector and to tangible economic benefits. A look at the results of the Meteosat programme justifies this political choice: Aerospatiale of France, which has built all the Meteosat satellites, was able to acquire a position among the world leaders in the space sector thanks to this programme. And the success of Meteosat, like that of Ariane, is a direct result of an R&D programme started by ESA in the early 1970s to serve a specific user community.
Today it is the aim of ESA to continue this success story well into the next century.