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Metop - Europe's First Weather Satellite in a Polar Orbit

Berlin/Friedrichshafen, 01 May 2002

Everybody knows the images from the European Meteosat weather satellites from the daily weather forecasts on television. Starting in 2005 these satellites, which have been successful since 1977, will be supplemented by an additional European weather satellite system: Metop (Meteorological Operational Polar Satellite). Astrium is the prime contractor for the construction of this new European weather satellite.

At present, the payload modules of the three Metop satellites are being integrated in Friedrichshafen. By October this year, the first flight module (FM 1) shall be completed and subsequently submitted to a test programme in the European Space Technology Centre ESTEC (Noordwiijk/the Netherlands) of the European Space Agency ESA which is identical with the one conducted for the engineering model one year ago. These tests will last until March 2003. Then, FM1 will be delivered to Toulouse for final integration.

As early as in summer 2001, the test programme conducted on the engineering model of Metop's payload module was successfully completed. The so-called thermal-balance and thermal-vacuum tests simulated the temperature and vacuum conditions in space. In addition, the correct function and the electromagnetic compatibility of the payload module were demonstrated. The mechanical tests on the structural module of the satellite were already completed with success in spring 2001. The influences of noise and vibration encountered during launch were simulated in these tests.

Nowadays, we have all come to expect reliable weather forecasts. They only became possible, however, with the help of satellite images provided by weather satellites, such as the European Meteosat and its successor MSG (Meteosat Second Generation). These satellites are positioned approximately 36,000 kilometres above the Earth in geostationary orbit, which means that they maintain a constant position relative to a reference point on the Earth's surface. It is still much more difficult for meteorologists to give medium and long-term weather forecasts than to predict the weather in the short-term. However, there are a lot of people who want to know on Tuesday what the weather will be doing at the weekend!

More detailed and comprehensive information than can be supplied by the geostationary satellites is required for medium and long-term weather forecasts. In particular, these data are needed globally, i.e. from the entire land and sea surface and especially from the polar caps which are hardly covered by geostationary weather satellites. This information can also be provided by weather satellites, but from a much lower orbit passing over the poles. At a given time they can provide information on only a comparatively small area, but the measurements carried out are more precise.

The three satellites of the Metop fleet will be the first European weather satellites which collect data for medium and long-term weather forecasts and climate research from a low-Earth orbit. The first Metop satellite is due to be launched in 2005. The Metop systems will then deliver valuable information on the atmosphere, landmasses and sea surfaces for about 14 years - both during the day and at night. The satellites' main task is to measure the temperature and humidity of the atmosphere. Additionally, Metop will observe clouds, measure the wind speed on the sea surface and monitor the ozone content of the atmosphere. Metop will also be able to collect data from ground and sea based measuring stations and transmit rescue signals. Astrium is the prime contractor for the construction of the Metop satellites and will supply both the platform and three of the most important measuring instruments.

Medium and Long-Term Weather Forecasts: Not an Expensive Luxury

Reliable long-term weather forecasts are not a luxury. They are extremely important for many areas of the economy, for instance for agriculture, where the yields depend on the weather for up to approximately 20 percent. Precise weather forecasts for several days or even weeks ahead enable farmers to optimise their resources and, as far as the weather is concerned, do the right thing at the right time - such as selecting the best time to sow seeds, gather in the harvest or spray the crops with pesticide. Agriculture is, however, by far not the only beneficiary of precise long-term forecasts. Medium-term weather forecasts also help to optimise power station utilisation, the demand for fuels such as heating oil or the production of drinks. Medium-term weather forecasts also mean more safety. They help in the identification of extreme weather phenomena, such as storms or heavy rainfall and the floods which accompany them. Preventive measures can then be undertaken in good time.

These are only some of the examples of the large demand for reliable weather forecasts. Satellites such as Metop can supply the data which are urgently needed for these forecasts. In addition, they signify an important progress for climate research, which - as the apparent recent increase in extreme weather phenomena such as hurricanes or flooding demonstrates - is also not an expensive luxury. Man is possibly the cause both of these phenomena as well as long-term climatic changes. Precise knowledge of the factors which determine the weather and the climate is therefore more important than ever.

In 100 Minutes around the Globe - with Technology from Astrium

With Metop, Europe will have its own weather satellite system in a low- Earth orbit as of 2005. The Metop system will be operated by Eumetsat, the European agency for satellite based meteorology. Metop will circle the Earth at an altitude of 835 kilometres in a so-called polar orbit, inclined at 98.7 degrees to the equator. The satellite requires about 100 minutes for one Earth orbit. The orbit shifts continuously further west due to the Earth's rotation, so Metop with its measuring instruments passes over each point on the Earth's surface in a five-day cycle. Metop moves in a sun-synchronous orbit, which means that the satellite always passes over its target areas in a north-south direction at approximately 9:30 a.m. local time.

The orbit was selected so that Metop supplements the "afternoon satellite" of the U.S. weather service NOAA (National Oceanic and Atmospheric Administration). This passes over its target areas at 2:30 p.m. local time. The data from the U.S. satellite are also available to Eumetsat and NOAA, in turn, will be able to use the data from the Metop system. Europeans and Americans are not only working closely together in space, but also on the ground: the U.S. ground station in Fairbanks/Alaska and the European ground station in Svalbard/Spitzbergen supplement each other by exchanging the data they receive. The common use of the Spitzbergen ground station for both satellites is also under discussion. A multitude of improvements, including greater storage and data transmission capabilities, an encoding system for data protection against unauthorised access, and a more sophisticated and comprehensive payload ensure that the performance of the Metop satellites is significantly better than that of the older NOAA system Tiros (Television Infrared Observation Satellite).

The data collected by the instruments on-board Metop are stored and transmitted to the ground station once on each orbit. They are then processed in the Eumetsat centre in Darmstadt and transmitted to the end user. The whole process takes less than three hours. Furthermore, that the satellite can also transmit data in real-time to receiving stations in the area over which it is passing.

Metop-1 measures 17.60 m x 6.70 m x 5,40 m with its solar arrays and antennas deployed. It weighs 4,300 kilograms. The solar array is 11.30m wide when extended and supplies 3,900 watts. The satellite is due for launch in 2005 on board a Russian Soyuz-ST rocket from Baikonur Cosmodrome in Kazakhstan. The Metop satellite is designed for an in-orbit lifetime of approximately five years.

As prime contractor, Astrium is responsible for the integration of the satellite. In addition, Astrium builds the satellite(s service module and payload module, as well as a number of measuring instruments.

The service module is built by Astrium in France and accommodates the equipment for power supply, attitude and orbit control, thermal control, and control of communications with the ground station. The payload module is built by Astrium in Germany and accommodates the measuring instruments, the systems for instrument control, formatting, encoding and storage of measured data, as well as for data transmission to the ground. The service module and the payload module will be identical for Metop-1 to Metop-3.

Astrium also supplies three important measuring instruments for Metop: MHS (Microwave Humidity Sounder), Ascat (Advanced Scatterometer) and Gras (GNSS Receiver for Atmospheric Sounding).

The Microwave Humidity Sounder (MHS), built by Astrium in Great Britain, is a microwave sensor for measuring atmospheric humidity profiles, as well as cloud and precipitation parameters. It primarily measures the humidity of the air, but also records the water which is contained in the clouds in a liquid state of aggregation, as well as precipitation. In comparison with the second microwave sensor on board Metop - the U.S. AMSU-A -, MHS has not only a higher resolution but also performs its measurements much faster. Since one measurement of the AMSU-A instrument corresponds to exactly one set of 3x3 MHS measurements, the measurement results of both instruments supplement each other perfectly.

The Advanced Scatterometer (Ascat), built by Astrium in Germany, is a radar instrument which measures the speed and the direction of the wind over the open sea. Ascat will also help to monitor the distribution of snow and ice on land and on the surface of the sea. Ascat can continue measuring in the dark and through cloud cover, a feature which is particularly useful in the polar regions. Ascat will scan two 500 kilometre- wide corridors with its three antenna pairs and can therefore provide data from practically every point on the Earth's surface within 24 hours.

The GNSS Receiver for Atmospheric Sounding (Gras), also built under Astrium's responsibility, is a receiver for the signals from the U.S. Global Positioning System (GPS). Gras collects the signals, which are modulated by the Earth's atmosphere. From these signals, vertical profiles of temperature can be obtained, as well as vertical profiles of water vapour in the lower part of the troposphere and pressure in the upper part of the troposphere and the lower part of the stratosphere. In addition, Gras provides real-time navigation data on board Metop, which help determine the precise position of the satellite.

Some of the other measurement instruments on board Metop are instruments which have been newly developed in Europe whilst others have been used successfully for years on NOAA's polar satellites.

Friedrichshafen, May 2002/02015

For further information:

Astrium
Earth Observation & Science
Mathias Pikelj
Tel.: +49-7545-8-9123
Fax: +49-7545-8-5589
presse-eo@astrium-space.com
Internet: http://www.astrium-space.com