By Jonathan Amos
Science reporter, BBC News
Europe is set to launch its most sophisticated weather and climate satellite to date.
Set to be the first European met satellite to fly over the poles
The Metop spacecraft will be lofted into its 850km-high polar orbit by a Soyuz-Fregat vehicle from Kazakhstan.
The platform should improve forecasting globally, and give scientists detailed data they can use to refine models describing how Earth's systems work.
Metop has eight instruments to gather a range of data about the planet's atmospheric and surface conditions.
The Soyuz is scheduled to lift off from Baikonur spaceport at 1628 GMT on Tuesday. Controllers will be hoping for a clean getaway having seen three previous launch attempts frustrated by technical difficulties.
Day and night, Metop will monitor temperature, humidity, wind velocity and ozone cover across the whole globe.
It has a further three instruments that will be used to assess the space environment and relay data.
Metop is a joint project of the European Space Agency (Esa) and Eumetsat, the intergovernmental organisation charged by European member states with operating a series of orbiting weather observatories.
"This is a huge step forward for Europe," said Dr Stephen Briggs, head of Esa's Earth Observation Science and Applications Department.
"Metop's technology will be the benchmark for future systems for the next 20 years. It continues a historical series of data collected by previous Esa satellites but takes brand new measurements with a new set of instruments.
"In particular, the French-built Iasi instrument - the Infrared Atmospheric Sounding Interferometer - will give us three-dimensional temperature, pressure and atmospheric chemistry soundings that are much better than anything we've had before."
The new platform weighs more than four tonnes and measures almost 18m (60ft) with its solar wing unfurled.
It is a first for Europe in that it circles the Earth via the poles. Eumetsat's familiar Meteosat class of observatories sit in geostationary orbits 36,000km (22,000 miles) above the equator. From here they provide an image of half of the Earth's surface every 15 minutes.
Metop will provide data to improve weather and climate models
Metop, on the other hand, will take high-resolution pictures of the whole planet over a much longer time span, between one and three days.
The difference for meteorologists is that high-altitude systems can track weather changes in real-time, while low-altitude platforms like Metop can provide much finer detail (albeit less often).
Metop will work in tandem with polar orbiting platforms operated by the US National Oceanic and Atmospheric Administration (Noaa).
The US has provided four of the instruments on board; the rest come from all over Europe with the French space agency (Cnes) having played a leading development role.
"Metop is a very ambitious satellite with 11 instruments. Normally, a satellite will carry just one or two instruments to speed development and get the data to scientists as quickly as possible," explained Dr Mike Healy from EADS-Astrium, the prime contractor on the platform.
THE METOP SATELLITE
Dimensions: 17.6m by 6.5m by 5.2m; Total mass: 4,093Kg
Full orbit every 101 minutes; Crosses day equator at 0930
Will take key temperature and humidity measurements
Monitors wind direction and speed, especially over oceans
Builds profiles of ozone and other trace atmospheric gases
Joint project for Eumetsat and the European Space Agency
"Metop is cutting edge. Its Microwave Humidity Sounder, for example, is a considerable step forward on previous technology, giving about 10 times better resolution.
"Built in the UK, the instrument will provide unprecedented maps of water vapour density in the upper part of the atmosphere," he told BBC News.
Metop is the first of three near-identical platforms. The two follow-ons will be launched over the next 10 years to ensure there is continuity of service. The programme is costing 2.4 bn euros (£1.6bn; $3bn).