By Helen Briggs
BBC News science reporter
Cryosat will study the Earth's ice fields (Image: European Space Agency)
A new satellite will give the clearest picture yet of climate change at the Earth's poles, UK researchers believe.
The Cryosat spacecraft will provide a map of ice thickness across the Arctic for the first time, the scientists say.
The European Space Agency mission has been designed to obtain definitive data on the rates at which the planet's white caps are shrinking.
Cryosat's launch is scheduled for Saturday, on a converted military missile, from Plesetsk in Russia.
"What Cryosat is going to do for us is understand just how much ice is being converted to water, and just how fast that's happening," explained chief scientist Professor Duncan Wingham.
"So it's concerned with numbers and kilograms of water.
"We need that information partly to find out how fast change is occurring and partly to find out what are the longer and wider effects of that change," the University College London researcher told the BBC News website.
Scientists have long warned that the planet's frozen poles would be first to feel the effects of global warming, in particular the thin crust of ice that floats on the Arctic Ocean around the North Pole.
Previous satellite imagery suggests this process is well underway.
Only last week, US scientists said the latest data had revealed a dramatic retreat of sea ice in the Arctic during the summer months for the fourth consecutive year.
Climate models predict that if global warming continues at current rates, Arctic sea ice will have disappeared entirely, at least in the summertime, by the end of the century.
"This prediction of the sea ice reducing is a critical test of these climate models, and this is why Cryosat is so important in being able to monitor what exactly is happening to both the Arctic and Antarctica in terms of ice sheets," explained Professor Alan Thorpe, chief executive of the UK's Natural Environment Research Council (Nerc), which has helped fund the mission.
Professor Thorpe said pictures from space had shown that since the beginning of the satellite era, in 1978, the aerial extent of sea ice had been reducing, probably because of warming connected to human-produced greenhouse gases, such as carbon dioxide.
How well is ice represented in computer models?
"But up to now, we haven't been able to precisely quantify the volume of sea ice," he told the BBC News website.
"We've been able to look at a picture of the extent but not the thickness - and you need both of these in order to work out the volume of sea ice."
Cryosat will circle the Earth in a polar orbit for three years, providing better coverage than existing satellites which miss a third of the Arctic Ocean.
Its main instrument is a radar altimeter, designed to measure the height of ice sheets and sea ice with unprecedented accuracy.
The new Cryosat data will feed into the climate prediction models used by government for policy-making.
"The purpose of Cryosat is to check that we've got a proper description of sea ice in these models," Professor Thorpe said.
"It's very complex from a physical science point of view and the representation of these processes is critical in knowing the level of confidence we can have in the models."
Cryosat is the first of the European Space Agency's (Esa) Earth Explorer missions, a series of fast, relatively low-cost Earth observing satellites.
Dr Stephen Briggs, head of the Earth observation science and applications department at Esa, said the satellites were designed to understand better the Earth's systems and processes.
"They are relatively small; time constants in their development are quite short, and yet they are producing very high-quality missions - so, we are going back to the old idea of faster, cheaper, better," he said.
The 135m-euro Cryosat mission was proposed by UK scientists.
British industry has played a key role in the mission technology. Some 80 research groups throughout the UK and Europe will use the new data.
KEY CRYOSAT INSTRUMENTS
1 Heat-radiating panel - The path of Cryosat's orbit means it will face extremes of heat and cold. The panel ensures the electronics are kept at an optimum working temperature
2 Star trackers - To get the best out of its radar system, Cryosat must know precisely how it is orientated in the sky and uses three star trackers to get the necessary references
3 Radar antennas - Cryosat's radar altimeter system sends multiple pulses to Earth, and then captures the echoes to determine the heights and angles of ice surfaces
4 "Doris" antenna - The device is a radio receiver that will help work out the precise position in the sky of Cryosat to within a few centimetres. It works off a network of ground beacons
5 Laser retro-reflector - Cryosat's position can also be determined by firing short laser bursts at it and timing the reflections. Both systems are necessary to make sense of the radar data
6 X-band data antenna - This transmits the huge volume of data gathered by the radar system. The data is picked up at the Kiruna receiving station in Sweden
7 S-band telecommand antenna - Engineers also need to speak to Cryosat. Commands can be uploaded. The antenna also transmits status and monitoring information
8 Unlike many spacecraft, which have solar wings, Cryosat has a series of solar panels along its back