21 July 2010, by Tamera Jones
The first set of data from ESA's ice mission, Cryosat-2, has been sent to a select group of scientists for fine-tuning. This brings polar scientists a step closer to accurately understanding how the Earth's ice caps are changing.
ESA's Cryosat-2.
The data – which comes just three months after the satellite was launched – has gone to around 150 scientists in 40 research institutions around the world. It's their job to help make sure the measurements made by the satellite up until now are accurate.
'These people are doing their own ground or airborne measurements, which will help calibrate the data Cryosat-2 is delivering,' explains Cryosat-2 chief scientist Professor Duncan Wingham from the Centre for Polar Observation and Modelling at University College London.
Professor Liz Morris from the Scott Polar Research Institute is one of the scientists involved. She's in Greenland right now making ground-based measurements to check the satellite's accuracy.
'So far the data is extremely high quality and confirms that the measurement concept we came up with over ten years ago works.'
Professor Duncan Wingham, University College London
'It's these sorts of measurements, as well as tide gauge measurements and measurements from sites in Antarctica, for example, that are essential to support data calibration,' says Wingham.
Data from Cryosat-2 is also being cross-calibrated with data from other satellites, like Jason-1, Jason-2 and Envisat, which are already making similar, but less accurate measurements.
'We're looking at measuring lots of small numbers, so we need lots of data,' explains Wingham.
This stage of the Cryosat-2 data validation and calibration process follows a testing phase, led by Wingham – who hatched the idea for the mission – and other colleagues at UCL.
Once the final part of this commissioning phase is complete, the data will be made available for the wider scientific community to use in the autumn.
'So far the data is extremely high quality and confirms that the measurement concept we came up with over ten years ago works,' says Wingham.
Wingham says that in about two months' time, they'll know whether or not the satellite can deliver to an accuracy of 3.3 centimetres.
Sharpen up
'At the moment the data is noisy - we're at the one metre scale, but over time the fuzzy picture we've got will sharpen up,' he says.
Cryosat-2 was launched onboard a Dnepr rocket - a converted intercontinental ballistic missile – from the Baikonur cosmodrome in Kazakhstan on 8 April this year.
The satellite will make precise measurements of both the shape and thickness of ice in the Arctic and Antarctica, helping scientists better understand how melting polar ice could affect ocean circulation patterns, sea-level rise and the global climate.
It'll do this using an instrument called an altimeter, which fires pulses of microwave energy at the ice and records how long it take for those pulses to return to the satellite.
Scientists will be able to calculate the thickness of the ice by comparing how long it takes for the echoes to return from the top of ice floes and from the water in cracks in the ice. Essentially the aim is to measure the freeboard - the part of the ice that sits above the waterline.
CryoSat-2 will also tell scientists how winds affect the Arctic Ocean by measuring differences in the height of the sea surface exposed between ice floes.
A second antenna on the tent-shaped satellite will measure the ice's shape, telling researchers about changes in the slopes and ridges at the edges of the great Antarctic and Greenland ice sheets. This is crucial, because the edges of ice sheets are where melting is happening the fastest.
