By Jonathan Amos
Science correspondent, BBC News
Cryosat's orbit will be modified slightly to get the best out of the instrument
The radar instrument on Europe's Cryosat-2 spacecraft has been switched on and is reported to be working well.
The satellite, which was launched last Thursday from Kazakhstan, will use the equipment to map the thickness and shape of the Earth's polar ice cover.
Controllers must now check all of Cryosat's systems while a calibration team fine-tunes the radar.
The science phase of the mission is expected to start in a few months' time and continue through to at least 2013.
Cryosat is the latest Earth observation venture to be flown by the European Space Agency (Esa).
A command was sent from its operation's centre in Darmstadt, Germany, on Sunday to activate the satellite's SAR/Interferometric Radar Altimeter (Siral).
The instrument then acquired sample data over the Antarctic and Arctic for relay back to Earth.
"We've tried the instrument out in all its modes," said Esa project manager Dr Richard Francis.
"The very first time we switched it on, it worked brilliantly," he told BBC News.
Siral advances the technology flown on previous European radar missions, such as ERS and Envisat.
It has an along-track (straight ahead) resolution of about 250m, which will allow it to see the gaps of open water between the protruding sea-ice floes of the Arctic.
With centimetre-scale accuracy, the altimeter will measure the difference in height between the two surfaces so scientists can work out the overall volume of the marine cover.
HOW TO MEASURE ICE THICKNESS FROM ORBIT
Cryosat's radar has the resolution to see the Arctic's floes and leads
Some 7/8ths of the ice tends to sit below the waterline - the draft
The aim is to measure the freeboard - the ice part above the waterline
Knowing this 1/8th figure allows Cryosat to work out sea ice thickness
A second antenna on Siral offset from the first by about a metre will enable the instrument to sense the shape of the ice below, returning more reliable information on slopes and ridges.
This interferometric observing mode will be used to assess the edges of Greenland and Antarctica where some rapid thinning has been detected in recent years.
Cryosat's Dnepr rocket gave the mission a perfect start by injecting the spacecraft about 100m above the requested 720km-high mean orbit.
Controllers will now modify this orbit slightly to enable the radar instrument to perform at its best.
Cryosat-2 spacecraft launches