The motion allows it to calibrate its accurate scientific instruments

Oct 17, 2011 15:00 GMT  ·  By
CryoSat is able to measure the freeboard (the height protruding above the water) of floating sea ice with its sensitive altimeter. From the freeboard, the ice thickness can be estimated
   CryoSat is able to measure the freeboard (the height protruding above the water) of floating sea ice with its sensitive altimeter. From the freeboard, the ice thickness can be estimated

The European Space Agency (ESA) announces in a new press release that its CryoSat-2 spacecraft has just turned 18 months in Earth's orbit. The satellite is arguably the best satellite ever designed to survey the thickness of ice above Greenland and Antarctica, and is currently operating flawlessly.

One of its most distinctive traits right now is the fact that it moves through Earth's orbit by tilting left and right in respect to its direction of motion. This is done in order to increase its sensitivity and precision its instruments have to the thickness of the ice sheets below.

At the same time, the maneuver also serves another purpose, which is to calibrate the advanced radar altimeter instrument on the spacecraft even further. This is done in order to ensure that no errors make their way into the highly-respected and often-used datasets the satellite returns to Earth.

Earlier this year, CryoSat released the first-ever map showing ice thickness throughout the Arctic. This impressive milestone was achieved after only a year of conducting scientific studies. Not even the satellite's ESA operators expected such success.

“Harsh conditions in space – with huge temperature differences between Sun and shade – can lead to the deterioration of CryoSat’s instruments, which can also lead to measurement errors. In order to quantify these errors, ESA ground controllers are working to recalibrate the altimeter,” the statement says.

“The altimeter has two antennas mounted on a bench about a meter [3 feet] apart. When it is working in the ‘SARIn’ mode, both antennas are used in parallel: one emits a signal and both receive the signals that bounce back,” the document goes on to add.

“Normally, this bench is parallel to Earth’s surface. But at the edges of the ice sheets, the ice surface is not always flat and the slopes affect the return signals,” the press release explains.

The rolling maneuver can only be carried out while CryoSat is flying over flat surfaces. Therefore, mission controllers must either find a patch of ice that covers a large surface, or conduct the procedure while the spacecraft is flying over Earth's oceans.

The calibration process lasts for a few minutes, but the satellite is traveling at very high speeds, and therefore covers a lot of ground in a short while.

“With the results from the different sets of rolls over different ocean surfaces and at different ambient conditions, we are aiming to characterize the instrument to a precision better than we thought we could make at the time of the launch,” CryoSat mission manager Tommaso Parrinello says.