CryoSat-2, the ice caretaker

For many, the extent and the thickness of the ice on our planet constitute a type of climate change “barometer”. As it happens, a satellite belonging to the ESA is going to take care of this.

 

CryoSat-2 satellite (illustration). Credit: ESA

The size of glaciers can undergo spectacular evolutions in accordance with climate changes. We know, for example, that our planet has known several ice ages, some of which were particularly severe such as that of Varanger, 750 million years ago, when ice masses stretched almost to the equator!

The thickness of the ice: a major factor
However, at the present time, there is no real fear of a rapid extension of the glaciers or ice fields, rather the contrary. Despite ice ages classed as recent on the geological time scale, like the Little Ice Age from the middle of the 14th century to the beginning of the 19th century (also known as the Maunder Minimum, see this article), we have noted a general retreat of the glaciers and a dwindling of the ice fields, especially in the Arctic, a region that experts believe to be particularly sensitive to climate variations.

To determine the thickness of the ice masses on the sea and on land and to observe any changes over time are the objectives of the CryoSat-2 mission. Crucial data which will enable us to understand the climate changes at work. Credit: ESA

The measuring of the ice masses on land and on sea is already a challenge in itself, but it does not pose any complex problems. It is quite a different matter though when it comes to gauging the thicknesses of the ice. It is not difficult to understand that this data is as essential as the surface area as climatologists need to monitor any changes in the volume (the product therefore of the surface area and the height) of the ice in order to refine climate models. Accuracy is also important as wide stretches such as the Antarctica have a high thermal inertia and are therefore less affected by any warming. But if we can accurately determine a slight reduction in the thickness of the ice in such regions, then the climatologists will have some extremely valuable data.

Accuracy to the nearest 3 cm!
It is obviously with this major issue in mind that the CryoSat mission was designed. In 2005, the satellite was unfortunately lost following the failure of its Russian-European Rockot launch vehicle. Aware of the importance of this mission to its Earth Explorer Programme, the European Space Agency quickly decided to build a CryoSat-2 as a replacement. Now that it has successfully been put into orbit at an altitude of 717 km thanks to the Dnepr (a converted SS-18 missile) launch vehicle belonging to the Russian-Ukrainian company Kosmotras, the European satellite can finally begin its measurement campaign. To achieve this, it will be using an instrument dubbed SIRAL or Synthetic aperture Interferometric Radar ALtimeter (built by Thales Alenia Space, EADS Astrium being the prime contractor for the satellite).

The Dnepr blasted off from Baikonur on 8 April 2010. This former missile converted into a launcher placed CryoSat-2 in a polar orbit at an altitude of 717 km. Therefore passing by the poles of our planet as the latter turns underneath it, the satellite will regularly scan the entire globe. Credit: ESA

This radar gives unequalled accuracy as regards the measurement of the thickness of ice, whether it is a matter of glaciers on land or the visible part of ice floating on the sea or ice fields. SIRAL should be accurate to the nearest 3 cm! A performance made possible due to another state-of-the-art measurement, that of the orbit altitude of CryoSat-2 which will be used as a reference, obtained with the DORIS system (Doppler Orbitography and Radio positioning Integrated by Satellite) developed by the CNES and a laser reflector. In its position as “ice caretaker”, CryoSat-2, is going to be surveying our ice for at least 3 years, providing the scientific community with valuable data as regards ongoing climate changes.

With unequalled accuracy for this type of measurement, CryoSat-2’s SIRAL instrument will make use of the radar echo technique to determine the thicknesses of the ice. Credit: ESA

Published on 8 April 2010