Satellites at the Service of Polar Research
24 May 2005 - Articles, Atmosphere & Space, Ice & Snow, Arctic, Antarctic
The European Space Agency's powerful ENVISAT satellite tracks ice and vegetation trends in the polar regions with extreme accuracy
© ESA
Satellites have become essential tools for polar research. For example, they track the movements of many birds and mammals at the poles. But they have proved particularly decisive when observing climate change; spatial teledetection has enabled study of changes to the extent of pack ice, the volume of ice caps, the productivity of oceanic waters, levels of stratospheric ozone and many other phenomena. Europe is one of the leaders in this field, thanks to the European Space Agency (ESA) which can boast the successful launch of several satellites: ERS 1 and 2, Envisat and, most recently, Cryosat.
Miniature ARGOS tracking devices
For several species of whale, seal, penguin or albatross, it was necessary to wait for the miniaturisation of ARGOS tracking devices before their astonishing movements could be tracked. During the 1990s, these systems revealed that elephant seals in the Antarctic Ocean were champion divers, frequently plunging to depths of 800 metres during the 10 months they spent at sea. The team led by Mette Mauritzen, at the Norwegian Polar Institute in Tromsø, has by this means been studying the adaptation of polar bears to changes in the pack ice around Spitzberg.
Ice monitoring
"Satellites have revolutionized the monitoring of polar ice", explains Frédérique Remy, from the Laboratory of Geophysics and Spatial Oceanography (LEGOS, CNRS) in Toulouse, France, "by allowing us to monitor regularly, and from a distance, areas which are difficult or even impossible to reach because of the winds and very low temperatures. Not to mention total darkness for several months each year!" ERS (European Remote Sensing) satellites have, for example, made it possible to quantify changes in the volume of the Antarctic ice cap: "The Antarctic ice sheet appears to be stable, apart from a sector in the west where the ice is losing its thickness."
Shrinkage of pack ice
The observations are identical with respect to Arctic pack ice, even though an average reduction of 37,000 km2 per year (compared with an average summer pack ice area of 7 million km2) has been measured during the past 30 years. However, we still have insufficient experience, because the first observations only go back to 1978. The altimeter on board CRYOSAT, the satellite which was launched by the ESA in October 2005, thanks to its ability to measure the thickness of pack ice (to half a metre), would have confirmed whether or not this is in fact a trend. However, on 8 October 2005, the mission was lost due to an anomaly in the launch sequence.
Heads in the clouds but feet firmly on the ground
Despite the rapid development of polar teledetection, work on the ground remains necessary. Firstly because some measurements are still difficult from space. "That is the case for atmospheric pressure", explains Alan Rodger, from the British Antarctic Survey, "and also the Earth's magnetic field, because 12 hours elapse between each measurement, while on the ground we can follow this parameter continuously". Field work is also essential to calibrate and validate satellite observations. This is true for the stratospheric ozone, which today is being measured by another ESA offspring, ENVISAT, the largest and most elaborate earth observation satellite ever constructed.
Finally, as explained by Bruno Delille, from the University of Liege in Belgium, "the increasing integration of ground and space measurements opens new fields of research: for several years now, we have been studying the role of the Antarctic Ocean and pack ice in exchanges of carbon dioxide between the ocean and the atmosphere. This has been made possible through oceanographic measurements collected in situ supplemented by satellite observations of important parameters such as the chlorophyll biomass, surface temperature, winds and the distribution of ice."
By: Jean de Pomereu
