A new formula could help Hamburg’s researchers to more accurately observe changes in the Arctic Ocean. Twenty-four hours a day, satellites survey the Earth, providing tremendous amounts of data. Hidden in these mountains of figures lies a wealth of information. Yet before that information can be put to use, climate researchers need to first uncover and decode it. In the course of this work, we sometimes stumble across a “mother lode” – just like we did in my recent discovery concerning Arctic ice.
Changes in the ice cover of the Arctic Ocean are an important indicator of climate changes. For years now, the area covered by ice has steadily declined, and many researchers fear this trend can no longer be reversed – which would have far-reaching consequences for our climate system. As such, this region has been monitored by satellites for more than 35 years. But how thick is the ice we see? After all, the thickness of the ice tells us more about its total volume, and therefore about its longevity, than its area does.
Since late 2010 we at the Cluster of Excellence for climate research have been able to measure ice thicknesses of up to one meter with the help of the SMOS research satellite, marking a major advance. The satellite can sense and measure the natural radiation produced by all bodies – including the ocean and the sea ice on its surface. In the course of its long journey into space, this radiation is constantly diverted and reflected. As a result, only part of the energy reaches the satellite, which receives a modified signal. This effect is most prominent at transition points, e.g. at the transition from ocean to ice, or from ice to air. First we use computer models to describe the physical processes at the respective boundaries; we then use the values to determine the distance between those boundaries – e.g. to arrive at the thickness of a layer of ice.
SMOS also gets a helping hand from the CryoSat-2 satellite. Whereas SMOS’s “visual depth” of up to one meter can be used to accurately measure the thinner edge areas of the sea ice, the CryoSat-2 is the expert when it comes to thicker ice. Unlike SMOS, it uses radar to measure how far the ice protrudes out of the water. Since we know that only ten percent of sea ice is above water and the remaining ninety percent is underwater, we can then calculate the total thickness.
However, this method can only work if the current snow conditions are also taken into account; masses of snow can weigh the ice down to such an extent that the normal 90:10 ratio no longer applies. But how can we measure snow cover? Until now, researchers have had to resort to outdated maps and could only make rough estimates.
While integrating a formula for the snow cover into our computer model, I discovered an unexpected solution in the SMOS data. At exactly the point where SMOS runs into its limitations – namely, for thick ice – the formula delivers values for the thickness of snow cover. The expeditions with observational flights over the Arctic so far have confirmed these values – a real success, as now for the first time I will be able to create comprehensive and up-to-date snow-cover maps.
The next challenge will then be to determine whether or not these maps can actually be used for the CryoSat calculations, which would allow us to more accurately monitor and comprehend changes in ice volume in the Arctic.
Author: Dr. Nina Maaß
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