1.3. Ice: ice sheets and sea ice
Topographic maps of Antarctica and the area around Lake Vostok (red circle), showing the ice plateau capping the lake (three kilometres below the surface).
Altimetry measurements can also be used to determine sea ice thickness and glacier topography. Ice motion and spread are major indices of global climate change: ice, including sea ice, plays an active role in the climate due to the strong feedback induced by its high albedo, whereas continental ice mostly acts as a huge reserve of fresh water (77% of the Earth's fresh water is frozen in Greenland and Antarctica), that could significantly contribute to sea level rise.
The cryosphere plays an important role in moderating the global climate, and as such, the consequences of receding ice cover due to global warming are far-reaching and complex. While evidence suggests that ice sheets are relatively stable, there are indications that rapid changes are occurring around their margins, where the ice reaches the sea: changes that could weaken the ice sheet.
Altimetry is one of the most powerful tools for observing sea ice and ice sheets. For sea ice, altimetry provides a unique way of measuring its thickness. For ice sheets, their topography can be measured by altimeters, at least by those that can reach high latitudes. Moreover, altimeters also provide other parameters such as backscatter coefficient and waveform shape that give information on surface roughness and snow pack characteristics such as stratification or ice grain size. These parameters are related to relevant unknown quantities affecting the climate, such as snow accumulation rate or snow drift caused by wind.
- Rémy, F., The new vision of the cryosphere thanks to 15 years of altimetry, 15 years of progress in radar altimetry Symposium, Venice, Italy, 2006
- Zwally, H.J. and A.C. Brenner, Ice sheet dynamics and mass balance, Satellite altimetry and Earth sciences, L.L. Fu and A. Cazenave Ed., Academic Press, 2001
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