Sorting ice from space

Image of the Month - June 2008

Classification of ice over Greenland for year 2004 from Envisat dual-frequency altimeter and radiometer measurements (so four frequencies total). Six different types of snow were defined, most being comparable with categories defined in previous studies (except for class 6 - purple): class 5 (red) and 4 (pink) match dry snow, class 2 percolation, 3 wet snow and 1 bare ice or land. (Credits CLS/Legos)

Satellite altimetry is a major tool to better understand ice sheet behaviour. In particular Envisat dual-frequency altimeter and radiometer provide measurements up to 82° of latitude,  and so covers a large part of the Earth's iced surfaces.

The frequencies used by the altimeter and radiometer penetrate differently within the snow (see e.g.  Image of the Month, October 2006: Altimeter looks into the crevasses). Moreover, the measurements taken depend on the snow characteristics. It is thus possible to separate regions of distinct snow morphology.

The different categories of snow thus defined are in good agreement with previous studies based on in situ or scatterometer data. They defined categories (facies) such as dry snow, percolation (when surface ice melt and percolates through the snow, refreezing eventually), wet snow (with free water), and bare ice (i.e. winter snow have melt, leaving the underlying ice exposed). Such partition of Greenland using spaceborn sensors enables finer  monitoring of areas highly sensitive to climate variations.

See also:

  • Applications: Ice


  • Tran, N, F. Rémy, P. Féménias, Snow facies over ice sheet derived from Envisat active and passive observations, IEEE Trans. Geosci. Remote Sens., Vol. 46,  No 11,  3694 - 3708,  November 2008, doi 10.1109/TGRS.2008.2000818.