Mobile version

Ice sheets

Modis image of Greenland, August 2007 . (Credits Nasa).

Altimetry is a powerful tool for measuring both the dynamics and mass balance of ice sheets. Continental ice has an impact on sea level: if both of the major Greenland and Antarctica ice sheets were to melt, the sea level would rise by about 80 m.

Topography is one of the parameters relevant to the processes acting on ice sheets. It contains the signature of the main physical processes (climate and dynamic) that act on an ice sheet on both a small and large scale, and important information about local anomalies or general trend behaviour. Nowadays topography is also an initial condition for studying future evolution. Large-scale topography controls flow direction and its mapping enables the balance velocity to be derived. Moreover, the deformation and sliding velocities depend on the basal shear stress and thus on surface slopes. Accurate information about topography is, therefore, crucial to predicting future evolution and understanding ice dynamics, either by providing an empirical parameterisation of the flow laws or by pointing out unknown physical processes.

Moreover, altimeters also provide other parameters such as backscatter coefficient and waveform shape that give information on surface roughness and snow pack characteristics, from the global to the kilometre scale. Since ERS-1 was launched, with an orbit as high as 82°N and S, our vision of the ice sheets has been radically transformed. This long series, with ERS-2 and Envisat following ERS-1, has made it possible to discern changes in the shape and volume of both ice sheets, Greenland and Antarctica, which are related to climate change. Moreover, from April 1994 to March 1995, ERS-1 was placed on a geodetic orbit (two shifted cycles with a 168-day repeat) so that the topography of both ice sheets could be mapped with a resolution of 2 km. This precise topography has led to the detection of subglacial lakes, subglacial hydrological networks, outlet glacier anomalies, etc.

The 15 years of data from ERS-1, ERS-2 and Envisat have also made it possible to map the ice mass balance. Results show that the Greenland ice sheet is thinning at low altitudes while thickening at its centre. A simultaneous increase in accumulation rate at high altitude and snow melting at low altitude explains this pattern and strongly agrees with the theoretical behaviour of snow when confronted with climate change. On average therefore, the Greenland ice sheet seems to be thickening slightly at a rate corresponding to a decrease of 0.03 mm/yr in sea level. On the contrary, the Antarctica ice sheet is found to be stable, although local increases or decreases can be observed. For instance, in the western part a large sector is found to be thinning, whereas a few sectors in the eastern part are found to be thickening.

Further information:

Rss feedsContactSitemapPartnersFAQGlossaryLexiconMobile
You must enable cookies in your browser preferences to save the modifications
You are using an older version of Internet Explorer, please update to take full advantage of Aviso+ features

Customize the home page

View all widgets
Reduce display
Public profile
User profile

Select/Deselect widgets

Discover AVISO+

Customizable home, reading tools, products search guide, etc.. Discover step by step the features of the new site AVISO+.

Customizable homepage

The new home page is composed of blocks called "widgets".

Rearrange the blocks with a "Click & Drop".

Hide a widget with the cross at the top right. Reset or add a widget with the "wrench" icon. The "User" and "Public" profiles offer a predefined organization.

All the modifications are automatically saved as cookies on your machine so as to enable you to have your own specific AVISO+.

Reading tools

Ease your reading by choosing the page background colour (black/white) and/or by modifying the font size.

Browsing menu and breadcrum trail

To ease your browsing through AVISO+, you can use at any time the main banner items with the interactive submenus or use the browsing menu on the left side of the screen (it is open by default). For more readiness of the page contents, you can fold and unfold the browsing menu by clicking on the tab. At any time you can know where you are thanks to the browsing menu or the breadcrum at the top of the page.

Products search guide

The first submenu of the "Data" banner item leads you to a new search form enabling you to find quickier the product that suits your needs. The list of results is updated according to your selection criteria.

AVISO+ Multimedia

The first submenu of the "Multimedia" banner item leads you to AVISO+ collections of images and videos linked to altimetry and its applications. Have a nice visit!