ceos   eesa
Capabilities of Earth Observation Satellites
  Earth Observation Plans by Measurement  
Measurement Timelines
Snow and Ice
Gravity and Magnetic Fields
  Catalogue of Satellite Missions  
Catalogue of Satellite Instruments


Ice Sheet Topography
Essential Climate Variables: Glaciers and Ice Caps

The state of the polar ice sheets and their volumes are both indicators and important parts of climate change processes and feedbacks. Consequently, it is important to monitor and study them in order to investigate the impact of global warming and to forecast future trends. The IPCC expects that, globally, ice sheets will continue to react to climate warming and contribute to sea level rise for thousands of years after the global climate has been stabilised. They note that:

— contraction of the Greenland ice sheet is projected to continue to contribute to sea level rise after 2100. Current models suggest virtually complete elimination of the Greenland ice sheet and a resulting contribution to sea level rise of about 7 m if global average warming in excess of 1.9 to 4.69C relative to pre-industrial values was sustained for millennia;

— ice dynamic models suggest that melting of the West Antarctic ice sheet could contribute up to 3 m of sea level rise over the next 1000 years, but such results are strongly dependent on model assumptions regarding climate change scenarios, ice dynamics and other factors.

Satellite remote sensing allows observations of the changes in the shape of ice sheets, and identification of the shape and size of large icebergs that have detached from the ice sheet. SAR instruments are one source of data on the polar ice sheets. RADARSAT provides routine surveillance of polar regions and has created the first high resolution radar images of Antarctica, enabling detection of changes in the polar ice sheet and improved understanding of the behaviour of the Antarctic glaciers. ASAR on the Envisat mission is continuing the observations of polar ice topography started by the ERS-1 and ERS-2 satellites.

Interferometric measurements by PALSAR, together with observations by the AVNIR-2 instrument on JAXA’s ALOS mission, are contributing to understanding the ice sheet mass balance and glacier variation near the South Pole and in Greenland.

Altimeters provide useful data on ice sheet topography. While many have high vertical resolution, their limited horizontal resolution means that their observations over smoother, near-horizontal portions of ice sheets are of greatest value. The RA-2 instrument on Envisat is providing improved mapping of ice caps.

Given the significance of information on changes in the continental ice sheets, two missions dedicated to their study have been developed: NASA’s ICESat (launched Jan 2003 but with reduced acquisition capabilities due to technical issues) and ESA’s CryoSat-2 (from 2010, following the loss on launch of CryoSat in 2005). CryoSat-2 will provide an instrument for the ice sheet interiors and margins, for sea ice and other topography, with three-mode operation:

— conventional pulse-limited operation for the ice sheet interiors (and oceans if desired);

— synthetic aperture operation for sea ice;

— dual-channel synthetic aperture/interferometric operation for ice sheet margins.

ICESat-II is scheduled for launch in 2015.

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Snow Cover, Edge and Depth
Essential Climate Variables: Snow Cover

Regular measurements of terrestrial snow cover are important because snow dramatically influences surface albedo, thereby making a significant impact on the global climate, as well as influencing hydrological properties and the regulation of ecosystem biological activity. The IPCC has found that – on the evidence of satellite data – there is likely to have been a decrease of about 10% in the extent of snow cover since the late 1960’s.

Snow forms a vital component of the water cycle. In order to make efficient use of meltwater runoff, resource agencies must be able to make early predictions of the amount of water stored in the form of snow. Coverage area, snow water equivalent and snow pack wetness are the key parameters to be determined in this process.

Snow cover information has a range of additional applications such as detecting areas of winterkill in agriculture that result from lack of snow cover to insulate plants from freezing temperatures. Locally, monitoring of snow parameters is important for meteorology and for enabling warnings of when melting is about to occur – which is crucial for hydrological research and for forecasting the risk of flooding.

A range of different instrument types can contribute to measurements of snow. Visible/near-infrared satellite imagery provides information of good horizontal and temporal resolution and accuracy on snow cover in the day-time in cloud-free areas. AVHRR provides snow cover information and this will be continued in the future by VIIRS. MODIS data are being used to monitor the dynamics of snow and ice cover over large areas (greater than 10 km2) and, on a weekly basis, to report the maximum area covered by both. The resulting snow maps should be available within 48 hours of MODIS data collection.

Passive microwave instruments such as SSM/I, AMSR and CMIS have all-weather and day/night monitoring capability, and are able to estimate the thickness of dry snow up to about 80 cm deep.


Data from RADARSAT and ERS-2 have shown the usefulness of SAR remote sensing techniques to determine snow area extent and to monitor the physical conditions of snow. Envisat, ALOS and RADARSAT-2 are providing continuity of such snow information.

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Sea Ice Cover, Edge and Thickness
Essential Climate Variables: Sea Ice

Sea ice variability is a key indicator of climate variability and change which is characterised by a number of parameters. Systematic global observation of sea ice extent and concentration, inferred from passive microwave radiometry, has produced a 30 year record. The length and consistency of this record has made it the most often cited data source for sea ice climate research. Sea ice observations from newer instruments have relatively short records, but offer complementary characteristics such as greater accuracy for determining ice concentration and improved resolution.

In addition to monitoring ice extent (the total area covered by ice at any concentration) and concentration (the area covered by ice per unit area of ocean), it is necessary to know ice thickness in order to estimate sea ice volume or mass balance. In the past, only scarce in situ data from boreholes, or upward-looking sonar from moored instruments or submarines, were available for this purpose. Now, satellite borne altimeters are emerging as an important new data source. Early work with radar altimeters demonstrated the utility of altimetry for ice thickness. The Geoscience Laser Altimeter System (GLAS) on board ICESat, launched in 2003, has provided high resolution ice thickness maps. CryoSat-2, due for launch in 2010, has a radar altimeter that will provide precise ice thickness maps.

All-weather, day and night active radar, including the low resolution QuikSCAT scatterometer and high resolution RADARSAT synthetic aperture radar, is sensitive to the unique electromagnetic signature of multiyear ice. This ice has survived a summer’s melt and is generally thicker than younger ice. Active radar and other new sensors played an important part in attributing the surprisingly low Arctic ice extent of September 2007 to various causes. Summer ice extent has had a downwards trend since the 1990s, as determined by the passive microwave record. The active microwave sensors provided data that showed that the Arctic Ocean had lost a considerable amount of multiyear sea ice over the past few years as a result of the prevailing circulation pattern, suggesting that the ice cover was unusually thin as summer began and predisposed to melting back further. Wide area sea ice motion and deformation products from visible band sensors, as well as higher resolution AMSR data, provided corroborating evidence. Finally, investigators using ICESat confirmed that the ice thickness at the beginning of summer was well below its typical average value.

Operational ice services place a higher priority on timeliness and accuracy than on consistency over a long data record, and accordingly use a wide variety of near-real-time remote sensing data to construct ice charts. These charts are used by shipping to avoid damage and delay, and to reduce fuel costs; offshore drilling companies; maritime insurance companies; and government environmental regulatory bodies.

High resolution synthetic aperture radars, such as those on Envisat and RADARSAT, offer the best source of data for operational services. Data from these instruments provide information on the nature, extent and drift of ice cover and are used not only for status reports, but also for ice forecasting and as an input for meteorological and ice drift models. JAXA’s PALSAR radar provides polarimetric data, which will improve the accuracy of sea ice classification. Low resolution scatterometer observations, such as those from ASCAT on MetOp, can also be used to retrieve information on sea ice extent and concentration in all weather conditions, day or night. Looking to the future, continuation of RADARSAT/ Envisat class radar-equipped missions is important in providing complementary high resolution data to further elucidate sea ice processes.


JAXA’s AMSR-E radiometer on Aqua and operational sensors such as the DMSP SSM/I will ensure continuity of the passive microwave global sea ice concentration data source in the near term. The MIS sensor, currently planned for the second NPOESS flight, will be the follow-on sensor for SSM/I. It will offer improved capabilities, including a baseline aperture size of 1.8 m compared to SSMIS’ 0.6 m. The baseline channel selection for MIS includes the SSM/I channel set with minor modifications, with channels at 6 and 10 GHz as well.

In 2006, CEOS defined a series of actions to better meet the GCOS-defined needs for the sea ice Essential Climate Variable:

— CEOS agencies will examine their respective plans to maintain provision of microwave brightness temperatures and visible/infrared radiances for the sea ice ECV;

— CEOS space agencies will consult with the science community on appropriate retrieval algorithms of passive microwave observation for reprocessing sea ice products;

— New space-based measurements and products, including ice thickness and ice drift, will be considered by CEOS agencies as part of their future research missions

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