The melting of glaciers in all the mountainous areas of the world, the retreat of sea ice around the North Pole in summer and the loss in mass of polar ice caps are major and well-known phenomena which directly and sometimes spectacularly illustrate global climate change.
These phenomena have very real and potentially negative consequences that will have a major impact on societies and the environment in the long term:
- The rise in seal level represents a major challenge for populations in coastal regions. Its progressive effects, difficult to reverse, imply immediate investment in new coastal infrastructures and, in the longer term, a shift in population location.
- Global warming will open up possibilities for exploiting natural resources (through mining and oil explorations) found in the rich subsoil of upper northern latitudes.
- The shrinking of the Arctic sea ice in summer opens up two new shipping lanes of tremendous economic interest (the North-West and North-East passages) but this also implies social and environmental changes in the regions crossed.
More locally and in the short term, variations in snowfall at ski resorts, the danger to infrastructures such as buildings or roads due to thawing permafrost or the rapid retreat of glaciers supplying mega-cities are major direct challenges for populations. Independent of the major environmental changes, avalanches, the viability of roads in winter and the state of water resources in mountainous areas have long been of concern to both public authorities and citizens.
The study of all the components of the cryosphere (land, sea and atmosphere) throughout the world (at the poles or in mountainous regions) must therefore rise to these numerous scientific and societal challenges.
The future of mountain glaciers, small or major ice caps and their impact on sea level is the focus of much research into the terrestrial cryosphere. The more or less immediate objective of this research is to establish the mass balance of the 200,000 odd glaciers spread over the globe and the two major ice caps (Antarctica and Greenland). To do so, it is necessary to establish the mass balance year after year. Satellite remote sensing instruments play a vital role in these generally inaccessible regions. The data from altimetry missions such as laser ICESat, ESA radar missions and, more recently, AltiKa; from the GRACE gravity measurement mission (since 2002), interferometry missions such as ERS, ENVISAT and ALOS; or photogrammetry missions such as SPOT 5-HRS have helped flesh out our knowledge on these ice mass balances.
A second major objective is to elucidate the processes that explain variations in mass, whether due to the surface component (precipitation, thawing, sublimation or advection of snow by wind) or the dynamic part (calving of icebergs) because this is a prerequisite to numerical modelling and the estimation of future ice mass balances. This requires the use of satellite observations of variables involved in the surface energy budget such as the albedo (MODIS, MERIS and SPOT), surface temperature (MODIS) or surface thaws (AMSR-E and Sentinel-1a). One of the more difficult barriers to overcome is detecting solid precipitations. More generally, a better understanding of snow and weather processes would enable us to improve the characterisation of cryosphere/climate feedback, especially positive feedback linked to the snow’s albedo, mostly responsible for the cryosphere’s increased response to global warming. Satellite observations of the albedo, meteorological variables and atmospheric aerosols would advance knowledge in this domain, which contributes directly to the issues being investigated by the Intergovernmental Panel on Climate Change (IPCC).
Finally, the seasonal snow cover is another key focus of research, whether for hydrological or meteorological applications; to study the subsoil, vegetation, or climate; or to forecast the risk of avalanches, flooding or water resources in mountainous regions. Whatever the regions concerned–from vast boreal expanses to mountain valleys–it is vital to determine the thickness and mass of snow cover. Currently, spaceborne remote sensing instruments shed little light on this subject because limited to mapping snow-covered surfaces using wide-swath optical sensors (MSG-SEVIRI, AVHRR and VGT), high-resolution sensors (SPOT, LANDSAT, ASTER, Pleiades and Sentinel-2A), or passive microwaves on a continental scale (AMSR-E, SSM/I). In addition, ongoing work aims to better model changes in snow cover over time and could be a useful complement for indirectly estimating snow thickness. This work is based on observations of the snow cover’s internal properties (water content, density, grain characteristics, presence of ice etc.) in the field and from space using active radars (Radarsat-2, TerraSAR-X) or passive microwave radiometers.
Beyond the continental cryosphere, studies of sea ice come across the same research issues, such as the snow cover’s role in radiation.
Whatever object in the cryosphere is studied, progress still needs to be made in methodologies. Data assimilation, i.e. the optimal combination of satellite observations, rare but valuable in situ observations and descriptive models of the cryosphere appear to be the ultimate approach, benefitting from the best of each individual approach. In the short term, this involves efforts to develop physical measurement models (such as a radiative transfer model) that link the characteristics of the environment with satellite observations. Such fundamental knowledge of interactions between electromagnetic waves and the environment often also sheds light on the way the environment being studied functions.
- SPIRIT project (SPOT 5 stereoscopic survey of Polar Ice: Reference Images and Topographies). This project aims to map polar ice using images and digital terrain models derived from SPOT 5’s HRS sensor. The acquisitions concentrate on the edges of the Antarctic and Greenland ice caps along with high-latitude glaciers. Since the International Polar Year (IPY 2007-2009), when data were distributed free of charge, over 80 publications have exploited SPIRIT data to date (2014). Another SPOT 5 image acquisition campaign was conducted after November 2013.
For more information, see http://www.legos.obs-mip.fr/recherches/projets-en-cours/spirit
Download products on http://theia.cnes.fr
- SPAMN project (SPot pour le suivi Alpin du Manteau Neigeux – SPOT to monitor snow cover in the Alps): seasonal snow cover dynamics in the French pre-Alps and Alps, vegetation phenology and hazards. This project involves several laboratoires based in Grenoble to assess and use SPOT 4 TakeFive data (download from http://spirit.cnes.fr/take5) on Alpine snow cover and plant ecology. SPOT 4 reflectance data were first compared with in situ measurements above the snow cover so as to assess their accuracy. They were also used to quantify the variability in snow cover within medium-resolution MODIS pixels. Then both SPOT 4 and Landsat 8 reflectance measurements were used to draw up snowpack maps for the whole mountain range (surface area and coverage fraction) in order to validate a snow clearance model. Finally, a comparative study was carried out with medium-resolution MODIS and SPOT-VEGETATION data. The results can be consulted at ttp://www.cesbio.ups-tlse.fr/multitemp/?p=4255. This project was prolonged within the framework of the SPOT 5 Take5 programme (April-August 2015) with the support of TOSCA-CNES/ESA.
- Détermination de l’albédo des surfaces enneigées par télédétection, application à la reconstruction du bilan de masse du glacier de Saint-Sorlin
LGGE – Laboratoire de glaciologie et géophysique de l’environnement
Université de Grenoble (15/12/2010), Gerhard Krinner ; Marc Bocquet (Dir.)
- Evolution récente des glaciers du Pamir-Karakoram-Himalaya : apport de l’imagerie satellite
LGGE – Laboratoire de glaciologie et géophysique de l’environnement
Université de Grenoble (19/12/2012), Paolo Laj ; Yves Arnaud (Dir.)