Fresh water, source of life on Earth and essential to human activities, is present in finite quantity on our planet (only 0.007% of all the planet water is accessible for the human consumption through rivers, streams, reservoirs and lakes) (Source: "World fresh water resources" de Igor Shiklomanov, 1993). The increase of the world population and the development of human activities definitely lead to an increasing imbalance between supply and demand. It is thus essential to find and to set up new tools for a better mean to preserve and exploit the Earth's water ressources.

Up to now, satellite missions enabled major progresses in climate domain and so far France succeeded to occupy a choice place in the study of water space data and more particularly in oceanography.

The scientific community estimates that space hydrology is 25 years late compared to space oceanography while the fresh water stakes is more than ever a priority.

The nowadays space resolution and network limitations of nadir altimetry (nadir altimetry gives punctual data along profiles spaces by several tens/hundreds of km) prevent the study of small scale structures in oceanography, and forbid the monitoring of most of the continental water bodies. It is thus necessary to develop new instruments able to overcome these limitations. It is the challenge of SWOT mission and of the new concept of its sensor, the KaRIN instrument (Ka-band Radar INterferometer).

Ground track of the two kinds of altimeters

SWOT mission objective is to measure water heights (and their space-time variations) of rivers, lakes and flooded zones as well as oceans. The interferometric altimetry will enable to give a bi-dimentional image with an horizontal resolution of about 50-100 m. This technique also enables to overcome the conventional altimetry issues, meaning the interference reflections problems due to dry grounds, the vegetation and the relief.

KaRIN includes two SAR antenna in Ka band at the end of 10 meters boom providing a ground track of 120 km large. With its large swath, SWOT satellite will cover all the lakes, rivers, reservoirs and oceans of the Earth, at least twice every 21 days.

SWOT functioning

SWOT mission constitutes a major design break in space altimetry. SWOT mission brings determining scientific and technological innovations.

In oceanography: SWOT main contribution consists in characterizing with accuracy meso- and sub-meso scale circulations which have a major role in the energy transport in oceans. SWOT also gives access to coastal circulation effects on marine life, ecosystems, water quality, transports and will enable a better modelling of ocean/atmosphere coupling.






In hydrology: For continental surfaces, this mission wil enable on one hand to measure at large scale changes in water storage of the main humid areas, lakes and reservoirs (one estimates at more than 30 millions of lakes in the world with a surface of larger than 1 hectare), and on the other hand, will enable to evalute with more accuracy the flow of the main rivers. These hydrological observations are extremely important to perfect our knowledge of the global dynamics of continental waters and their interaction with the coastal part of the oceans at the estuaries. This new capability will enable to monitor the evolution of fresh water supply in the climate change context, notably in the regions where few observations exist.

Distribution of lakes in the world (Downing, 2006)

The CNES funds the required studies in the framework of the TOSCA programme. The main French laboratories involved are the CNRM, the LEGOS, the IFREMER, the LMD, the LOCEAN as well as CLS company.

For more information, please visits the JPL website dedicated to SWOT