Measuring the salinity of the oceans on a large scale is something oceanographers have sought to do for decades. This is because salinity – and variations in salinity – is a good indicator of conditions in the intercontinental ocean currents, which among other things control climate on Earth.
Monitoring of global water circulation
The outflow of water from rivers affects ocean salinity, and by combining our knowledge of salinity with knowledge of soil moisture and thus stored water resources, we are able to monitor global water circulation far more accurately than ever before. Not only can information about global water circulation help improve meteorological methods and local populations in the many parts of the world where water is scarce, it can also contribute new information about climate change. Global, regularly updated maps charting salinity and soil moisture thus provide key information for numerous fields of research.
Up until the mid-1990s a satellite project for measuring ocean salinity and soil moisture was unfeasible due to a lack of technological expertise, but with the development of a whole new type of ‘radiometers’, it became possible to build a suitable satellite.
Quite simply, a radiometer is a highly sensitive radio receiver that can register and distinguish the extremely minute amounts of electromagnetic energy that all forms of matter with a temperature above absolute zero emit when their molecules interact with each other. Studies show that different matter emits different amounts of energy, and by modifying the receiver, it is possible to optimise its sensitivity to precisely soil moisture and salinity.
The SMOS satellite (Soil Moisture & Ocean Salinity) represents the culmination of fifteen years of hard work, and DTU Space has been involved in developing the satellite from the very outset.
SMOS: Measuring Soil Moisture & Ocean Salinity. Photo: ESA.
In addition to measuring the desired Earth parameters, the satellite carries experimental technology for combined technological and scientific research, and in recent years DTU Space has played a pivotal role in both these areas. Most recently we have been closely involved in extensive experiments to verify and refine the models that link satellite measurements to physical conditions on Earth. Presently, these experiments are expanded to include actual calibration of the satellite and its measurements.
Using an instrument that simulates measurements from space, DTU Space has completed missions in such different places as Norway, Finland, France, Spain and Australia.