Credits to European Space Agency (ESA)
http://www.esa.int/SPECIALS/smos/
http://www.esa.int/esa-mmg/mmg.pl?type=V&mission=SMOS

An Earth Explorer
The Soil Moisture and Ocean Salinity (SMOS) mission is ESA’s second Earth Explorer in orbit. It follows on from the Gravity field and steady-state Ocean Circulation Explorer (GOCE), which was launched in March 2009. Known as ESA’s water mission, SMOS makes global observations of soil moisture over land and sea-surface salinity over the oceans to improve our understanding of the water cycle. Data from SMOS is important for weather and climate modelling, water resource management, agriculture and also contribute to the forecasting of hazardous events such as floods.

Mapping soil moisture and ocean salinity
SMOS will provide:
  • Global maps of soil moisture every three days within an accuracy of 4% at a spatial resolution of 50 km – comparable to detecting one teaspoon of water mixed into a handful of soil.
  • Global maps of sea-surface salinity down to 0.1 practical salinity units for a 30-day average over an area of 200×200 km – comparable to detecting 0.1 g of salt in a litre of water.

Improving our understanding of the water cycle
Understanding if, and how, Earth’s water cycle is being modified by climate change is becoming increasingly important, not only for understanding how Earth works, but also for environmental policy and decision-making. A warmer climate is likely to lead to changes in evaporation patterns over the land and oceans, increasing the moisture content of the atmosphere – hence influencing weather patterns. This brings many concerns, especially for water consumption and agricultural needs. By regularly and consistently mapping soil moisture and ocean salinity, ESA’s SMOS mission aims to improve our understanding of the role these two key variables play in regulating the water cycle.
Introducing a novel use of technology
SMOS will have only one instrument: an L-band radiometer named MIRAS. MIRAS is not the first L-band radiometer to be flown in space, but its truly novel approach sets it apart.

MIRAS’s job is to detect moisture in soil and salinity in water. The theory behind being able to do this is based on the contrast between the electromagnetic properties of liquid water and dry soil, and pure water and saline water.
The interferometric measurements will result in images from within a hexagon-like field of view about 1000 km across, enabling total coverage of Earth in under three days.


More about SMOS:
'Tuned' images from Esa's Smos water mission
http://news.bbc.co.uk/2/hi/science/nature/8533265.stm
ESA's SMOS water mission goes live
http://www.physorg.com/news193665344.html