SMOS scientific objectives
The principal objective of the SMOS mission is to provide maps of soil moisture and ocean salinity of specified accuracy, sensitivity, spatial resolution, spatial coverage and temporal coverage. In addition, the mission is expected to provide useful data for cryosphere studies.
A novel instrument has been especially developed to make these observations and the objective is also therefore to demonstrate the use of a new radiometer that is capable of observing both soil moisture and ocean salinity by capturing images of emitted microwave radiation around the frequency of 1.4 GHz (L-band). SMOS will carry the first-ever, polar-orbiting, space-borne, 2-D interferometric radiometer.
In summary, the SMOS science objectives are to:
- globally monitor surface soil moisture over land surfaces,
- globally monitor surface salinity over the oceans, and
- improve the characterisation of ice and snow covered surfaces.
In order to:
- advance climatological, oceanographic, meteorological, hydrological, agronomical, and glaciological science, and
- assess the potential of such measurements to contribute to improving the management of water resources.
Measurement goals
For soil moisture:
Moisture is a measure of the amount of water within a given volume of material and is usually expressed as a percentage. From space, the SMOS instrument can measure as little as 4% moisture in soil on the surface of the Earch - which is about the same as being able to detect less than one teaspoonful of water mixed into a handful of dry soil.
- accuracy of 4% volumetric soil moisture
- spatial resolution 35-50 km
- revisit time 1-3 days
For ocean salinity:
Salinity describes the concentration of dissolved salts in water. It measures in practical salinity units (psu), which expresses a conductivity ratio. The average salinity of the oceans is 35 psu, which is equivalent to 35 grams of salt in 1 litre of water. SMOS aims to observe salinty down to 0.1 psu (averaged over 10-30 days and an area of 200 km x 200 km) - which is about the same as detecting 0.1 gram of salt in a litre of water.
- accuracy of 0.5-1.5 practical salinity units (psu) for a single observation
- accuracy of 0.1 psu for a 10-30 day average for an open ocean area of 200 km x 200 km
Last update: 2 November 2009
SMOS: ESA's water mission 
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