Mapping Soil Moisture and Ocean Salinity to improve understanding of the Earth’s water cycle – By Mark Drinkwater, Head, Mission Science Division (European Space Agency)
The European Space Agency’s Earth Explorer series of research-driven satellite missions continues with the upcoming 2nd November launch of the Soil Moisture and Ocean Salinity (SMOS) mission. Known as ESA’s Water Mission, SMOS is the first satellite dedicated to providing global measurements of soil moisture and ocean salinity. The mission’s new technologies will extend key European capabilities in Earth Observation and help advance research towards improving our understanding of the global water cycle.
The amount of water in the soil and the salinity of the oceans may not seem connected, but, in fact, they are both key variables closely linked to the water cycle. Variations in soil moisture and ocean salinity are a consequence of the continuous exchange of water between the oceans, the atmosphere and the land – Earth’s water cycle – which not only sustains life on Earth but also plays an important role in weather and climate.
Data from SMOS will help to address the current lack of global and continuous observations of soil moisture and ocean salinity. This will help understand more about how a changing climate may be affecting patterns of evaporation over the land and oceans. Data from SMOS will help improve weather and climate models, and will have practical applications in areas such as agriculture and water resource management.
SMOS will provide global information on surface soil moisture every three days to within an accuracy of 4% by volume at a spatial resolution of 50 km. This required accuracy is comparable to being able to detect one teaspoonful of water mixed into a handful of soil. SMOS will observe ocean salinity down to 0.1 practical salinity units for a 30-day average over an area of 200km x 200 km, which is comparable to detecting 0.1 g of salt in a litre of water.
Designed and built by a European consortium of industry and science, SMOS demonstrates what European cooperation can achieve. SMOS embodies European excellence in engineering and science by adopting a completely unique approach for observing Earth from space. SMOS will carry a fundamentally new instrument called the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS). MIRAS is the first-ever spaceborne, 2D interferometric passive microwave radiometer operating at a frequency of 1.4 GHz (L-band, wavelength ~21 cm). The antenna aperture is synthesised from 69 separate receiving antenna elements, which are equally distributed over three deployable arms (which form a Y-shape) and the central structure. MIRAS will make uninterrupted, day and night, all weather global observations of emitted microwave radiation, and will revisit each point on the Earth’s surface at least once every three days.
SMOS is scheduled for a dual launch on 2 November 2009 on a Rockot launch vehicle from Plesetsk Cosmodrome in northern Russia – together with ESA’s Proba-2 satellite. SMOS will be launched into a sun-synchronous, 23-day repeat cycle, with a 3-day sub-cycle. The nominal mission lifetime is three years (including a six-month commissioning phase) with a possible two-year extension. (Learn more about SMOS in a one-minute video.)
SMOS is an ESA Earth Explorer mission with national contributions provided by the French and Spanish space agencies, CNES and CDTI. For the operations phase, ESA will be responsible for the overall coordination of the mission and the ground segment operations, whereas CNES will operate the spacecraft. The design and construction of SMOS involved more than 20 European companies and was led by Thales Alenia Space Industries (France) for the satellite, EADS CASA Espacio (Spain) for the payload, and INDRA (Spain) for the Data Processing Ground Segment.