Professor Meric Srokosz of the National Oceanography Centre, Southampton, a co-investigator on the mission, has been involved in the project since its inception, having proposed the mission with colleagues in France and Spain back in 1998. He said: "Eleven years has been a long wait. Obviously, I am excited and absolutely delighted that the launch has gone to plan. I am now looking forward to using data from the satellite in my research."

SMOS is the first-ever satellite to attempt to measure ocean salinity from space. It will provide global maps of soil moisture over land and surface salinity over the ocean. SMOS is part of ESA's Living Planet Programme, aimed at improving our understanding of the Earth system and the impacts of human activity. A second salinity satellite, the US/Argentinian mission Aquarius, is expected for launch in Fall 2010. Salinity data from SMOS and Aquarius will help to determine the role of the ocean in the global water cycle, and help forecast weather and floods, better manage water resources, and understand long-term climate change.

Scientists at the National Oceanography Centre, Southampton are leading the UK contribution to a large international effort coordinated by ESA to help calibrate and validate SMOS salinity data. Srokosz and his colleague Dr Christine Gommenginger, Principal Investigator on the SMOS Cal/Val project for ESA and on a Natural Environment Research Council (NERC)-funded project to validate SMOS salinity data, are interested in the links between surface salinity, rain, ocean circulation and climate. Ocean circulation depends to a large degree on the density structure of the oceans, which, in turn, is controlled by temperature and salinity, both of which can be measured from ships and buoys. However, only satellites can provide the global synoptic picture needed to understand what is going on.

Sea surface temperature has been measured from space since the 1970s using infrared and more recently microwave techniques, but measuring salinity from space is a much tougher problem.

SMOS measures the ocean's natural emission at a microwave frequency (L-band) corresponding to a wavelength around 23 cm, which is sensitive to the salinity of the surface water. Measuring the amount of energy being emitted at a particular microwave frequency allows inferences to be made about the salinity.

The problem is that at the frequency used, a very large antenna, 5-10m in size, is needed to make a measurement at a sensible scale in the ocean -- say 30-50 kilometres -- which is difficult to fit in a standard rocket launcher.

To get round the problem, mission engineers borrowed a clever idea from radio-astronomers -- 'synthetic aperture synthesis' -- who routinely link radio-telescopes located in different places to 'pretend' that they have a much larger antenna than they actually have. To make an antenna practical enough to launch into space, the SMOS engineers built the MIRAS instrument. MIRAS has three foldable arms, each 3 meters long once deployed, carrying a total of 69 small antennas. Once in space, the arms open up to form a Y-shape -- which provides measurements as if it was simply one large antenna.

Satellite salinity data provided by SMOS should allow scientists such as Gommenginger and Srokosz to learn more about ocean currents and circulation and their role in the climate system.

"Possible changes in the ocean circulation are important for our future on the planet and it is still very unclear how changes in surface salinity and the global water cycle relate to ocean circulation and climate," says Gommenginger: "The oceans are interacting with the atmosphere, transporting and exchanging heat and freshwater. Such interactions are important and will affect and be affected by global warming."

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