Smos satellite unfurls instrument

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The Smos spacecraft launched on Monday to study the Earth's water cycle has passed a key mission milestone.

The European Space Agency (Esa) satellite has successfully unpacked the three-armed antenna it will use to acquire its data.

Smos will investigate the hydrological cycle by measuring changes in soil moisture and ocean salinity.

It will do this by observing variations in the natural microwave emission coming up off the planet's surface.

The data is expected to have wide uses but should improve weather forecasts and warnings of extreme events, such as floods.

The Esa satellite was launched by a Rockot vehicle from the Plesetsk Cosmodrome, Russia, in the early hours of Monday.

It carries a single instrument - an interferometric radiometer called Miras - which at some eight metres across had to be folded to fit inside the Rockot.

Signals from 69 mini-antennas on Miras are combined to image Earth

On Tuesday, French mission controllers gave the command for a series of pyro-bolts securing the arms of Miras to be released. The whole procedure would have taken three minutes.

Engineers say it will take a week to fully prepare the spacecraft to begin its commissioning phase - a six-month period over which the instrument will be set up properly to obtain scientific data.

Smos information will result in a better understanding of the hydrological cycle - the description of how water is constantly exchanged between the Earth's land and ocean surfaces and the atmosphere.

The satellite is expected to help improve short and medium-term weather forecasts, and also have practical applications in areas such as agriculture and water resource management.

In addition, climate models should benefit from having a more precise picture of the scale and speed of movement of water in the different components of the hydrological cycle.

The satellite is part of Esa's Earth Explorer programme - eight spacecraft that will acquire data on issues of pressing environmental concern.

The Smos programme cost is about 315m euros ($465m; £280m). It is led by Esa but with significant input from French and Spanish interests. The satellite is expected to operate for at least three years.

Jonathan Amos takes a look around the Smos satellite

<a href="mailto:Jonathan.Amos-INTERNET@bbc.co.uk" ><i>Jonathan.Amos-INTERNET@bbc.co.uk</i></a>