Water mission returns first data

By Jonathan Amos
Science reporter, BBC News

Smos builds up its map data in strips as it sweeps around the Earth

Europe's latest Earth observation satellite has returned its first data.

Smos was launched earlier this month on a quest to help scientists understand better how water is cycled around the Earth.

The spacecraft will make the first global maps of the amount of moisture held in soils and of the quantity of salts dissolved in the oceans.

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

"Smos is performing like a dream," said Dr Yann Kerr, a lead investigator on the mission from the Centre for the Study of the Biosphere from Space (Cesbio), Toulouse, France.

"Everything went as clockwork and exactly as expected or better up to now. We did not expect to have images so soon," he told BBC News.

The European Space Agency's (Esa) Soil Moisture and Ocean Salinity (Smos) satellite was launched on 2 November.

The mission will run for three years in the first instance

After its initial check-out in orbit, its sole instrument - an interferometric radiometer called Miras - was sent live on Tuesday this week.

The first publicly released image on this page has not been properly calibrated by researchers but they say it proves the instrument is in good shape.

Miras is some eight metres across; it has the look of helicopter rotor blades.

It measures changes in the wetness of the land and in the salinity of seawater by observing variations in the natural microwave emission coming up off the surface of the planet.

It does this through 69 antennas positioned on a central structure and along the lengths of its three arms.

Generally speaking, the "colder" (blue) the "temperature brightness" of the microwave signal, the saltier the water and the wetter the soil; but a lot of processing will be needed before any real values can be attached to the measurements coming down from Smos.

"Moreover, there seem to be radio frequency interferences (RFIs) over China, western Russia and parts of Europe (the reddish stripes)," explained Dr Kerr.

"We will have to tune the reconstruction algorithm before we can reduce or address these."

Scientists were well aware before launch that RFIs might be a problem. Smos is operating in the so-called L-band (21cm) which is supposed to be protected, but pre-flight testing established known interference hotspots, such as airports.

The 315m-euro ($465m; £280m) Smos programme, although led by Esa, has with significant input from French and Spanish interests. The satellite is expected to operate for at least three years.

The amount of water retained in soils varies between about 5% and 50%

This will cover most conditions from 'bone dry' to 'mud bath'

Smos sees the entire range with an accuracy of 4% at the 50km scale

Natural salinity in water covers the range from near zero to 30%

Drinking water might be one extreme; salt lakes would be the other extreme

Smos is seeking sea waters which are typically in the 3-3.5% range

This needs high accuracy (0.01-0.02%). Maps are at the 200km scale

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