Page last updated at 11:27 GMT, Wednesday, 5 May 2010 12:27 UK

Europe's Smos 'water mission' battles interference

By Jonathan Amos
Science correspondent, BBC News, Vienna

Australia (CESBIO)
The bright feature in central Australia is soil soaked by rain

Europe's Smos spacecraft is returning valuable new data on the way water is cycled around the globe, despite experiencing continued interference.

The satellite was launched in November to track changes in the wetness of soils and the saltiness of the oceans using a three-armed microwave antenna.

Its detailed maps will soon begin flowing to the scientific community.

But in some parts of the world, Smos is still being blinded by radar networks, and even TV and radio links.

The radio frequency interference (RFI) is a frustration for the mission team. The part of the electromagnetic spectrum in which Smos sees the planet is supposed to be reserved for Earth observation.

Southern Europe, the Middle East and the Asian continent are particular problem zones.

"In Africa, for example, there are a couple of sources - one in Khartoum, one in South Africa," explained Dr Yann Kerr, one of the Smos principal investigators.

"They are damaging the signal over much larger areas, affecting a good part of Africa. And this is one of the areas of the world where information on soil moisture for better water resources management is crucial. So it's really a hindrance," the CESBIO, France, researcher told BBC News.

The European Space Agency satellite will complete its commissioning phase in the next month, and the first results from early observations were presented here at the European Geosciences Union meeting.

Smos carries a single instrument - an interferometric radiometer called Miras.

Some eight metres across, it has the look of helicopter rotor blades.

Miras measures changes in soil moisture and ocean salinity by observing variations in the natural microwave emission (L-band) coming up off the surface of the planet.

Tracking such trends will have wide applications, but should improve weather forecasts and warnings of extreme events, such as floods.

Before and after Spanish switch-off (CESBIO)
Reds indicate bad RFI sources. Spain was blighted by major interference from a radio link (top). Matters improved substantially when it was shut down (bottom)

The early data suggests Miras is performing exceptionally well, picking out subtle features that will be of huge value to hydrologists, meteorologists, oceanographers, and many others.

Smos watched recently as large areas of eastern Australia were soaked by rainwater and then tracked how the soli dried out over the following days. And in arid areas of the continent, too, the spacecraft has demonstrated its capability.

"In several instances, we had phenomena that we identified but which seemed highly improbable," said Dr Kerr.

"We saw banana-shaped features in the data and we wondered if it was a problem with the instrument or RFI. But then we looked with rain radars and saw exactly the same pattern, so it was obviously a rain event."

In addition, Smos is returning some fascinating information on the polar regions. Scientists can discern in the satellite data where ice thins at the rocky edges of Antarctica. They can even see melt-water sitting on top of sea-ice.

Such observations will be very useful to researchers studying changes in the cryosphere.

Antarctica (CESBIO)
Ponding of meltwater on top of sea-ice is marked in yellow (top ring). Thin ice on rock is seen in yellow in coastal locations (ring bottom-right)

Steady progress is being made in dealing with the man-made sources of emission that bleed across Miras's operational frequencies (1400-1427MHz).

The European Space Agency is working with authorities such as the International Telecommunications Union to try to identify and shut off offending emitters.

Smos (Smos/Mira)
The Smos mission is led by the European Space Agency

The Smos science team is also learning how to tune its algorithms to filter out some of the RFI.

There is considerable support coming from the US, too. The Americans are expected to launch two L-band missions of their own this decade: Smap, to measure soil moisture; and Aquarius, to monitor ocean salinity (a joint undertaking with the Argentine space agency, CONAE).

"In some ways it's a pity for Smos that we are the first L-band mission in space, because we will basically look at all these things as the first people," commented Dr Susanne Mecklenburg, the Smos mission manager.

"But of course there will be two more missions in L-band operating, and there will be more re-enforcement of the rules following this. Also, I think the Chinese are presently planning an instrument in that spectral band, so that might help us in switching off sources over Asia which is largely contaminated by RFI."

L-band explainer (BBC)
Both moisture and salinity strongly affect the electrical properties of matter
All matter emits energy in the form of electromagnetic radiation
The Smos signal is detected in the microwave portion of the spectrum
Long wavelength reception generally requires large antenna set-ups

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