Smos satellite to map Earth's water

The Smos satellite

A new European satellite is to map the water cycles of the planet, charting the amount of moisture held in soils and of the quantity of salts dissolved in the oceans.

Launched today in Cosmodrome in Russia, the Smos spacecraft is amongst the first of a new fleet of satellites designed to study the planet. Smos' mission however, is monitoring Earth's water cycle.

Circle of life

By circling around the planet, the satellite will tell scientists how water is cycling around the planet - from the surface to the atmosphere and back again.

"These two variables have never been measured from space before; that means never measured globally," says Dr Yann Kerr, a lead investigator on the mission from the Center for the Study of the Biosphere from Space (Cesbio), Toulouse, France said to the BBC.

Everyone studied the water cycle in school, how as the Sun heats the ocean, water is evaporated and the vapour rises into the sky becoming clouds. Once the clouds move across the land and it rains, the precipitation will soak the earth eventually flowing back into the sea - evaporation, transpiration, precipitation, the three main stages of the water cycle.

Smos aim is to see these changes and give precise figures to scientists aiming to understand key features of the climate system as well as predict more accurate weather forecasts.

Unique features

But how will it do this? Well unlike most satellites, Smos carries one main instrument, an 8 metre long interferometric radiometer called Miras, that resembles helicopter rotor blades. 69e small antennas are positioned on a central box and along the lengths of three extending arms.

Once in orbit, the arms unfold and whilst the satellite sweeps around the Earth, Smos uses the Y-shaped instrument to map a 1,000km-wide swath.

Critically, the antenna arrays can synthesise images that have detail at a scale down to 50km for soil moisture; and at 200km for ocean salinity.

Speaking to the BBC, Achim Hahne, the Esa Smos project manager said "With our technology, we get a global picture with reasonable spatial resolution within three days everywhere on the Earth."

According to the European Space Agency, another crucial part of Smos' mission is gaining data on soil moisture and ocean salinity - soil moisture plays an important role in the global water cycle, but more accurate data is needed to improve extreme weather forecasting.

The same is true for data on ocean salinity. There are few historical measurement data, and only a small fraction of the ocean is currently sampled on any regular basis. Salinity and temperature determine the density of seawater, and in turn density is an important factor driving the currents in our oceans. Ocean circulation plays a crucial role in moderating the climate by, for example, transporting heat from the Equator to the poles. Ocean salinity is therefore one of the key variables for monitoring and modelling ocean circulation.

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