December 17, 2010

European Scientists Plan To Map Ocean’s Magnetism

European scientists are planning to measure the movement of the oceans just by tracing their magnetism.

The effort will be achieved using three super-sensitive spacecraft known as SWARM, which will be launched in 2012.

The magnetic signal of the tides has been seen before, but the new mission would aim to observe far more detail.

The new system should provide additional data on how the oceans transfer heat around the Earth, a key feature of the climate.

"When salty ocean water flows through the magnetic field of the Earth, an electric field is generated and this electric field again makes a magnetic field," explained Dr Hermann Lhr, from the German Research Centre for Geosciences (GFZ) and a leading investigator on SWARM.

"We hope to have the possibility to measure the ocean currents which are so important for climate dynamics, because oceans are transporting a lot of heat. The German Champ mission was the first to see at least the tidal signal, but with SWARM we want to be able to monitor the currents themselves."

The new mission is one of the several innovative European Space Agency (ESA) endeavors that are being talked about at the American Geophysical Union (AGU) Fall Meeting this week. 

A big part of Earth's global magnetic field is generated by convection of molten iron within the planet's outer liquid core.  However, there are other components that contribute to the overall signal, including the magnetism retained in rocks.

Dr. Mark Drinkwater from ESA's Earth observation division said that SWARM's goal is to investigate all the components, but pulling out the small part produced by ocean movement will probably be its biggest challenge.

"We're talking about tens of thousands of nanoteslas for the total field measured at satellite level, of which one part in 50,000 approximately is contributed by ocean circulation," he told BBC News.

"So it's a akin to finding a needle in a haystack, but the modeling which has shown the retrievability of this element of the magnetic field has demonstrated that it might be possible with [our satellite system]."

The satellites have to be built with extreme care because the magnetism generated by the spacecraft's own workings has to be minimized as much as possible. 

The satellite, which is currently under construction with manufacturer EADS Astrium, looks like giant mechanical rats with long tails.

The tails are booms designed to hold SWARM's sensitive magnetometer instruments away from the "noise" that would come from the electronics inside the main body of the spacecraft.

"You can't go near the spacecraft with a standard spanner or screwdriver - all the tools you would normally use on a spacecraft build. You have to de-gauss them," said platform project manager Andy Jones.

"You have to test them and make sure they're magnetically clean so they'll leave no trace, because if you touch a bolt with a magnetized spanner you will leave a field behind on that bolt."

Researchers currently use an array of methods to track the currents, including altimetry.

"All these different forms of measurement give you a different answer," Lhr told BBC.

"If you consider altimetry, this relies on seeing how the surface of the water is deformed by the current. But this can also be deformed by other effects like warming up, or having less salt in the water."

"However, if you look into the magnetic field this is just the integral motion from top to bottom of the water, and it will give you a really independent answer about the net transport of that water."

The SWARM satellites will launch on a single rocket into a polar orbit about 186 to 311 miles above the Earth.

Two of the satellites will circle the planet in tandem while the plane of the third spacecraft will be offset and gradually diverge over the course of the mission.

Scientists say they still have a lot to understand about the Earth's magnetism.


Image 2: Artist's impression of Swarm constellation. Credits: EADS-Astrium


On the Net: