Volcanic ash pushes case for new satellite sensors

By Jonathan Amos
Science correspondent, BBC News, Vienna

Some of the best instruments do not have a constant eye on Europe

Iceland's ongoing eruption is likely to press the case for new satellite instruments to monitor volcanic ash thrown into the atmosphere.

More flights were grounded this week because of ash from Eyjafjallajokull.

Remote sensing expert Dr Fred Prata told a major Earth sciences meeting in Vienna that current monitoring from space was good but could be improved.

"Of the present suite of satellite instruments, none were developed for the volcanic ash problem," he said.

"Therefore, they are sub-optimal for detecting and determining quantities of volcanic ash."

Dr Prata has been speaking here at the European Geosciences Union (EGU) conference in the Austrian capital.

He is a senior scientist with the Norwegian Institute for Air Research, and leads a group called Savaa - Support to Aviation for Volcanic Ash Avoidance.

Seviri tracks the progression of the ash plume (predominantly orange)

This team is supported by the European Space Agency and aims to improve the way that satellite data is collected for use in the dispersion models that help airlines and the authorities decide whether it is safe to fly planes.

Dr Prata said several space instruments currently in operation had been critical to the present monitoring efforts.

He cited the Seviri instrument on Europe's Meteosat 8 and 9 spacecraft which sit in a geostationary orbit, returning images of the Earth every 15 minutes. Seviri has helped distinguish the volcanic ash from other clouds, determining its extent - mass loading - in two dimensions.

The lidar on the US Calipso spacecraft had brought a unique and extremely valuable capability, he explained.

"Because it's an active instrument that fires pulses of light down to the Earth and gets the backscatter radiation, it gives us height-resolved information. You can see the top of the cloud and its bottom, so that means you get the thickness.

"Once we get the thickness, combining that with our two-dimensional picture of the mass loading we can get the concentration; and that's the number that the airlines would like to have."

The airlines at this time are working to a safe limit of two milligrams of ash per cubic metre of air.

A version of Iasi will go on Europe's next-generation Meteosats

The third instrument noted by Dr Prata is Iasi, an infrared sounding interferometer on Europe's polar orbiting Metop platform which he said was sending back exceptional data on the presence of ash, sulphur dioxide (SO2), ice, and even the conversion of SO2 to sulphuric acid.

The downside of Metop and Calipso is that they circle the Earth and do not have permanent vision over Iceland and the rest of Europe. A version of Iasi is due to go on the next generation of Meteosats but the first of these platforms will not fly until 2018.

Dr Prata said there was a case now for fast-tracking the launch of this instrument.

"Everyone's looking at what the best solutions might be. Nobody wants to spend lots of money so fast-tracking an existing programme would be a good solution," he told BBC News.

"Another possibility is to have a scanning lidar in space. Calypso looks straight down. If it's scanning, you'd get a lot more information."

Calipso's lidar can determine the thickness of the ash plume

EGU has also heard some of the latest science being done by volcanologists and seismologists at Eyjafjallajokull.

Dr Thor Thordarson from Edinburgh University, UK, is working with a team that is now collecting large numbers of samples of the ash fall, both in Iceland and beyond.

The group is trying to explain why precisely the volcano ejected so much fine material in the sizes that could be transported great distances.

This far-flung dust ranged in size from about 30-40 microns (millionths of a metre) down to even the sub-micron scale.

Dr Thordarson said it was clear that melt waters getting into the vent from the glacier on the volcano had contributed to the explosive fragmentation of rock, but what exactly happened remained a mystery.

"Why this event disintegrated the magma so intensely, we don't know; and it's something we desperately want to find out," he told BBC News.

"If we get enough observations from a good number of sites then we can reconstruct the total grain-size distribution that was coming out of the vent. And when you have that information, then you can start looking at models to explain the fragmentation processes involved and why they were so intense."

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