Keeping an Eye on Volcanic Ash

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Meteosat-9 observes the ash cloud from the volcanic eruption under Eyjafjallajoekull Glacier in Iceland. Initially the cloud shows a distinctive black colour, due to ice particles which mask the ash signature. As the cloud progresses eastwards the cloud takes a reddish hue, clearly indicating the presence of volcanic ash.

Meteosat-9 observes the ash cloud from the volcanic eruption under Eyjafjallajoekull Glacier in Iceland. Initially the cloud shows a distinctive black colour, due to ice particles which mask the ash signature. As the cloud progresses eastwards the cloud takes a reddish hue, clearly indicating the presence of volcanic ash.

The recent ash clouds from Iceland’s EyjafjÌ_lla volcano grounded hundreds of flights across Europe causing travel chaos and costing the European airline industry billions of Euros. The volcanic ash, which caused such turmoil in European airspace, was monitored using both satellite and ground based technologies. To take stock of what has been learned about ash cloud detection, monitoring and prediction, and identify future opportunities, ESA and EUMETSAT recently organised a workshop in Frascati, Italy (May 2010) for more than 50 experts from around the world.

‰ÛÏI think the workshop assembled the best expertise there is on ash-cloud monitoring and modelling. It was a very impressive meeting because it really gave all of us the latest knowledge and capabilities that exist around the world,‰Û said Jean-Paul Malingreau, Head of Unit Work Programme and Strategy of the Joint Research Centre of the European Commission.

The participants of the workshop comprised a wide range of experts including ground-based and remote sensing specialists and modellers as well as representatives from the Volcanic Ash Advisory Centres.

Key Role of Satellite Observations

Fred Prata, Senior Scientist for Atmosphere and Climate Change at the Norwegian Institute for Air Research, said: ‰ÛÏSatellite data are extremely important for volcanic eruptions because these events can occur anywhere at any time, so you need a measurement system that can see the entire globe, all of the time.‰Û

‰ÛÏWe currently have geostationary and polar-orbiting satellites in orbit that provide information every 15 minutes and almost every hour, respectively. One of the missing parts of the story, however, is the vertical resolution. Lidars – like radar except it uses light instead of microwaves – in space can provide this, and ESA will launch two Lidar missions in the future, including ADM-Aeolus.

The crucial role of infrared instruments was emphasised in several talks for future volcanic-ash monitoring.

‰ÛÏInfrared instruments are absolutely vital for a couple of reasons. Firstly, infrared does not require sunlight so we can see volcanic emissions equally well day or night. Secondly, and perhaps most importantly, the infrared radiation that we use is in a band between eight and twelve micrometers, and it turns out that the particles that cause problems for aviation are micron size so they look in just the right wavelength region,‰Û Prata said.

Meteosat Third Generation

The importance of continued observations from geostationary orbit, as well as the use of observations from infrared and ultraviolet/visible sounding instruments, was emphasised in several presentations. EUMETSAT’s Meteosat Third Generation (MTG) satellites, to be developed by ESA, will carry infrared sensors.

They will therefore be essential for monitoring volcanic ash in the future. In addition to improved imagery at 10-minute repeat cycles, the provision of data from the MTG infrared and ultraviolet/visible sounding missions will be crucial for the derivation of quantitative products for volcanic ash modelling.

Specially modified MSG Ash product image showing the volcanic ash plume from the recent Eyjafjallajokull eruption circulating in the Atlantic

Specially modified MSG Ash product image showing the volcanic ash plume from the recent Eyjafjallajokull eruption circulating in the Atlantic

Combining Satellite with Ground-Based Data

The presentations on ground-based observations and modelling showed very good consistency, also with satellite observations, and it was well recognised that for the best results all data and information needs to be combined.

‰ÛÏThere has been an unprecedented amount of ground-truth data collected by the European community on this ash cloud, and this is a great opportunity to learn more about the processes,‰Û said David Schneider, Research Geophysicist at the US Geological Survey, Alaska Volcano Observatory. ‰ÛÏGround and aircraft measurements can also be used to compare to satellite data to help you understand whether what you are gathering is accurate.‰Û

Evolving Requirements for Ash Monitoring

Philippe Husson, Aviation Weather Forecast Deputy and the Toulouse VAAC Manager for Meteo France, explained that requirements on observations of the volcanic ash evolved during the eruption to include numbers and expressed how this will impact his job and his needs from satellite missions.

‰ÛÏIn the past, we used qualitative results to depict hazards, but now that we have been provided with figures on the threshold we will probably be required to provide concentration maps with absolute numbers to aviation users. As we must go from qualitative to quantitative information about ash concentrations and the distribution and size of particles, we need satellites to provide numbers,‰Û he said.

Testing Ash in Engines?

Husson explained that the threshold figures are not definitive and are now being reassessed by aviation authorities as the decision was made very quickly during the crisis. Several factors will have to be taken into consideration, such as the results of trials with real ash in real engines, the types of engine used and the rate of ingestion, as flying 10 minutes in high concentration could be equivalent to flying six hours in weak concentrations.

‰ÛÏAs the decision was taken quickly, there was not a lot of input from scientists, but now there is time to go to scientists and ask them what confidence we can have in these numbers,‰Û he added.

Image captured by AVHRR instrument on EUMETSAT's Metop-A polar-orbiting satellite shows the extent of the volcanic ash cloud coming from the volcano. Image was captured at 10:13 UTC 6 May 2010

Image captured by AVHRR instrument on EUMETSAT's Metop-A polar-orbiting satellite shows the extent of the volcanic ash cloud coming from the volcano. Image was captured at 10:13 UTC 6 May 2010

Schneider, who works during eruption crisis episodes in Alaska to provide information about the location of ash clouds and to help set up warnings for the North Pacific, emphasised the fact that the satellite sensors monitoring ash clouds were not designed for this purpose but rather for meteorological, climate or pollution studies.

‰ÛÏThese sensors work great, but maybe this eruption will help push the notion that there are no remote volcanoes. Just because you can’t see it, doesn’t mean the effects are out of reach,‰Û Schneider said.

Future Satellite Missions Monitor Ash in Combination

The capabilities of future satellite missions already planned now, like the Global Monitoring for Environment and Security (GMES) Sentinel-3, -4 and -5 and ESA Earth Explorer Lidar missions, like ADM-Aeolus and Earthcare, were highlighted.

The crucial role of MTG as a provider of space-based observations in the future for volcanic ash monitoring was emphasised in several talks. The improved capabilities of the imagery mission will provide further details on the extent of the ash plume, whereas the capabilities of the MTG sounding mission will be essential for the derivation of quantitative products with additional information on the composition and density of the ash cloud.

The EC’s Malingreau said: ‰ÛÏWe need to assess whether the instruments available now and in the near future are sufficient, so there will be some recommendations maybe for adjusting some of the future instruments to be sure they are ready to do the job. These can be made available to policymakers to decide what to finance.‰Û

A set of recommendations outlined at the workshop will be documented in a joint ESA-EUMETSAT publication and will be made available online.