This year two new European satellites will be added to the suite of weather satellites in orbit over the Earth helping monitor weather and environmental phenomena such as volcanoes.

But how do you monitor a volcano eruption from space?

During a volcanic eruption, large amounts of ash and trace gases, especially sulphur dioxide (SO₂), are injected into the atmosphere. Because eruptions can happen at any time having a global, constant monitoring system available is vital and the two new satellites to be launched this year will maintain constant monitoring for many years.

Knowing where a plume is helps forecasters at the Volcanic Ash Advisory Centres (VAACs), who issue the volcanic ash advisories. The warnings issued by the VAACs are vital for air travel. While the impacts of volcanic emissions on aircraft are still not fully resolved and currently under investigation, there have been incidence when planes’ engines have stopped working after travelling through volcanic clouds.

Research following the Eyjafjallajökull eruption shows that VAACs rely heavily on access to real-time satellite imagery and products to identify and locate volcanic clouds. The primary types of data used are images — visible and infrared. Animating the images also proves to be very useful. Interpreting these data requires a high degree of meteorological skill and training. Experts are able to use context and experience to quickly identify and interpret volcanic features within satellite images. Locations of volcanic features within images are compared with the output of atmospheric dispersion models and an estimate of the extent and location of the volcanic hazard is made.

Animation of geostationary imagery from Eyjafjallajökull eruption

Monitoring ash

Our Meteosat Second Generation (MSG) geostationary satellites are the only ones in orbit that can be used to derive near real-time imagery (every 15 minutes) of the movement of volcanic clouds over Europe. The SEVIRI imaging radiometer on Meteosat-9 has 12 channels (at visible and infrared wavelengths), experts are able to construct red-green-blue (RGB) images which have proved very useful for identifying volcanic clouds. The SEVIRI data allow the retrieval of quantitative ash properties like the total column loading of ash. In addition to SEVIRI on MSG, volcanic ash can also be detected by the hyperspectral Infrared Atmospheric Sounding Interferometer (IASI) instrument on Metop-A. The concentration of particles, which is important data for air traffic control, can be determined by combining satellites products with other available information or models. EUMETSAT produces a Volcanic Ash Detection product for VAACs and National Meteorological Services. The input data used for the product includes the reflectances in the VIS0.6 and the IR3.9 channels; the brightness temperatures in the IR3.9, IR8.7, IR10.8 and IR12.0 channels, and the total column loading of ash.

RGB composite image of Grímsvötn ash plume (Click to enlarge)

Volcanoes are also a major source of sulphur dioxide (SO₂), which may or may not always travel together with the ash. SO₂ detection is useful because, often, SO₂ emissions precede eruptions. The GOME-2 (Global Ozone Monitoring Experiment-2) scanning spectrometer on the Metop-A polar-orbiting satellite can monitor SO₂ using the specific absorption features of this gas in the ultraviolet spectral region. Also measurements by IASI on Metop-A are sensitive to SO₂. The concentration is derived from the variations observed in the measured infrared radiation, derived as brightness temperature levels.

Metop-A/GOME-2 SO2 (15-18 April 2010)
Source: O3M-SAF/DLR

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