In April and May 2010, large parts of the European airspace were shut down for several days as a consequence of the eruption of the volcano Eyjafjallajökull in Iceland, with the total financial impact estimated to be €5 billion. Volcanic ash and – to a lesser extent – sulphuric gases are major hazards to aviation, with the largest threat being that volcanic ash can damage plane engines and cause them to stall. Volcanic ash can abrade windscreens, damage avionic equipment and navigation systems, and reduce the pilots’ visibility. Moreover, sulphuric gases may also damage aircraft paint and windows, create sulphate deposits on and inside the engines, and might also be dangerous for the health of the passengers.
Strong winds at high altitudes present a significant difficulty in mitigating volcanic hazards to aviation as fine ash can rapidly be transported thousands of kilometres from the volcano, and in the process cross major air routes. As only a small number of the active volcanoes on Earth are regularly monitored using ground equipment, the use of space-based instruments is particularly relevant to aviation safety, as it enables the continuous and global monitoring of volcanic plumes in an effective, economical, and risk-free manner.
Volcanic Ash Advisory Centres
The International Civil Aviation Organization (ICAO) has designated nine Volcanic Ash Advisory Centres (VAACs) worldwide as a part of the International Airways Volcano Watch (IAVW). These centres are responsible for the continuous monitoring of volcanic activity within their designated areas and for issuing Volcanic Ash Advisory Statements that warn users of the presence of volcanic ash and its expected movement over a period of hours to days.
These Advisory Statements are mainly intended for the airline industry and provide the location, name, and elevation of the eruption source; details of observed ash plume location; dimensions; recent motion; general discussion of the expected path of the plume; and reference to any current aviation hazard warnings, known as SIGMETs (SIGnificant METeorological aviation hazard).
The VAACs generate their Advisory Statements by gathering information from a variety of sources, including real-time alerts from aircraft that encounter ash plumes and from ground-based radar, airborne ranging measurements (e.g. lidar), ground-based sun photometers, long-distance lightning detection networks, reconnaissance and research aircraft, and, importantly, from satellites. The initial conditions of the eruption are input into ash dispersion models, including winds; temperature; humidity; and eruption source parameters such as the height of the plume, mass eruption rate of ash, and the size distribution of ash particles – all of which can be observed in part by satellites.
The models are run frequently (e.g., every 6 hours) to make use of the observations and the forecasts are routinely validated and verified against all available observations (satellite, radar, lidar, and research aircraft) and compared to model outputs from the other VAACs around the world.
April 2010 Eyjafjallajökull eruption in Iceland led to the worst disruption to air transport operations since World War II.
SACS volcanic ash notifications based on IASI and AIRS measurements from 2002–2014: Worldwide coverage of VAACs.
Image credit BIRA/IASB
The Role of EO Satellites
The problem of transport of ash and its interaction with aviation is a global problem and requires a global approach. Satellite data are best suited for ash detection and observation because of the global perspective, timeliness and, in the case of volcanoes, because there is no risk during acquisition.
Data for monitoring come from meteorological and non- meteorological satellites, with both visible and infrared images used to monitor large geographical areas. Geostationary satellites provide images several times an hour covering only parts of the Earth, while much lower- altitude polar-orbiting satellites provide global coverage, but at a frequency on the order of days to weeks. Multi-spectral sensors on both types of satellites provide inputs that are used to identify ash-contaminated areas. Some data can be used to provide estimations of ash particle size and height, as well as estimates of how much ash is in a vertical atmospheric column.
Satellites provide objective global coverage, which crosses national and administrative boundaries. This helps to ensure that warnings are comprehensive and provide a basis for inclusion and comparison to amongst forecasts created by the various VAACs, helping to ensure the most accurate information is available to decision makers.
Volcanic Ash Forecast Process and Inputs for the London VAAC.
Image credit: UK MetOffice
Support to Aviation Control Services (SACS) and Volcanic Ash Strategic initiative Team (VAST)
Until recently, the ICAO applied a policy of zero tolerance to airlines regarding operations in the vicinity of volcanic ash. This policy was changed over Europe with the introduction of ash concentration thresholds following the eruption of the Icelandic volcanoes Eyjafjallajökull (April–May 2010) and Grímsvötn in May 2011. The reason for the change was that both eruptions caused partial or total closure of airspace over many European countries, with the associated disruption to societies and their economies.
The introduction of ash-concentration thresholds led to requirements for improved monitoring and forecasting services. These include the early detection and near real-time monitoring of volcanic emissions and plumes for the entire eruptive period. In addition, quantitative measurement of volcanic ash and sulphur dioxide (SO2) concentration and altitude, as well as the ash particle size distribution, are now required.
The primary objective of SACS and VAST is to address as closely as possible these enhanced requirements, in particular in support of the VAACs in their official task of informing aviation control organisations about the risks associated with volcanic activity. SACS makes use of ash and SO2 data products provided in near real-time by polar- orbiting satellites as a part of a multi-sensor warning system for volcanic emissions. The system is optimised to avoid false notifications and to date, 95% of SACS notifications have corresponded to true volcanic activity.
VAST aims to demonstrate the suitability of EO data for these types of activities and improve on the existing monitoring and forecasting services for ash transport and its interaction with aviation. With the VAST project, the following targets for service improvement will be addressed:
– Provision of a database providing satellite, ground-based, in-situ, and modelling data for six selected volcanic eruptions
– Provision of a volcanic eruption warning system based mainly on geostationary satellite data;
– Further development of dispersion forecast models (global and regional) including data assimilation, inverse modelling, and ensemble techniques to generate a measure of uncertainty of the forecast;
– Provision of an operational volcanic ash plume forecasting demonstration service at the Austrian Meteorological Office for 1 year (autumn 2014–autumn 2015).
SACS and VAST are projects funded by ESA.
Three-step contours plot of Ash Mass Loadings for the Eyjafjallajökull eruption as retrieved from MODIS measurements for May 6 2010.
Image credit: NILU
While the number and location of volcanic eruptions varies naturally, the number of aircraft flying is only expected to increase in the future. This will increase our exposure to the risk of both an in-flight incident, as well as to the societal and economic impacts caused by service disruptions arising from the volcanic ash hazard. By leveraging satellite observations to improve the availability of information on volcanic eruptions, global coverage can be achieved; more timely observations can be made available; and more timely, targeted, and higher fidelity warnings can be issued.
While services like SACS and VAST represent a strong first step towards increasing the amount of information available from satellites, in the future we can expect the incorporation of more sensors into ash-plume observing systems. This should improve the quality of products available and add to the range and types of parameters that can be monitored – both of which are expected to improve the quality of reporting possible.
Kelut ash plume plot for February 14, 2014 as retrieved from IASI measurements
Image credit: BIRA/IASB
Case study contributors
Claus Zehner (ESA)
Nicolas Theys (BIRA/IASB)
Fred Prata (NILU)
Ian Davies (easyJet)