Satellite-based Volcanic Ash Cloud Detection Intercomparison

A workshop at the University of Wisconsin-Madison (USA) from 29 June to 2 July considered 22 algorithms using passive satellite imagery as part of a WMO Satellite-based Volcanic Ash Cloud Detection Intercomparison.

This activity aims at improving knowledge in this area mainly in support of aeronautical meteorological services. Consistent ash prediction and information products for aviation are required to inform the services provided by the Volcanic Ash Advisory Centres (VAAC) and international regulations established by International Civil Aviation Organization (ICAO) (Annex 3 of the ICAO Convention, and the International Airways Volcano Watch Roadmap) and WMO.

Eruption at Eyjafjallajökull April 17, 2010 (Photo: Árni Friðriksson)

Currently, satellite-derived ash products are not consistent because the quantification of volcanic ash parameters is difficult, no inter-nationally-agreed validation protocol exists for such products, the strengths and weaknesses of available products are not known or comparable, many are produced on an ad-hoc basis and not sustained or operationally available, and there is no WMO-endorsed standard for volcanic cloud geophysical parameters. Thus, the objectives of the WMO intercomparison included establishing a basic validation protocol for satellite-based volcanic ash products; quantifying and understanding the differences in the products for six selected volcanic eruptions in order to extract best practices; and standardizing volcanic cloud geophysical parameters in the context of WMO and ICAO. The performance of algorithms is also to be studied in view of the sensors available on the next generation of meteorological satellites in the 2015-2020 timeframe.

The University of Wisconsin-Madison also used reference data from the CALIPSO CALIOP space-borne lidar instrument, the United Kingdom FAA aircraft, and the EARLINET ground-based lidar data. The six volcanic eruption cases considered in the intercomparison were Eyjafallajökull (2010), Grimsvötn (2011), Sarychev Peak (2009), Kelut (2014), Puyehue-Cordón Caulle (2011) and Kirishimayama (2011).

Eyjafjallajökull eruption (8 May 2010): MSG SEVIRI imager-based RGB composite, showing ash clouds (in bright orange) and CALIPSO CALIOP space-borne lidar ground track (used for comparison).

Results of the intercomparison are currently being synthesized. The guidance derived from these results will be beneficial not only to aviation but also to other meteorological applications such as nowcasting and air quality forecasting. The activity has been established as part of WMO Sustained, Co-Ordinated Processing of Environmental Satellite Data for Nowcasting (SCOPE-Nowcasting, reporting to the WMO Commission for Basic Systems), and is contributing to the WMO/ IUGG Volcanic Ash Scientific Advisory Group (VASAG, reporting to the Commission for Aeronautical Meteorology and ICAO), the ICAO MET Panel and its Working Group on Meteorological Information and Service Development (with sub-group on volcanic ash), and the WMO Global Atmosphere Watch (GAW) and World Weather Research Programmes (WWRP).

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