Stereoscopic Estimation of Volcanic Ash Cloud-Top Height from Two Geostationary Satellites

The characterization of volcanic ash clouds released into the atmosphere during explosive
eruptions includes cloud height as a fundamental physical parameter. A novel application is proposed
of a method based on parallax data acquired from two geostationary instruments for estimating ash
cloud-top height (ACTH). An improved version of the method with a detailed discussion of height
retrieval accuracy was applied to estimate ACTH from two datasets acquired by two satellites in
favorable positions to fully exploit the parallax effect. A combination of MSG SEVIRI (HRV band;
1000 m nadir spatial resolution, 5 min temporal resolution) and Meteosat-7 MVIRI (VIS band, 2500 m
nadir spatial resolution, 30 min temporal resolution) was implemented. Since MVIRI does not acquire
data at exactly the same time as SEVIRI, a correction procedure enables compensation for wind
advection in the atmosphere. The method was applied to the Mt. Etna, Sicily, Italy, eruption of
23 November 2013. The height of the volcanic cloud was tracked with a top height of ~8.5 km. The ash
cloud estimate was applied to the visible channels to show the potential accuracy that will soon be
achievable also in the infrared range using the next generation of multispectral imagers. The new
constellation of geostationary meteorological satellites will enable full exploitation of this technique
for continuous global ACTH monitoring.