A Multi-Sensor Approach for Volcanic Ash Cloud Retrieval and Eruption Characterization: The 23 November 2013 Etna Lava Fountain

Abstract

Volcanic activity is observed worldwide with a variety of ground and space-based remote sensing instruments, each with advantages and drawbacks. No single system can give a comprehensive description of eruptive activity, and so, a multi-sensor approach is required. This work integrates infrared and microwave volcanic ash retrievals obtained from the geostationary Meteosat Second Generation (MSG)-Spinning Enhanced Visible and Infrared Imager (SEVIRI), the polar-orbiting Aqua-MODIS and ground-based weather radar. The expected outcomes are improvements in satellite volcanic ash cloud retrieval (altitude, mass, aerosol optical depth and effective radius), the generation of new satellite products (ash concentration and particle number density in the thermal infrared) and better characterization of volcanic eruptions (plume altitude, total ash mass erupted and particle number density from thermal infrared to microwave). This approach is the core of the multi-platform volcanic ash cloud estimation procedure being developed within the European FP7-APhoRISM project. The Mt. Etna (Sicily, Italy) volcano lava fountaining event of 23 November 2013 was considered as a test case. The results of the integration show the presence of two volcanic cloud layers at different altitudes. The improvement of the volcanic ash cloud altitude leads to a mean difference between the SEVIRI ash mass estimations, before and after the integration, of about the 30%. Moreover, the percentage of the airborne "fine" ash retrieved from the satellite is estimated to be about 1%-2% of the total ash emitted during the eruption. Finally, all of the estimated parameters (volcanic ash cloud altitude, thickness and total mass) were also validated with ground-based visible camera measurements, HYSPLIT forward trajectories, Infrared Atmospheric Sounding Interferometer (IASI) satellite data and tephra deposits.

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

“…All these estimates of the ash cloud height released during the Mt. Etna eruption event on 23 November 2013 are in close agreement with the results obtained herein and are thoroughly presented and discussed in a separate article by Corradini et al [50] in this special issue. …”

“…All these estimates of the ash cloud height released during the Mt. Etna eruption event on 23 November 2013 are in close agreement with the results obtained herein and are thoroughly presented and discussed in a separate article by Corradini et al [50] in this special issue. The results of ACTH can be compared with those obtained from radiosonde profiles of temperature and wind speed acquired on 23 November 2013 at 12:00 UTC by the WMO meteorological station of Trapani (Sicily, Italy).…”

“…The dark part of the plume is recognized as ash using BTD and the bright part as a meteorological cloud. Given that both are of volcanic origin, the focus here is only on the bright part of the cloud (which is probably composed of a mixture of ash and ice crystals or water droplets [50]), because the dark part of the plume is too transparent to be clearly detected in the visible bands. This brighter, highly-reflective cloud can be observed with both instruments and is used here to apply the ACTH estimation method.…”

“…Furthermore, the ACTH estimation presented here refers to a cloud for which a visual inspection of both image sequences identifies as being of clear volcanic origin. Conversely, the positive BTD that can be found on the SEVIRI images of the same part of the volcanic cloud used for the ACTH estimate, does not detect it as composed of volcanic ash, but rather of ice or water droplets [50]. Nevertheless, this case study is very useful to demonstrate the potential of the proposed method which, in principle, can be used to estimate the ACTH of any type of cloud using GEO multispectral imagers, regardless of whether they are volcanic ash or SO 2 clouds derived from a detection and retrieval procedure, or meteorological clouds directly identified in the satellite datasets.…”

“…According to Corradini et al [50], the 550 nm AOD of the ash cloud was below 0.5. The ash part of Etna's cloud could not be accurately identified with SEVIRI's HRV channel, nor with MVIRI's VIS channel.…”