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| Titel |
A new simplified approach for simultaneous retrieval of SO2 and ash content of tropospheric volcanic clouds: an application to the Mt Etna volcano |
| VerfasserIn |
S. Pugnaghi, L. Guerrieri, S. Corradini, L. Merucci, B. Arvani |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 5 ; Nr. 6, no. 5 (2013-05-22), S.1315-1327 |
| Datensatznummer |
250017895
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| Publikation (Nr.) |
 copernicus.org/amt-6-1315-2013.pdf |
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| Zusammenfassung |
A new procedure is presented for simultaneous estimation of SO2 and ash
abundance in a volcanic plume, using thermal infrared (TIR) MODIS data.
Plume altitude and temperature are the only two input parameters required to
run the procedure, while surface emissivity, temperature, atmospheric
profiles, ash optical properties, and radiative transfer models are not
necessary to perform the atmospheric corrections. The procedure gives the
most reliable results when the surface under the plume is uniform, for
example above the ocean, but still produces fairly good estimates in more
challenging and not easily modelled conditions, such as above land or
meteorological cloud layers. The developed approach was tested on the Etna
volcano.
By linearly interpolating the radiances surrounding a detected volcanic
plume, the volcanic plume removal (VPR) procedure described here computes
the radiances that would have been measured by the sensor in the absence of
a plume, and reconstructs a new image without plume. The new image and the
original data allow computation of plume transmittance in the TIR-MODIS
bands 29, 31, and 32 (8.6, 11.0 and 12.0 μm) by applying a simplified
model consisting of a uniform plume at a fixed altitude and temperature. The
transmittances are then refined with a polynomial relationship obtained by
means of MODTRAN simulations adapted for the geographical region, ash type,
and atmospheric profiles.
Bands 31 and 32 are SO2 transparent and, from their transmittances, the
effective ash particle radius (Re), and aerosol optical depth at 550 nm
(AOD550) are computed. A simple relation between the ash transmittances of bands 31 and 29 is demonstrated and used for SO2 columnar content (cs)
estimation. Comparing the results of the VPR procedure with MODTRAN
simulations for more than 200 000 different cases, the frequency
distribution of the differences shows the following: the Re error is less than
±0.5 μm in more than 60% of cases; the AOD550 error is less than
±0.125 in 80% of cases; the cs error is less than ±0.5 g m−2
in more than 60% of considered cases. The VPR procedure was
applied in two case studies of recent eruptions occurring at the Mt Etna
volcano, Italy, and successfully compared with the results obtained from the
established SO2 and ash assessments based on look-up tables (LUTs).
Assessment of the sensitivity to the plume altitude uncertainty is also
made.
The VPR procedure is simple, extremely fast, and can be adapted to other ash
types and different volcanoes. |
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