Publication Date:
2021-12-02
Description:
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 gm−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.
Description:
Published
Description:
1315–1327
Description:
5V. Sorveglianza vulcanica ed emergenze
Description:
5IT. Osservazioni satellitari
Description:
JCR Journal
Description:
open
Keywords:
volcanic monitoring, remote sensing, volcanic eruption, retrieval techniques, MODIS instrument
;
04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
;
05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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