Publication Date:
2017-04-04
Description:
The simultaneous presence of SO2 and ash in
a volcanic plume can lead to a significant error in the SO2
column abundance retrieval when multispectral Thermal InfraRed
(TIR) data are used. The ash particles within the
plume with effective radii from 1 to 10μm reduce the Top Of
Atmosphere (TOA) radiance in the entire TIR spectral range,
including the channels used for SO2 retrieval. The net effect
is a significant SO2 overestimation.
In this work the interference of ash is discussed and two
correction procedures for satellite SO2 volcanic plume retrieval
in the TIR spectral range are developed to achieve an
higher computational speed and a better accuracy.
The ash correction can be applied when the sensor spectral
range includes the 7.3 and/or 8.7μm SO2 absorption bands,
and the split window bands centered around 11 and 12μm
required for ash retrieval. This allows the possibility of simultaneous
estimation of both volcanic SO2 and ash in the
same data set. The proposed ash correction procedures have
been applied to the Moderate Resolution Imaging Spectroradiometer
(MODIS) and the Spin Enhanced Visible and Infrared
Imager (SEVIRI) measurements. Data collected during
the 24 November 2006 Mt. Etna eruption have been used
to illustrate the technique. The SO2 and ash estimation is carried
out by using a best weighted least squares fit method and
the Brightness Temperature Difference (BTD) procedures,
respectively. The simulated TOA radiance Look-Up Table
(LUT) needed for the SO2 column abundance and the ash
retrievals have been computed using the MODTRAN 4 Radiative
Transfer Model.
The results show the importance of the ash correction on
SO2 retrievals at 8.7μm, where the corrected SO2 column abundance values are less than 50% of the uncorrected values.
The ash correction on SO2 retrieval at 7.3μm is much
less important and only significant for low SO2 column abundances.
Results also show that the simplified and faster
correction procedure underestimates the ash correction compared
with the more time consuming but more accurate correction
procedure. Such underestimation is greater for instruments
having better ground pixel resolution, i.e. greater for
MODIS than for SEVIRI.
Description:
Published
Description:
177–191
Description:
1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
Description:
1.10. TTC - Telerilevamento
Description:
N/A or not JCR
Description:
open
Keywords:
volcanic ash retrieval
;
volcanic so2 retrieval
;
ash correction
;
remote sensing
;
MODIS
;
SEVIRI
;
Etna volcano
;
01. Atmosphere::01.01. Atmosphere::01.01.07. Volcanic effects
;
01. Atmosphere::01.01. Atmosphere::01.01.08. Instruments and techniques
;
04. Solid Earth::04.08. Volcanology::04.08.01. Gases
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
;
04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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