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| Titel |
A model sensitivity study of the impact of clouds on satellite detection and retrieval of volcanic ash |
| VerfasserIn |
A. Kylling, N. Kristiansen, A. Stohl, R. Buras-Schnell, C. Emde, J. Gasteiger |
| 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 ; 8, no. 5 ; Nr. 8, no. 5 (2015-05-06), S.1935-1949 |
| Datensatznummer |
250116353
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| Publikation (Nr.) |
 copernicus.org/amt-8-1935-2015.pdf |
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| Zusammenfassung |
| Volcanic ash is commonly observed by infrared detectors on board Earth-orbiting satellites. In the presence of ice and/or liquid-water clouds, the detected volcanic ash signature may be altered.
In this paper the sensitivity of detection and retrieval of
volcanic ash to the presence of ice and liquid-water clouds was
quantified by simulating synthetic equivalents to
satellite infrared images with a 3-D radiative transfer model.
The sensitivity study was made for the two recent eruptions of
Eyjafjallajökull (2010) and Grímsvötn (2011) using realistic
water and ice clouds and volcanic ash clouds.
The water and ice clouds were taken from European Centre for
Medium-Range Weather Forecast (ECMWF) analysis data and the
volcanic ash cloud fields from simulations by the
Lagrangian particle dispersion model FLEXPART.
The radiative transfer simulations were made both with and without
ice and liquid-water clouds for the geometry and channels of the Spinning
Enhanced Visible and Infrared Imager (SEVIRI).
The synthetic SEVIRI images were used as input to standard reverse
absorption ash detection and retrieval methods.
Ice and liquid-water clouds were
on average found to reduce the number of detected ash-affected pixels
by 6–12%. However, the effect was highly variable and for individual
scenes up to 40% of pixels with mass loading >0.2 g m−2 could
not be detected due to the presence of water and ice clouds.
For coincident pixels, i.e. pixels where ash was both present in the
FLEXPART (hereafter referred to as "Flexpart") simulation and detected by the algorithm, the presence of
clouds overall increased the retrieved mean mass
loading for the Eyjafjallajökull (2010) eruption by about 13%,
while for the Grímsvötn (2011) eruption ash-mass loadings the
effect was a 4% decrease of the retrieved ash-mass loading.
However, larger differences were seen between scenes
(standard deviations of ±30 and ±20% for
Eyjafjallajökull and Grímsvötn, respectively) and even
larger ones within scenes.
The impact of ice and liquid-water clouds on the
detection and retrieval of volcanic ash, implies that to fully
appreciate the location and amount of ash, hyperspectral and spectral
band measurements by satellite instruments should be combined with
ash dispersion modelling. |
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