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| Titel |
Theoretical description of functionality, applications, and limitations of SO2 cameras for the remote sensing of volcanic plumes |
| VerfasserIn |
C. Kern, F. Kick, P. Lübcke, L. Vogel, M. Wöhrbach, U. Platt |
| 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 ; 3, no. 3 ; Nr. 3, no. 3 (2010-06-29), S.733-749 |
| Datensatznummer |
250001118
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| Publikation (Nr.) |
 copernicus.org/amt-3-733-2010.pdf |
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| Zusammenfassung |
The SO2 camera is a novel device for the remote sensing of volcanic
emissions using solar radiation scattered in the atmosphere as a light
source for the measurements. The method is based on measuring the
ultra-violet absorption of SO2 in a narrow wavelength window around
310 nm by employing a band-pass interference filter and a 2 dimensional
UV-sensitive CCD detector. The effect of aerosol scattering can in part be
compensated by additionally measuring the incident radiation around 325 nm,
where the absorption of SO2 is about 30 times weaker, thus rendering
the method applicable to optically thin plumes. For plumes with high aerosol
optical densities, collocation of an additional moderate resolution
spectrometer is desirable to enable a correction of radiative transfer
effects. The ability to deliver spatially resolved images of volcanic
SO2 distributions at a frame rate on the order of 1 Hz makes the
SO2 camera a very promising technique for volcanic monitoring and for
studying the dynamics of volcanic plumes in the atmosphere.
This study gives a theoretical basis for the pertinent aspects of working
with SO2 camera systems, including the measurement principle,
instrument design, data evaluation and technical applicability. Several
issues are identified that influence camera calibration and performance. For
one, changes in the solar zenith angle lead to a variable light path length
in the stratospheric ozone layer and therefore change the spectral
distribution of scattered solar radiation incident at the Earth's surface.
The varying spectral illumination causes a shift in the calibration of the
SO2 camera's results. Secondly, the lack of spectral resolution
inherent in the measurement technique leads to a non-linear relationship
between measured weighted average optical density and the SO2 column
density. Thirdly, as is the case with all remote sensing techniques that use
scattered solar radiation as a light source, the radiative transfer between
the sun and the instrument is variable, with both "radiative dilution" as
well as multiple scattering occurring. These effects can lead to both, over
or underestimation of the SO2 column density by more than an order of
magnitude. As the accurate assessment of volcanic emissions depends on our
ability to correct for these issues, recommendations for correcting the
individual effects during data analysis are given.
Aside from the above mentioned intrinsic effects, the particular technical
design of the SO2 camera can also greatly influence its performance,
depending on the setup chosen. A general description of an instrument setup
is given, and the advantages and disadvantages of certain specific
instrument designs are discussed. Finally, several measurement examples are
shown and possibilities to combine SO2 camera measurements with other
remote sensing techniques are explored. |
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