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| Titel |
Observing the plume of Popocatépetl and Colima with a novel SO2-Camera |
| VerfasserIn |
Peter Lübcke, Nicole Bobrowski, Sebastian Illing, Christoph Kern, Leif Vogel, Johannes Zielcke, Ulrich Platt |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050804
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| Zusammenfassung |
| Sulfur dioxide (SO2) emissions are related to the volume of magma degassing beneath the
Earth’s surface. SO2 emission flux measurements can therefore be an important tool for
monitoring volcanoes and eruption risk assessment. For instance, changes in the SO2 flux
have been recorded together with an increased seismic tremor prior to volcanic eruptions at
Santa Ana volcano (El Salvador). The SO2 camera is a technique for remote sensing of
volcanic sulfur dioxide emissions based on measuring the ultra-violet absorption of SO2 in a
narrow wavelength window around 310 nm by employing band-pass interference filters and a
2-D UV-sensitive CCD detector. Solar radiation scattered in the atmosphere is used as a light
source for the measurements. The effect of aerosol scattering can be eliminated by
additionally measuring the incident radiation around 325 nm where the absorption of SO2 is
no longer significant, thus rendering the method applicable to plumes containing aerosols.
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. The high time resolution allows the calculation of the
wind-speed directly from the measurements, thus largely eliminating this error source
in the flux measurements. Another advantage of the high time resolution is the
possibility to correlate the gas flux with other data sets, i.e. seismic data, on shorter
timescales than previously possible. Here we present results of measurement campaigns
conducted at Popocatépetl and Colima, Mexico in April 2010 and February 2011,
which were performed with a new prototype of a SO2 camera incorporating an
additional Differential Optical Absorption Spectroscopy (DOAS) system. The DOAS
system was used to apply a new calibration method, besides making the correction
for radiative transfer effects possible. The built in DOAS system carried out point
measurements of the volcanic plume in a region that corresponds to the center of
the SO2 camera images. This yields column density / apparent absorption pairs
that can be used to determine the calibration curve for the SO2 camera images.
In order to test and validate this approach, simultaneous measurements with an
imaging-DOAS (IDOAS) were conducted. The IDOAS measures two dimensional trace
gas distributions using the DOAS technique. A two dimensional detector is used.
The incident radiation is spectrally dispersed along one dimension, while the other
dimension corresponds to a dimension in space. The second image dimension is
obtained by using a scanning mirror. Despite the lower measurement time resolution
(about 30 minutes for one image), the inherent calibration of the IDOAS allows
verification of the camera calibration. For this, each column of the IDOAS image has is
compared to the respective column of the contemporaneously taken SO2 camera image. |
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