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| Titel |
A field scale laser-tomography spectrometer for mapping trace-gases |
| VerfasserIn |
Mike Schwank, Oliver Bens, Oliver Henneberg, Michael Böhm, Hans-Gerd Löhmannsröben |
| 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 |
250048479
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| Zusammenfassung |
| Evaporation and condensation of water play an important role in redistributing energy as they
transfer heat from the Earth’s surface to the atmospheric boundary layer. If the spatial
distribution of water vapor is known, it can be used in modeling all kinds of processes taking
place in the critical zone. Likewise, knowing the areal distribution of atmospheric trace gases
within the lowermost meters of the atmosphere is of great interest for exploring
fundamental questions related to soil carbon cycling. Currently, concentrations of water
vapor and trace gases, such as carbon dioxide (CO2) and methane (CH4), close to
the terrestrial surface are mostly measured on the point scale using atmometers
and soil chambers. The possibility to detect the areal distribution of, e.g., CO2
concentration has been demonstrated by means of passive infrared remote sensing
techniques. However, such measurements reveal concentrations integrated over the
paths between the surface and the sensor position that is typically high above the
surface. Recently tomographic setups of active infrared spectroscopy have been
proposed to measure spatially resolved gas concentrations. Most of this research
was either performed on relatively small spatial scales for industrial applications
(e.g. for thin film deposition chambers), or in environments (such as e.g. above
volcanoes) exhibiting plumes with high gas concentrations relative to the background
concentration.
Aiming to increase the understanding of the basic biological and chemical processes
within the undisturbed vadose zone that drive the carbon exchange across the soil-atmosphere
interface we propose the construction of a field scale laser-spectroscopy system that allows
for the tomographic reconstruction of the spatial distribution of CO2 concentration including
isotopic sensitivity at atmospheric conditions. The system proposed uses tunable diode lasers,
allowing for measuring high-resolution absorption spectra centered at around 2004Â nm and
2744Â nm along approximately 300 intersecting atmospheric paths in close proximity to the
ground. The 2004Â nm measurements are almost exclusively sensitive to the integrated
concentration of the 12CO2 isotope, while the spectra obtained at around 2744Â nm will
provide information on the isotopology 12CO2Â /Â 13CO2. Simulations of the spectral
transmission of a 100Â m path across a standard atmosphere were performed to
estimate the system sensitivity with regard to CO2 concentration. This investigation
showed that it is feasible to detect a 1% change (3.3Â ppmV) of the standard CO2
concentration (330Â ppmV) along a 1Â m segment. This ensures that spectroscopy
it not the limiting factor for the spatial resolution expected for the tomographic
inversion.
The tomographic spectrometer will be realized in the framework of the development
of a new terrestrial observatory in the German northeastern lowlands within the
Terrestrial Environmental Observatories initiative (TERENO) of the Helmholtz
association. After setting up the system, careful characterization of the performance, and
optimizing the tomographic inversion, the field scale spectrometer will be installed on the
CarboZALF site in Dedelow which is already part of the TERENO´s SoilCan activities. |
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