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| Titel |
Evaluation wavelength range mapping, a tool to optimize the evaluation window in differential absorption spectroscopy |
| VerfasserIn |
L. Vogel, H. Sihler, J. Lampel, T. Wagner, U. Platt |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067606
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| Zusammenfassung |
| Optical remote sensing via Differential Optical Absorption Spectroscopy (DOAS) has
become a standard technique to assess various trace gases in the atmosphere. Measurement
instruments are usually classified into active instruments applying an artificial light source
and passive instruments using natural light sources, e.g., scattered or direct sunlight.
Platforms range from ground based to satellites and trace gases are studied in all kinds of
different environments. Naturally, the evaluation of gathered spectra needs to be tuned to
each specific case and trace gas of interest due to the wide range of measurement
conditions, atmospheric compositions and instruments used. A well chosen evaluation
wavelength range is crucial to the DOAS technique. It should be as large as possible and
include the largest differential absorption features of the trace gas of interest in
order to maximize sensitivity. However, the differential optical densities of other
absorbers should be minimized in order to prevent interferences between different
absorption cross sections. Furthermore, instrumental specific features and wavelength
dependent radiative transfer effects may have malicious effects and lead to erroneous
values. Usually a compromise needs to be found depending on the conditions at
hand.
Evaluation wavelength range mapping is an easily applied tool to visualize wavelength
depending evaluation features of DOAS and to find the optimal retrieval wavelength range.
As an example, synthetic spectra are studied which simulate passive DOAS measurements of
stratospheric bromine monoxide (BrO) by Zenith-DOAS and Multi-Axis DOAS
(MAX-DOAS) measurements of BrO in volcanic plumes. The influence of the I0-effect and
the Ring-effect on the respective retrievals are demonstrated. However, due to the general
nature of the tool it is applicable to any DOAS measurement and the technique also allows to
study any other wavelength dependent influences on retrieved trace gas columns. |
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