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| Titel |
Autonomous long-term trace gas measurements using Long-Path Differential Optical Absorption Spectroscopy |
| VerfasserIn |
Jan-Marcus Nasse, Denis Pöhler, Philipp Eger, Stefan Schmitt, Udo Frieß, Ulrich Platt |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140497
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| Publikation (Nr.) |
 EGU/EGU2017-3893.pdf |
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| Zusammenfassung |
| Long-Path DOAS (Differential Optical Absorption Spectroscopy) is a well-established, very
specific and reliable remote sensing technique for the observation of a large variety of trace
gases. So far DOAS has been mostly applied in the UV-Vis spectral region; detectable species
are for example ClO, OClO, BrO, OBrO, IO, OIO, I2, OIO, O3, formaldehyde, glyoxal, NO2,
H2O, O4, or SO2.
In the Long Path DOAS setup, a dedicated light source and a measurement path of up to
10 km between a telescope and a reflector yield continuous path averaged concentrations
independent of solar radiation and still on scales below the ground pixel sizes of satellite
instruments.
Here we present an advanced LP-DOAS instrument incorporating several technical
improvements to a setup that allows for the first time autonomous and continuous
long term measurements with very high measurement accuracy necessary for the
measurement of low trace gas concentrations. The setup uses an optical fiber bundle
in the telescope for transmission and reception of the measurement signal. The
traditional Xe-arc lamp has been replaced by a Laser Driven Light Source with a
long life time and very good optical stability. Using this light source also allows
an improved wavelength selective coupling from light source into the fiber which
reduces stray light. The coupling and configuration of the optical fiber was optimised
compared to previous designs to maximise light throughput and reduce stray light.
Additionally, the fibers were treated in order to reduce noise caused by irregular grating
illumination.
These changes drastically lower detection limits (e.g. to 1 pptv for BrO or 8 pptv for ClO)
and improve the long-term reliability. To facilitate an autonomous operation, the
measurement software incorporates features such as an automatic reflector search and
intensity optimisation as well as a selection from the available measurement paths based on
atmospheric visibility. Since January 2016, we are successfully running the LP-DOAS
instrument continuously under the challenging environmental conditions of Antarctica at the
German Neumayer III station. We present technical features of the instrument with a focus on
physical phenomena the technique is based on and limited by and discuss its long-term
performance. |
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