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Project name:IRDAS – Differential Absorption Spectroscopy in the SWIR for Greenhouse Gas Monitoring using Coherent Signal Sources in a Limb Sounding Geometry
Project leader:Peter Bernath (Dept of Chemistry, Univ. of York; IRDAS prime contractor)
Gottfried Kirchengast (of WegCenter part; IRDAS main subcontractor)
Project team:Univ. of York:
Peter Bernath
Barry Thomas
Jeremy Harrison
Nick Allen

Gottfried Kirchengast
Susanne Schweitzer
Veronika Proschek
Florian Ladstädter

Georg B. Larsen
Stig Syndergaard
Partners:Dept of Chemistry, Univ. of York, York, UK
Danish Meteorological Institute (DMI), Copenhagen, DK
M. Riese (consulting expert), Inst. for Chemistry and Dynamics of the Geosphere, FZ Juelich, Germany
Sponsor:European Space Agency ESA



 The main objective of the IRDAS project is to consolidate the scientific basis for active occultation measurements in the Shortwave Infrared (SWIR) spectral region as proposed in the link\{ACCURATE climate satellite mission proposal to ESA\}. In this method differential absorption of laser beams, in the 2.0–2.5 ìm spectral region with propagation in limb sounding geometry, is employed to accurately measure atmospheric concentrations of greenhouse gases. Related to this, IRDAS will focus on the spectroscopic properties of the atmosphere and the relevant (greenhouse gas) target species in the Upper Troposphere and Lower Stratosphere (UTLS).

Active occultation measurements in the SWIR region are novel and could form the basis of a standalone mission (e.g., for demonstration) or be combined with microwave occultation (full climate mission) as discussed in the ACCURATE proposal. Under its overall objective to aid consolidation of the scientific basis for an ACCURATE-type mission, the IRDAS project will focus on:

  •     Consolidating the basic science objectives, the related geophysical data requirements, and the (in turn) related observational requirements for an ACCURATE-type mission
  •     Assessing the possible science contribution and scientific impact of an ACCURATE-type mission and synergies with other instruments
  •     Comparing the expected performance with passive (down-looking) sounding, to identify possible synergies and to highlight the complementary nature of both approaches
  •     Characterizing broadband atmospheric effects in the differential absorption technique and developing a functional model for the SWIR spectral region
  •     Consolidating the baseline selection of absorption lines and reference spectral regions for sensing the relevant greenhouse gases
  •     Recommending representative laser line pairs near 2.1 ìm for demonstration purposes
  •     Providing an error budget, with focus on atmospheric and spectral uncertainties

Under these foci, IRDAS will analyze the uncertain effects of broadband atmospheric “distortions” of the laser beam as well as errors in spectroscopic line parameters on the accuracy of the retrieved trace gas concentrations using the SWIR laser occultation technique. The project will heavily employ software simulation, validated using existing actual SWIR limb observations of the UTLS region. Overall IRDAS will significantly aid to more clearly define the possible contributions to atmosphere and climate science of a dedicated mission based on an ACCURATE-type concept.

Univ.-Prof. Mag. Dr.rer.nat.

Gottfried Kirchengast

Phone:+43 316 380 - 8431

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