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Laboratory spectroscopy at DLR

This workshop presentation discusses the laboratory spectroscopy infrastructure, tools, and spectroscopic database work at the German Aerospace Center (DLR). Topics covered include equipment, new absorption path cells, improved detector design, a new IDL multispectrum fitting tool, and specific research on N2O, H2O, and BrONO2. Current work focuses on measurements of stable and unstable species across a wide range of wavelengths.

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Laboratory spectroscopy at DLR

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  1. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 Laboratory spectroscopy at DLR Manfred Birk, Georg Wagner, Joep Loos German Aerospace Center (DLR)

  2. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 Background • Group established in 1990 • Emphasis on quantitative spectroscopy of atmospheric trace gases • Support of atmospheric remote sensing • Initial focus on far infrared • Soon extended to mid and near infrared; extended to UV in 2010 • Participation in several EU-, ESA- and nationally-funded projects • Member of HITRAN scientific advisory committee

  3. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 Infrastructure • Bruker IFS 120HR Fourier-transform spectrometer • Replaced by new Bruker IFS 125HR in August 2010, extension to UV (250 nm) • Coolable (190 K), heatable (950 K) cells, 170 m multireflection cell • Lab equipment for production/handling of stable/unstable species

  4. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 New short absorption path cell • 20 cm absorption path • Path length accuracy 0.1 % - requires raytracing! • Coolable to 190 K • High temperature homogeneity (0.1 K) • Two window pairs allowing UV+MIR, MIR+FIR, UV+FIR

  5. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 Multireflection cell • Designed at DLR in 1991, refurbished in 2012 • 80 cm baselength, up to 170 m absorption path • Coolable to 190 K • Equipped for flow experiments with unstable species

  6. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 Improved detector design for thermal IR • Adaptable detector FOV to reduce background photon noise • Coolable optical filter • Photoconductive MCT with 700 cm-1 cut-on @ 45 K Intercomparison standard Bruker MCT – DLR design • Optical band pass filter, varying central wavenumber • Detector@ 45 K • 200 cm filterbandwidth • 1 mm and 2 mm Brukerentranceaperture • No absorber- and 90% absorption-setup

  7. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 New IDL multispectrumfittingtool • Line models • Voigt • Speed-dependentVoigt (C. Boone) • Speed-dependentGalatry + LM (F. Hase) • pCqSDHC + LM (Ngo, Tran) • Versatile interactivemode • Choice oflinemodel, fitparameters • ILS, calibrationfactors, baseline, channelling, … • Automaticmode • Microwindow-, spectra-, fitparameterselection (Voigt) • Goodness-of-fit • Residuaanalysis (planned) • Identification/preventionofcorrelationbetweenfittedparameters • Filecuts(resultsof single-spectra-fits vs. ms-fit) • Identificationofsystematicspectrum-specificerrors

  8. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 New IDL multispectrumfittingtool

  9. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 Spectroscopic database work at DLR

  10. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 N2O: linemixing in n3rovibrational band

  11. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 H2O: Linestrengthintercomparison in 1 µm region • NIST: cavitiyringdown by Joseph T. Hodges • HIT: HITRAN 2008, mainly experimental data by Robert A. Toth • Excellent agreement DLR-NIST, mostly < 1 % • HITRAN2008 shows bias and large scatter

  12. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 H2O: Linestrengthintercomparison in 1 µm region • Lodi: ab initio calculations • Good agreement for 2 0 1  0 0 0 and 0 0 3  0 0 0 withoccasionaloutliers • Entiresubbandsshifted: 1 2 1  0 0 0 , 3 0 0  0 0 0, 1 0 2  0 0 0upto 8 % Average differences 1 2 1  0 0 0 4.1% 2 0 1  0 0 0 0.0% 3 0 0  0 0 0 4.0% 1 0 2  0 0 0 -7.6% 0 0 3  0 0 0 -0.1%

  13. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 H2O: IASI retrieval improvements in H2O n2region using DLR linestrength and pressure broadening parameters Red: residuals DLR, pink: residuals HITRAN 2008 Plots providedby S.A. Clough

  14. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 BrONO2: New absorption cross sections • Q-branch peak intensity increases by 50 % from 296 K to 203 K • Cross sections measured with 0.025 cm-1 resolution • High resolution measurements @0.0017 cm-1 recorded at 296 K and 223 K, showing resolved features

  15. > 2014 GEISA Workshop > J. Loos • Laboratory spectroscopy at DLR > 03.06.2014 Summary andcurrentwork • Laboratory equipment for measurements of stable and unstable species from FIR to UV at atmospheric pressures and temperatures • Data reduction software including various quality assessment procedures • Emphasis on defined error bars • DFG-project • H2O & CH4 in 1750-4000 cm-1 spectral range • Application in ground based solar occultation atmospheric measurements • ESA-project: SEOM-Improved Atmospheric Spectroscopic Databases (IAS) • TROPOMI on Sentinel-5 Precursor • Improve CH4, H2O, CO in the 2.3 µm region • Resolve discrepancy of O3 in the UV/10 µm regions • Improve SO2 in the UV

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