line parameters of water vapor in the near- and mid-infrared regions determined using tuneable laser...
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LINE PARAMETERS OF WATER VAPOR LINE PARAMETERS OF WATER VAPOR IN THE NEAR- AND MID-INFRARED REGIONSIN THE NEAR- AND MID-INFRARED REGIONS
DETERMINED USINGDETERMINED USINGTUNEABLE LASER SPECTROSCOPYTUNEABLE LASER SPECTROSCOPY
Nofal IBRAHIM, Pascale CHELIN, Johannes ORPHALLaboratoire Interuniversitaire des Systèmes Atmosphériques (LISA)
Université de Paris-XII, 91405 Créteil Cedex, France
YURI I. BARANOVOptical Technology Division, NIST, Gaithersburg, MD 20899-8441, USA
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H2O: The most important atmospheric trace gas It has a crucial role in the Earth's radiation budget
(responsible for ~70% of absorption of incoming sunlight ) Principal contributor to the greenhouse effect
MotivationMotivation MotivationMotivation
Absorption of solar radiation in the near-IR region Infrared remote sensing of atmosphere using aircraft and
satellite sensors
Necessity to provide: precise spectral line parameters
in the near-IR region
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MotivationMotivation MotivationMotivation
Solar Spectrum with Atmospheric Absorptions
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R. A. Toth, J. Mol. Spectrosc., 166, 176-183 (1994). J.-M. Flaud et al., J. Mol. Spectrosc., 185, 211-221 (1997). P. L. Ponsardin et al., J. Mol. Spectrosc., 185, 58-70 (1997). A. Lucchesini et al., Eur. Phys. J. D., 8, 223-226 (2000). R. Schermaul et al, J. Mol. Spectrosc. 208, 32-42 (2001). A. Ray et al., Appl. Phys. B, 79, 915-921(2004).
Previous measurement in the near IR regionPrevious measurement in the near IR regionPrevious measurement in the near IR regionPrevious measurement in the near IR region
Example of measurement: line intensities (S1023/cm molecule-1)
position (cm-1) HITRAN04 Ponsardin Schermaul Ray
12014.1431 1.679 --- 1.960 1.504
12218.8248 1.865 2.185 2.290 1.888
12244.7233 3.236 3.81 5.080 ---
12244.7873 0.8886 1.08 --- ---
! Differences between different authors exceed stated accuracy (up to 30%) need for more measurements
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Chopper
Wavemeter
ECDLECDL (External External Cavity Diode Laser) and DFGDFG (Difference Frequency Generation Laser) coupled with multi-path absorption cell:
Experimental set-upExperimental set-upExperimental set-upExperimental set-up
Mid IR
ECDL: •30 mW•810-880 nm•Linewidth 1MHz
DFG•3-5 µm•Linewidth 1MHz
•Lock-in detection•LabVIEW acquisition•S/N>1000 •Measurement time: few minutes
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Experimental set-upExperimental set-upExperimental set-upExperimental set-up
ECDL: •30 mW•810-880 nm•Linewidth 1MHz
DFG•3-5 µm•Linewidth 1MHz
•Lock-in detection•LabVIEW acquisition•S/N>1000 •Measurement time: few minutes
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Experimental set-upExperimental set-upExperimental set-upExperimental set-up
L = 1 m, maximum path length 100 m, CaF2 windows
3 MKSBaratrons
Water sample
Thermometer
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Experimental PrecautionsExperimental PrecautionsExperimental PrecautionsExperimental Precautions
HDO lines (probed in the mid-IR by the DFG laser) to validate H2O pressure values (assumption: natural HDO abundance).
Background emission of the ECDL narrow spectral filter.
Validation of detector linearity using neutral density filters.
Linearization of the wavenumber axis: FP etalon (1MHz)
H2O samples: Distilled, ultrasonic
…
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ResultsResultsResultsResults Example1: Self broadening of the line at 12226.101 cm-1
Very high S/N ratio( >1000) Experimental lines very well modeled using Voigt profile Observation of « Dicke narrowing »
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ResultsResultsResultsResults
Example2: Air-broadening of the line at 12226.101 cm-1
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ResultsResultsResultsResults
Example3: 3 lines near 12259 cm-1
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Results : Line IntensitiesResults : Line IntensitiesResults : Line IntensitiesResults : Line Intensities
• Up to 10 % between fixed and free D Voigt profile
• MEAN value (!) 15 % above HITRAN2004
• Good agreement (5%) with Ponsardin and Browell, JMS 1997
• Difference can not be explained by line profile
FixedFree
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Results : Self-broadening coefficientResults : Self-broadening coefficientResults : Self-broadening coefficientResults : Self-broadening coefficient
• 40 lines measured
• RMS < 1%
• 10 % lower thanHITRAN2004
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Results : Air-broadening coefficientResults : Air-broadening coefficientResults : Air-broadening coefficientResults : Air-broadening coefficient
• 40 lines measured
• RMS < 1%
• Very good agreement with HITRAN2004(less than 5%)
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Conclusion and prospectiveConclusion and prospectiveConclusion and prospectiveConclusion and prospective
40 different H2O lines measured between 815 and 835 nm.
Intensities in the 830 nm band 15% higher than HITRAN2004.
Self-broadening coefficients 10% lower than HITRAN2004.
Air-broadening coefficients in good agreement (< 5%) with HITRAN2004.
Dicke-narrowing although weak, check impact on intensities using other profiles (Galatry, Rautian,…)
New, independent experiments (FTS?)Update of HITRAN2004 ?