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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10

10

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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10

10

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 ?