1. Nofal IBRAHIM, Pascale CHELIN, Johannes ORPHAL
LINE PARAMETERS OF WATER VAPOR IN THE NEAR- AND MID-INFRARED REGIONS DETERMINED USING TUNEABLE LASER SPECTROSCOPY
Nofal IBRAHIM, Pascale CHELIN, Johannes ORPHAL
Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA)
Université de Paris-XII, Créteil Cedex, France
YURI I. BARANOV
Optical Technology Division, NIST, Gaithersburg, MD , USA

2. Motivation 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
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
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

3. Solar Spectrum with Atmospheric Absorptions
Motivation
Solar Spectrum with Atmospheric Absorptions
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

4. Previous measurement in the near IR region
R. A. Toth, J. Mol. Spectrosc., 166, (1994).
J.-M. Flaud et al., J. Mol. Spectrosc., 185, (1997).
P. L. Ponsardin et al., J. Mol. Spectrosc., 185, (1997).
A. Lucchesini et al., Eur. Phys. J. D., 8, (2000).
R. Schermaul et al, J. Mol. Spectrosc. 208, (2001).
A. Ray et al., Appl. Phys. B, 79, (2004).
Example of measurement: line intensities (S1023/cm molecule-1)
position (cm-1)
HITRAN04
Ponsardin
Schermaul
Ray
1.679
---
1.960
1.504
1.865
2.185
2.290
1.888
3.236
3.81
5.080
0.8886
1.08
! Differences between different authors exceed stated accuracy (up to 30%)
 need for more measurements
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

5. Experimental set-up
ECDL (External External Cavity Diode Laser) and DFG (Difference Frequency Generation Laser) coupled with multi-path absorption cell:
Chopper
Wavemeter
ECDL:
30 mW nm
Linewidth 1MHz
DFG
3-5 µm
Linewidth 1MHz
Lock-in detection
LabVIEW acquisition
S/N>1000
Measurement time: few minutes
Mid IR
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

6. Experimental set-up ECDL: DFG Lock-in detection LabVIEW acquisition
30 mW nm
Linewidth 1MHz
DFG
3-5 µm
Linewidth 1MHz
Lock-in detection
LabVIEW acquisition
S/N>1000
Measurement time: few minutes
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

7. L = 1 m, maximum path length 100 m, CaF2 windows
Experimental set-up
L = 1 m, maximum path length 100 m, CaF2 windows
3 MKS Baratrons
Water sample
Thermometer
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

8. Experimental 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 …
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

9. Example1: Self broadening of the line at 12226.101 cm-1
Results
Example1: Self broadening of the line at cm-1
10
10
Very high S/N ratio( >1000)
Experimental lines very well modeled using Voigt profile
Observation of « Dicke narrowing »
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

10. Example2: Air-broadening of the line at 12226.101 cm-1
Results
Example2: Air-broadening of the line at cm-1
10
 10
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

11. Example3: 3 lines near 12259 cm-1
Results
Example3: 3 lines near cm-1
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

12. Results : Line Intensities
Fixed Free
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
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

13. Results : Self-broadening coefficient
40 lines measured
RMS < 1%
10 % lower than HITRAN2004
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

14. Results : Air-broadening coefficient
40 lines measured
RMS < 1%
Very good agreement with HITRAN2004 (less than 5%)
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006

15. Conclusion 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 ?
CNRS-LISA
MSS 2006, Columbus, June 19-23, 2006