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

CNRS-LISAMSS 2006, Columbus, June 19-23, H 2 O: 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 Motivation Motivation 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-LISAMSS 2006, Columbus, June 19-23, Motivation Motivation Solar Spectrum with Atmospheric Absorptions

CNRS-LISAMSS 2006, Columbus, June 19-23, 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). Previous measurement in the near IR region Example of measurement: line intensities ( S  /cm molecule -1 ) position (cm -1 )HITRAN04PonsardinSchermaulRay ! Differences between different authors exceed stated accuracy (up to 30%)  need for more measurements

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

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

CNRS-LISAMSS 2006, Columbus, June 19-23, Experimental set-up L = 1 m, maximum path length 100 m, CaF 2 windows 3 MKS Baratrons Water sample Thermometer

CNRS-LISAMSS 2006, Columbus, June 19-23, Experimental Precautions HDO lines (probed in the mid-IR by the DFG laser) to validate H 2 O 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) H 2 O samples: Distilled, ultrasonic …

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

CNRS-LISAMSS 2006, Columbus, June 19-23,   10 ResultsResults Example2: Air-broadening of the line at cm -1

CNRS-LISAMSS 2006, Columbus, June 19-23, ResultsResults Example3: 3 lines near cm-1

CNRS-LISAMSS 2006, Columbus, June 19-23, Results : 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 Fixed Free

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

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

CNRS-LISAMSS 2006, Columbus, June 19-23, Conclusion and prospective 40 different H 2 O 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 ?