Resonator spectrometer for precise broadband investigations of atmospheric absorption in discrete lines and water vapor related continuum in millimeter wave range.

The instrument and methods for measuring spectral parameters of discrete atmospheric lines and water-related continuum absorption in the millimeter wave range are described. The instrument is based on measurements of the Fabry-Pérot resonance response width using fast phase continuous scanning of the frequency-synthesized radiation. The instrument allows measurement of gas absorptions at the cavity eigenfrequencies ranging from 45 to 370 GHz with the highest to date absorption variation sensitivity of 4x10(-9) cm(-1). The use of a module of two rigidly bounded maximum identical resonators differing in length by exactly a factor of two allows accurate separation of the studied gas absorption and spectrometer baseline, in particular, the absorption by water adsorbed on the resonator elements. The module is placed in a chamber with temperature controlled between -30 and +60 degrees C, which permits investigation of temperature dependence of absorption. It is shown that systematic measurement error of discrete atmospheric line parameters does not exceed the statistical one and the achieved accuracy satisfies modern demands for the atmospheric remote sensing data retrieval. Potential systematic error arising from the neglect of the effect of water adsorption on mirror surfaces is discussed. Examples of studies of water and oxygen spectral line parameters as well as continuum absorption in wet nitrogen are given.

[1]  Gerald T. Fraser,et al.  Investigation of the water-vapor continuum in the THz region using a multipass cell , 2005 .

[2]  J. Flaud,et al.  Molecular Line Parameters for the “MASTER” (Millimeter Wave Acquisitions for Stratosphere/Troposphere Exchange Research) Database , 2005 .

[3]  G. T. Fraser,et al.  Continuum and magnetic dipole absorption of the water vapor-oxygen mixtures from 0.3 to 3.6 THz , 2008 .

[4]  G. Chantry.  Modern aspects of microwave spectroscopy , 1979 .

[5]  A. F. Krupnov,et al.  Pressure shift and broadening of 110–101 water vapor lines by atmosphere gases , 2008 .

[6]  G. Golubiatnikov,et al.  Shifting and broadening parameters of the water vapor 183-GHz line (313-220) by H2O, O2, N2, CO2, H2, He, Ne, Ar, and Kr at room temperature , 2005 .

[7]  K. Künzi,et al.  Water vapor continuum: absorption measurements at 350 GHz and model calculations , 2002 .

[8]  Modern Millimeter-Wave Resonator Spectroscopy of Broad Lines , 2000 .

[9]  V. V. Parshin,et al.  Broadening and shifting of the 321-, 325- and 380-GHz lines of water vapor by pressure of atmospheric gases , 2007 .

[10]  C. Boulet,et al.  History and future of the molecular spectroscopic databases , 2005 .

[11]  F. D. Lucia,et al.  Laboratory measurements of dry air atmospheric absorption with a millimeter wave cavity ringdown spectrometer , 2007 .

[12]  Gerald T. Fraser,et al.  New measurements of the water vapor continuum in the region from 0.3 to 2.7 THz , 2008 .

[13]  Hugh C. Pumphrey,et al.  Instrumental and spectral parameters: their effect on and measurement by microwave limb sounding of the atmosphere , 2000 .

[14]  A. Hauchecorne,et al.  A review of remote sensing techniques and related spectroscopy problems , 2005 .

[15]  G. Golubiatnikov,et al.  Pressure Broadening of the Rotational Line of Oxygen at 425 GHz , 2002 .

[16]  Hans J. Liebe,et al.  The atmospheric water vapor continuum below 300 GHz , 1983, 1983 Eighth International Conference on Infrared and Millimeter Waves.

[17]  Extension of the range of resonator scanning spectrometer into submillimeter band and some perspectives of its further developments , 2006 .

[18]  D. S. Makarov,et al.  60-GHz oxygen band: precise broadening and central frequencies of fine-structure lines, absolute absorption profile at atmospheric pressure, and revision of mixing coefficients , 2005 .

[19]  P. Rosenkranz.  Water vapor microwave continuum absorption: A comparison of measurements and models , 1998 .

[20]  A. F. Krupnov,et al.  Reinvestigation of pressure broadening parameters at 60-GHz band and single 118.75 GHz oxygen lines at room temperature , 2003 .

[21]  A. F. Krupnov,et al.  Experimental study of the line mixing coefficient for 118.75 GHz oxygen line , 2004 .

[22]  R. H. Tipping,et al.  A simple analytical parameterization for the water vapor millimeter wave foreign continuum , 2003 .

[23]  D. S. Makarov,et al.  Collisional parameters of the 118-GHz oxygen line: Temperature dependence , 2008 .

[24]  Frank C. De Lucia,et al.  Broadband absolute absorption measurements of atmospheric continua with millimeter wave cavity ringdown spectroscopy , 2005 .

[25]  P. Rosenkranz.  Shape of the 5 mm oxygen band in the atmosphere , 1975 .

[26]  V. V. Parshin,et al.  Studies of 183 GHz water line: broadening and shifting by air, N2 and O2 and integral intensity measurements , 2003 .