Experimental and theoretical study of line mixing in methane spectra. II. Influence of the collision partner (He and Ar) in the v3 IR band

Line mixing effects are studied in the v3 band of CH4 perturbed by Ar and He at room temperature. Experiments have been made in the 2800-3200 cm-1 spectral region using four different setups. They cover a wide range of total densities, including low (0.25-2 atm), medium (25-100 atm), and high (200-1000 atm) pressure conditions. Analysis of the spectra demonstrates that the spectral shapes (of the band, the Q branch, the P and R manifolds,...) are significantly influenced by line mixing. The theoretical approach proposed in the preceding paper is used in order to model and analyze these effects. As done previously, semiclassical state-to-state rates are used together with a few empirical constants. Comparisons between measurements and spectra computed with and without the inclusion of line mixing are made. They prove the quality of the approach which satisfactorily accounts for the effects of pressure and of rotational quantum numbers on the spectral shape. It is shown that collisions with He and Ar lead to different line-coupling schemes (e.g., more coupling within the branches and less between branches) and hence to different shapes. The influence of line coupling between different branches and manifolds is evidenced and studied using high pressure spectra and absorption in the band wings. © 1999 American Institute of Physics.Peer Reviewe

Interaction at mm and optical frequencies. Pt. 2 Specific atmospheric absorption and emission features: Investigation and modelling. Final report

This study deals with: Numerical analysis of the accuracy of recent models for atmospheric molecular absorption, in particular, studies of line mixing, line narowing (Dicke effect) and line shift effects; Establishment of a radiative transfet code for the computation of non-LTE outgoing radiation in the infrared spectrum; Analysis of up-to-date accuracy of initial spectroscopic information and its influence on outgoing radiation calculations in different spectral domains; Numerical investigations of the errors due to calculations of transmittance and outgoing radiation by k-distribution method. The investigations performed permit a more accurate estimate of up-to-date methods and algorithms for the calculation of atmospheric radiative transfer and to supply enhanced radiative transfer codes. (orig./KW)SIGLEAvailable from TIB Hannover: RR 1857(18) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekEuropean Space Agency (ESA), 75 - Paris (France)DEGerman

Interaction at mm and optical frequencies. Pt. 1 Current problems in radiative transfer simulations. Final report

An extensive literature survey of recent developments in the field of radiative transfer has been done. Within the scope of plane-parallel solutions of the RTE several solution methods have been presented: E.g. spherical harmonics, discrete ordinates, adding, doubling, matrix-operator, finite difference, and Gauss Seidel iteration. Solutions of the vector RTE permitting to take into account polarization and the subject of multidimensional geometry have been examined. General information and some models commonly used for solving the spherical RTE are presented. The subjects of RTM at millimetre wavelengths and the state of considering non-LTE effects has been reviewed. Models for the purpose of spectral integration have been discussed: GOMETRAN, LOWTRAN, MODTRAN, FASCOD-3, GENLN-2, and RADTRAN. Processes in the atmosphere influencing radiative transfer have been discussed: Monochromatic molecular absorption/emission properties (line parameters, line-mixing, and Dicke effect), broadband features (if required), scattering, properties of clouds and aerosols, and the lower boundary condition. Within a review of campaigns the validation problem has been discussed. (orig./KW)SIGLEAvailable from TIB Hannover: RR 1857(17) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekEuropean Space Agency (ESA), 75 - Paris (France)DEGerman