The Joint Airborne IASI Validation Experiment: An evaluation of instrument and algorithms

The Joint Airborne IASI Validation Experiment (JAIVEx) was designed to investigate the absolute radiometric accuracy of the Infrared Atmospheric Sounding Interferometer (IASI) and test the radiative transfer algorithms on which applications using IASI radiances rely. Two comprehensively instrumented research aircraft participated in coordinated measurements co-aligned with overpasses on the IASI instrument, with airborne interferometers obtaining radiance observations alongside intensive measurements of the atmospheric state. The JAIVEx data set has been used to place an upper bound on the absolute radiometric accuracy of IASI radiances. Further, a set of clear air case studies have been used to test competing formulations of the CO₂ line shape, water vapor spectroscopic line parameters and continuum. The current state-of-the art performance of line-by-line models is established with implications for optimal use of IASI radiances in numerical weather prediction.     

Line-by-line calculations of thermal infrared radiation representative for global condition: CFC-12 as an example

We estimate a current direct radiative forcing due to CFC-12 of 0.18 Wm^-2, which is likely to be the peak radiative forcing for CFC-12. Global measurements of CFC-12 show at present an almost negligible trend for CFC-12 and measurement in an industrialized region show evidence that the peak concentration is reached. It is expected that concentration of CFC-12 in industrialized regions begins to decline 1-3 years before the global concentration.Our radiative forcing calculations are based on a line-by-line model appropriate for simulation of global mean radiative forcing, including clouds and stratospheric temperature adjustment. The radiative forcing of 0.33 Wm^-2/ppbv is close to earlier published results for this compound. New spectroscopic measurements for CFC-12 are performed and compared to previously published results.     

A line-by-line calculation of low-resolution radiative properties of CO2-CO-transparent nonisothermal gases mixtures up to 3000 K

Low-resolution radiative properties (absorptivities, transmissivities, intensities) of nonisothermal or inhomogeneous gas mixtures at high temperatures, suitable for radiative heat transfer applications (e.g., in combustion) are obtained from a line-by-line calculation, using recently published high-resolution spectroscopic data at 296 K given by AFGL. It is shown that absorptivities obtained for isothermal mixtures of CO₂, CO, N₂ (and sometimes H₂O) agree with the corresponding measured spectra.     

A multi-spectral reordering technique for the full spectrum SLMB modeling of radiative heat transfer in nonuniform gaseous mixtures

A Multi-Spectral Reordering (MSR) scheme is introduced to improve the performances of the Spectral-Line Moment-Based (SLMB) modeling for the handling of full spectrum radiative heat transfer calculations in nonuniform media. Using this simultaneous reordering of the spectrum for several thermophysical conditions together with employing approximate formulations to evaluate path-averaged transmission functions for nonisothermal and nonhomogenous gaseous paths, a novel full spectrum gas radiation modeling method in nonuniform gaseous mixtures is constituted. The method is presented in details as well as the building of associated databases for CO₂ and H₂O at atmospheric pressure and for the temperature range of 300-2700 K. The new model is validated against line-by-line reference computations for a series of existing benchmarks and for a flame configuration. The MSR-SLMB modeling is shown to perform accurately and better than the standard SLMB one, while involving reasonable additional computational costs.     

Validation of the community radiative transfer model

To validate the Community Radiative Transfer Model (CRTM) developed by the U.S. Joint Center for Satellite Data Assimilation (JCSDA), the discrete ordinate radiative transfer (DISORT) model and the line-by-line radiative transfer model (LBLRTM) are combined in order to provide a reference benchmark. Compared with the benchmark, the CRTM appears quite accurate for both clear sky and ice cloud radiance simulations with RMS errors below 0.2 K, except for clouds with small ice particles. In a computer CPU run time comparison, the CRTM is faster than DISORT by approximately two orders of magnitude. Using the operational MODIS cloud products and the European Center for Medium-range Weather Forecasting (ECMWF) atmospheric profiles as an input, the CRTM is employed to simulate the Atmospheric Infrared Sounder (AIRS) radiances. The CRTM simulations are shown to be in reasonably close agreement with the AIRS measurements (the discrepancies are within 2 K in terms of brightness temperature difference). Furthermore, the impact of uncertainties in the input cloud properties and atmospheric profiles on the CRTM simulations has been assessed. The CRTM-based brightness temperatures (BTs) at the top of the atmosphere (TOA), for both thin (τ<5) and thick (τ>30) clouds, are highly sensitive to uncertainties in atmospheric temperature and cloud top pressure. However, for an optically thick cloud, the CRTM-based BTs are not sensitive to the uncertainties of cloud optical thickness, effective particle size, and atmospheric humidity profiles. On the contrary, the uncertainties of the CRTM-based TOA BTs resulting from effective particle size and optical thickness are not negligible in an optically thin cloud.     

The spectral-line moment-based (SLMB) modeling of the wide band and global blackbody-weighted transmission function and cumulative distribution function of the absorption coefficient in uniform gaseous media

The spectral-line moment-based (SLMB) modeling is proposed for the calculation of radiative properties of gases on any spectral width. The associated mathematical formulation is obtained by applying several concepts of the k-distribution methods such as the reordering of the wavenumber scale by monotonic variations of the absorption coefficient, together with the application of the k-moment method's principles. This approach gives both a general formula for the BTF and a simple and readily applicable approximation for the blackbody-weighted cumulated k-distribution function of the absorption coefficient. The model is applied for the computation of wide band BTFs and cumulative k-distributions for uniform columns of CO₂ and H₂O in the temperature range (300-2400 K) at atmospheric pressure. Model parameters are deduced from line-by-line (LBL) spectra calculated using the HITEMP database. Comparisons with LBL reference data as well as with contemporary modeling approaches (SLW, FSK, SNB) are performed and discussed.     

Evaluation of errors from neglecting polarization in the forward modeling of O2A band measurements from space, with relevance to CO2 column retrieval from polarization-sensitive instruments

Sensitivity studies have been performed to evaluate the errors resulting from ignoring polarization in analyzing spectroscopic measurements of the O₂A band from space, using the Orbiting Carbon Observatory (OCO) as a test case. An 11-layer atmosphere, with both gas and aerosol loading, and bounded from below by a lambertian reflecting surface, was used for the study. The numerical computations were performed with a plane-parallel vectorized discrete ordinate radiative transfer code. Beam and viewing geometry, surface reflectance and aerosol loading were varied one at a time to evaluate and understand the individual errors. Different behavior was observed in the line cores and the continuum because of the different paths taken by the photons in the two cases. The errors were largest when the solar zenith angle was high, and the aerosol loading and surface reflectance low. To understand the effect of neglecting polarization on CO₂ column retrievals, a linear error analysis study was performed on simulated measurements from the OCO spectral regions, viz. the 1.61 and 2.06 μm CO₂ bands and the O₂A band. It was seen that neglecting polarization could introduce errors as high as 10 ppm, which is substantially larger than the required retrieval precision of ∼2 ppm. A variety of approaches, including orders of scattering, spectral binning and the use of lookup tables are being explored to reduce the errors.     

Approximate radiative properties of methane at high temperature

Band model parameters for high-temperature methane have been generated up to 2000 K from an extended spectroscopic database. Part of the spectroscopic data are issued from calculations made in the framework of the effective Hamiltonian approach. These data have been completed by a statistical extrapolation. The calculations of global radiative properties such as band absorbtances and total emissivities are in good agreement with the available experimental data showing that the contribution of the hot bands is correctly taken into account. Finally, the degree of correlation between CH₄, CO₂ and H₂O spectra in typical conditions of combustion applications is discussed. Band model parameters are available upon request.     

An improved treatment of overlapping absorption bands based on the correlated k distribution model for thermal infrared radiative transfer calculations

This paper discusses several schemes for handling gaseous overlapping bands in the context of the correlated k distribution model (CKD). Commonly used methods are generally based on certain spectral correlation assumptions; thus they are either less accurate or less efficient and rarely apply to all overlapping bands. We propose a new treatment, which we developed from the traditional absorber amount weighted scheme and improved for application to various bands. This approach is quite efficient for treating the gaseous mixture as if it were a “single gas.” Numerical experiments demonstrate that the new scheme achieves high accuracy with a fast operating speed. To validate the new scheme, we conducted spectrally integrated calculations and sensitivity experiments in the thermal infrared region. Compared to line-by-line integration results, errors in cooling rates were less than 0.2 K/day below 70 Km and rose to 1 K/day from above 70 Km up to 100 Km; flux differences did not exceed 0.8 W/m² at any altitude. Changes in CO₂ and H₂O concentrations slightly influenced the accuracy of the results.     

Detecting annual and seasonal variations of CO2, CO and N2O from a multi-year collocated satellite-radiosonde data-set using the new Rapid Radiance Reconstruction (3R-N) model

The NOAA polar meteorological satellites have embarked the TIROS-N operational vertical sounder (TOVS) since 1979. Using radiosondes and NOAA-10 TOVS measurements which are collocated within a narrow space and time window, we have studied the differences between the TOVS measurements and simulated measurements from a new fast, Rapid Radiance Reconstruction Network (3R-N), non-linear radiative transfer model with up to date spectroscopy. Simulations use radiosonde temperature and humidity measurements as the prime input. The radiative transfer model also uses fixed greenhouse gas absorber amounts (CO₂,CO,N₂O) and reasonable estimates of O₃ and of surface temperature. The 3R-N model is first presented and validated. Then, a study of the differences between the simulated and measured radiances shows annual trends and seasonal variations consistent with independent measurements of variations in CO₂ and other greenhouse gases atmospheric concentrations. The improved accuracy of 3R-N and a better handling of its deviations with respect to observations allow most of difficulties met in a previous study (J. Climate 15 (2002) 95) to be resolved.     

Infrared radiation modeling of NO,OH, CO,H2O,and CO2 for emissivity/radiance prediction at high temperature

In the present study, infrared radiation modeling of NO, OH, CO, H₂O, and CO₂ molecules was devised based on a line-by-line method by utilizing a structured radiation analysis package, SPRADIAN07, coupled with up-to-date spectroscopic parameters and recent high-resolution radiation databases. An infrared calculation module was newly implemented in SPRADIAN07 for simulating the emissivity/radiance of NO and OH. The line positions of NO and OH molecules were determined by diagonalizing the Hamiltonian matrices of each molecule. The Einstein coefficients were obtained from either radiation databases or available calculated temperature-related line intensities. H₂O, CO₂, and CO were also modeled based on the high-resolution radiation databases, HITEMP2010 and CDSD-4000. When the line-by-line calculations were performed using the radiation databases, a parallel computing technique based on PC clusters was adopted for fast and efficient evaluation. The line-by-line model devised in the present study was validated by comparing the results with existing measurements. The simulations with room air absorption composed of H₂O and CO₂ were also carried out. The spectra taken from a plasma torch and those from a rocket plume were calculated by utilizing the present radiation model. It was shown that the calculated spectra are in good agreement with observed ones.     

Line parameters of H2O around 0.8 μm studied by tuneable diode laser spectroscopy

The absorption spectrum of H₂O has been extensively studied over the past decades in the near-infrared and visible regions, but there remain significant discrepancies in the 10,000-12,500 cm⁻¹ range even for the most intense lines. We have studied 24 lines of H₂O using an external-cavity diode laser emitting in the 810-830 nm range, in order to measure absolute line intensities as well as air- and self-broadening coefficients. Comparisons were made with values obtained from the HITRAN database and also with other parameters from recent experiments or predicted calculations. It is suggested that neglecting the effects of H₂O collisional narrowing in radiative transfer calculations of the Earth's atmosphere may have a small but significant impact on the radiative budget of the Earth.     

Infrared radiative transfer in planetary atmospheres—I. Effects of computational and spectroscopic economies on thermal heating/cooling rates

The availability of accurate spectroscopic data and improved knowledge of continuum absorption characteristics has required a further detailed study of i.r. radiative transfer. A sophisticated radiative transfer scheme based upon the Mayer-Goody random band model is developed and the derived transmissivities for H₂O, CO₂ and O₃ are calibrated against laboratory measurements. This calibrated scheme is used to assess the effects on calculated heating/cooling rate profiles of introducing computational and spectroscopic economies.     

The method of lines solution of discrete ordinates method for non-grey media

A radiation code based on method of lines (MOL) solution of discrete ordinates method (DOM) for radiative heat transfer in non-grey absorbing-emitting media was developed by incorporation of a gas spectral radiative property model, namely wide band correlated-k (WBCK) model, which is compatible with MOL solution of DOM. Predictive accuracy of the code was evaluated by applying it to 1-D parallel plate and 2-D axisymmetric cylindrical enclosure problems containing absorbing-emitting medium and benchmarking its predictions against line-by-line solutions available in the literature. Comparisons reveal that MOL solution of DOM with WBCK model produces accurate results for radiative heat fluxes and source terms and can be used with confidence in conjunction with computational fluid dynamics codes based on the same approach.     

Conversion issues between microwave radiance and brightness temperature

Microwave radiances are usually converted into brightness temperatures for data assimilation and retrievals. The Rayleigh-Jeans approximation has been believed to be a good approximation for the conversion at low frequencies, but inaccurate at high frequencies. However, the simplified radiative transfer models under the Rayleigh-Jeans approximation (hereafter referred as BT-RTE) have been successfully applied in radiance simulations for frequencies below 183 GHz, which has somewhat puzzled the radiative transfer community. This paper clarifies the confusion. In addition, the conversion formula for the third and the fourth Stokes components are derived.Simulations for a polarized sensor, the Special Sensor Microwave Imager and Sounder, show that the BT-RTE is generally accurate. Results for a polarimetric sensor, WINDSAT, show that the third and the fourth Stokes radiances should be converted using the exact conversion formula given in this study rather than using a direct Planck function conversion.     

The 2003 edition of the GEISA/IASI spectroscopic database

The content of the current (2003) version, GEISA/IASI-03, of the computer-accessible spectroscopic database, GEISA/IASI, is described. This “system” or database is comprised of three independent spectroscopic archives, which are (a) a database of individual spectral line parameters on 14 molecules, H₂O, CO₂, O₃, N₂O, CO, CH₄, O₂, NO, SO₂, NO₂, HNO₃, OCS, C₂H₂, N₂, and the related 51 isotopomers and isotopologues, representing 702,550 entries, in the spectral range 599-, (b) a database of spectral absorption cross-sections (6,572,329 entries related to six molecules, CFC-11, CFC-12, CFC-14, HCFC-22, N₂O₅, CCl₄), and a catalogue of microphysical and optical properties (mainly, the refractive indices) of atmospheric aerosols. The modifications and improvements, which have been implemented since the earlier editions of this database, in terms of content and management, have been explained in detail. GEISA/IASI has been created with the specific purpose of assessing the capability of measurement by the IASI instrument within the designated goals of ISSWG in the frame of the CNES/EUMETSAT European Polar System preparation.All the archived data can be handled through a user-friendly associated management software, which is posted on the ARA/LMD group web site at http://ara.lmd.polytechnique.fr.     

Microwave scattering properties of sand particles: Application to the simulation of microwave radiances over sandstorms

The single-scattering properties of sand/dust particles assumed to be ellipsoids are computed from the discrete dipole approximation (DDA) method at microwave frequencies 6.9-89.0 GHz in comparison with the corresponding Lorenz-Mie solutions. It is found that the single-scattering properties of sand particles are strongly sensitive to the shapes of the particles. The bulk scattering properties of sandstorms composed of spherical or nonspherical particles are investigated by averaging the single-scattering properties of these particles over log-normal particle size distributions. Furthermore, a vector radiative transfer model is used to simulate microwave radiances. The microwave brightness temperatures in the vertical polarization model are essentially not sensitive to sand particle habit, whereas microwave brightness temperature polarization differences are influenced by particle habit. It is shown that microwave brightness temperatures and brightness temperature polarization differences may be useful for estimating the effective particle sizes and mass loading of sandstorms.     

Ultrasound promoted the synthesis of N-propargylic β-enaminones

The synthesis of 14 novel N-propargylic β-enaminones from the reaction of β-alkoxy vinyltrihalomethyl[carboxyethyl] ketones [R³C(O)CHC(R¹)OMe, where R³ = CF₃, CCl₃, CO₂Et and R¹ = Me, Et, Pr, Bu, i-Pent, CH₂CH₂CO₂Me] with propargyl amines [R²NHCH₂CCH, where R² = Pr, PhCH₂] is reported. Yields, solvents and reaction times needed for reaction completion, by microwave irradiation (MW), conventional thermal heating (TH) and under ultrasound irradiation (US) are compared. The best results were obtained under US irradiation in good to excellent yields (70-93%).     

Oxygen codoping of ZnS:Tb,F electroluminescent thin film

Thin films of ZnS:Tb,F were sputter deposited from a ZnS:TbF₃ target in an oxygen-argon ambient. The highest electroluminescent brightness (82 cd/m² at 60 Hz) was measured from ZnS:Tb,F films with a 3.6 at% oxygen concentration. Oxygen concentrations above or below this concentration resulted in sharp decreases in brightness (56 cd/m² at 2.2 at% oxygen, and 42 cd/m² at 8.1 at% oxygen). The brightness improvement by oxygen codoping between 0 and 3.6 at% results from increased conduction charge with increasing oxygen concentrations. The brightness decrease for oxygen >3.6 at% is attributed to decreases of both excitation and radiative efficiencies. Improved electroluminescent brightness from oxygen codoping during sputter deposition of ZnS:Tb,F films was equivalent to the improvement observed in films deposited from a ZnS:TbOF target.     

CDSD-4000: High-resolution, high-temperature carbon dioxide spectroscopic databank

We present a high-resolution, high-temperature version of the Carbon Dioxide Spectroscopic Databank called CDSD-4000. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths, coefficients of temperature dependence of air- and self-broadened half-widths, and air-broadened pressure shifts) of the four most abundant isotopologues of CO₂. A reference temperature is 296 K and an intensity cutoff is 10⁻²⁷ cm⁻¹/molecule cm⁻² at 4000 K. The databank has 628,324,454 entries, covers the 226-8310 cm⁻¹ spectral range and designed for the temperature range 2500-5000 K. Format of CDSD-4000 is similar to that of HITRAN-2008. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. The databank is useful for studying high-temperature radiative properties of CO₂, including exoplanets atmospheres, aerothemal modeling for Mars entry missions, high-temperature laboratory spectra, and industrial applications. CDSD-4000 is freely accessible via the Internet site ftp://ftp.iao.ru/pub/CDSD-4000.