| 1. |
- Buehler, Stefan A., et al.
(författare)
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ARTS, the atmospheric radiative transfer simulator
- 2005
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 91:1, s. 65-93
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Tidskriftsartikel (refereegranskat)abstract
- RTS is a modular program that simulates atmospheric radiative transfer. The paper describes ARTS version 1.0, which is applicable in the absence of scattering. An overview over all major parts of the model is given: calculation of absorption coefficients, the radiative transfer itself, and the calculation of Jacobians. ARTS can be freely used under a GNU general public license. Unique features of the program are its scalability and modularity, the ability to work with different sources of spectroscopic parameters, the availability of several self-consistent water continuum and line absorption models, and the analytical calculation of Jacobians.
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| 2. |
- Buehler, Stefan, et al.
(författare)
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Recent developments in the line-by-line modeling of outgoing longwave radiation
- 2006
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 98:3, s. 446-457
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Tidskriftsartikel (refereegranskat)abstract
- High frequency resolution radiative transfer model calculations with the Atmospheric Radiative Transfer Simulator (ARTS) were used to simulate the clear-sky outgoing longwave radiative flux (OLR) at the top of the atmosphere. Compared to earlier calculations by Clough and coworkers the model used a spherical atmosphere instead of a plane parallel atmosphere, updated spectroscopic parameters from HITRAN, and updated continuum parameterizations from Mlawer and coworkers. These modifications lead to a reduction in simulated OLR by approximately 4.1%, the largest part, approximately 2.5%, being due to the absence of the plane parallel approximation. As a simple application of the new model, the sensitivity of OLR to changes in humidity, carbon dioxide concentration, and temperature were investigated for different cloud-free atmospheric scenarios. It was found that for the tropical scenario a 20% change in humidity has a larger impact than a doubling of the carbon dioxide concentration. The sensitive altitude region for temperature and humidity changes is the entire free troposphere, including the upper troposphere where humidity data quality is poor.
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| 3. |
- Eriksson, Patrick, et al.
(författare)
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Qpack : a general tool for instrument simulation and retrieval work
- 2005
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 91:1, s. 47-64
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing requires a complete observation system, consisting of the instrument, a forward model and a retrieval environment. This paper presents a software tool to complement atmospheric sensors, with focus on passive instruments operating in the mm and sub-mm wavelength regions. The tool is of general character and offers a complete, flexible and fast calculation environment, demonstrated in both preparatory instrument studies and operational inversions. Its features include a rapid approach for modelling of sensor characteristics, several types of data reduction, simple definition of covariance matrices, a large number of retrieval and error quantities, inversion characterisation and random realisation of measurements. The software is freely available for scientific use.
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| 4. |
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| 5. |
- Foltynowicz, Aleksandra, et al.
(författare)
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Wavelength modulation absorption spectrometry from optically pumped collision broadened atoms and molecules
- 2007
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - Oxford : Pergamon Press. - 0022-4073 .- 1879-1352. ; 108:2, s. 220-238
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation of the influence of optical pumping on wavelength modulation absorption spectrometry (WMAS) signals from collision broadened atoms and molecules is presented. General expressions for the nf-WMAS signal from atomic and molecular systems, modeled as three-level systems that can accommodate both optical saturation and optical pumping, are derived by the use of a previously developed Fourier series-based formalism in combination with rate equations solved under steady-state conditions. The expressions are similar to those describing the nf-WMAS signal from two-level systems that can accommodate optical saturation [Schmidt FM, Foltynowicz A, Gustafsson J, Axner O, WMAS from optically saturated collision-broadened transitions. JQSRT 2005;94:225–54], the difference being the value of the saturation flux, wherefore the general parametric dependence of WMAS signals from optically pumped systems is the same as that from optically saturated systems. The additional effect of optical pumping on the WMAS signal is investigated for three typical cases: molecules or atoms in an ordinary atmosphere, atoms in an inert atmosphere, and atoms or molecules possessing metastable states. The possibility to describe any of these systems with a two-level model is investigated.
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| 6. |
- Kratz, David P., et al.
(författare)
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An inter-comparison of far-infrared line-by-line radiative transfer models
- 2005
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 90:3-4, s. 323-341
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Tidskriftsartikel (refereegranskat)abstract
- A considerable fraction (>40%) of the outgoing longwave radiation escapes from the Earth's atmosphere-surface system within a region of the spectrum known as the far-infrared (wave-numbers less than ). Dominated by the line and continuum spectral features of the pure rotation band of water vapor, the far-infrared has a strong influence upon the radiative balance of the troposphere, and hence upon the climate of the Earth. Despite the importance of the far-infrared contribution, however, very few spectrally resolved observations have been made of the atmosphere for wave-numbers less than . The National Aeronautics and Space Administration (NASA), under its Instrument Incubator Program (IIP), is currently developing technology that will enable routine, space-based spectral measurements of the far-infrared. As part of NASA's IIP, the Far-Infrared Spectroscopy of the Troposphere (FIRST) project is developing an instrument that will have the capability of measuring the spectrum over the range from 100 to at a resolution of . To properly analyze the data from the FIRST instrument, accurate radiative transfer models will be required. Unlike the mid-infrared, however, no inter-comparison of codes has been performed for the far-infrared. Thus, in parallel with the development of the FIRST instrument, an investigation has been undertaken to inter-compare radiative transfer models for potential use in the analysis of far-infrared measurements. The initial phase of this investigation has focused upon the inter-comparison of six distinct line-by-line models. The results from this study have demonstrated remarkably good agreement among the models, with differences being of order 0.5%, thereby providing a high measure of confidence in our ability to accurately compute spectral radiances in the far-infrared.
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| 7. |
- Menmuir, Sheena, et al.
(författare)
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Molecular contribution to the D alpha emission in the divertor of the ASDEX Upgrade experiment
- 2007
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 105:3, s. 425-437
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Tidskriftsartikel (refereegranskat)abstract
- Spectral line emission from the deuterium Balmer alpha line and from molecular deuterium in the Fulcher band, d(3)Pi(u)-> a(3)Sigma(+)(g), was studied in the outer divertor region of the ASDEX Upgrade plasma with a pair of relatively calibrated spectrometers. A dependence of the signals on the proximity of the plasma strike point and on divertor gas puffing was noted. The rotational spectrum of the lowest diagonal vibrational molecular bands indicated rotational temperatures of ca. 1000 K and hence, through calculation of relative upper state populations, a ground state vibrational temperature of ca. 4000 K. Calculating the particle fluxes, the molecular deuterium was found to contribute up to 1% of the D alpha intensity, the relative importance of the molecules at some divertor heights was affected by the position of the strike point.
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| 8. |
- Rothman, Laurence S., et al.
(författare)
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Special issue on planetary atmospheres
- 2008
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 109:6, s. 881-
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Tidskriftsartikel (refereegranskat)
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| 9. |
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| 10. |
- Schmidt, Florian, et al.
(författare)
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Wavelength modulation absorption spectrometry from optically saturated collision-broadened transitions
- 2005
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - Oxford : Pergamon Press. - 0022-4073 .- 1879-1352. ; 94:2, s. 225-254
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation of the influence of optical saturation on wavelength modulation absorption spectrometry (WMAS) signals from collision-broadened transitions is presented. Expressions are derived for the nth Fourier coefficient of the analytical detector signal, and thereby also for the nth harmonic signal from a WMAS instrumentation (i.e. the nf-WMAS signal), from a wavelength modulated collision-broadened transition exposed to optical saturation. The flux- (or irradiance-) and modulation-amplitude dependences of the nf-WMAS signal on resonance are scrutinized in detail. It is shown that the nth Fourier coefficient of the wavelength modulated analytical detector signal from an optically saturated collision-broadened transition can be written as a product of a flux-dependent (φ) bleaching function, given by (1+φ/φsat)-1 and identical to that appearing for ordinary, unmodulated absorption spectrometry (AS), and a flux-, detuning-, and modulation-amplitude-dependent wavelength modulated peak-normalized saturation-broadened Lorentzian lineshape function, specific for the WMAS technique. It is found that the nf-WMAS signal on resonance decreases faster than an ordinary AS signal as a function of laser flux when smaller-than-optimum modulation amplitudes are used, but slower when larger-than-optimum modulation amplitudes are used. When optimum (or close-to-optimum) modulation amplitudes are being used, on the other hand, the flux dependence of the WMAS signal resembles to a large degree that of ordinary AS. The conditions for when WMAS from collision-broadened transitions has the same flux dependence as ordinary AS are identified.
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| 11. |
- Sreerekha, T.R., et al.
(författare)
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A strong ice cloud event as seen by a microwave satellite sensor : simulations and observations
- 2008
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 109:9, s. 1705-1718
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Tidskriftsartikel (refereegranskat)abstract
- In this article, brightness temperatures observed by channels of the Advanced Microwave Sounding Unit-B (AMSU-B) instrument are compared to those simulated by a radiative transfer model, which can take into account the multiple scattering due to ice particles by using a discrete ordinate iterative solution method. The input fields, namely, the pressure, temperature, humidity, and cloud water content are taken from the short range forecast from the Met Office mesoscale model (UKMES). The comparison was made for a case study on the 25 January 2002 when a frontal system associated with significant cloud was present over the UK. It is demonstrated that liquid clouds have maximum impact on channel 16 of AMSU whereas ice clouds have maximum impact on channel 20. The main uncertainty for simulating microwave radiances is the assumptions about microphysical properties, such as size distribution, shape and orientation of the cloud particles, which are not known in the mesoscale model. The article examines the impact of these parameters on the cloud signal. The polarisation signal due to oriented ice particles at these frequencies is also discussed.
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| 12. |
- Teichmann, C., et al.
(författare)
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Understanding the polarization signal of spherical particles for microwave limb radiances
- 2006
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 10:1, s. 179-190
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a simple conceptual model to explain that even spherical scatterers lead to a polarization difference signal for microwave limb radiances. The conceptual model relates the polarization difference measured by a limb-looking sensor situated inside a cloud with the anisotropy of the radiation. In the simulations, it was assumed that the cloud consists of spherical ice particles with a radius of ...
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| 13. |
- Verdes, C. L., et al.
(författare)
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Partition function data and impact on retrieval quality for an mm/sub-mm limb sounder
- 2005
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 90:2, s. 217-238
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Tidskriftsartikel (refereegranskat)abstract
- The partition function plays a major role as it mainly governs the dependence of the spectral line strength (or line intensity) on the temperature. A wrong partition function will lead to an incorrect line strength, which will lead to a systematic error in the retrieval. Therefore, a careful investigation of the available partition function data and the sensitivity of the retrieval to this is required. Two partition function data sets, the HITRAN and the JPL, are considered in this paper. In a first step, we investigate the spread of the partition function ratios from the simple approximation values given by theory. We find that the HITRAN partition functions are usually higher than the values quoted by the simple approximation. The JPL partition functions are much closer to the values given by the approximation. Comparing directly the two datasets, with some exceptions, a good agreement is found. Only for 16 molecules (from 66 considered molecules), the deviations in the two data sets are larger than 2%. The retrieval error analysis shows that, for the case of the molecular species with strong signatures, an uncertainty in the partition function is directly translated into a retrieval error of the species in question. However, the uncertainty in the partition function of this species can have a high impact on the quality of weak species retrieval.
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| 14. |
- Li, Zhipeng, et al.
(författare)
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Electromagnetic energy flow near metal nanoparticles - II: Algorithms for the calculation of the light scattering of multi-spheres and photon energy transport via linear chains of Ag nanoparticles
- 2007
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Ingår i: Journal of Quantitative Spectroscopy & Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 103:2, s. 394-401
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Tidskriftsartikel (refereegranskat)abstract
- We present a new algorithm to calculate the near-field distribution of scattered light of multiple nanospheres based on recursive order-of-scattering (OS) and the matrix inversion approaches, which avoids the divergent problem encountered in origin OS method at the resonance condition. Using this method, we investigate the light-transport properties of linear chains of Ag nanospheres. We found a maximum 3 dB damping length of 1.4 mu m of the light propagation when the first sphere of the linear Ag spheres with the radius R = 25 nm was illuminated. The optimal configurations that favor the photon energy transport are investigated as well. (c) 2006 Elsevier Ltd. All rights reserved.
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| 15. |
- Ricaud, P., et al.
(författare)
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Measurements of mid-stratospheric formaldehyde from the Odin/SMR instrument
- 2007
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 107:1, s. 91-104
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of mid-stratospheric formaldehyde (H2CO) have been obtained from the limb-viewing sub-millimeter radiometer (SMR) instrument aboard the Odin satellite. The analysis is based upon the only weak (808 -> 707) rotational transition line Of H2CO that can be measured by Odin/SMR at 576.7083150GHz in the band dedicated to the measurement of carbon monoxide (CO). The signal-to-noise ratio is increased by averaging about 1000 spectra within 2-km width vertical layers in the stratosphere over periods from I to 7 days and within 3 latitude bands: Southern Hemisphere (90 degrees S-45 degrees S), tropics (30 degrees S-30 degrees N), and Northern Hemisphere (45 degrees N-90 degrees N). The faint H2CO line can then be retrieved using the standard scientific ground-segment developed for the Odin/SMR measurements. The mid-stratospheric H2CO shows maxima in the tropics for every period considered (January 2006, February 2005, March 2005, and September 2005). The spring-time extra-tropical mid-strato spheric H2CO is more intense than the fall-time extra-tropical amounts. The simulations from the three-dimensional chemical- transport model Reprobus satisfactorily show these general features. (C) 2007 Elsevier Ltd. All rights reserved.
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| 16. |
- Seta, Takamasa, et al.
(författare)
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Pressure broadening coefficients of the water vapor lines at 556.936 and 752.033 GHz
- 2008
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0273-1177 .- 0022-4073. ; 109:1, s. 144-150
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Tidskriftsartikel (refereegranskat)abstract
- The air induced broadening coefficients of the pure rotational transitions of H2O at 556.936 GHz (110←101), and 752.033 GHz (211←202) were measured by terahertz time-domain spectroscopy. The air broadening coefficient was determined to be for the 556.936 GHz line and for the 752.033 GHz line, respectively. The present broadening coefficients for the 556.936 GHz water line are significantly smaller than those of Markov and Krupnov [Measurements of the pressure shift of the 1(10)–1(01) water line at 556.936 GHz produced by mixtures of gases. J Mol Spect 1995:172;211–4] but relatively close to the values of the HITRAN database. The measured data may improve the accuracy of the abundance of water vapor retrieved from spectra obtained by the Odin/SMR satellite instrument. The effect on the satellite retrieval processing is discussed.
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| 17. |
- Walewski, Joachim, et al.
(författare)
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Prediction of temperature-insensitive molecular absorption lines in laser-assisted combustion diagnostics
- 2005
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Ingår i: Journal of Quantitative Spectroscopy & Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 91:4, s. 415-436
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Tidskriftsartikel (refereegranskat)abstract
- In laser-assisted combustion diagnostics it is a recurring task to predict molecular transitions whose signal strength depends only weakly on variations in temperature. The signal strength is proportional to the Boltzmann fraction of the level probed and the amplitude of the absorption line profile. In the past investigations have been presented in which this task was attack by detailed numerical calculations of the temperature dependence of pertinent physical properties of the molecule. Another widely applied approach relies on an analytical formula for the Boltzmann fraction of hetero-nuclear diatomic molecules and the neglect of line shape effects. The analytical approach experiences a continuing popularity in laser-assisted combustion diagnostics, which is why we compared both approaches with each other. The objective of this comparison was to assess the accuracy of the analytical approach and to reveal its potential pitfalls. Our comparison revealed that the analytical approach suffers from mediocre accuracy, which makes it unfit for practical applications. One cause is the neglect of higher lying vibrational levels, which show a non-negligible population for typical flame temperatures. Another reason is the neglect of fine structure splitting in molecules with non-zero orbit angular momentum in the ground state. Another reason for the observed inaccuracy is the neglect of line shape effects quenching, which were found to have a significant effect on the temperature sensitivity of a line. Because of its insufficient accuracy due to both oversimplified models of the molecular energy levels and the neglect of line shape effects and quenching we discourage from applying the analytical approach and recommend the use of detailed numerical approaches that are free of the above limitations.
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| 18. |
- Xu, Huailiang, et al.
(författare)
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Improved atomic data for iridium atom (Ir I) and ion (Ir II) and the solar content of iridium
- 2007
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 104, s. 52-70
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Tidskriftsartikel (refereegranskat)abstract
- From a combination of radiative lifetime measurements, performed with a time-resolved laser-induced fluorescence technique, for nine odd-parity levels of Ir I and four odd-parity levels of Ir II and branching fraction calculations, extended sets of transition probabilities have been derived for transitions of astrophysical interest. The new results are compared with the few experimental data available in the literature and a good agreement is found. They extend considerably the previous sets of transition probabilities available in the literature. Implications of the new results regarding the solar content of iridium are briefly discussed.
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