Journal of Quantitative Spectroscopy & Radiative Transfer最新文献

Monitoring the evolution of the anthropogenic light emissions is a priority task in light pollution research. Among the complementary approaches that can be adopted to achieve this goal stand out those based on measuring the direct radiance of the sources at ground level or from low Earth orbit satellites, and on measuring the scattered radiance (known as artificial night sky brightness or skyglow) using networks of ground-based sensors. The terrestrial atmosphere is a variable medium interposed between the sources and the measuring instruments, and the fluctuation of its optical parameters sets a lower limit for the actual source emission changes that can be confidently detected. In this paper we analyze the effect of the fluctuations of the molecular and aerosol optical depths. It is shown that for reliably detecting changes in the anthropogenic light emissions of order ∼1 % per year, the inter-annual variability of the annual means of these atmospheric parameters in the measurement datasets must be carefully controlled or efficiently corrected for.

We introduce the Quantization Monte Carlo method to solve thermal radiative transport equations with possibly several collision regimes, ranging from few collisions to massive number of collisions per time unit. For each particle in a given simulation cell, the proposed method advances the time by replacing many collisions with sampling directly from the escape distribution of the particle. In order to perform the sampling, for each triplet of parameters (opacity, remaining time, initial position in the cell) on a parameter grid, the escape distribution is precomputed offline and only the quantiles are retained. The online computation samples only from this quantized (i.e., discrete) version by choosing a parameter triplet on the grid (close to actual particle’s parameters) and returning at random one quantile from the precomputed set of quantiles for that parameter. We first check numerically that the escape laws depend smoothly on the parameters and then implement the procedure on a benchmark with good results.

Four spectra of formaldehyde in natural isotopic abundance in the 3700–5200 cm^-1 region were recorded at low temperature 160–166 K at Synchrotron SOLEIL for various pressures. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures in the range 3700–4450 cm^-1 and analyzed using ab initio based effective Hamiltonian and line intensities computed using new ab initio dipole moment surface. A new measured line list contains positions and intensities for 6177 features. Refined parameters of effective Hamiltonian were fitted to all assigned line positions with the RMS deviations of 0.001 cm^-1. Updated line lists include intensity values based on ab initio variational calculations which were subsequently empirically optimized. Comparison of our theoretical simulation with previously available data as well as with high-resolution and low-resolution experimental spectra are reported.

This work reports benchmark data sets for radiative heat transfer in two distinct fire configurations obtained from the Measurement and Computation of Fire Phenomena (MaCFP) working group database. The cases include a 19.2 kW non-sooting turbulent methanol pool fire and a 15 kW sooting ethylene flame (referred to as the FM burner). The base configurations were simulated with large eddy simulation (LES) approaches using two different codes, namely FireFOAM and Fire Dynamics Simulator, respectively. Multiple frozen snapshots from these LES runs were radiatively evaluated using a photon Monte Carlo radiation solver and a line-by-line spectral model. The results were presented at three levels: Firstly, the radiative fields, including radiative emission, reabsorption, and heat flux contours, were shown. Secondly, the global radiative contributions from molecular gas species, soot, and wall boundaries were compared. Thirdly, a detailed spectral analysis of radiative fields for different components within five distinct spectral bands was presented. In the case of the non-sooting methanol pool fire, the radiative emission from CO₂ predominates. However, for the radiation reaching the boundaries, both CO₂ and H₂O contribute almost equally. Conversely, for the sooty FM burner configuration, radiative emission from soot, CO₂, and H₂O all contribute similarly. In terms of radiation reaching the boundary, soot is the primary contributor in FM Burner. In the methanol pool fire, the pool surface receives a comparable contribution from CO₂, H₂O, and burner rim radiation, whereas, for the FM burner, the burner inlet surface primarily receives radiation from soot.

Computations of room-temperature N${}_2$-broadening coefficients are performed for 3546 lines in the ${\nu }_7$ infrared absorption band of ethylene to provide data required for atmospheric studies but missing in spectroscopic databases. The calculations are done in the framework of a semi-classical exact-trajectory approach developed previously (Buldyreva and Nguyen, 2008). The active molecule is rigorously treated as an asymmetric top and the perturber is traditionally considered to be in its ground vibrational state. The data are provided for the ${}^{\mathrm{P,R}}$P-, ${}^{\mathrm{P,R}}$Q- and ${}^{\mathrm{P,R}}$R-subbranches (lines with $\Delta K_a=\pm 1$ having observable intensities) for (initial) rotational quantum numbers $J$ up to 22, limited by the available numerical energies for the excited vibrational level. Moreover, potentially detectable lines with $\Delta K_a=\pm 3$ are also considered for $J\le 13$, limited by high computational cost. Being validated by comparison with existing experimental results, these data can replace unavailable measurements and will be useful for atmospheric/industrial applications.

The highly congested absorption spectrum of ethylene (C₂H₄) is analyzed between 6075 and 8050 cm^-1. In the 6200–8050 cm^-1 range, a list of about 32,650 lines is retrieved from a room temperature spectrum recorded by Fourier transform spectroscopy (P = 15.72 mbar, L = 45 m). This dataset was merged with a set of about 3460 lines available in the literature in the region of the strong ν₅+ν₉ band near 6150 cm^-1. In addition, two FTS spectra at 130 K provide complementary information in the 6020–6320 cm^-1 range (about 7570 lines).

Relying on the position and intensity agreements with a line list of ¹²C₂H₄ transitions calculated by the variational method, a total of 4090 transitions is assigned to eighteen bands, ten of them being newly reported. All the reported assignments are confirmed by Lower State Combination Difference (LSCD) relations i.e. all the upper states (1749 in total) have coinciding determinations of their energies through several transitions (up to 6). The obtained empirical energy values are given and compared to their variational counterpart. As an additional validation test of the lower state assignments, the room temperature intensities are extrapolated at 130 K and compared to their experimental values. Overall, a large fraction of the strong lines of the region is assigned and the total intensity of the assigned transitions represents 46 and 55% of the total variational and experimental intensities at 296 K, respectively. In the considered range, variational positions deviate from measurements by a few cm^-1 and the total variational absorption is underestimated by 40 %.

The weighted contribution of ground-reflected component of light emissions from artificial sources gradually increases as the transitioning from bad-shielded to modernized light sources with low or zero direct uplight takes place in cities or towns. In this work, we demonstrate that the modeling of reflected light on a large domain for Lambertian flat surfaces does not require information about the height of the light sources and directional distribution of photons their produce. This kind of "invariance principle" becomes invalid when the homogeneity condition for the surface albedo is violated. However, we have shown that an analytical solution exists also for position-dependent albedo and even for angle-dependent reflectance which is the effect we now include to the light pollution models for the first time. This effect is known from the observation of sunbeams entering uneven surfaces at different zenith angles. Here in analogy with that daylight model we derive formulae for ground surfaces illuminated by artificial lights located at different heights above the surrounding terrain.

Wavelength calibration in diffraction spectroscopy typically depends on identifying strong, well-known lines in the recorded spectra and fitting a calibration function to them. In this paper, we outline a novel method (order penalization) for improving spectroscopic calibrations by extending non-linear least squares fitting of the calibration curve. The method introduces an extra term into the minimized quantity that penalizes disagreement in the positions of spectral lines observed in multiple diffraction orders. The primary advantage of this method is that the lines used do not have to be identified, except for establishing the fact that they are different orders of the same line. This increases the number of constraints on the calibration curve, potentially in spectral regions where no regular calibration lines are available. The mathematical basis of this method is described, and the performance of this method is evaluated on simulated data and experimental data from the National Institute of Standards and Technology (NIST) Electron Beam Ion Trap. We demonstrate the effectiveness of the method on the spectra of highly charged Ag-like Re${}^{28+}$ and nearby charge state ions.

We propose a laser occultation method for simultaneous profiling atmospheric temperature and pressure. Measurements can be performed on the optical link between two low-orbit satellites, where frequency-stepwise laser pulses are transmitted from one to the other. These pulses, covering several oxygen absorption lines in the wavelength domain, measure the broadened atmospheric absorption optical depth along the transmission path with a spectral resolution of tens of megahertz. In this way, atmospheric temperature and pressure are obtained by analysing the retrieved shape and intensity of the spectral lines. With the motion of the two satellites, the inter-satellite optical link penetrates different atmospheric layers at various altitudes, enabling the measurement of the vertical structure of atmospheric thermodynamic parameters from the troposphere to the lower thermosphere. This paper presents an end-to-end simulation of the proposed method, including models for laser occultation beam tracing, radiative transfer, and data inversion. The simulation results reveal that with minimal satellite payload resources, this method can accurately measure temperature and pressure at a vertical resolution of 100 m from 5 km to 90 km altitude with accuracies of ±1.5 K and 5 %, respectively. As the proposed differential absorption laser occultation method is independent of the hydrostatic equilibrium hypothesis for data inversion, it can eliminate errors associated with prior data at reference altitudes. It is believed that our method has provided a promising approach to laser satellite constellation for atmospheric observation.

This work is a supplement the article “Influence of arable land location incorporating its roughness on blue-sky albedo variation” [J Quant Spectrosc Radiat Transf. 296 (2023) 108,440]. It quantifies the influence of the location (expressed by latitude) of bare arable land on a global scale and its roughness on the optimal time (T_o) of land observation with acceptable errors to determine its mean diurnal blue-sky albedo (α_d). The article also discusses how the risk of making these errors changes with the change in land latitude. The study focuses on the influence of the location of one soil unit, Cambisol, common to all latitudes in both hemispheres. This is the same unit whose albedo variation was analyzed in the supplementary article mentioned above.