The SPARK Line-by-Line code

The High-temperature nonequilibrium database CDSDv

The CDSDv database has been developed on the basis of the CDSD4000 database, and tailored for broadband radiative transfer applications such as Martian entries.

At the price of a limited loss in accuracy, a much more compact database is achieved, allowing fast and efficient radiative transfer calculations involving for high-temperature gas mixtures containing CO₂. It also allows calculating emission and absorption spectra with different rotational and vibrational temperatures, making it particularly suited for Spacecraft atmospheric entry applications.

The routine is described in the article "J. Vargas, B. Lopez, and M. Lino da Silva, CDSDv: A Compact Database For The Modeling of High-Temperature CO₂ Radiation, J. Quant. Spectrosc. Radiat. Transf., https://doi.org/10.1016/j.jqsrt.2020.106848". The paper can be downloaded here.

The database and source code files are provided below, allowing a list of line parameters (line position; emission and absorption coefficients; Lorentz and Doppler widths) to be obtained from the gas input parameters such as pressure, temperatures, chemical composition, and spectral window.

The code and associated database are supplied under a Lesser GNU 3.0 license, and should be cited as the JQSRT article listed above. The relevant files are downloadable through the direct link below:

link to CDSDv

Detailed description of the code

The SPARK Line-by-Line code has been written for simulating low-pressure plasma applications in aerospace applications (simulation of planetary atmospheric entry radiation), using the line-by-line method. The code can however be applied to a variety of different applications, which include the simulation of plasma radiation in low-pressure test facilities, the simulation of atmospheric opacities, the simulation of radiation from combustion processes, or even other applications.

The code numerical routines are capable of simulating bound-bound atomic and molecular radiation with fine-structure effects (singlet, doublet and triplet transitions, with Lambda-doubling effects). Bound-free radiation like photodissociation, photoionization and photodetachment transitions can be accounted for according to available cross-sections from the literature, regardless of whether they are cross-sections integrated over specific temperature ranges, or state-specific cross-sections. Free-free transitions like Bremsthrahlung are also accounted for, using the most popular theoretical and semi-empirical expressions found in the literature.

The Voigt line profile routine is able to account for Doppler broadening, typically the dominant broadening process in low-pressure plasmas, but also Lorentz collisional broadening processes which can be important for higher pressures or higher electron densities (Stark broadening). The line profile routine has been specifically tailored for allowing fast and accurate spectral simulations of about a million of lines, through the application of an innovative algorithm which has recently been developed (2007). The line calculation accuracy is also fully customizable by the user, allowing to chose application-specific compromises between results accuracy, for a larger number of line points, and speed of calculation, for a lower number of points. The numerical efficiency of the line calculation routine is the main factor that enables the application of the SPARK Line-by-Line to large-scale spectral simulations with millions of lines (with a particularly relevance for CO₂ IR radiation, which can be simulated through the more detailed line-by-line method).

The numerical code has been built with the maximum concern for flexibility. The spectral database is fully decoupled from the numerical routines, being handled in the form of ASCII text files. The code provides a graphical interface, useful for quick spectral simulations, but this merely works as an additional layer, as all the inputs-outputs of the SPARK Line-by-Line code are handled through text-files. The SPARK Line-by-Line code can therefore be utilized coupled to an hydrodynamic and a radiative transfer code, provided that the former provides inputs in text-file format, and the latter accepts outputs in the same format. Finally, the code has been programmed in two separate blocks: An excitation module, which provides the populations of the atomic and molecular species internal levels, and a radiative module, which calculates the emission and absorption coefficients from the levels handled by the excitation routine. The excitation routine currently calculates the internal levels populations considering multitemperature (Tr,Tv,Texc) Boltzmann distributions, but is also able to take into account arbitrary user-supplied nonequilibrium populations.

Spectral database of the code

CO₂ Discrete	Infrared
H₂ Discrete	Lyman, Werner, Fulcher, B'-X, D-X, B"B-X, D'X
C₂ Discrete	Swan, Philips, Mulliken, Deslandres-D’Azambuja, Fox-Herzberg, Ballik-Ramsay, Freymark, Herzberg-f, Herzberg-g, Herzberg-F
CN Discrete	Violet, Red, Leblanc
CO Discrete	Infrared, 4^th Positive, Angstrom, 3^rd Positive, Triplet, Asundi, Hopfield-Birge, C-X, E-X, F-X, G-X
CO⁺ Discrete	1^st Negative, Comet Tail, Baldet-Johnston
N₂ Discrete	1^st Positive, 2^nd Positive, Vegard-Kaplan, Lyman-Birge-Hopfield, Birge-Hopfield 1, Birge-Hopfield 2, Worley-Jenkins, Caroll-Yoshino, Worey, e-X, Wu-Benesh, IR Afterglow
N₂⁺ Discrete	1^st Negative, 2^nd Negative, Meinel
NO Discrete	γ, β, δ, ε, β’, γ’
O₂ Discrete	Schumann-Runge, Schumann-Runge Continuum
C₃ Discrete	VUV, Swings (only T-dependent cross-sections)
Atomic Lines	n=1 (H) to n=36 (Kr) including neutrals, single and double ionized species, Mo, Xe, Xe⁺, Ba, Hg
Atomic Photoionization	n=1 (H) to n=12 (Mg) including neutrals, single and double ionized species, Si, Si⁺, Si⁺⁺, S, S⁺, S⁺⁺, Ar, Ar⁺, Ar⁺⁺, Ca, Ca⁺, Ca⁺⁺, Fe⁺⁺
Molecular Photoionization	CO₂, CO, CN, C₂, N₂, O₂, NO, H₂, C₃, C₂H
Molecular Photodissociation	H₂, H₂⁺
Bremstrahlung	H, He, He⁺, C, C⁺, N, N⁺, O, O⁺, Ne, Ar, Xe, H₂^-, N₂, N₂^-, O₂
Photodetachment	H^-, He^-, C^-, N^-, O^-, O₂^-

Associated packages

The SPARK Line-by-Line code includes a database routine (RKR-SCH) which is capable of producing accurate potential curves and transition probabilities from spectroscopic constants and transition moments found in the literature. The code works as follows: Spectroscopic constants from different bibliographical resources are imputed in a numerical routine which reconstructs the potential curves for the transition electronic states using an RKR method and calculates the upper and lower states wavefunctions solving the radial Schrodinger equation. Such wavefunctions are then coupled to accurate electronic transition moments from the literature, to yield appropriate Einstein coefficients.
A sample calculation of the full set of known potential curves for N₂, obtained using RKR-SCH, is presented here.

The SPARK Line-by-Line code has an associated radiative transfer routine (RADTRANS) which utilizes the ray-tracing method for the calculation of the radiative fluxes impacting a surface (such as a spacecraft thermal protections or a facility radiation detector). This routine is capable of running in a parallelized fashion in multiprocessor computers, and handling the very fine spectral grids (several million points) obtained using the SPARK Line-by-Line code. Radiative transfer is therefore fully calculated resorting to the line-by-line method. The radiative transfer routine has insofar successfully been applied to the simulation of the radiative fluxes of a Martian atmospheric entry in the case of several different missions: The 2008 NASA PHOENIX and the 2016 ESA Schiaparelli entries in Mars, The 1995 Galileo entry in Jupiter, and upcoming M1 class entries in Uranus/Neptune have also been successfully simulated.

Example of a Ray-tracing calculation for a Jupiter entry at 47.5km/s.

License and how to obtain a version of the code

The SPARK Line-by-Line code is distributed under a GNU Lesser General Public License, a free software license allowing researchers and developers to use and/or integrate the SPARK Line-by-Line code into their own (even proprietary) software.

Any user wishing to use the code, and agreeing to the license terms, should fill the form below in order to request a copy of the latest version of the code. For verification purposes and to avoid spambots, it is also required to fill a CAPTCHA verification at the end of the registration form.

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User's manual of the code

The code user's manual can be downloaded here.

Sample calculations using the SPARK line-by-line code

Sample calculations using the SPARK line-by-line code.

Emission coefficient for a 97% CO₂ - 3% N₂ (Martian-type) equilibrium mixture at 1000 K

Absorption coefficient for a 97% CO₂ - 3% N₂ (Martian-type) equilibrium mixture at 1000 K

Emission coefficient for a 97% CO₂ - 3% N₂ (Martian-type) equilibrium mixture at 5000 K

Absorption coefficient for a 97% CO₂ - 3% N₂ (Martian-type) equilibrium mixture at 5000 K

Emission coefficient for a 97% CO₂ - 3% N₂ (Martian-type) equilibrium mixture at 5000 K

Absorption coefficient for a 97% CO₂ - 3% N₂ (Martian-type) equilibrium mixture at 5000 K

Comparison of a synthetical spectra generated by the SPARK line-by-line code and a measured spectra for the CN VIolet Δv=0 System

Comparison of a synthetical spectra generated by the SPARK line-by-line code and a measured spectra for the CN VIolet Δv=-1 System

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