Spectral Emissivity Model Research Articles

Multi-spectral radiation thermometry based on the reconstructed spectral emissivity model

With the aim of solving the problem of detecting the true temperature of objects using multi-spectral radiation thermometry, this paper proposes a multi-spectral radiation thermometry method based on the reconstructed spectral emissivity model. Compared with traditional hypothetical spectral emissivity models, this model is a reconstruction emissivity model based on actual measured brightness and known wavelength quantities, which can improve the characterization of the real emissivity state of the measured object and not be affected by any hypothetical conditions or artificial preset parameters. In order to verify the effectiveness of the proposed method for detecting the temperature of real problems, a total of eight typical spectral emissivity models, spectral data of Si3N4 ceramics and ZrO2 ceramics, and measurement data of rocket motor casings are selected for experiments. The experimental results indicate that the true temperature calculated by the proposed method has a relative error of less than 1 %, and the calculation time is kept at the millisecond level, which meets the real-time multi-spectral temperature measurement requirements.

Prediction of Isotropic Rough Surface Directional Spectral Emissivity with Surface-Morphology-Dependent Modelling

The surface directional spectral emissivity of rough metal surfaces in industry is of concern in infrared temperature measurement. In this research, the height and slope possibility density functions are introduced as variables, and the directional spectral emissivity of isotropic rough surface is modelled accordingly. The model is designed to derive the directional spectral emissivity of rough metal surfaces from the surface morphology (possibility distribution of the height and slope) and the material property parameters (refractivity). Then, a sandblasted surface is taken as a case study. The sandblasted surface morphology is measured. A Polynomial surface is proposed to describe the sandblasted surface morphology and is compared with a Gaussian surface and a Cox–Munk surface. Finally, the directional spectral emissivity measurement and infrared temperature measurement are conducted. It is shown that the predicted directional spectral emissivity and measured temperature with the surface-morphology-dependent isotropic rough surface directional spectral emissivity model have high precision. In this work, the possibility distribution of the height and slope of the surface is introduced as independent variables to provide better accuracy compared to the reported models. In some cases, the error of the infrared temperature measurement could be reduced to 20% (80 degrees, compared to Gaussian surface). This work contributes to improving the accuracy of IR temperature measurement of rough surfaces.

Multiple Inversion Techniques with Multispectral Pyrometry for the Estimation of Temperature and Emissivity of Liquid Niobium and 100c6 Steel

The article presents the estimation of temperature and emissivities of niobium and 100c6 steel around their melting points using techniques based on the minimization of the least squares norm or on Bayesian inference. Two models were considered for the spectral emissivity, including a linear variation with respect to the wavelength and independent spectral values. The measured data used for the solution of the parameter estimation problem were radiative fluxes collected from a five-wavelength pyrometer. The experimental apparatus used in this work was designed for the characterization of metal samples with sizes of few millimeters at high temperatures, combining aerodynamic levitation and laser heating. The use of the linear spectral emissivity model provided quite consistent results with the ordinary least squares estimator and with stochastic simulations using the Metropolis-Hastings algorithm. Similarly, the model of independent spectral emissivities resulted in accurate emissivities, but it required an informative prior for temperature, such as the known melting point of the metal sample. Therefore, whatever the inverse method used, a priori supplementary information in terms of emissivities or temperatures are needed due to the temperature-emissivity correlation and the unknow emissivity behavior.

True temperature inversion for a multi-spectral pyrometer based on the inner penalty function constrained optimization algorithm

A data processing algorithm based on the inner penalty function for constrained optimization is presented for a multi-wavelength pyrometer. It can directly obtain the true temperature and spectral emissivity simultaneously without requiring for the spectral emissivity model beforehand. The simulation results show that the algorithm is suitable for continuous thermal radiation materials, and the absolute error is less than 15 K when the true temperature is 1800 K. The experimental results also verify the reliability of the algorithm. This data processing algorithm resolves the true temperature measurement by thermal radiation problem which was due to the unknown emissivity model.

Development of a multivariate spectral emissivity model for an advanced high strength steel alloy through factorial design-of-experiments

Variations in the spectral emissivity of advanced high strength steels (AHSS) during intercritical annealing leads to errors in pyrometry measurements, which, in turn, cause thermal excursions that impact the mechanical properties of the steel. This paper presents an empirical approach for modelling the spectral emissivity of advanced high strength steel. Samples of two dual-phase steel (DP980) alloys, having Si/Mn ratios of 0.04 and 0.23, are heated within a galvanizing simulator in atmospheres of 95%/5% N2/H2 and dew points of 10°C and −30°C. The spectral hemispherical reflectance of the annealed samples was measured with an FTIR spectrometer. The variation of the spectral emissivity with dew point, alloy composition, pre-annealed surface state, and wavelength is analyzed using full factorial designs. The significant main and interaction effects vary across the spectral range, with the ratio of alloy components and pre-annealed surface state dominating at shorter and longer wavelengths, respectively. The predicted spectral emissivity values obtained from the model fitted for a three-channel pyrometer shows good agreement with the measurements. This study shows response surface methods (RSM) to be a viable approach for developing spectral emissivity models for pyrometry applications.

Non-scanning wide range multi-wavelength imaging temperature measurement technology

Multi-wavelength temperature measurement technology is an advanced radiation temperature measurement technology, which assumes a functional relationship between emissivity and spectrum. The measured multi-wavelength radiation signals and the function relationship between emissivity and spectral is used to obtain the true temperature and emissivity of the target. Multi-wavelength imaging temperature measurement technology detects the multi-wavelength radiation image information of the target and inversely calculates the temperature field distribution of the target. Aiming at the inadequacy of color CCD-based multi-wavelength imaging temperature measurement, such as adaptability of the nonlinear spectral emissivity model, and the narrow dynamic range of temperature measurement, and so on, a four-wavelength non-scanning imaging temperature measurement method based on non-equal ratio filter color splitting at the diaphragm was proposed. This method could effectively compress the band imaging bandwidth to form four narrow band imaging detections, and was suitable for wide dynamic range temperature field measurement of nonlinear spectral emissivity model targets. A four-wavelength imaging thermometer was developed according to the proposed temperature measurement method. The thermometer was mainly composed of a window, a neutral optical attenuator, a four-color filter, an optical objective lens, a visible/near infrared integrated sensor, a measurement control unit, and software. The real temperature distribution of the target was obtained according to the multi-wavelength warming algorithm by the thermometer software. The target high-temperature field (800-2500 ℃) was tested under laser heating conditions. The comparison between the measurement result and the thermocouple data shows that the error is less than 1%, and the method has higher accuracy and better dynamic range adaptability.

Multi-spectral temperature measurement based on adaptive emissivity model under high temperature background

When the object surface temperature in high temperature environment is measured by multi-spectral temperature measurement method, the radiation generated by the reflection of the high temperature background on the surface of the object and the radiation emitted by the object itself are both received by the pyrometer. For one thing, the amount of radiation received by the pyrometer increases. On the other hand, the surface emissivity model may change. So a large temperature measurement error may occur. In order to accurately measure the true surface temperature of an object in a high temperature environment, a multi-spectral temperature measurement method based on adaptive emissivity model is proposed in this paper. First, BP neural network is used to identify the shape of spectral data and obtain the correspondence between spectral data and emissivity model, then output the emissivity model that conforms to the measured target and specific environment. Moreover, the traditional NSGA-II algorithm (Non-dominant sorting genetic algorithm-II) is prone to falling into local optimal solutions and the numerical values obtained are not accurate enough. In this paper, the concepts of clustering algorithm, difference operator and symmetrical solution are introduced in the process of crossover and mutation, and then the new algorithm of INSGA-II (Improved Non-dominant sorting genetic algorithm-II)) is proposed. On the basis of this algorithm, the emissivity model of BP network is combined to solve the target true temperature. The experimental results show that the maximum temperature measurement error can reach 60 K if the influence of high temperature background is ignored. After removing the influence of high temperature background, the non-adaptive emissivity model was used to obtain the maximum temperature error of 30 K, and the fluctuation between adjacent temperature points was large. The multi-spectral temperature measurement method based on adaptive emissivity model proposed in this paper can obtain more accurate temperature measurement results with the maximum error of 8 K.

Combining UV Spectra and Physical Chemistry to Constrain the Hot Electron Fraction in the Io Plasma Torus

AbstractWe have developed a spectral emission model that is a function of the plasma composition, electron temperature, and density in the Io plasma torus. The lines are excited by electron collisions and spontaneously decay resulting in UV emission that is diagnostic of the plasma conditions. In a previous study we used a single Maxwellian distribution to model the UV spectra obtained by the Cassini UVIS instrument in January 2001. We now try to determine the fraction of hot electrons using a double Maxwellian distribution where the core, thermal electron distribution is combined with a hot electron distribution, also assumed to be a Maxwellian. This spectral emission model does not well constrain the fraction of hot electrons, which can be seen by the χ2 output. By using physical chemistry modeling of equilibrium conditions, we determine the fraction of hot electrons. Our physical chemistry model shows that in order to match the plasma composition and temperatures near the orbit of Io during the Cassini flyby of Jupiter we need the hot electrons to comprise <0.3% of the total electron density.

Synchrocurvature modelling of the multifrequency non-thermal emission of pulsars

ABSTRACT We apply a synchrocurvature spectral emission model based on characterizing the dynamics of magnetospheric particles to fit the phase-average spectra of the most extended data base for the non-thermal spectra of pulsars. We consider 36 pulsars with well-determined non-thermal spectra from X-rays to gamma-rays. The sample includes Crab and the Crab twin, for which the spectra extend even to the optical/ultraviolet and infrared energies. We find that the model – with just three physical parameters and a global scaling – can fit the observations well across eight orders of magnitude for 18 of the 36 pulsars studied. Additionally, we find a set of eight pulsars for which the model still provides arguably good fits and another set of 10 pulsars for which the model fails in reproducing the spectra. We discuss why, propose and provide physical interpretations for a simple model extension (related to the geometry of the accelerating system with regards to the observer) that allows dealing with all such cases, ultimately providing very good fits for all pulsars. The extended model is still austere, adding only two additional parameters to the former set, of the same kind of the ones previously used. We use these fits to discuss issues going from the observed spectral origin, to the extent of the dominance of synchrotron or curvature regimes, the use of a model as predictor for searching new non-thermal pulsars starting from gamma-ray surveys, and how the model offers a setting where phase shifts between X-ray and gamma-ray light curves would naturally arise.

Concerning the adequacy of the emissivity model to experimental data when determining the true temperature of an opaque material by the thermal radiation spectrum

When determining the thermodynamic (true) temperature of an opaque material by the thermal radiation spectrum, the parametric model of spectral emissivity is chosen so that this model and sought material temperature can be considered adequate to the initial experimental data. The possible adequacy conditions are analyzed. The process of choosing a model on the basis of experimental data published for a tungsten sample heated in vacuum at a constant temperature is considered as an example.

Theoretical investigation on spectral emissivity of thermal control coatings with optical-rough surface

A theoretical model for calculating the spectral emissivity of the thermal control coating with rough surfaces is proposed based on the Monte Carlo method in this paper. Instead of treating the surface of the coating as a smooth surface, a diffuse surface or a rough surface using an empirical formula, the model applies a Gaussian random rough surface to the spectral emissivity calculation of the coating. Firstly, the Gaussian rough surface is established, and its properties are mainly determined by two parameters: the root-mean-square roughness(δ) and the coherent length(l). Then the spectral emissivity model of the thermal control coating with the rough surface is established by Monte Carlo method. The directional spectral emissivity of the smooth surface and the rough surface with different roughness is compared. Finally, the reasons for their differences in spectral emissivity are explained.

Determination of Opaque Material Temperature from the Spectral Distribution of Emitted Radiation Intensity with Unknown Emissivity

The thermodynamic temperature of an opaque material with unknown emissivity was determined from the recorded distribution of spectral intensities of the emitted radiation. The initial system of equations was derived in the logarithmic form in accordance with the Planck formula. At the first stage, the spectral dependence of the material emissivity was investigated with a special function—relative emissivity. Based on the analysis of spectral dependences of this function at different reference temperatures, a parametric model for the material emissivity was chosen. At the second stage, the desired parameters of the chosen model of spectral emissivity and the thermodynamic temperature of the material were determined. An example of the determination of a temperature of a tungsten sample from the spectral distribution of emitted radiation intensities is given. A method for narrowing the range, which includes the thermodynamic temperature of the material, is presented.

Directly data processing algorithm for multi-wavelength pyrometer (MWP).

Data processing of multi-wavelength pyrometer (MWP) is a difficult problem because unknown emissivity. So far some solutions developed generally assumed particular mathematical relations for emissivity versus wavelength or emissivity versus temperature. Due to the deviation between the hypothesis and actual situation, the inversion results can be seriously affected. So directly data processing algorithm of MWP that does not need to assume the spectral emissivity model in advance is main aim of the study. Two new data processing algorithms of MWP, Gradient Projection (GP) algorithm and Internal Penalty Function (IPF) algorithm, each of which does not require to fix emissivity model in advance, are proposed. The novelty core idea is that data processing problem of MWP is transformed into constraint optimization problem, then it can be solved by GP or IPF algorithms. By comparison of simulation results for some typical spectral emissivity models, it is found that IPF algorithm is superior to GP algorithm in terms of accuracy and efficiency. Rocket nozzle temperature experiment results show that true temperature inversion results from IPF algorithm agree well with the theoretical design temperature as well. So the proposed combination IPF algorithm with MWP is expected to be a directly data processing algorithm to clear up the unknown emissivity obstacle for MWP.

Spectral emissivity model of steel 309S during the growth of oxide layer at 800–1100 K

This work strived to determine the analytical relationships between the spectral emissivity and the wavelength at different temperatures during the growth of oxide layer on the specimen surface of steel 309S. In the experiment, the spectral emissivity was measured at eight wavelengths, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, and 2.1μm, at temperatures from 800 to 1100K in increments of 20K by multispectral radiation thermometry. To accurately measure the normal spectral emissivity, the detector employed in the thermometry should be perpendicular to the surface of specimens as accurately as possible. The temperature of specimen surface was measured by the two thermocouples, which were symmetrically welded onto the front surface of specimens. The average of their readings was regarded as the true temperature. With the spectral emissivity measured here, the variation in the spectral emissivity with wavelength was evaluated at different temperatures and different heating times. Ten emissivity models were evaluated. The effect of number of the parameters used in the models on the fitting accuracy was studied. Both the five-parameter LLWE and LWE models were very suitable for fitting the spectral emissivity and could farthest relieve the effect of heating time on the accuracy of temperature prediction. The uncertainties in the temperature prediction of steel 309S specimens were basically within 10K by thermometry using the two models over the present temperature and wavelength ranges.

Measurement on the Surface Temperature of Dispersed Chars in a Flat-Flame Burner Using Modified RGB Pyrometry

A new spectral-emittance method to modify RGB pyrometry is developed for the surface temperature measurements of dispersed chars in a Hencken flat-flame burner. Nikon D300s, with calibrated spectral response, was used as the detector for the measurement. First, we calculated an original lookup table for ratio–temperature of the camera on the basis of the blackbody assumption. Second, 420/440 two-color pyrometry using an intensified charge-coupled device (ICCD) combined with two adjacent bandpass filters centered at 420 and 440 nm was adopted here for a verified comparison to RGB pyrometry. On the basis of the normalized spectral emission distribution of char particles in the visible light region (390–710 nm) acquired by an Ocean2000 spectrometer, a calibrated normalized spectral emissivity model of burning chars was built. Then, the lookup table of the Nikon camera was further modified by this calibrated spectral emissivity model, enabling better predictions on char particle temperatures in cases of all d...

A Two-stage Polynomial Method for Spectrum Emissivity Modeling

Spectral emissivity is a key in the temperature measurement by radiation methods, but not easy to determine in a combustion environment, due to the interrelated influence of temperature and wave length of the radiation. In multi-wavelength radiation thermometry, knowing the spectral emissivity of the material is a prerequisite. However in many circumstances such a property is a complex function of temperature and wavelength and reliable models are yet to be sought. In this study, a two stages partition low order polynomial fitting is proposed for multi-wavelength radiation thermometry. In the first stage a spectral emissivity model is established as a function of temperature; in the second stage a mathematical model is established to describe the dependence of the coefficients corresponding to the wavelength of the radiation. The new model is tested against the spectral emissivity data of tungsten, and good agreement was found with a maximum error of 0.64%

White dwarf masses in intermediate polars observed with the Suzaku satellite

Context. White dwarfs (WDs) in cataclysmic variables (CVs) are important experimental laboratories where the electron degeneracy is taking place on a macroscopic scale. Magnetic CVs increase in number especially in the hard X-ray band (>10 keV) thanks to sensitive hard X-ray missions. Aims. From X-ray spectroscopy, we estimate the masses of nearby WDs in moderately-magnetized CVs, or Intermediate Polars (IPs). Methods. Using the Suzaku satellite, we aquired wide-band spectra of 17 IPs, covering 3-50 keV. An accretion column model of Suleimanov et al. (2005) and an optically-thin thermal emission code were used to construct a spectral emission model of IPs with resolved Fe emission lines. By simultaneously fitting the Fe line complex and the hard X-ray continuum of individual spectra, the shock temperature and the WD mass were determined with a better accuracy than in previous studies. Results. We determined the WD masses of the 17 IPs with statistical fitting errors of ~0.1-0.2 Msun in many cases. The WD mass of a recently-found IP, IGR J17195-4100, was also estimated for the first time (1.03+0.24-0.22 Msun). The average WD mass of the sample is 0.88 \pm 0.25 Msun. When our results were compared with previous X-ray mass determinations, we found significant deviation in a few systems although the reason of this is unclear. The iron abundance of the accreting gas was also estimated, and confirmed the previously reported sub-solar tendency in all sources with better accuracy.

Cassini UVIS observations of the Io plasma torus: II. Radial variations

On January 14, 2001, shortly after the Cassini spacecraft's closest approach to Jupiter, the Ultraviolet Imaging Spectrometer (UVIS) made a radial scan through the midnight sector of Io plasma torus. The Io torus has not been previously observed at this local time. The UVIS data consist of 2-D spectrally dispersed images of the Io plasma torus in the wavelength range of 561–1912 Å. We developed a spectral emissions model that incorporates the latest atomic physics data contained in the CHIANTI database in order to derive the composition of the torus plasma as a function of radial distance. Electron temperatures derived from the UVIS torus spectra are generally less than those observed during the Voyager era. We find the torus ion composition derived from the UVIS spectra to be significantly different from the composition during the Voyager era. Notably, the torus contains substantially less oxygen, with a total oxygen-to-sulfur ion ratio of 0.9. The average ion charge state has increased to 1.7. We detect S(V) in the Io torus at the 3 σ level. S(V) has a mixing ratio of 0.5%. The spectral emission model used can approximate the effects of a nonthermal distribution of electrons. The ion composition derived using a kappa distribution of electrons is identical to that derived using a Maxwellian electron distribution; however, the kappa distribution model requires a higher electron column density to match the observed brightness of the spectra. The derived value of the kappa parameter decreases with radial distance and is consistent with the value of κ=2.4 at 8 R J derived by the Ulysses URAP instrument (Meyer-Vernet et al., 1995). The observed radial profile of electron column density is consistent with a flux tube content, NL 2, that is proportional to r −2.

Molecular Beams in Space: Sources of OH(A→X) Emission in the Space Shuttle Environment

OH(A→X) emission bands have been observed in the molecular beam jets produced by Space Shuttle engine exhaust using the GLO imager spectrograph located in the payload bay. Spectra were collected at a resolution of 4 Å for both daytime and nighttime solar illumination conditions, all at an altitude of ∼390 km. A spectral analysis is presented that identifies and quantifies four separate OH(A) excitation processes. These include (i) solar-induced fluorescence of the OH(X) in the exhaust flow, (ii) solar-induced photodissociation of H2O in the exhaust at the strong Lyman-α solar emission line (1216 Å), (iii) solar-induced photodissociation of H2O in the far UV, at shorter wavelengths than Lyman-α, and (iv) luminescent collisions between atmospheric species and exhaust constituents, most probably the reaction O + H2O → OH(A) + OH(X). Process (i) produces a very rotationally cold and spectrally narrow component due to the rapid cooling of the OH(X) in the supersonic expansion of the exhaust flow. Processes (ii) and (iii) produce extremely excited OH(A), not well characterized by thermal vibrational or rotational distributions. The O + H2O chemiluminescent reaction has a substantial activation energy, 4.79 eV, and is only slightly above threshold for the ram geometry, where the engine exhaust is directed into the atmospheric wind. Evidence for process (iv) is observed in the night ram but not the night perpendicular exhaust atmospheric interaction, consistent with the threshold energy. Through the use of a nonequilibrium spectral emission model for OH, the integrated intensity, spectral distribution, and OH(A) internal state characterization for each of the above processes was deduced. Additional confirmation of the analysis is provided through the use of a model simulation of the space experiment to predict the total integrated intensities for processes (i) and (ii), for which the underlying spectroscopy, absorption cross sections, and solar excitation intensities are well established. Analysis of process (iii) has established, for the first time, a value for the far-UV conversion efficiency of absorbed photons to OH(A) photons of 0.26, which is twice the established value for Lyman-α. Under the assumption that O + H2O collisions are the source of process (iv), the analysis has established a chemiluminescence cross section at ram conditions of 1.7 × 10-2 Å2. Evidence of OH(A) emission bands from predissociated vibrational levels suggests that the total reaction cross section for process (iv) may be significantly higher. While this cross section assumes a single-step reaction of O with H2O, the possibility of a two-step process of O with other plume species has yet to be explored.

New model of iron spectra in the extreme ultraviolet and application to SERTS and EUV observations: A solar active region and capella

We report new predictions for the EUV spectral emission of FeIX-FeXXIV, based on data now available from the Solar EUV Rocket Telescope and Spectrograph (SERTS) and the Extreme Ultraviolet Explorer (EUVE) spectrometers. The iron spectral emission model is the first result of a larger effort to revise the Raymond & Smith model and to update the atomic rates. We present here predicted emissivities for selected densities and temperatures applicable to various astrophysical plasmas. Comparisons of our predicted spectra with two recent observations provide important tests of the atomic data. They also test to some extent some basic assumptions of coronal emission codes: optically thin spectral lines and ionization equilibrium.