Bands Of O2 Research Articles

Temperature retrieval of near space with the combined use of O2(a1Δg) and O2(b1∑+ g) dayglow emissions under self-absorption effect correction

Atmospheric temperature information in the near space is of great academic significance and engineering value to support the development and utilization of the near space. Based on the theory of O2 molecular dayglow spectroscopy and the mechanism of atmospheric radiative transfer, a method is proposed for the joint retrieval of temperature profiles in the near space using O2(a1Δg) and O2(b1∑+g) bands dayglow spectroscopy signal with the self-absorption effect. First, the temperature dependence of O2(a1Δg) and O2(b1∑+g) bands dayglow is investigated, and the influence of the self-absorption effect on the radiative transfer characteristics is analyzed in the limb-view mode. Then, with the use of the onion peeling algorithm, the dayglow emission spectra signals of the O2(a1Δg) and O2(b1∑+g) bands measured by the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) in the limb-viewing mode were processed, and combined with optimization algorithms, the temperature profiles from 35 km to 120 km is successfully retrieved. Finally, the accuracy and reliability of the self-absorption effect correction as well as the joint temperature retrieval were verified by comparing with temperature product data from remote sensing satellites such as Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), Atmospheric Chemistry Experiment Fourier-Transform Spectrometer (ACE-FTS), and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). The error analysis shows that the temperature retrieval error after correction for the self-absorption effect is about 3 K minimum and 20 K maximum.

Three‐Dimensional Modeling of the O2(1∆) Dayglow: Dependence on Ozone and Temperatures

AbstractFuture space missions dedicated to measuring CO2 on a global scale can make advantageous use of the O2 band at 1.27 μm to retrieve the air column. The 1.27 μm band is close to the CO2 absorption bands at 1.6 and 2.0 μm, which allows a better transfer of the aerosol properties than with the usual O2 band at 0.76 μm. However, the 1.27 μm band is polluted by the spontaneous dayglow of the excited state O2 (1∆), which must be removed from the observed signal. We investigate here our quantitative understanding of the O2(1∆) dayglow with a chemistry‐transport model. We show that the previously reported −13% deficit in O2(1∆) dayglow calculated with the same model is essentially due a −20% to −30% ozone deficit between 45 and 60 km. We find that this ozone deficit is due to excessively high temperatures (+15 K) of the meteorological analyses used to drive the model in the mesosphere. The use of lower analyzed temperatures (ERA5), in better agreement with the observations, slows down the hydrogen‐catalyzed and Chapman ozone loss cycles. This effect leads to an almost total elimination of the ozone and O2(1∆) deficits in the lower mesosphere. Once integrated vertically to simulate a nadir measurement, the deficit in modeled O2(1∆) brightness is reduced to −4.2 ± 2.8%. This illustrates the need for accurate mesospheric temperatures for a priori estimations of the O2(1∆) brightness in algorithms using the 1.27 μm band.

Orange-red-emitting BaSrGd4O8:Sm3+ phosphors with high thermal stability for applications in w-LEDs and latent fingerprints

Orange-red BaSrGd4O8:Sm3+ phosphors were obtained by a high-temperature solid-phase reaction. During this study, lattice environment, phase purity, element distribution, Photoluminescence (PL) spectra, thermal stability, and color purity of BaSrGd4O8:Sm3+ was systematically explored. The phosphors present a strong excitation with the charge transfer band (CTB) of O2− and Sm3+at 253 nm. Under 253 nm excitation, the BaSrGd4O8:Sm3+ phosphor shows characteristic peaks at 566, 605, 651, and 708 nm, which can be consistent with the 5G5/2→6HJ (J = 5, 7, 9, 11). And 605 nm is the most vigorous emission. The optimal doping concentration of BaSrGd4O8: Sm3+ is x = 1 mol%. Notably, as the temperature rises to 420 K, the BaSrGd4O8:Sm3+ still has outstanding thermal stability, reaching 95.38% of the initial luminescence intensity. Internal quantum efficiency (IQE) is tested as 64.83%. After calculation, the color purity of all phosphors reaches 96.5% or above. In addition, the w-LED (white light emitting diode) and single-colored LED were successfully prepared with 405 nm chips. The CIE (Commission International de L' Eclairage) coordinate of the packaged w-LED is (0.348, 0.335), which has the high color rendering index (CRI) of 90. Besides, the latent fingerprints (LFPs) visualized by BaSrGd4O8:Sm3+ phosphor can be clearly displayed. These experimental results exhibit the BaSrGd4O8:Sm3+ orange-red phosphors have promising application prospects in lighting devices and LFPs.

Evaluation of EPIC oxygen bands stability with radiative transfer simulations over the South Pole

The Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) satellite orbiting the Sun at the Lagrange-1 point was launched without onboard calibration systems. Vicarious calibration is conducted for 8 of the 10 UV/VIS/NIR channels using other low earth orbiting satellite instruments, while its two O2 bands (688 nm and 764 nm) rely on indirect moon-view calibrations because the same narrow-band O2 bands are not readily available from other in-flight instruments. This study compares EPIC measurements from the four O2 bands aiming at examining sensor stability over a uniquely suited location, i.e., the permanently snow-covered South Pole. The study utilizes radiative transfer model simulations with in-situ atmospheric soundings taken at South Pole during months of December and January from 2015 to 2022. The absolute discrepancy between the model simulations and observations is less than 1.0% for the two reference bands, but 5.75% and 15.63% for the 688 nm, and 764 nm absorption bands, respectively. The simulated A-band and B-band ratios are 16.09% and 4.74% higher than that from the observations. Various sensitivities are conducted to estimate possible contributions to the discrepancies from input atmospheric profiles, spectral surface albedos and surface BRDF. While none of the input uncertainties is likely to account for the large discrepancies in the oxygen absorption bands, a small shift in the instrument response function could be the main reason for these biases. On the other hand, the model simulations are able to capture systematic variations with observed angular measurements and explain the multi-year trends found in observed O2 band ratios due to satellite orbit shifting. When model simulated contributions from the angle variations are deducted from the observed O2 band ratios, the residual O2 band ratios are found to be stable since 2015.

Determination of Greenhouse Gas Concentrations from the 16U CubeSat Spacecraft Using Fourier Transform Infrared Spectroscopy.

Greenhouse gases absorb the Earth's thermal radiation and partially return it to the Earth's surface. When accumulated in the atmosphere, greenhouse gases lead to an increase in the average global air temperature and, as a result, climate change. In this paper, an approach to measuring CO2 and CH4 concentrations using Fourier transform infrared spectroscopy (FTIR) is proposed. An FTIR spectrometer mockup, operating in the wavelength range from 1.0 to 1.7 μm with a spectral resolution of 10 cm-1, is described. The results of CO2 and CH4 observations throughout a day in urban conditions are presented. A low-resolution FTIR spectrometer for the 16U CubeSat spacecraft is described. The FTIR spectrometer has a 2.0-2.4 μm spectral range for CO2 and CH4 bands, a 0.75-0.80 μm range for reference O2 bands, an input field of view of 10-2 rad and a spectral resolution of 2 cm-1. The capabilities of the 16U CubeSat spacecraft for remote sensing of greenhouse gas emissions using a developed FTIR spectrometer are discussed. The design of a 16U CubeSat spacecraft equipped with a compact, low-resolution FTIR spectrometer is presented.

Parameterized model to approximate theoretical collision-induced absorption band shapes for O2-O2 and O2-N2

Collision-induced absorption from vibronic transitions of O2-O2 and O2-N2 collision complexes is an important contributor to light-matter interaction in the atmosphere with relevance to radiative heat transfer and remote sensing. Despite in-depth studies involving quantum calculations of this effect, comparisons between experiment and theory would benefit from less computationally burdensome calculations that closely approximate the temperature dependence of the theoretical band shape and intensity. Accordingly, we present a parameterized representation of recent quantum calculations for collision-induced absorption by O2-O2 and O2-N2 about the 1.27 μm monomer band of O2. This approach leverages the theoretical decomposition of the spectra into exchange and spin-orbit contributions, with each component having a distinct temperature-dependent band shape. Composite spectra are approximated as a linear combination of the theoretical profiles with seven adjustable parameters that scale the component intensities and their dependences on temperature. We demonstrate that this empirical representation can accurately simulate the theoretical calculations, and we present a global fit of the model to previously reported collision-induced absorption spectra (O2-O2, O2-N2, and O2-air) measured by cavity ring-down spectroscopy over the temperature range 271 K–332 K.

Влияние колебательно-возбужденного молекулярного азота на инфракрасное свечение газов O3 и N2O на высотах средней атмосферы Земли

The concentrations of N2(X1g+, v' = 1) and the emission intensities of infrared bands of ozone O3 and nitrous oxide N2O are calculated at altitudes of 30–70 km of the Earth's middle atmosphere during precipitation of electrons with energies E = 2, 4, 10 MeV. It is shown that for a given relativistic electron flux of 105 e/cm2·s·ster, the concentrations of vibrationally excited molecular nitrogen N2(X1g+, v' = 1) are about 105–106 cm–3 at altitudes of 50–70 km of the middle atmosphere. The emission profiles of the infrared bands of ozone at 4.7 µm and 9,9 µm, as well as the infrared band of nitrous oxide at 4.5 µm, are calculated for precipitation of high-energy electrons with energies E = 2, 4, 10 MeV. It has been shown for the first time that vibrationally excited nitrogen N2(X1g+, v' = 1) plays an important role in changing the infrared balance of the middle atmosphere as a result of inelastic molecular collisions with O3 and N2O molecules during precipitation of high-energy electrons.

Performances between the FY‐4A/GIIRS and FY‐4B/GIIRS Long‐Wave InfraRed (LWIR) channels under clear‐sky and all‐sky conditions

AbstractThe observation‐minus‐background (O − B) bias characteristics are compared for the Long‐Wave InfraRed (LWIR) channels of the Geostationary Interferometric Infrared Sounder (GIIRS) on board Fengyun‐4A (FY‐4A) and Fengyun‐4B (FY‐4B) satellites under clear‐sky and all‐sky conditions. Under the clear‐sky condition, the data quality of the FY‐4B/GIIRS is better than that of the FY‐4A/GIIRS. Specifically, the standard deviations (<1 K) of the O − B values for FY‐4B/GIIRS LWIR channels are smaller than those (>1 K) of the FY‐4A/GIIRS, especially in carbon dioxide (CO2) and ozone (O3) absorption bands. The diurnal variations of the mean O − B biases for the O3 band of the FY‐4B/GIIRS are less than those of FY‐4A/GIIRS. To our surprise, the diurnal variations of O − B biases for the FY‐4B/GIIRS and FY‐4A/GIIRS channels show an obvious antiphase characteristic in the CO2 band, which could be caused by diurnal environmental field variations from the different geostationary (GEO) platforms. In addition, the FY‐4B/GIIRS channel 7 (703.75 cm−1) has smaller pixel‐dependent biases than those of FY‐4A/GIIRS. Under the all‐sky condition, the observation and cloudy simulation () for channels 7 (703.75 cm−1), 36 (721.875 cm−1), and 320 (900 cm−1) of the FY‐4B/GIIRS are more consistent than those of FY‐4A/GIIRS with smaller root‐mean‐square errors (RMSEs), which also indicates a better observation quality in the cloudy area.

Influence of Scattered Sunlight for Wind Measurements with the O2(a1Δg) Dayglow

Observing the O2(a1Δg) dayglow with the limb-viewing DASH instrument enables remote sensing of neutral wind in near space. Many advantages are gained by using this new approach, but the influence factors on measurement accuracy have not been thoroughly investigated. This paper reports the quantitative evaluation of the wind error caused by scattered sunlight. The spectral concept of the O2(a1Δg) band and the measurement technique are briefly described. A comprehensive truth model simulation that is based on atmospheric limb radiance spectra and the instrument concept are used to obtain interferogram images. The algorithm, which uses these images to retrieve the interferogram containing information solely from the target altitude, is described. The self-absorption effect is taken into account in the unraveling of the line-of-sight integration. The influence of scattered sunlight on the limb-viewing weight and signal-to-noise ratio, two definitive factors for wind definitive factors, are also described. Representative wind precision profiles and their variation with surface albedo, aerosol loading, and cloud are presented. This indicates that the random error for Doppler wind is in the range of 2–3 m/s for the tangent height range from 45–80 km, and the wind precision under 45 km suffers significantly from scattered sunlight background.

O2 based resonantly ionized photoemission thermometry analysis of supersonic flows.

Characterization of the thermal gradients within supersonic and hypersonic flows is essential for understanding transition, turbulence, and aerodynamic heating. Developments in novel, impactful non-intrusive techniques are key for enabling flow characterizations of sufficient detail that provide experimental validation datasets for computational simulations. In this work, Resonantly Ionized Photoemission Thermometry (RIPT) signals are directly imaged using an ICCD camera to realize the techniques 1D measurement capability for the first time. The direct imaging scheme presented for oxygen-based RIPT (O2 RIPT) uses the previously established calibration data to direct excite various resonant rotational peaks within the S-branch of the C3Π, (v = 2) ← X3Σ(v' = 0) absorption band of O2. The efficient ionization of O2 liberates electrons that induce electron avalanche ionization of local N2 molecules generating N2 +, which primarily deexcites via photoemissions of the first negative band of N2+(B 2 Σ u+-X 2 Σ g+). When sufficient lasing energy is used, the ionization region and subsequent photoemission signal is achieved along a 1D line thus, if directly imaged can allow for gas temperature assignments along said line; demonstrated here of up to five centimeters in length. The temperature gradients present within the ensuing shock train of a supersonic under expanded free jet serves as a basis of characterization for this new RIPT imaging scheme. The O2 RIPT results are extensively compared and validated against well-known and established techniques (i.e., CARS and CFD). The direct imaging capability fully realizes the technique's fundamental potential and is expected to be the standard of implementation going forward. The direct imaging capability can play instrumental roles in future scientific studies that rely upon acute characterization of thermal gradients within a medium that cannot be easily resolved by a point. Furthermore, the removal of the spectrometer greatly reduces the cost, complexity, and optical alignment associated with prior RIPT measurements.

Simulation of Mesosphere Wind Measurement with Multiple Emission Lines of the O2(0-1) Band Using Space-Based Doppler Asymmetric Spatial Heterodyne

For space-based atmospheric wind measurements, full-link simulation is critical for the optimization of the instrument indicators and the evaluation of the measurements’ performance. This paper presents observation simulations and error verification of the mesosphere wind measurement with four emission lines of the O2(0-1) band by using the space-based Doppler Asymmetric Spatial Heterodyne (DASH), named the Mesosphere Wind Image Interferometer (MWII). The passive wind measurement principle and the DASH concept are first described. The full-link simulation consists of radiation simulation, the instrument forward model, and the wind retrieval model. The four emission lines at about 866.5 nm of the O2(0-1) band were selected as the observation targets. The radiation characteristics of the target lines were studied and calculated, as well as the background radiation. Based on the LOS radiation integral model, a numerical simulation of the raw observation data was carried out using the instrument model. The interference fringe priority strategy and joint wind decision method were proposed to achieve multiple-emission-line wind retrieval with higher precision. In the simulation, multiple-line retrieval could improve the precision by more than 30% compared to single-line retrieval under the same conditions. The error simulation indicated that the wind profile precision was 3–9 m/s in the altitude range of 50–110 km, with an average accuracy of about 1 m/s, proving that the scheme of MWII has good altitude coverage of the whole mesosphere and a part of the lower thermosphere.

Remarkably High Conductivity and Power Factor in D–D′‐type Thermoelectric Polymers Based on Indacenodithiophene

AbstractThree p‐type thermoelectric (TE) polymers based on the indacenodithiophene moiety substituted with bis(alkylsulfanyl)methylene side‐chains (IDTS) are synthesized. The TE characteristics of IDTS‐based donor–donor’ (D–D′) type PIDTSDTTT and donor–acceptor (D–A) type polymers, PIDTSBT and PIDTS2FBT are investigated. Remarkably higher electrical conductivity (σ = ≈1000 S cm−1) and power factor (PF = ≈120 μW m−1 K−2) by doping with AuCl3 are measured for PIDTSDTTT compared to D–A type polymers. The higher σ of PIDTSDTTT originates from its higher carrier concentration compared to those of PIDTSBT and PIDTS2FBT. Moreover, the facile polaron‐to‐bipolaron transition is measured, and the charge carriers are calculated to be more stable with extended delocalization in PIDTSDTTT compared to D–A polymers. The significantly higher doping stability in PIDTSDTTT can be explained in terms of the higher conduction band of bipolarons than the valence band of O2 and H2O, which blocks the facile reduction of bipolarons in air. The energetic structures of doped polaron and bipolaron states, as well as pristine TE polymers, must be carefully considered to realize efficient and stable p‐type thermoelectric polymers, where a D–D′ type structure with further enhanced carrier mobility can be considered as a potential molecular framework.

Solid-state synthesis, characterizations and luminescent properties of EuBO3 phosphors with various Gd3+ concentrations for X-ray screen material application

In the present work, EuBO3 phoshors doped with various Gd3+ ion concentration, Eu1-XGdXBO3; (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7), were synthesized by solid state reaction method at 900° for 18 h. Their crystal structure was determined by X-ray diffraction (XRD) technique showing triclinic EuBO3 (JCSD 01-089-7888) and hexagonal crystal EuBO3 (JCDD 00-013-0485). Structure dependence luminescence concentration quenching was observed. The photoluminescence behaviors of Eu3+ in the phosphor material were investigated by the excitation and emission spectra which show the charge-transfer band (CTB) of O2−→Eu3+. The excitation bands of Gd3+ ions were observed at 275 nm (8S7/2 → 6I9/2) and 313 (8S7/2 → 6D7/2). The emission spectra displayed two prominent peaks of magnetic dipole (5D0→7F1) and electric dipole (5D0→7F2) transitions which signify the symmetry of the lattice. The CIE chromaticity coordinates were reddish-orange emission (x = 0.6635, y = 0.364) which corresponds to excited by the UVGL-25 Compact UV Lamp at 365 nm and X-ray Cu target (40 kV, 30 mA).

Trends in spectrally resolved outgoing longwave radiation from 10 years of satellite measurements

In recent years, the interest has grown in satellite-derived hyperspectral radiance measurements for assessing the individual impact of climate drivers and their cascade of feedbacks on the outgoing longwave radiation (OLR). In this paper, we use 10 years (2008–2017) of reprocessed radiances from the infrared atmospheric sounding interferometer (IASI) to evaluate the linear trends in clear-sky spectrally resolved OLR (SOLR) in the range [645–2300] cm−1. Spatial inhomogeneities are observed in most of the analyzed spectral regions. These mostly reflected the natural variability of the atmospheric temperature and composition but long-term changes in greenhouse gases concentrations are also highlighted. In particular, the increase of atmospheric CO2 and CH4 led to significant negative trends in the SOLR of −0.05 to −0.3% per year in the spectral region corresponding to the ν2 and the ν3 CO2 and in the ν4 CH4 band. Most of the trends associated with the natural variability of the OLR can be related to the El Niño/Southern Oscillation activity and its teleconnections in the studied period. This is the case for the channels most affected by the temperature variations of the surface and the first layers of the atmosphere but also for the channels corresponding to the ν2 H2O and the ν3 O3 bands.

Temperature Dependence of the Collision‐Induced Absorption Band of O2 Near 1.27 µm

AbstractThe 1.27 μm O2 band is increasingly called upon for air‐mass determination from ground‐based and space‐borne atmospheric spectra because of its spectral proximity to CO2, and CH4 bands at 1.6 μm, in contrast to the more distant A‐band at 0.76 μm. For this purpose, it is important to well characterize not only the narrow absorption lines but also the strong underlying broad collision‐induced absorption (CIA) structure and its temperature dependence. Spectra of pure O2, and of O2 in N2, were recorded by cavity ring down spectroscopy (CRDS) at 271 K and 332 K, with the help of a newly developed temperature regulated cell. The quality of the spectra allowed determining the small variations (at the few percent level) of the , , and binary coefficients with temperature. Together with the binary coefficients at 297 K reported previously, they allow characterizing the temperature dependence of the O2 CIA at 1.27 µm in atmospheric conditions. The obtained results are compared with previous measurements by Fourier transform spectroscopy (FTS) and recent theoretical calculations. In the wings of the O2‐O2 CIA, an increase with temperature is observed in agreement with calculations but contrary to these calculations, a decrease is observed near the maximum of the CIA band. The temperature dependence is found in good agreement with the theoretical values and the experimental values derived from the FTS measurements. Binary coefficients integrated over the entire band show almost no variation with temperature for O2‐N2 and a small increase for pure O2, in agreement with the theoretical predictions.

High accuracy spectroscopic parameters of the 1.27 µm band of O2 measured with comb-referenced, cavity ring-down spectroscopy

We present broadband spectroscopic parameters in the a1Δg−X3Σg−(0,0) band of 16O2 centered near 1.27 µm. High-fidelity absorption spectra were acquired on room-temperature air samples over the pressure range of 3.3 kPa to 100 kPa using a length-stabilized cavity ring-down spectrometer, with spectrum frequencies linked to a Cs clock via an optical frequency comb. Parameters were determined by multi-spectrum fitting of advanced line profiles to the measured spectra. This analysis yielded line intensities, positions, collisional broadening and shifting coefficients, Dicke narrowing and speed dependent line shape parameters, first-order line mixing coefficients, and O2-air binary absorption coefficients for collision-induced absorption. We report relative standard uncertainties in the line intensities and broadening coefficients of 0.16 % and 0.05 %, respectively, and line position uncertainties of 60 kHz (2 × 10−6 cm−1). Our analysis reveals strong numerical correlation in fits of the Dicke narrowing and speed dependent widths and shows that inclusion of a recently proposed modification to the Hartmann Tran line profile can increase fitted Dicke narrowing frequencies by as much as 50 %.

Refined Telluric Absorption Correction for Low-resolution Ground-based Spectroscopy: Resolution and Radial Velocity Effects in the O2 A-band for Exoplanets and K i Emission Lines

Abstract Telluric correction of spectroscopic observations is either performed via standard stars that are observed close in time and airmass along with the science target, or recently growing in importance, by theoretical telluric absorption modeling. Both approaches work fine when the telluric lines are resolved, i.e., at a spectral resolving power larger than about 10,000, and it is sufficient to facilitate the detection of spectral features at lower resolution. However, a meaningful quantitative analysis also requires the reliable recovery of line strengths. Here, we show for the Fraunhofer A-band of molecular O2 that the standard telluric correction approach fails in this at lower spectral resolutions, as an example for the general problem. Doppler-shift-dependent errors of the restored flux may arise, which can amount to more than 50% in extreme cases, depending on the line shapes of the target spectral features. Two applications are discussed: the recovery of the O2 band in the reflected light of an Earth analog atmosphere, as facilitated potentially in the future using an orbiting starshade and a ground-based extremely large telescope; and the recovery of the intrinsic ratio of the K i lines in the post-nova V4332 Sgr tracing the optical depth of the emitting region, to exemplify the relevance using present-day instrumentation. We show how one should derive correction functions for the compensation of the error in dependence of radial velocity shift, spectral resolution, and target line-profile function by use of high-resolution atmospheric transmission modeling, which has to be solved for the individual case.

Validation of spectroscopic data in the 1.27 µm spectral region by comparisons with ground-based atmospheric measurements

Various spectroscopic data for absorption lines due to the magnetic dipole transitions of the a1Δg−X3Σg−(0−0) band of O2 centered at 1.27 µm are tested by comparison with high-resolution ground-based atmospheric measurements recorded by Fourier Transform Spectrometers at Park Falls and Caltech (USA). This band is of importance for atmospheric remote sensing since it will be used (together with the O2 A-band near 760 nm) by the passive short wave infrared spectrometer onboard the MicroCarb satellite mission (i.e. this band includes the B4 band of MicroCarb, from about 7800 cm−1 to 7912 cm−1) for the determination of surface pressure and atmospheric aerosols. Spectroscopic data of the HITRAN2016 and GEISA2015 databases as well as those from recent laboratory studies are here used in a radiative transfer code to simulate atmospheric transmissions under the conditions of the measurements. Comparisons are made for different solar zenith angles and for the whole B4 spectral range considered by MicroCarb. Spectroscopic data of water vapor are also tested by considering both relatively dry and humid atmospheric conditions. Averaging the “calculated-observed” residuals over numerous recordings made for close values of the solar zenith angle and humidity enables reduction of the uncertainties due to the radiometric noise of the instrument and to the imperfect description of the atmospheric state. This enables the detection of systematic differences in the spectral residuals caused by small changes in spectroscopic data. The results show that the spectroscopic parameters in the HITRAN2016 and GEISA2015 databases lead to large residuals while data of two recent laboratory studies, obtained from spectra measured with the cavity ring-down spectroscopy technique using the speed-dependent Nelkin-Ghatak profile lead to much better agreement with atmospheric measurements. Significant residuals are noted for water vapor absorption lines simulated using parameters provided by both the HITRAN and GEISA databases.

A Spectra Classification Methodology of Hyperspectral Infrared Images for Near Real-Time Estimation of the SO2 Emission Flux from Mount Etna with LARA Radiative Transfer Retrieval Model

Fast and accurate quantification of gas fluxes emitted by volcanoes is essential for the risk mitigation of explosive eruption, and for the fundamental understanding of shallow eruptive processes. Sulphur dioxide (SO2), in particular, is a reliable indicator to predict upcoming eruptions, and its systemic characterization allows the rapid assessment of sudden changes in eruptive dynamics. In this regard, infrared (IR) hyperspectral imaging is a promising new technology for accurately measure SO2 fluxes day and night at a frame rate down to 1 image per second. The thermal infrared region is not very sensitive to particle scattering, which is an asset for the study of volcanic plume. A ground based infrared hyperspectral imager was deployed during the IMAGETNA campaign in 2015 and provided high spectral resolution images of the Mount Etna (Sicily, Italy) plume from the North East Crater (NEC), mainly. The LongWave InfraRed (LWIR) hyperspectral imager, hereafter name Hyper-Cam, ranges between 850–1300 cm−1 (7.7–11.8 µm). The LATMOS (Laboratoire Atmosphères Milieux Observations Spatiales) Atmospheric Retrieval Algorithm (LARA), which is used to retrieve the slant column densities (SCD) of SO2, is a robust and a complete radiative transfer model, well adapted to the inversion of ground-based remote measurements. However, the calculation time to process the raw data and retrieve the infrared spectra, which is about seven days for the retrieval of one image of SO2 SCD, remains too high to infer near real-time (NRT) SO2 emission fluxes. A spectral image classification methodology based on two parameters extracting spectral features in the O3 and SO2 emission bands was developed to create a library. The relevance is evaluated in detail through tests. From data acquisition to the generation of SO2 SCD images, this method requires only ~40 s per image, which opens the possibility to infer NRT estimation of SO2 emission fluxes from IR hyperspectral imager measurements.

Deep-red photoluminescence from enhanced 5D0-7F4 transition in Eu3+ doped Ca2Ga2GeO7 phosphors

In order to explore diverse luminescence properties of Eu3+ in inorganic phosphors, a series of novel deep-red-emitting Ca2Ga2GeO7 phosphors were successfully synthesized by solid-state reactions. The phase formation was verified by the X-ray diffraction patterns and Rietveld refinement and there is only one kind of Ca2+ site in Ca2Ga2GeO7. The excitation spectrum shows typical excitation peaks of Eu3+ and the broad band ranging from 200 nm to 300 nm was composed of the charge transfer band of O2–-Eu3+ and Ga3+-O2– transition band. The emission spectrum depicts that the intensity of the peak located at 704 nm (5D0 → 7F4) is higher than that of 618 nm (5D0 → 7F2), which finally leads to the deep-red emission of the phosphor with high color saturation. The coordination dodecahedron of EuO8 distorted from a cubic geometry to the square antiprism is responsible for the unusual emission of Eu3+. The research of the concentration quenching behavior, lifetime and luminescence decay curves imply that the energy transfer between Eu3+ ions finally leads to the concentration quenching, and the interaction type is d-d interaction. The charge compensation, quantum efficiency and the thermal stability of Ca2Ga2GeO7:Eu3+ were also studied.