CO2 Absorption Band Research Articles

Atmospheric CO(2) column measurements in cloudy conditions using intensity-modulated continuous-wave lidar at 1.57 micron.

This study evaluates the capability of atmospheric CO2 column measurements under cloudy conditions using an airborne intensity-modulated continuous-wave integrated-path-differential-absorption lidar operating in the 1.57-μm CO2 absorption band. The atmospheric CO2 column amounts from the aircraft to the tops of optically thick cumulus clouds and to the surface in the presence of optically thin clouds are retrieved from lidar data obtained during the summer 2011 and spring 2013 flight campaigns, respectively. For the case of intervening thin cirrus clouds with an average cloud optical depth of about 0.16 over an arid/semi-arid area, the CO2 column measurements from 12.2 km altitude were found to be consistent with the cloud free conditions with a lower precision due to the additional optical attenuation of the thin clouds. The clear sky precision for this flight campaign case was about 0.72% for a 0.1-s integration, which was close to previously reported flight campaign results. For a vegetated area and lidar path lengths of 8 to 12 km, the precision of the measured differential absorption optical depths to the surface was 1.3 - 2.2% for 0.1-s integration. The precision of the CO2 column measurements to thick clouds with reflectance about 1/10 of that of the surface was about a factor of 2 to 3 lower than that to the surface owing to weaker lidar returns from clouds and a smaller CO2 differential absorption optical depth compared to that for the entire column.

Earth Infrared Radiation Spectra During Global Warming Hiatus


 
 
 
 Background: Since 1997-98, observations of annual mean surface temperature have shown a slowdown of global temperature increases, suggesting a hiatus in global warming. Given this finding, we are interested in diagnosing trends in the Earth’s outgoing longwave radiation (OLR) spectrum throughout the last decade.
 Methods: We calculated the trend in OLR measured by the Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite between 2003 and 2013, and compared these results with the trend in atmospheric and surface temperature and tropospheric absolute humidity, obtained from AIRS retrieval product and from the ECMWF (European Center for Medium range Weather Forecasting) Re-Analysis (ERA) interim product. We also isolated the greenhouse effect from the OLR trend by subtracting the amount of surface radiation emitted from the total radiation received by the sounder.
 Results: The OLR trend is negative in the CO2 absorption band, negative in the window spectral region, and positive in the water vapor band. The trend in surface and tropospheric temperature is negative, as is the trend in tropospheric absolute humidity. The greenhouse effect is increasing in the CO2 band, generally slightly increasing in the window region, and decreasing in the H2O band.
 
 
 
 
 Conclusion: Our results show that the CO2 forcing was still present globally through the last decade, with steadily increasing effects. Contributors to the negative trend in OLR in the window region are a small decrease in surface temperature and a strong decrease in tropospheric temperature, where tropospheric H2O emit radiation to space. The decreasing effect of water vapor in the H2O band is due to decreasing tropospheric humidity. This analysis will allow us to detect the changes in greenhouse gas forcing, to examine the correlated surface temperature response, and to study changes and effects in tropospheric water vapor concentration.
 
 
 

Instantaneous three-dimensional thermal structure of the South Polar Vortex of Venus

The Venus thermal radiation spectrum exhibits the signature of CO2 absorption bands. By means of inversion techniques, those bands enable the retrieval of atmospheric temperature profiles. We have analyzed VIRTIS-M-IR night-side data obtaining high-resolution thermal maps of the Venus south polar region between 55 and 85km altitudes. This analysis is specific to three Venus Express orbits where the vortex presents different dynamical configurations. The cold collar is clearly distinguishable centered at ∼62km (∼100mbar) altitude level. On average, the cold collar is more than 15K colder than the pole, but its specific temperature varies with time. In the three orbits under investigation the South Polar Vortex appears as a vertically extended hot region close to the pole and squeezed by the cold collar between altitudes 55 and 67km but spreading equatorwards at about 74km. Both the instantaneous temperature maps and their zonal averages show that the top altitude limit of the thermal signature from the vortex is at ∼80km altitude, at least on the night-side of the planet. The upper part of the atmosphere (67–85km) is more homogeneous and has long-scale horizontal temperature differences of about 25K over horizontal distances of ∼2000km. The lower part (55–67km) shows more fine-scale structure, creating the vortex morphology, with thermal differences of up to about 50K over the same altitude range and ∼500km horizontal distances. This lower part of the atmosphere is highly affected by the upper cloud deck, leading to stronger local temperature variations and larger uncertainties in the retrieval. From the temperature maps, we also study the vertical stability of different atmospheric layers for the three vortex configurations. The static stability is always positive (ST>0) in the considered altitude range (55–85km) and in the whole polar vortex. The cold collar is the most vertically stable structure at polar latitudes, while the vortex and sub-polar latitudes show lower stability values. Furthermore, the hot filaments present within the vortex exhibit lower stability values than their surroundings. The layer between 62 and 67km resulted to be the most stable. These results are in good agreement with conclusions from previous radio occultation analyses.

Simultaneous sensing of temperature, CO, and CO2 in a scramjet combustor using quantum cascade laser absorption spectroscopy

A mid-infrared laser absorption sensor was developed for gas temperature and carbon oxide (CO, CO2) concentrations in high-enthalpy, hydrocarbon combustion flows. This diagnostic enables non-intrusive, in situ measurements in harsh environments produced by hypersonic propulsion ground test facilities. The sensing system utilizes tunable quantum cascade lasers capable of probing the fundamental mid-infrared absorption bands of CO and CO2 in the 4–5 µm wavelength domain. A scanned-wavelength direct absorption technique was employed with two lasers, one dedicated to each species, free-space fiber-coupled using a bifurcated hollow-core fiber for remote light delivery on a single line of sight. Scanned-wavelength modulation spectroscopy with second-harmonic detection was utilized to extend the dynamic range of the CO measurement. The diagnostic was field-tested on a direct-connect scramjet combustor for ethylene–air combustion. Simultaneous, laser-based measurements of carbon monoxide and carbon dioxide provide a basis for evaluating combustion completion or efficiency with temporal and spatial resolution in practical hydrocarbon-fueled engines.

A signature of chromospheric activity in brown dwarfs revealed by 2.5–5.0 μm AKARI spectra

We propose that the 2.7 micron H_2O, 3.3 micron CH_4 and 4.6 micron CO absorption bands can be good tracers of chromospheric activity in brown dwarfs. In our previous study, we found that there are difficulties in explaining entire spectra between 1.0 and 5.0 microns with the Unified Cloudy Model (UCM), a brown dwarf atmosphere model. Based on simple radiative equilibrium, temperature in a model atmosphere usually decreases monotonically with height. However, if a brown dwarf has a chromosphere, as inferred by some observations, the temperature in the upper atmosphere is higher. We construct a simple model that takes into account heating due to chromospheric activity by setting a temperature floor in an upper atmosphere, and find that the model spectra of 3 brown dwarfs with moderate H-alpha emission, an indicator of chromospheric activity, are considerably improved to match the AKARI spectra. Because of the higher temperatures in the upper atmospheres, the amount of CH_4 molecules is reduced and the absorption band strengths become weaker. The strengths of the absorption bands of H_2O and CO also become weaker. On the other hand, other objects with weak H-alpha emission cannot be fitted by our treatment. We also briefly discuss magnetic heating processes which possibly operate in upper atmospheres, by extending our numerical simulations for the Sun and stars with surface convection to brown dwarf atmospheres.

Effects of spectral sampling rate and range of CO2 absorption bands on XCO2 retrieval from TanSat hyperspectral spectrometer

The spectral sampling rate and range of CO2 absorption bands are critical for the optimal design of hyperspectral instrument for CO2 observation satellite. Undersampling of spectra in space-based spectrometer significantly contaminates signals measured in the CO2 1.61 μm-band. The CO2 dry-air column (XCO2) error due to spectral undersampling can be up to ~1 ppm, which is the target precision of the Chinese Carbon Satellite (TanSat) for a single sounding. Undersampling error depends on surface albedo, solar zenith angle, and scattering properties in the atmosphere. The spectral sampling rate is recommended to be greater than 2.0 pixels per full width at half maximum to avoid undersampling. Reduction of spectral resolution and the use of narrower spectral regions can improve spectral sampling with little changes in CO2 retrieval sensitivity without losing much information. The full-band approach provides direct constraints on the wavelength-dependent surface albedo and particle scattering from the measurements. To keep a broader band, we recommend reduction of the spectral resolution by a factor of two.

FT-IR spectroscopy combined with DFT calculation to explore solvent effects of vinyl acetate

The infrared vibration frequencies of vinyl acetate (VAc) in 18 different solvents were theoretically computed at Density Function Theory (DFT) B3LYP/6-311G* level based on Polarizable Continuum Model (PCM) and experimentally recorded by FT-IR spectroscopy. The solvent-induced long-range bulk electrostatic solvation free energies of VAc (ΔGelec) were calculated by the SMD model. The CO stretching vibration frequencies of VAc were utilized as a measure of the chemical reactivities of the CC group in VAc. The calculated and experimental CO stretching vibration frequencies of VAc (νcal(CO) and νexp(CO)) were correlated with empirical solvent parameters including the KBM equation, the Swain equation and the linear solvation energy relationships (LSER). Through ab initio calculation, assignments of the two CO absorption bands of VAc in alcohol solvents were achieved. The PCM, SMD and ab initio calculation offered supporting evidence to explain the FT-IR experimental observations from differing aspects.

Dispersive infrared spectroscopy measurements of atmospheric CO2 using a Fabry–Pérot interferometer sensor

In this paper, we present the first dispersive infrared spectroscopic (DIRS) measurement of atmospheric carbon dioxide (CO2) using a new scanning Fabry–Pérot interferometer (FPI) sensor. The sensor measures the optical spectra in the mid infrared (3900nm to 5220nm) wavelength range with full width half maximum (FWHM) spectral resolution of 78.8nm at the CO2 absorption band (~4280nm) and sampling resolution of 20nm. The CO2 concentration is determined from the measured optical absorption spectra by fitting it to the CO2 reference spectrum. Interference from other major absorbers in the same wavelength range, e.g., carbon monoxide (CO) and water vapor (H2O), was taken out by including their reference spectra in the fit as well. The detailed descriptions of the instrumental setup, the retrieval procedure, a modeling study for error analysis as well as laboratory validation using standard gas concentrations are presented. An iterative algorithm to account for the non-linear response of the fit function to the absorption cross sections due to the broad instrument function was developed and tested. A modeling study of the retrieval algorithm showed that errors due to instrument noise can be considerably reduced by using the dispersive spectral information in the retrieval. The mean measurement error of the prototype DIRS CO2 measurement for 1minute averaged data is about ±2.5ppmv, and down to ±0.8ppmv for 10minute averaged data. A field test of atmospheric CO2 measurements were carried out in an urban site in Hong Kong for a month and compared to a commercial non-dispersive infrared (NDIR) CO2 analyzer. 10minute averaged data shows good agreement between the DIRS and NDIR measurements with Pearson correlation coefficient (R) of 0.99. This new method offers an alternative approach of atmospheric CO2 measurement featuring high accuracy, correction of non-linear absorption and interference of water vapor.

CO2 phonon mode renormalization using phonon-assisted energy up-conversion

Molecular dissociation under incident light whose energy is lower than the bond dissociation energy has been achieved through multi step excitation using a coupled state of a photon, electron, and multimode-coherent phonon as known as the dressed photon phonon (DPP). Here, we have investigated the effects of the DPP on CO2, a very stable molecule with high absorption and dissociation energies, by introducing ZnO nanorods to generate the DPP. Then, the changes in CO2 absorption bands were evaluated using light with a wavelength longer than the absorption wavelength, which confirmed the DPP-assisted energy up-conversion. To evaluate the specific CO2 modes related to this process, we measured the CO2 vibration-rotation spectra in the near-infrared region. Detailed analysis of the 3ν3 vibrational band when a DPP source is present showed that DPP causes a significant increase in the intensity of certain absorption bands, especially those that require higher energies to activate.

Modeling of intensity-modulated continuous-wave laser absorption spectrometer systems for atmospheric CO2 column measurements

The focus of this study is to model and validate the performance of intensity-modulated continuous-wave (IM-CW) CO(2) laser absorption spectrometer (LAS) systems and their CO(2) column measurements from airborne and satellite platforms. The model accounts for all fundamental physics of the instruments and their related CO(2) measurement environments, and the modeling results are presented statistically from simulation ensembles that include noise sources and uncertainties related to the LAS instruments and the measurement environments. The characteristics of simulated LAS systems are based on existing technologies and their implementation in existing systems. The modeled instruments are specifically assumed to be IM-CW LAS systems such as the Exelis' airborne multifunctional fiber laser lidar (MFLL) operating in the 1.57 μm CO(2) absorption band. Atmospheric effects due to variations in CO(2), solar radiation, and thin clouds, are also included in the model. Model results are shown to agree well with LAS atmospheric CO(2) measurement performance. For example, the relative bias errors of both MFLL simulated and measured CO(2) differential optical depths were found to agree to within a few tenths of a percent when compared to the in situ observations from the flight of 3 August 2011 over Railroad Valley (RRV), Nevada, during the summer 2011 flight campaign. In addition, the horizontal variations in the model CO(2) differential optical depths were also found to be consistent with those from MFLL measurements. In general, the modeled and measured signal-to-noise ratios (SNRs) of the CO(2) column differential optical depths (τd) agreed to within about 30%. Model simulations of a spaceborne IM-CW LAS system in a 390 km dawn/dusk orbit for CO(2) column measurements showed that with a total of 42 W of transmitted power for one offline and two different sideline channels (placed at different locations on the side of the CO(2) absorption line), the accuracy of the τd measurements for surfaces similar to the playa of RRV, Nevada, will be better than 0.1% for 10 s averages. For other types of surfaces such as low-reflectivity snow and ice surfaces, the precision and bias errors will be within 0.23% and 0.1%, respectively. Including thin clouds with optical depths up to 1, the SNR of the τd measurements with 0.1 s integration period for surfaces similar to the playa of RRV, Nevada, will be greater than 94 and 65 for sideline positions placed +3 and +10 pm, respectively, from the CO(2) line center at 1571.112 nm. The CO(2) column bias errors introduced by the thin clouds are ≤0.1% for cloud optical depth ≤0.4, but they could reach ∼0.5% for more optically thick clouds with optical depths up to 1. When the cloud and surface altitudes and scattering amplitudes are obtained from matched filter analysis, the cloud bias errors can be further reduced. These results indicate that the IM-CW LAS instrument approach when implemented in a dawn/dusk orbit can make accurate CO(2) column measurements from space with preferential weighting across the mid to lower troposphere in support of a future ASCENDS mission.

From Selenium- to Tellurium-Based Glass Optical Fibers for Infrared Spectroscopies

Chalcogenide glasses are based on sulfur, selenium and tellurium elements, and have been studied for several decades regarding different applications. Among them, selenide glasses exhibit excellent infrared transmission in the 1 to 15 µm region. Due to their good thermo-mechanical properties, these glasses could be easily shaped into optical devices such as lenses and optical fibers. During the past decade of research, selenide glass fibers have been proved to be suitable for infrared sensing in an original spectroscopic method named Fiber Evanescent Wave Spectroscopy (FEWS). FEWS has provided very nice and promising results, for example for medical diagnosis. Then, some sophisticated fibers, also based on selenide glasses, were developed: rare-earth doped fibers and microstructured fibers. In parallel, the study of telluride glasses, which can have transmission up to 28 µm due to its atom heaviness, has been intensified thanks to the DARWIN mission led by the European Space Agency (ESA). The development of telluride glass fiber enables a successful observation of CO2 absorption band located around 15 µm. In this paper we review recent results obtained in the Glass and Ceramics Laboratory at Rennes on the development of selenide to telluride glass optical fibers, and their use for spectroscopy from the mid to the far infrared ranges.

Very high cloud detection in more than two decades of HIRS data

This paper reports on the use of High‐resolution Infrared Radiation Sounder (HIRS) measurements to infer the presence of upper tropospheric and lower stratospheric (UT/LS) clouds. UT/LS cloud detection is based on the fact that, when viewing an opaque UT/LS cloud that fills the sensor field of view, positive lapse rates above the tropopause cause a more absorbing CO2 or H2O‐sensitive spectral band to measure a brightness temperature warmer than that of a less absorbing or nearly transparent infrared window spectral band. The HIRS sensor has flown on 16 polar‐orbiting satellites from TIROS‐N through NOAA‐19 and Metop‐A and –B, forming the only 30 year record that includes H2O and CO2‐sensitive spectral bands enabling the detection of these UT/LS clouds. Comparison with collocated Cloud‐Aerosol Lidar with Orthogonal Polarization data reveals that 97% of the HIRS UT/LS cloud determinations are within 2.5 km of the tropopause (defined as the coldest level in the National Centers for Environmental Prediction Global Data Assimilation System); more clouds are found above the tropopause than below. From NOAA‐14 data spanning 1995 through 2005, we find indications of UT/LS clouds in 0.7% of the observations from 60N to 60S using CO2 absorption bands; however, in the region of the Inter‐Tropical Convergence Zone (ITCZ), this increases to 1.7%. During El Niño years, UT/LS clouds shift eastward out of their normal location in the western Pacific region. Monthly trends from 1987 through 2011 using data from NOAA‐10 onwards show decreases in UT/LS cloud detection in the region of the ITCZ from 1987 until 1996, increases until 2001, and decreases thereafter.

Spectral features of Earth-like planets and their detectability at different orbital distances around F, G, and K-type stars

We investigate the spectral appearance of Earth-like exoplanets in the HZ of different main sequence stars at different orbital distances. We furthermore discuss for which of these scenarios biomarker absorption bands may be detected during primary or secondary transit with near-future telescopes and instruments.We analyze the spectra taking into account different filter bandpasses of two photometric instruments planned to be mounted to the JWST. We analyze in which filters and for which scenarios molecular absorption bands are detectable when using the space-borne JWST or the ground-based telescope E-ELT. Absorption bands of CO2, H2O, CH4 and O3 are clearly visible in high-resolution spectra as well as in the filters of photometric instruments. However, only during primary eclipse bands of CO2, H2O and O3 are detectable for all scenarios when using photometric instruments and an E-ELT telescope setup. CH4 is only detectable at the outer HZ of the K star since here the atmospheric modeling results in very high abundances. Since the detectable CO2 and H2O bands overlap, separate bands need to be observed to prove their existence in the atmosphere. In order to detect H2O in a separate band, a S/N>7 needs to be achieved for E-ELT observations, e.g. by co-adding at least 10 transit observations. Using a spaceborne telescope like the JWST enables the detection of CO2 at 4.3mu, which is not possible for ground-based observations due to the Earth's atmospheric absorption. Hence combining observations of spaceborne and groundbased telescopes might allow to detect the presence of the biomarker molecule O3 and the related compounds H2O and CO2 in a planetary atmosphere. Other absorption bands using the JWST can only be detected for much higher S/Ns, which is not achievable by just co-adding transit observations since this would be far beyond the planned mission time of JWST.(abridged)

Atmospheric CO2 column measurements with an airborne intensity-modulated continuous wave 157 μm fiber laser lidar

The 2007 National Research Council (NRC) Decadal Survey on Earth Science and Applications from Space recommended Active Sensing of CO(2) Emissions over Nights, Days, and Seasons (ASCENDS) as a midterm, Tier II, NASA space mission. ITT Exelis, formerly ITT Corp., and NASA Langley Research Center have been working together since 2004 to develop and demonstrate a prototype laser absorption spectrometer for making high-precision, column CO(2) mixing ratio measurements needed for the ASCENDS mission. This instrument, called the multifunctional fiber laser lidar (MFLL), operates in an intensity-modulated, continuous wave mode in the 1.57 μm CO(2) absorption band. Flight experiments have been conducted with the MFLL on a Lear-25, UC-12, and DC-8 aircraft over a variety of different surfaces and under a wide range of atmospheric conditions. Very high-precision CO(2) column measurements resulting from high signal-to-noise ratio (>1300) column optical depth (OD) measurements for a 10 s (~1 km) averaging interval have been achieved. In situ measurements of atmospheric CO(2) profiles were used to derive the expected CO(2) column values, and when compared to the MFLL measurements over desert and vegetated surfaces, the MFLL measurements were found to agree with the in situ-derived CO(2) columns to within an average of 0.17% or ~0.65 ppmv with a standard deviation of 0.44% or ~1.7 ppmv. Initial results demonstrating ranging capability using a swept modulation technique are also presented.

A Simulated Climatology of Spectrally Decomposed Atmospheric Infrared Radiation

Abstract A simulation experiment is conducted to inquire into the mean climate state and likely trends in atmospheric infrared radiation spectra. Upwelling and downwelling spectra at five vertical levels from the surface to the top of the atmosphere (TOA) are rigorously calculated from a climate-model-simulated atmosphere for a 25-yr period. Tracing the longwave radiation flux vertically and spectrally renders a dissection of the greenhouse effect of the earth atmosphere and its change due to climate forcings and feedbacks. The results show that the total outgoing longwave radiation (OLR) at the TOA may be conserved due to 1) compensating temperature and opacity effects and 2) contrasting temperature changes in troposphere and stratosphere. The tightly coupled tropospheric temperature and opacity effects reduce the overall tropospheric contribution to OLR change to be comparable to the overall stratospheric contribution, which suggests that transient OLR change is constrained by the relative strengths of stratospheric and tropospheric temperature changes. The total OLR energy, however, is redistributed across its spectrum. The earliest detectable global climate change signal lies in the CO2 absorption bands, which results from stratospheric cooling and the CO2 opacity effect. This signal can be detected much sooner than surface temperature change and is little affected by achievable instrument accuracy. In contrast, both tropospheric temperature and opacity effects increase downwelling longwave radiation (DLR), which makes DLR a verifiable aspect of global warming. The time it takes to detect surface DLR change roughly equals that of surface temperature change. Measuring downwelling radiances at strong water vapor lines at the tropopause can particularly help monitor stratospheric water vapor.

AKARIOBSERVATIONS OF BROWN DWARFS. III. CO, CO2, AND CH4FUNDAMENTAL BANDS AND PHYSICAL PARAMETERS

We investigate variations in the strengths of three molecular bands, CH4 at 3.3 um, CO at 4.6 um and CO2 at 4.2 um, in 16 brown dwarf spectra obtained by AKARI. Spectral features are examined along the sequence of source classes from L1 to T8. We find that the CH4 3.3 um band is present in the spectra of brown dwarfs later than L5, and the CO 4.6 um band appears in all spectral types. The CO2 absorption band at 4.2 um is detected in late-L and T type dwarfs. To better understand brown dwarf atmospheres, we analyze the observed spectra using the Unified Cloudy Model (UCM). The physical parameters of the AKARI sample, i.e., atmospheric effective temperature Teff, surface gravity logg and critical temperature Tcr are derived. We also model IRTF/SpeX and UKIRT/CGS4 spectra in addition to the AKARI data in order to derive the most probable physical parameters. Correlations between the spectral type and the modeled parameters are examined. We confirm that the spectral type sequence of late-L dwarfs is not related to Teff, but instead originates as a result of the effect of dust.

Retrieval of tropospheric CO column from hyperspectral infrared sounders – application to four years of Aqua/AIRS and MetOp-A/IASI

Abstract. Four years of tropospheric integrated content of CO were retrieved from infrared hyperspectral observations of AIRS onboard Aqua and IASI onboard MetOp-A, for the period July 2007–June 2011. The retrieval method is based on a double differential approach that relies on the difference between brightness temperatures observed by the sounder and BT simulated by the Automatised Atmospheric Absorption Atlas (4A) radiative transfer model on colocated ECMWF reanalyses, for several couples of channels located in the 4.67 μm CO band. AIRS and IASI give access to similar integrated contents of CO with a maximum sensitivity near 450 hPa and a half-height width of the weighting function between 200 and 750 hPa depending on the thermal contrast (i.e., the difference between the surface temperature and the temperature of the first pressure level). However, differences in their spectral and radiometric characteristics yield differences in the retrieval characteristics with AIRS selected couples of channels being more sensitive to surface characteristics. Moreover, IASI covers the whole CO absorption band, with a 3 times better spectral resolution, giving access to channels presenting a 3 times higher signal to noise ratio. This results in a better precision and lower standard deviation of the IASI retrievals. Conservatively, comparisons with CARIBIC aircraft measurements yield an averaged relative difference of 3.4% for IASI and 4.9% for AIRS. On average, AIRS and IASI retrievals are in very good agreement, showing the same seasonality, seasonal amplitudes, interannual variability and spatial distribution. The analysis of the monthly evolution of CO particularly highlights the expected strong influence of biomass burning on the evolution of CO in several tropical regions. In particular, a sharp increase in CO in 2010 in the southern tropics, especially over South America and South Africa, is observed, and is shown to be related to El Niño and to the Atlantic Multidecadal Oscillation.

Laboratory infrared reflection spectrum of carbon dioxide clathrate hydrates for astrophysical remote sensing applications

We present 1–5μm IR reflectance spectra of CO2 clathrate hydrates acquired under temperature and pressure conditions representative of the icy moons’ surfaces. The IR reflectance spectrum of the CO2 clathrate hydrates is similar to the water ice IR reflectance spectrum except for two main absorption bands corresponding to the CO2 guest molecule at 2.71 and 4.28μm (3693 and 2334cm−1). The specific configuration of the clathrate hydrate structure is identified through the ν3 absorption band splitting which produces a band at 4.26μm (2347cm−1) for molecules trapped in small cages and a band at 4.28μm (2334cm−1) for molecules trapped in large cages. In general, the reflection spectra are similar to spectra obtained in transmission spectroscopy. But, it appears that the aspect of the ν3 absorption band is strongly influenced by physical (roughness, thickness, mixing properties) and optical (n and k) characteristics of the sample. A qualitative discussion of the effects of these sample properties on near-IR signatures of clathrate hydrates is proposed. Finally, a comparison between the absorption bands of CO2 clathrate hydrates obtained in this work and CO2 absorption bands as detected by VIMS on the icy satellites of Saturn is achieved. The experimental near-IR reflection spectra, made in pressure–temperature (P–T) conditions close to those of the icy surfaces, confirm that VIMS data are not consistent with the presence of structure I CO2 clathrate hydrates on the surface of the icy moons.

Growth and optical properties of Co,Nd:LaMgAl11O19

Nd,Co:LaMgAl11O19 (abbreviated as Co,Nd:LMA) was grown using the Czochralski method. The structure, polarized absorption spectrum, fluorescence spectrum, and fluorescence decay time were analyzed. The as-grown crystal had very wide absorption bands at 794nm, which can be pumped by GaAs laser diode without temperature stabilization. Two strong emission bands were present at 1056nm and 1082nm with full-width at half-maximum (FWHM) of 6 and 8nm, respectively. The large FWHM is due to the inhomogeneity of the Nd ion sites. The lifetimes of the 4F3/2 manifold of Co,Nd:LMA at room temperature monitored at 905nm, 1056nm, and 1344nm were 292, 288, and 350μs, respectively, which was caused by the different contribution of the three different sites with D3h and C2v symmetry. The absorption band of Co is from 1.3μm to 1.6μm, and Co,Nd:LMA still has a strong emission around the 1.38μm, indicating that the Co,Nd:LMA can be applied as a potential self-Q-switched material operating at 1.3μm.

Assignment and rotational analysis of new absorption bands of carbon dioxide isotopologues in Venus spectra

We present absorption bands of carbon dioxide isotopologues, detected by the Solar Occultation for the Infrared Range (SOIR) instrument on board the Venus Express Satellite. The SOIR instrument combines an echelle spectrometer and an Acousto-Optical Tunable Filter (AOTF) for order selection. It performs solar occultation measurements in the Venus atmosphere in the IR region (2.2–4.3μm), at a resolution of 0.12–0.18cm−1. The wavelength range probed by SOIR allows a detailed chemical inventory of the Venus atmosphere above the cloud layer (65–150km) to be made with emphasis on the vertical distributions of gases. Thanks to the SOIR spectral resolution, a new CO2 absorption band was identified: the 21101–01101 band of 16O12C18O with R branch up to J=31. Two other previously reported bands were observed dispelling any doubts about their identifications: the 20001–00001 band of 16O13C18O [Villanueva G, et al. J Quant Spectrosc Radiat Transfer 2008;109:883–894] and the 01111–00001 band of 16O12C18O [Villanueva G, et al. J Quant Spectrosc Radiat Transfer 2008;109:883–894 and Wilquet V, et al. J Quant Spectrosc Radiat Transfer 2008;109:895–905]. These bands were analyzed, and spectroscopic constants characterizing them were obtained. The rotational assignment of the 20001–00001 band was corrected. The present measurements are compared with data available in the HITRAN database.