Atmospheric modelling using FASCOD to identify CO2 absorption bands and their suitability analysis in variable concentrations for remote sensing applications

Recent climate studies have proven that both temperature and CO₂ content of the earth's atmosphere followed a regular 100,000-year cycle of change and that they are closely correlated. Moreover, the observed increase of CO₂ in the atmosphere exceeds the predicted values extrapolated from historical data. Other than industrialization and rapid urbanization, geo-natural hazards such as leakage from hydrocarbon reservoirs and spontaneous combustion of coal contribute a considerable amount of CO₂ to the atmosphere. Several researchers have studied the possibilities and reliabilities of atmospheric CO₂ retrieval by the point-based method (nearly accurate but much localized) and globally (wider observation but many uncertainties). Radiative transfer codes, such as FASCOD (Fast Atmospheric Signature Code) with the HITRAN (High-Resolution Transmission) spectral database can simulate atmospheric transmission and path radiance with customized gas composition (CO₂, water vapour, CO, etc.) and concentration in order to understand the phenomena in a specific wavelength region. In the present study, a number of atmospheric models were constructed with different CO₂ concentrations (ppmv) with a combination of water vapour and other atmospheric gases such as CO, CH₄, N₂O, SO₂, etc., to find out the interference patterns of these gases over CO₂ absorption bands. The transmission features of these gas combinations were analysed by partial least-squares regression models. These models show that the most suitable CO₂ absorption bands are located around 2 μm, such as 1.998 and 2.001 μm. The spectral information derived from different concentrations of CO₂ can be fitted in multivariate models to predict the CO₂ concentration from spectral information in a controlled environment. Furthermore, the present study explores the sensitivity of some available remote sensing sensors in variable CO₂ concentrations for use in real world.     

The influence of water vapour and temperature on depletion of carbon monoxide in D.C. corona discharge

The plasmochemical and/or electrocatalytical reactions of carbon monoxide with water vapour were studied. Dc corona discharge of both polarities at room temperature and temperatures enhanced up to 70°C was applied at pressures close to atmospheric. The reaction products were analysed by IR absorption spectrometry. The main products in the gas phase were CO₂ and CH₄. The reactions are influenced by the formation of a catalytically active surface layer on electrodes. The composition of this layer depends on the polarity of electrode.     

Quasi-tunable I2-laser for absorption measurements in the near infrared

The properties and output data of an I₂-laser pumped by a pulsed dye laser have been investigated. The separation between lines to which the laser can be tuned in the region 1.0–1.3 μm is typically 0.5 cm^-1. Lines are emitted in R-P doublets with a separation of 5–15 cm^-1. The possibility of measuring low gas concentrations by recording the intensity ratio of the components in selected doublets has been tested in atmospheric water vapour.     

The cloud chamber as a tool in cloud physics

Since 1875 when Coulier and, a little later, Aitken made the first simple expansion cloud chambers to study the condensation of water vapour on atmospheric particles, and particularly since 1895 when C. T. R. Wilson made his famous instrument with the initial object of studying optical phenomena in clouds, the cloud chamber has been one of the principal tools for investigating condensation phenomena and for simulating natural cloud-forming processes. The cloud physicist commonly employs expansion-, mixing- and diffusion-cloud chambers (he has yet to find a use for the bubble chamber) for studying the spontaneous condensation of water vapour; condensation upon ions and atmospheric particles; the production, nucleation and crystallization of super-cooled clouds; the properties of ice-forming nuclei; and the growth of ice crystals from the vapour. The purpose of this article is to review some of the more important aspects of this work.     

Evidence for the contribution of water dimers to the near-IR water vapour self-continuum

The nature of the water vapour continuum absorption and the possible contribution of water dimers (WD) to this phenomenon have been a matter of debate for many years. The current work presents an overview and analysis of a number of experiments, both recent and old, where spectral signatures, similar to recent theoretical predictions for WD, have been observed in equilibrium laboratory conditions within near-infra-red (IR) water vapour absorption bands. These experiments, in contrast to those where water complexes are usually studied in non-equilibrium and low-temperature conditions, can give direct information about the possible WD amount in atmospheric conditions. Intercomparison of the results of these works and the recent ab initio prediction for WD band intensities and positions testifies in favour of a significant contribution of WD absorption to the water vapour self-continuum in the centre of the strongest near-IR water vapour absorption bands.     

Atmospheric emission and attenuation in the range 100 to 600 GHz measures from a mountain site

Further measurements of atmospheric emission from a site in the Canary Islands (Izana, âltitude 2.4 km) have been made during the month of August 1980. The measurements were made with a polarising Interferometer and a composite Ge bolometer. An independent measurement of the precipitable water vapour was made using Infrared Hygrometers. The experimental details are described and the spectra obtained are compared with model spectra using the measured precipitable water vapour.     

Assessment of the consistency of H2O line intensities over the near-infrared using sun-pointing ground-based Fourier transform spectroscopy

We report on the consistency of water vapour line intensities in selected spectral regions between 800-12,000 cm⁻¹ under atmospheric conditions using sun-pointing Fourier transform infrared spectroscopy. Measurements were made across a number of days at both a low and high altitude field site, sampling a relatively moist and relatively dry atmosphere. Our data suggests that across most of the 800-12,000 cm⁻¹ spectral region water vapour line intensities in recent spectral line databases are generally consistent with what was observed. However, we find that HITRAN-2008 water vapour line intensities are systematically lower by up to 20% in the 8000-9200 cm⁻¹ spectral interval relative to other spectral regions. This discrepancy is essentially removed when two new linelists (UCL08, a compilation of linelists and ab-initio calculations, and one based on recent laboratory measurements by Oudot et al. (2010) [10] in the 8000-9200 cm⁻¹ spectral region) are used. This strongly suggests that the H₂O line strengths in the HITRAN-2008 database are indeed underestimated in this spectral region and in need of revision. The calculated global-mean clear-sky absorption of solar radiation is increased by about 0.3 W m⁻² when using either the UCL08 or Oudot line parameters in the 8000-9200 cm⁻¹ region, instead of HITRAN-2008. We also found that the effect of isotopic fractionation of HDO is evident in the 2500-2900 cm⁻¹ region in the observations.     

Surface modification of polypropylene with an atmospheric pressure plasma jet sustained in argon and an argon/water vapour mixture

In this paper, an atmospheric pressure plasma jet sustained in pure argon and an argon/water vapour mixture has been used to modify the surface of polypropylene (PP) films. The gas temperature of the plasma jet was found to be 625 K in an active zone between the electrodes and was found to increase in the afterglow. Based on these results, the PP films are placed as close as possible to the edge of the capillary in order to avoid thermal damage to the polymer. XPS results on the untreated and modified PP samples revealed incorporation of a significant amount of oxygen on the polymer surface, however, this oxygen inclusion is more pronounced for the argon/water vapour jet due to the higher radicals density in the jet afterglow. One can therefore conclude that adding water vapour to an argon plasma jet can be a convenient way to increase the efficiency of plasma surface modification.     

Cavity ring down spectroscopy: detection of trace amounts of substance

We describe several applications of cavity ring-down spectroscopy (CRDS) for trace matter detection. NO₂ sensor was constructed in our team using this technique and blue-violet lasers (395–440 nm). Its sensitivity is better than single ppb. CRDS at 627 nm was used for detection of NO₃. Successful monitoring of N₂O in air requires high precision mid-infrared spectroscopy. These sensors might be used for atmospheric purity monitoring as well as for explosives detection. Here, the spectroscopy on sharp vibronic molecular resonances is performed. Therefore the single mode lasers which can be tuned to selected molecular lines are used. Similarly, the spectroscopy at 936 nm was used for sensitive water vapour detection. The opportunity of construction of H₂O sensor reaching the sensitivity about 10 ppb is also discussed.     

Diode laser spectroscopy of He,N2 and air broadened water vapour transitions belonging to the (2ν1 + ν2 + ν3) overtone band

The line shape parameters of rovibrational transitions of water vapour belonging to the (2ν₁ + ν₂ + ν₃) overtone band due to collisions between absorber molecules and noble gas helium have been measured in the spectral range between 11988.494 cm^?1 and 12218.829 cm^?1 using NIR diode laser spectrometer. In addition nitrogen and air broadening effects on some water vapour transitions belonging to the same band have also been studied. Wavelength modulation spectroscopy along with phase sensitive detection technique are used to record first derivative (1f) signal of buffer gas broadened water vapour transitions. Observed line shapes are fitted to standard Voigt profiles by non-linear least squares fitting program to extract the line shape parameters, like line strength and pressure broadening coefficients. The broadening effects induced by different types of buffer gases on water vapour line shapes are compared. Rotational quantum number (J) dependence of broadening coefficients of water vapour transitions is also examined.     

Continuous measurements of stable isotopes of carbon dioxide and water vapour in an urban atmosphere: isotopic variations associated with meteorological conditions

Isotope ratios of carbon dioxide and water vapour in the near-surface air were continuously measured for one month in an urban area of the city of Nagoya in central Japan in September 2010 using laser spectroscopic techniques. During the passages of a typhoon and a stationary front in the observation period, remarkable changes in the isotope ratios of CO₂ and water vapour were observed. The isotope ratios of both CO₂ and water vapour decreased during the typhoon passage. The decreases can be attributed to the air coming from an industrial area and the rainout effects of the typhoon, respectively. During the passage of the stationary front, δ¹³C–CO₂ and δ¹⁸O–CO₂ increased, while δ²H–H₂Ov and δ¹⁸O–H₂Ov decreased. These changes can be attributed to the air coming from rural areas and the air surrounding the observational site changing from a subtropical air mass to a subpolar air mass during the passage of the stationary front. A clear relationship was observed between the isotopic CO₂ and water vapour and the meteorological phenomena. Therefore, isotopic information of CO₂ and H₂Ov could be used as a tracer of meteorological information.     

超光谱红外卫星资料同步反演不同地表类型的大气廓线、地表温度和地表发射率

大气温度、水汽、地表温度和地表发射率是大气和地表的本征信息量。利用卫星红外资料精确反演大气温湿廓线有利于准确预报天气和研究气候变化,同时地表温度和地表发射率光谱的反演为研究植物生长与作物产量、地表水分蒸发与循环、能量平衡、地表成分及物理性质、气候变迁与全球环境提供重要参数指标。把大气和地面作为一个整体系统来考虑,建立一种能同步反演大气温度廓线、大气水汽廓线、地表温度和地表发射率的反演方法,利用超光谱红外卫星资料(atmospheric infrared sounder, AIRS),针对我国新疆地区沙漠和雪地两种典型发射率地表同步反演大气温度廓线、水汽廓线、地表温度和地表发射率。反演方法首先线性化地球-大气系统红外辐射传输方程, 提出通过经验正交函数构建大气廓线和地表发射率光谱,有效减少反演变量数,建立同步物理反演模式,然后以美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)的预报结果(初始大气温度、水汽廓线以及地表参数)作为初始值,最后通过牛顿迭代得到最优化解。反演观测区域覆盖我国新疆塔克拉玛干沙漠和准噶尔盆地,分别选择位于塔克拉玛干沙漠腹地的塔中探测站(纬度38.98°, 经度83.64°)和准噶尔盆地的阜康荒漠生态系统国家野外科学观测研究站(纬度44.2°, 经度87.9° )为反演地面验证点。反演结果表明,塔克拉玛干沙漠地表温度明显高于准噶尔盆地地表温度,与实际情况相一致;根据反演的8.6和13.4 μm处的地表发射率分布情况,可以看出在8.6 μm处沙漠地表发射率明显低于雪地发射率,在6～15 μm范围内,反演的沙漠地区(塔中站)地表发射率和雪地地区(阜康站)地表发射率与美国喷气推进实验室测量的沙漠发射率光谱和雪地发射率光谱相一致。研究表明,把大气和地面作为一个整体系统来考虑,把地表发射率加入到反演中,通过比较和分析沙漠地区(塔中)和雪地地区(阜康)的大气廓线反演结果与当地气象探空值和传统反演方法反演值,改进了大气温度廓线和水汽廓线反演精度,特别是边界层温度和水汽改进尤为明显;同时分析表明在发射率光谱变化较大的沙漠地区, 大气廓线反演精度的改进比雪地要高,这是由于地表发射率光谱在沙漠、戈壁地区变化较大,而雪地的发射率光谱变化不大。用该方法针对地表发射率光谱变化较大的地区(沙漠)同步反演大气廓线、地表温度和地表发射率,可以更有效的提高大气温度廓线、水汽廓线的反演精度。该研究结果可以为数值天气预报和我国未来超光谱红外卫星应用提供服务和有力支持, 具有十分重要的意义。     

IRMA as a Potential Phase Correction Instrument: Results from the SMA Test Campaign

The Infrared Radiometer for Millimetre Astronomy (IRMA) is a real-time water vapour monitor, whose sensitivity and temporal response make it a candidate instrument for the correction of phase distortion caused by atmospheric water vapour in millimetre wavelength interferometers. We present results from a test campaign in which two IRMA devices were mounted on two antennae of the Smithsonian Submillimeter Array (SMA) located atop Mauna Kea, Hawaii. The IRMA measurements are compared to each other, and to phase information derived from astronomical interferometric data to assess their utility as a potential tool in phase correction.     

Optimization of growth parameters for MOVPE-grown GaSb and Ga1−xInxSb

The triethylgallium/trimethylantimony (TEGa/TMSb) precursor combination was used for the metal-organic vapour phase epitaxial growth of GaSb at a growth temperature of 520 °C at atmospheric pressure. Trimethylindium was added in the case of Ga_1−xIn_xSb growth. The effects of group V flux to group III flux ratio (V/III ratio) on the crystallinity and optical properties of GaSb layers are reported. It has been observed from the crystalline quality and optical properties that nominal V/III ratios of values greater than unity are required for GaSb epitaxial layers grown at this temperature. It has also been shown that Ga_1−xIn_xSb can be grown using TEGa as a source of gallium species at atmospheric pressure. The relationship between Ga_1−xIn_xSb vapour composition and solid composition has been studied at a V/III ratio of 0.78.     

Effective potential for ammonia vapour

The modified free-energy averaged potential for water vapour is extended to NH₃ vapour. The resulting temperature-dependent parameters are used to compute the second virial coefficient of NH₃ vapour which agrees with experimental results particularly at higher temperatures.     

Recent improvements on atmospheric CO2 measurements at Mt. Cimone observatory, Italy

Summary Continuous atmospheric CO₂ measurements have been carried out at Mt. Cimone from 1979 up to the present. Omitting here a measurement presentation, in this paper we show the current experimental procedures adopted and NDIR apparatus performances. Quality measurements have been recently improved by introducing an ULTRAMAT-5E (SIEMENS) NDIR analyzer controlled, for operating mode, by computer: the routine precision attained is ±0.1 p.p.m. An interesting performance of the analyzer is its nondetectable sensitivity to water vapour infrared absorption, enabling us also to determine CO₂ measurements in wet air. A flask sampling technique and an investigation of the flask deterioration risk, against storing time, are presented. Results of the investigation validate the use of electropolished stainless-steel flasks for high-quality measurements.     

Multistep ionization of CS2 vapour

We report on the multistep ionization process observed in CS₂ vapour irradiated by 337 nm nitrogen laser light. We propose and discuss a model in which optical as well as collisional excitation are involved in the ionization process.     

Calculation of solar radiation atmospheric absorption with different H2O spectral line data banks

A comparison of the atmospheric absorption calculated with different data banks of water vapour absorption lines is made. The HITRAN database, Barber-Tennyson line list (BT2), calculation of Partridge and Schwenke (PS) are considered. The contribution of H₂O lines, absent in HITRAN, to the atmospheric transmission, calculated with 10 cm⁻¹ spectral resolution in the 10 000-20 000 cm⁻¹ spectral region is up to 1.5% for a vertical path and 4% for a solar zenith angle of 70 deg. The highest difference is observed in the 940 nm band. The incoming fluxes of solar radiation, measured by a rotating solar spectroradiometer, were modeled with BT2 and HITRAN database. The difference between measured and calculated fluxes does not exceed the instrumental uncertainties.     

大气光学湍流估算模式及其相似性函数

地表热通量和水汽通量对全球气候变化和大气环流有着重要而广泛的影响,而Monin-Obukhov(M-O)相似性函数在计算近地层热通量和水汽通量的过程中扮演着重要的角色;同时M-O相似性函数是大气光学湍流估算模式中不可或缺的因子。通过对合肥西郊35 m铁塔上气象数据的分析,利用非线性最小二乘法拟合得到了一套全新的M-O相似性函数。将之与前人提出的相似性函数作对比,展现出了较好的一致性。同时,该函数大气光学湍流的估算模式中,估算值与实测值具有较好的吻合度。分析结果表明:在稳定条件和非常不稳定条件下,可以认为温度相似性函数等于湿度相似性函数,在弱不稳定条件下两者不再满足这种相似性。