Relative-humidity profiling in the troposphere with a Raman lidar

We describe a Raman-lidar-based approach to acquiring profiles of the relative humidity of air. For this purpose we combined in one instrument the Raman-lidar techniques that are used for the profiling of water vapor and temperature. This approach enabled us to acquire, for the first time to our knowledge, vertical profiles of relative humidity through the entire troposphere exclusively from Raman-lidar data. The methods applied to determining the water-vapor mixing ratio, temperature, and relative humidity and the corresponding uncertainties caused by systematic errors and signal noise are presented. The lidar-derived profiles are compared with profiles measured with radiosondes. Radiosonde observations are also used to calibrate the Raman lidar. Close agreement of the profiles of relative humidity measured with lidar and those measured with radiosonde demonstrates the potential of this novel approach.     

Use of high-resolution measurements for the retrieval of temperature and gas-concentration profiles from outgoing infrared spectra in the presence of cirrus clouds

We explore ways in which high-spectral-resolution measurements can aid in the retrieval of atmospheric temperature and gas-concentration profiles from outgoing infrared spectra when optically thin cirrus clouds are present. Simulated outgoing spectra that contain cirrus are fitted with spectra that do not contain cirrus, and the residuals are examined. For those lines with weighting functions that peak near the same altitude as the thin cirrus, unique features are observed in the residuals. These unique features are highly sensitive to the resolution of the instrumental line shape. For thin cirrus these residual features are narrow (< or = 0.1 cm(-1)), so high spectral resolution is required for unambiguous observation. The magnitudes of these unique features are larger than the noise of modern instruments. The sensitivities of these features to cloud height and cloud optical depth are also discussed. Our sensitivity studies show that, when the errors in the estimation of temperature profiles are not large, the dominant contribution to the residuals is the misinterpretation of cirrus. An analysis that focuses on information content is also presented. An understanding of the magnitude of the effect and of its dependence on spectral resolution as well as on spectral region is important for retrieving spacecraft data and for the design of future infrared instruments for forecasting weather and monitoring greenhouse gases.     

Influence of temperature on water and aqueous glucose absorption spectra in the near- and mid-infrared regions at physiologically relevant temperatures

Near- and mid-infrared absorption spectra of pure water and aqueous 1.0 g/dL glucose solutions in the wavenumber range 8000-950 cm-1 were measured in the temperature range 30-42 degrees C in steps of 2 degrees C. Measurements were carried out with an FT-IR spectrometer and a variable pathlength transmission cell controlled within 0.02 degree C. Pathlengths of 50 microns and 0.4 mm were used in the mid- and near-infrared spectral region, respectively. Difference spectra were used to determine the effect of temperature on the water spectra quantitatively. These spectra were obtained by subtracting the 37 degrees C water spectrum from the spectra measured at other temperatures. The difference spectra reveal that the effect of temperature is highest in the vicinity of the strong absorption bands, with a number of isosbestic points with no temperature dependence and relatively flat plateaus in between. On the basis of these spectra, prospects for and limitations on data analysis for infrared diagnostic methods are discussed. As an example, the absorptive properties of glucose were studied in the same temperature range in order to determine the effect of temperature on the spectral shape of glucose. The change in water absorption associated with the addition of glucose has also been studied. An estimate of these effects is given and is related to the expected level of infrared signals from glucose in humans.     

探测低空大气温度分布的转动拉曼激光雷达

提出了一种新的探测对流层低层大气温度的转动拉曼激光雷达方法,通过测量N2和O2的后向散射的纯转动拉曼谱的强度,计算它们的比值来确定大气温度的垂直分布,并对其性能进行了数值模拟。转动拉曼激光雷达的光源是一个调Q的Nd:YAG激光器,经扩束器后输出能量200mJ;采用双光栅单色仪提取所需要的氮气和氧气的转动拉曼谱;接收机采用光电倍增管和双通道光子计数器,量子效率是10%(48000个脉冲累加)。夜晚它对近地面10.2km高度内的探测信噪比在10:1以上,白天它对近地面3.6km高度内的探测信噪比在10:1以上,计算的温度与模拟用的温度真值阔线相差约0.3K。     

Detection and identification of a methanol-water complex by factor analysis of infrared spectra

Fourier transform infrared absorption spectra, between 1850 and 2700 cm(-)(1), were used to study the intermolecular interactions between methanol and water. Digitized spectra obtained from methanol-water mixtures, with methanol mole fraction varying from 0 to 1.00, were subjected to factor analysis. Principal factor analysis indicated that three chemical factors were responsible for the data. Window factor analysis, a model-free method, was used to extract the concentration profiles of three species, which were identified as water, methanol, and a methanol-water complex. The profiles were used to deduce the stoichiometry of the complex, which was found to consist of one molecule of methanol and two molecules of water. The dissociation constant of the complex was determined to be 306 ± 33 M(2). These results differ from those reported by other investigators.     

Spontaneous anti-stokes Raman probe for gas temperature measurements in industrial furnaces.

A compact, pulsed Nd:YAG laser-based instrument has been built to measure in situ absolute gas temperatures in large industrial furnaces by use of spontaneous anti-Stokes Raman scattering. The backscattering configuration was used to simplify the optics alignment and increase signal-to-noise ratios. Gated signal detection significantly reduced the background emission that is found in combustion environments. The anti-Stokes instead of the Stokes component was used to eliminate contributions to spectra from cold atmospheric nitrogen. The system was evaluated in a methane/air flame and in a bench-top oven, and the technique was found to be a reliable tool for nonintrusive absolute temperature measurements with relatively clean gas streams. A water-cooled insertion probe was integrated with the Raman system for measurement of the temperature profiles inside an industrial furnace. Gas temperatures near 1500-1800 K at atmospheric pressure in an industrial furnace were inferred by fitting calculated profiles to experimental spectra with a standard deviation of less than 1% for averaging times of ~200 s. The temperatures inferred from Raman spectra are in good agreement with data recorded with a thermocouple probe.     

Calibration-free estimates of batch process yields and detection of process upsets using in situ spectroscopic measurements and nonisothermal kinetic models: 4-(dimethylamino)pyridine- catalyzed esterification of butanol

In this paper, we report the use of an NIR fiber-optic spectrometer with a high-speed diode array for calibration-free monitoring and modeling of the reaction of acetic anhydride with butanol using the catalyst 4-(dimethylamino)pyridine in a microscale batch reactor. Acquisition of spectra at 5 ms/scan gave information relevant for modeling these fast batch processes with a single multibatch kinetic model. Nonlinear fitting of a first-principles model directly to the reaction spectra gave calibration-free estimates of time-dependent concentration profiles and pure component spectra. The amount of catalyst was varied between different batches to permit accurate estimation of its effect in the multiway model. A wide range of different models with increasing complexity could be fit to each batch individually with low residuals and apparent low lack of fit. However, only one model properly estimated the concentration profiles when all five batches were fitted simultaneously in a multiway kinetic model. Inclusion of on-line temperature measurements and use of an Arrhenius model for the estimated rate constant gave significantly improved model fits compared to an isothermal kinetic model. Augmentation of prerun batches with data from an additional batch permitted model-based forecasts of reaction trajectories, reaction yield, reaction end points, and process upsets. One batch with added water to simulate a process upset was easily detected by the calibration free process model.     

Measurement of the temperature-dependent optical constants of water ice in the 15-200 microm range

The real and imaginary refractive indices of water ice in the far infrared (IR) are used in the satellite interpretation of cloud properties as well as to obtain information on ice throughout the solar system. However, few measurements of these values exist. We have measured the real and imaginary refractive indices of water ice in the far IR every 10 deg over the temperature range of 106-176 K. Ice films ranging from 0 to 140 microm thick were grown by the condensation of water vapor onto a cold silicon substrate, and the film transmission was measured from 650 to 50 cm(-1). The thickness of the ice films was determined using optical interference from a reflected He-Ne laser (lambda = 623.8 nm). The optical constants were then determined by simultaneously fitting the calculated spectra of films of varying thickness to their respective measured transmission spectra with an iterative Kramers-Kronig technique. The results are compared with previously measured data and show large discrepancies at some wavelengths while good agreement exists at others. Possible reasons for the differences are discussed. Our data clearly distinguish crystalline and amorphous ice. In addition, we note a slight shoulder in our spectra, which can be used to distinguish between cubic and hexagonal ice, although this distinction is difficult.     

Some Results on the Measurement of Temperature and Density in a Flame by Raman Spectroscopy

Temperature and molecular concentration profiles in a premixed laminar flame, generated by a multi-hole burner, have been investigated by spontaneous Raman spectroscopy. Experimental data obtained using a chopped Ar ion laser beam as a source are presented. Analyses of the observed N₂ vibro-rotational spectra for the determination of temperature in the reaction and post reaction zone of the flame are discussed. Concentration of the various species are obtained from the corresponding spectra and the measured temperature. Results show that this method provides satisfactory space resolution and good reliability.     

Computation of the range of feasible solutions in self-modeling curve resolution algorithms

Self-modeling curve resolution (SMCR) describes a set of mathematical tools for estimating pure-component spectra and composition profiles from mixture spectra. The source of mixture spectra may be overlapped chromatography peaks, composition profiles from equilibrium studies, kinetic profiles from chemical reactions and batch industrial processes, depth profiles of treated surfaces, and many other types of materials and processes. Mathematical solutions are produced under the assumption that pure-component profiles and spectra should be nonnegative and composition profiles should be unimodal. In many cases, SMCR may be the only method available for resolving the composition profiles and pure-component spectra from these measurements. Under ideal circumstances, the SMCR results are accurate quantitative estimates of the true underlying profiles. Although SMCR tools are finding wider use, it is not widely known or appreciated that, in most circumstances, SMCR techniques produce a family of solutions that obey nonnegativity constraints. In this paper, we present a new method for computation of the range of feasible solutions and use it to study the effect of chromatographic resolution, peak height, spectral dissimilarity, and signal-to-noise ratios on the magnitude of feasible solutions. An illustration of its use in resolving composition profiles from a batch reaction is also given.     

Study of complexation in methanol/water mixtures by infrared and Raman spectroscopy and multivariate curve resolution-alternating least-squares analysis

The structure of the mobile phase in liquid chromatography plays an important role in the determination of retention behavior on reversed-phase stationary materials. One of the most commonly employed mobile phases is a mixture of methanol and water. In this work, infrared and Raman spectroscopic methods were used to investigate the structure of species formed in methanol/water mixtures. Chemometric methods using multivariate curve resolution by alternating least-squares analysis were used to resolve the overlapped spectra and to determine concentration profiles as a function of composition. The results showed that the structure of these mixtures could be described by a mixture model consisting of four species, namely, methanol, water, and two complexes, methanol/water (1:1) and methanol/water (1:4). The spectral frequencies and concentration profiles found from the Raman and infrared measurements were consistent with one another and with theoretical calculations.     

Simulation of multiple scattering in lidar measurements using pure rotational raman scattering (PRRS)

Abstract

Pure rotational Raman scattering signals from atmospheric gases such as nitrogen and oxygen can be used to deduce the temperature of the atmosphere. Previously, this method has been successfully implemented as a remote temperature sensing lidar system. In this paper, theoretical studies of the method have been carried out using Monte Carlo simulations for different temperature profiles from radio sonde data. The geometry of the lidar as well as the aerosol profiles of the atmosphere can be specifically defined in this method. It is important to understand whether or not multiple scattering will have a significant effect on the accuracy of temperature retrieval from the measured lidar returns. From the exact pure rotational Raman scattering matrix, we have computed the lidar returns of individual Raman lines. We have given the ratios of multiple to single scattering return signals for atmospheres without clouds, with water clouds and with cirrus clouds. The results indicate that the effect of multiple scattering does not give errors to the temperature inversion for typical atmospheric conditions.     

Transmittance Fourier transform infrared spectra of liquid water in the whole mid-infrared region: temperature dependence and structural analysis

Transmittance Fourier transform infrared (FT-IR) spectra of liquid water in the 4-80 degrees C temperature range are reported in the whole mid-infrared (MIR) region (4000-360 cm (-1)). The spectra were recorded by using a newly developed, home-made transmittance cell, working in light vacuum conditions (pressures of the order of 3-4 millibar). This permits the elimination of the aqueous vapor bands from the liquid spectra, particularly in the bending region, and the rapid collection of data without fluxing large amounts of nitrogen through the interferometer sample chamber. The temperature evolution of the OH stretching and HOH deformation bands is discussed in terms of Gaussian components analysis and a two-state model describing the equilibrium between different H-bond structures of liquid water. From this picture, structural and thermodynamic information about the hydrogen-bonding network of water is obtained.     

Comparison of coherent anti-Stokes Raman-scattering thermometry with thermocouple measurements and model predictions in both natural-gas and coal-dust flames

Mobile coherent anti-Stokes Raman-scattering equipment was applied for single-shot temperature measurements in a pilot-scale furnace with a thermal power of 300 kW, fueled with either natural gas or coal dust. Average temperatures deduced from N(2) coherent anti-Stokes Raman-scattering spectra were compared with thermocouple readings for identical flame conditions. There were evident differences between the results of both techniques, mainly in the case of the natural-gas flame. For the coal-dust flame, a strong influence of an incoherent and a coherent background, which led to remarkable changes in the spectral shape of the N(2)Q-branch spectra, was observed. Therefore an algorithm had to be developed to correct the coal-dust flame spectra before evaluation. The measured temperature profiles at two different planes in the furnace were compared with model calculations.     

Development of multipoint vibrational coherent anti-Stokes Raman spectroscopy for flame applications

A novel technique for coherent anti-Stokes Raman spectroscopy (CARS) measurements in multiple points is presented. In a multipass cavity the pump and Stokes laser beams are multiply reflected and refocused into a measurement volume with an adjustable number of separated points along a line. This optical arrangement was used in a vibrational CARS setup with planar BOXCARS phase-matching configuration. The CARS spectra from spatially separated points were recorded at different heights on a CCD camera. Measurements of temperature profiles were carried out in the burned gas zone of a premixed one-dimensional flame to demonstrate the applicability of this method for temperature measurements in high-temperature regions. The ability to measure in flames with strong density gradients was demonstrated by simultaneous measurements of Q-branch spectra of N2 and CO in a Wolfhard-Parker burner flame. Interference phenomena found in multipoint spectra are discussed, and possible solutions are proposed. Merits and limitations of the technique are discussed.     

Interferometer for ground-based observations of emitted spectral radiance from the troposphere: evaluation and retrieval performance

We evaluate the spectral quality, radiometric noise, and retrieval performance of a Fourier transform infrared spectrometer, which has been developed for recording spectrally resolved observations in a region of the spectrum which is important both for the science of Earth's climate and applications, such as the remote sensing of temperature and atmospheric gas species. This spectral region extends from 100 to 1600 cm(-1) and encompasses the two fundamental, rotation and vibration, absorption bands of water vapor. The instrument is a customized version of a Bomem AERI (Atmospheric Emitted Radiance Interferometer) spectrometer, whose spectral coverage has been extended in the far infrared with the use of uncooled pyroelectric detectors. Retrieval examples for water vapor and temperature profiles are shown, which also allow us to intercompare the retrieval performance of both H(2)O vibration and rotation bands.     

Role of the deposition parameters and aging on the optical and photoluminescence properties of C70 films

We have investigated the influence of the growth parameters (substrate temperature and deposition rate) and the aging process on the optical properties of C₇₀ thin films, by means of absorption and photoluminescence spectra. The Urbach energy, obtained from the absorption spectra, indicates that the substrate temperature influences the film optical properties more than the deposition rate. The luminescence spectra suggest the important role of the disorder in the radiative efficiency. The main structures of the emission spectra have been assigned to an intramolecular polaron-exciton. The analysis of the temperature dependence of the photoluminescence spectra of the as-deposited samples shows that the vibronic transitions are dominant at low temperature, whereas the singlet purely electronic recombination (due to Frenkel-type exciton) is visible at a sufficiently high temperature. On the contrary, in the aged samples this purely electronic transition is well resolved from low to high temperature. This anomalous behaviour is discussed and attributed to the disorder introduced in the film.     

Study of thermal dynamics of defatted bovine serum albumin in D2O solution by Fourier transform infrared spectra and evolving factor analysis

Fourier transform infrared (FT-IR) spectra have been measured for defatted bovine serum albumin (BSA) in D(2)O with a concentration of 2.0 wt % over a temperature range of 26-90 degrees C and the corresponding difference spectra have been calculated by subtracting the contribution of D(2)O at the same temperature. Evolving factor analysis (EFA) by selecting two factors and three factors has been employed to analyze the temperature-dependent difference IR spectra in the 1700-1600 cm(-1) spectral region of the defatted BSA in D(2)O solution. Three-factor EFA has been employed to determine the distinction of the three protein species involved in the process of temperature elevation: native, transitional, and denatured protein. The temperature profiles obtained from three-factor EFA indicate that heat-induced conformational change in the secondary structures of defatted BSA in D(2)O undergoes two two-state transitions, a drastic transition and a slight transition, which occur in the temperature ranges of 68-82 degrees C and 56-76 degrees C, respectively.     

Si-based photonic quantum dots with the self-similar distributed Bragg reflectors

In this letter, optical microcavities are deposited directly on mesa-patterned substrates, and three dimensional Bragg cavities are formed due to the conformal deposition process. The room temperature photoluminescence spectra of three-dimensional Bragg microcavity exhibit a series of discrete resonant peaks. Optical field profiles of corresponding resonant peaks were given, by finite difference time domain simulation. These discrete peaks obviously show cavity resonant characteristics and optical field is mostly localized in the cavity layer. Also size dependence of cavity modes was concluded from our experimental results.     

Two-dimensional attenuated total reflection infrared and near-infrared correlation study of the structure of butyl alcohol/water mixtures

The effect of temperature on attenuated total reflection infrared (ATR-IR) and near-infrared (NIR) transmission spectra of pure butan-1-ol, butan-2-ol, 2-methyl-propan-1-ol, 2-methyl-propan-2-ol, and mixtures with a small water content (X(H2O) 相似文献