This work presents the model calculations of the radiation attenuation of the lidars used to diagnose gas-aerosol pollution in the atmosphere in the range from UV to mid-IR. The contributions of the main atmospheric gases (vapor of H2O, CO2, O3) as well as a number of industrial gases for the spectral ranges of the most prominent gas-aerosol impurities in the atmosphere for remote sensing using NIR and LWIR-lidars, are taken into account.
Lidar, as an important tool for studying atmospheric aerosol, is widely used in studying the distribution of atmospheric aerosol pollution. In environmental monitoring, especially when using mobile lidar for measurements, it's important to know not only situations of the pollution, but also the coordinates of their sources, and their dynamics distribution. The article introduces a method for calculating the coordinates of the objects locations according to the coordinates of the lidar, the detection direction and the distance between the lidar to the objects. Finally, the programming implementation of the method and its application in the development of auxiliary lidar systems.
The current level of technical development has led to increased number of anthropogenic hazards including emissions from industrial and agricultural enterprises, terrorist threats using chemical and organic components etc. An important factor in ensuring safety is the timely detection, identification, and localization of sources of danger. In this regard, remote methods, including laser ones, become more and more important allowing detecting and identifying danger in real time and at a distance from its source. The paper presents a calculation of the laser radiation absorption by water vapor for the wavelengths of CO2-laser generation lines. It is shown that absorption caused by H2O, C2H4 and NH3 at some laser generation lines can significantly affects the results of remote detection of organic components depending on the concentration of these gases in the atmosphere. These results can be useful for specialists that develop instruments and methods for remote detection of organic compounds in the atmosphere.
Lidar, as an important tool for studying atmospheric aerosol, is widely used in studying the distribution of atmospheric aerosol pollution. In environmental monitoring, especially when using mobile lidar for measurements, it's important to know not only situations of the pollution, but also the coordinates of their sources, and their dynamics distribution . The article introduces a method for calculating the coordinates of the objects locations according to the coordinates of the lidar, the detection direction and the distance between the lidar to the objects. Finally, the programming implementation of the method and its application in the development of auxiliary lidar systems.
In this work, photodetectors with a built-in cooling system based on Peltier elements and with a cooling system based on a Dewar flask filled with liquid nitrogen are experimentally studied with the aim of practical estimation and comparison of capabilities of the photodetectors with different photosensitive element cooling types.
Substances with different absorption spectra have different backscatter spectra. If the range of sounding wavelengths is narrow, but includes evident absorption bands of an aerosol substance, then this substance can be detected from the backscattering spectrum. This is a ground for the use of the differential scattering (DICS) technique for the detection of known organic compounds in natural and anthropogenic aerosol. CO2 lasers with the wavelength tuning range 9–11 μm, which includes the absorption bands of many organic substances, are apparently the most suitable for DICS implementation. It should be borne in mind that when the imaginary part of the refractive index changes (for example, when an absorbing substance is added to a water drop), the real part of the refractive index is also changes. For large particles (r ≥ 10 μm), even small changes in the refractive index significantly affect the backscattering efficiency. The accuracy of the literature data is insufficient for preliminary (a priori) calculation of aerosol backscatter coefficients. Therefore, the development of DICS requires extensive field measurements and their complex mathematical processing with the use of machine learning algorithms. This research sets out the task of systematization of the backscattering radiation by atmospheric aerosol with different organic substances and finding out the wave lengths where the backscatter signal is higher than the selective and continuum atmospheric molecular absorption.
Small sets of chemical kinetics equations for reactions with the water monomers and dimers are solved. Equilibrium complex concentration distribution as a function of the complex dimension at the number of monomers in a complex up to 10 shows a nonmonotonic form for some values of the total monomer unit number and reaction rates with tetramers and dimers.
Small sets of chemical kinetics equations describing the cluster formation of complexes in water vapor are investigated. Sets of equations for N≤10 are solved by means of the implicit Eulerian method of the first order of accuracy for the model systems with unit rate constants and with real rate constants available in the literature. The character of cluster concentration distribution in the steady state as a function of their dimensions is changed at variations of the total monomer number A.
Small sets of chemical kinetics equations describing the formation of complexes in water vapor in the particular case of a system containing four molecules of water (monomer) with reaction rates equal to 1 are investigated. The steady state of the system is a stable focal point in the monomer-dimer plane and a complex singular point in the trimer-tetramer plane. The algorithm for deriving equations in the case of arbitrary number of monomers is described, convenient for program realization.
The results of calculations of the H2O continuum absorption coefficients for IR spectra in 1000-1300 cm-1 and 2000-2700 cm-1 regions and absorption coefficients in the wings of the CO2 bands in the IR spectrum are presented. It is shown that the calculation of the local line contribution to the total absorption should be related to the line shape so that the maximum boundary of local line contribution does not fall into the region of frequency detunings corresponding to the exponential decay. The tendencies to a change of the continuum absorption with variations in the local line contribution boundary remain the same in cases of using both the experimental coefficient and calculated according the asymptotic line wing theory as the total absorption coefficient.
Small sets of chemical reactions involving four water monomers with real values of the rate constants and concentrations are discussed. The steady states and the molecular complex concentrations as functions of the total concentration and the rate constants of the reactions between dimers are examined. It is found that the concentrations of complexes in their approach to a steady state pass through a state with very slowly changing concentrations.
Formation of molecular water complexes that presumably affect the continuum water vapor absorption under nearatmospheric conditions is discussed within a chemical kinetics approach. Small sets of reactions responsible for a homogeneous nucleation of complexes comprised of simple structural units (water monomers) are considered. Sets with complexes containing no more than 5 monomers are examined. Steady states are found for the sets of model equations used, and the stability properties and time dependent concentrations of molecular complexes near the physical steady state are defined. The special features inherent in the behavior of the concentrations depending on the initial conditions and fraction of a foreign gas are revealed.
For the first time, the low-temperature (from -9 to 15 ° C) Fourier Transform Spectroscopy laboratory measurements of the pure water vapor absorption spectra are performed in the near-infrared spectral region, and self-continuum absorption is retrieved within 1600 cm-1 (6.25 μm) and 3600 cm-1 (2.7μm) absorption bands. The proportion of true-bound and quasi-bound water dimers in the equilibrium water vapor is derived by fitting their model spectra to the spectral features of the retrieved continuum. The results are in reasonable agreement with statistical calculations and support the idea of complimentary contribution stable and metastable dimers to the spectral structure of water vapor continuum within absorption bands.
For the first time, the low-temperature (from -9 to 15 ° C) Fourier Transform Spectroscopy laboratory measurements of the pure water vapor absorption spectra are performed in the near-infrared spectral region, and self-continuum absorption is retrieved within 1600 cm-1 (6.25 μm) and 3600 cm-1 (2.7μm) absorption bands. The proportion of true-bound and quasi-bound water dimers in the equilibrium water vapor is derived by fitting their model spectra to the spectral features of the retrieved continuum. The results are in reasonable agreement with statistical calculations and support the idea of complimentary contribution stable and metastable dimers to the spectral structure of water vapor continuum within absorption bands.
The vibrational dependence of the Н2О-N2 interaction potential due to the line shifts and line wing absorption in the 3−5 μm region is discussed. Evidence in favor of the vibrational dependence of the repulsive part of the potential is given.
A line-by-line calculation of the continuum absorption coefficient in the 1600 and 3600 cm-1 water vapor bands with the line wing shape corresponding to asymptotic line shape theory is presented. The calculation results agree closely with quasi-bound dimer absorption estimates made in the context of a dimer hypothesis. An examination of the classical part of the problem at hand enables the fraction of the quasi-bound dimers to be estimated.
Factors influencing the determination of the continuum absorption have been assessed, using the 4.3 μm CO2 band as an example. The local contribution to the total absorption plays a primary role in the case where the continuum absorption is obtained from experiment. The continuum absorption may be found unambiguously from absorption measurements in band wings. For measurements within the bands, the local contribution can be calculated as the difference between the total measured coefficient and the continuum contribution obtained from measurements in band wings.
The self-broadened H2O continuum absorption data for the 3−5 μm window available in the literature are described in the framework of asymptotic line wing theory. Use is made of a diffusion model taking into account violation of the long-wave approximation in spectral line wings.
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