Vol 30, No 2 (2017)

Further development of the asymptotic line wing theory is presented where the long-wave approximation for the molecular centers of mass is violated. This provides long molecular trajectories going far beyond an elementary volume in the case of nonresonance light absorption. The occurrence of long trajectories is evidence for a certain degree of ordering of molecular chaos. The latter can be described by means of a modified semiclassical representation method to establish correlation between the displacement and velocity operators. An expression for the absorption coefficient is derived that allows an ambiguity concerning the estimation of the parameters of the potentials to be avoided, and the temperature dependence of the absorption coefficient in line wings to be described. In our earlier work, calculations of the absorption coefficient were performed with violation of the long-wave approximation for molecular centers of mass for H₂O molecule in the 8–12 μm region using a diffusion model. This model is also employed in the present work for H₂O absorption in the 3–5 μm window regions and for CO₂ absorption in the 4.3-μm band wing to describe the temperature dependence of the absorption coefficient. Long molecular trajectories essential for the 8–12 and 3–5 μm H₂O regions are shown to hardly play a role in the 4.3-μm CO₂ band wing.

The D₂О absorption spectrum was recorded between 10000 and 11400 cm^–1 by a Fourier transform spectrometer with a spectral resolution of 0.05 cm^–1. A multipass White-type cell with an optical path length of 24 m was used for the spectrum measurements. A light-emitting diode served as a radiation source, because it provides a higher brightness as compared to other emitters. A signal-to-noise ratio of 10⁴ was gained for the strongest lines. During the D₂О spectrum treatment, the experimental line list of about 100 lines of the ν₁ + 3ν₃ band was created. Spectroscopic parameters (line positions, intensities, and half widths) were calculated from fitting the experimental data to the Voigt line profiles by the least squares method. The analysis of the spectrum allowed us to derive new energy levels belonging to the vibrational state (103) of D₂¹⁶О.

Systematization of information resources in quantitative spectroscopy is performed using the methanol molecule as an example and applying the facilities of the W@DIS information system (W@DIS IS). The choice of quantum numbers for a methanol state is explained; brief descriptions of about 40 publications containing spectral characteristics of methanol and the description of main applications of W@DIS IS are given. The interfaces used for the analysis of consistency of wavenumbers in all data sources are described, as well as the interface of the application for forming the list of measured transitions.

Asymptotic solutions for the problem of retrieving the distribution of the structure characteristic of refractive index fluctuations from measurement data on the backscattering enhancement factor have been found. The solutions are written in terms of fractional derivatives of the enhancement factor in the case of receivers with a small aperture or via usual derivatives in the case of receivers with a large aperture. Properties of the kernel of the integral equation from which the asymptotic formulas follow have been studied in detail. Attention is paid to the fact that the kernel is oscillating in the general case. The kernel oscillations slightly affect the magnitude of the enhancement factor; however, their effect on derivatives of this factor can be significant.

This article belongs to the series of works aimed at improving computing capacity of radiation codes implementing the Monte Carlo statistical method. A short description is given of the main blocks of basic (FORTRAN version) and optimized (C version) codes designed for calculation of sky radiance in a vertically heterogeneous medium. We present the results of tests which were aimed at evaluating the performance of each of the codes under different conditions in numerical experiments. In the cases examined, the performance indicators of the optimized C code were higher as compared with the basic one. It is shown that differences in execution time of the codes are reduced by increasing the optical density of the atmosphere, and using more productive computers. The developed C code can serve as a basis for creating a high-performance radiation code.

Earlier, the method for retrieval of the atmospheric turbulence profile in two intersecting laser beams that produce laser guide stars has been suggested by the authors. Results of further development of this method are given in this work. For a Kolmogorov turbulence, the integral equation with a sharp kernel like a delta function is built, which allows a simpler and more exact way for retrieving the high-altitude profile as compared to the initial version. Data of a numerical experiment show a good retrieval of the profile of actual turbulence up to altitudes of 10 km.

In this paper, we studied the method for measuring the cloud bottom boundary altitude using the stereo pair of cloud images obtained using two digital photo cameras. We suggested a method for determining the camera orientation parameters using the nighttime images of star sky. The range to the cloud is calculated using the shift of the image of a cloud fragment as a whole. A given fragment on the photographs is identified using the methods of morphological image analysis. When the stereo base is 60 m and images are taken with a resolution of 1200 pixels within a field of view of 60°, the uncertainty does not exceed 10% when cloud altitude is less than 4 km. Optimizing the parameters of photography and increasing the stereo base may substantially improve the accuracy of the cloud base altitude estimation. Examples are presented of cloud bottom boundary determination using a prototype of the experimental setup as compared to data of a laser range finder.

A control algorithm for adaptive optics systems using the focal spot of a light beam is suggested. The algorithm is based on the analytical relationship between the spot radius and a change in shape of the deformable mirror surface. A numerical simulation has been carried out, which verifies this relationship and its applicability to the wavefront correction. Some experimental results confirm the algorithm applicability for practical use.

The content of CO₂ and H₂O in vacuum-extracted tree-ring wood of stem and root discs of certain conifer species was measured. Annual distributions of these gas components were found to exhibit cyclic behavior. Moreover, distinct cyclicity was also revealed in interannual variations of the total pressure of the vacuum-extracted tree-ring gas samples. It may be safely assumed that diffusion of stem CO₂ into the atmosphere will show the same periodic variability. Two hypotheses about the origin of the cyclicity in the treering CO₂ distributions are examined.