Home – Home – Jornals – Atmospheric and Oceanic Optics 2018 number 7

The results of experimental measurements of H₂O absorption coefficients for some lines of ¹²CO₂ and ¹³CO₂ lasers at high temperatures are presented, as well as line-by-line calculated absorption coefficients. The measured and calculated H₂O absorption coefficients are compared.

Absorption of the fourth harmonic of the YAG laser radiation (266 nm) in mixtures of water vapor and sulfur dioxide with nitrogen in dependence on the total pressure of the mixtures and the content of H₂O and SO₂ molecules was investigated by time-resolved photo-acoustic technique. The differences between the experimental data for mixtures of H₂O with nitrogen and the similar experimental data for absorbing SO₂ molecules in mixtures with nitrogen prove the lack of H₂O absorption band in the UV spectral range 250-320 nm.

Based on the diffraction-ray representation of the nonlinear propagation of laser pulses the examples of the visualization of filamentation of high-power femtosecond laser pulses in air are considered by constructing evolutionary paths of diffraction beams and light tubes. It is ascertained that a filament is supported by the light energy of only the part of the beam that is in the beam tube with an initial peak power exceeding the critical power of self-focusing. This light tube is the energy reservoir of the filament. The peripheral part of the light beam holds this diffraction-beam tube containing the filament by forming a “diffractive” waveguide.

Various methods for predicting wind gusts speed based on numerical atmospheric models are considered. On the basis of different methods’ skill scores a new hybrid method for forecasting gusts is proposed. This method takes into account wind gusts of different formation mechanisms. Seven methods for forecasting wind gusts are evaluated based on the data of high-frequency measurements and the network of synoptic stations are given. The hybrid method gives more stable results throughout the year.

The problem of determining the dynamics of land-use change and differential albedo was solved with the help of high-resolution images from satellites of Landsat group for the city of Perm in 1987-2013. It is shown that the method suggested for processing of multi-temporal images allows quick qualitative assessment of changes in the underlying surface of the city. It was revealed that human activity is the main factor affecting the changes in the structure of land use and albedo of the territory.

Parametric statistical models of the image textures and physical parameters of cloudiness over various natural regions of the Russian Federation during snow cover are presented. The cloud texture description is based on the GLCM, GLDV, SADH, and OSDH methods of statistical approach to describing the texture of their images in the visible spectral range (0.62-0.67 μm). The probability densities and estimates of their parameters are found. They describe the fluctuations in the physical parameters of the clouds and the texture features of their images, determined from MODIS satellite data. The most repetitive cloud types during periods of snow cover are given. The comparative analysis results of statistical cloud models for various natural regions and cloud models over snow-covered territory and a snow-free surface are discussed. The variability of characteristic values of texture features and physical parameters of clouds observed over different natural regions of the Russian Federation is noted.

The data of airborne and satellite sounding at the ocean-land boundary near the Kara Sea in October, 2014, are compared. In total, 11 profiles synchronously measured over a continental part and 7 profiles over the ocean are used. It turned out that CH₄ and CO₂ concentrations are typically overestimated in a layer of 0-8 km over a continental part of the Arctic region and underestimated over the ocean. The overestimation by the satellite of the methane concentrations over the continent makes 28 ppb in the boundary layer and sharply increases in the middle (182 ppb) and upper (113 ppb) troposphere. The underestimation over the ocean averages 37 ppb in the boundary layer, 73 and 71 ppb in the middle and upper troposphere. The difference in CO₂ concentrations measured with different devices over the continent averages 18.2 ppm in the boundary layer and can change from 3.2 to 26.5 ppm. In the middle troposphere (4 km), the average differences decrease down to 10.8 ppm; the range of differences even slightly increases (0.6-25.5 ppm). In the upper troposphere (8 km), the average difference in measurements with both instruments decreases down to 2.8 ppm. The underestimation of the amplitude is higher over the ocean. The comparison for CO and O₃ comparison yielded acceptable results.

The requirements to the transceiver system of a Raman-lidar intended for studying the atmospheric boundary layer and predicting the danger of smog formation are determined. Synthesis of the optical layout of a lidar transceiver system with narrow field of view and minimal dead zone is carried out. The results of computer simulation of the lidar overlap functions obtained by the ray tracing for several variants of the optical layout of the receiving optical system are presented. It is shown that when using a multi-element transceiver based on a combination of four receiving apertures of different diameters, a lidar sensing range from 5 to 3000 m can be obtained in a dynamic range of the lidar response of no more than 10.

Previous and new results obtained at the Institute of Atmospheric Optics, Siberian Branch of the Russian Academy of Sciences, on problems of optical communication on scattered laser radiation in the UV wavelength range are discussed. Examples of implementation of field experiments on optoelectronic communication at night and in the day time in 2017 and 2018 are presented.

The paper describes the features of the two-mirror adaptive system for correcting atmospheric disturbances of the Large Solar Vacuum Telescope, developed with allowance for the correction of instrumental vibrations of telescopes in a wide amplitude-frequency range with an open siderostat supply mirror. Corrections of the general slopes of the light wave front and its deformations are carried out separately. The adaptive optics system is designed to work with extended light sources (the Sun), which have a low contrast of image details.

The temporal resolution of an adaptive optics system depends on the dynamic characteristics of the flexible mirror and on the way the mirror is affected at the stress points. When constructing a prediction of optical signal distortion, both of these factors must be taken into account for effective mirror control. The results the study of the dynamic properties of the adaptive optics system as functions of the temporal transformation of the mirror stresses are presented

To create an effective unified control system for several objects in the conditions of error budget constraints, a new algorithm for controlling a multi-element mirror of a large telescope is generally considered and justified in the general case for a large number of joints between element rows. A version of this algorithm is suggested in the autostabilization system of Millimetron. An error in the relative positioning of the elements and the search for the location of the sensors was evaluated. The results obtained make it possible to state quite accurately the successful applicability of this control algorithm as a part of the contour of adaptation of large telescopes with multi-element primary mirrors.

Possible variants of the sensor equipment based on the pseudo-circulation of the wave front of the measuring beam and photoelectronic-optics amplification of the angular misalignment signal are considered. Evaluation of the characteristics of these sensors allows us to conclude a possibility of creating measuring systems that meet the requirements of the “Millimetron” telescope.