Home – Home – Jornals – Atmospheric and Oceanic Optics 2023 number 9

The results of the numerical simulations on optical radiation focusing by a cluster of identical nanospheres densely packed into a spherical volume (a "metaparticle") are presented. The parameters of the focal region (intensity, longitudinal and transverse dimensions) formed by metaparticles with different internal structure are calculated. We show that in certain cases, the problem of focusing optical radiation by a globular cluster of nanoparticles can be reduced to the problem of light focusing by a homogeneous spherical particle with an effective refractive index obtained from the effective medium theory. Moreover, certain globular cluster topologies make it possible to improve the optical focusing in the near-field region, in particular, by increasing the focal intensity or enhancing the spatial localization of the focal area.

The conditions for the occurrence of extreme concentrations of submicron particles and black carbon in their composition in the surface air layer are analyzed on the basis of monitoring measurements of aerosol characteristics and acoustic sounding of the lower air layer in the winter periods of 2016-2022 in Akademgorodok, Tomsk. It is shown that with a combination of surface air temperature inversion and weak (up to 1.5 m/s) wind (air stagnation), the average aerosol characteristics under study increase by up to 3 times, and with a weak northwest wind, up to 7-8 times relative to the season averages. It is found that under several-day air stagnation conditions, the typical daily variation, characterized by the afternoon minimum, is transformed. The increase in the concentrations continues until 15:00; the values exceed nighttime minimum by 1.8 times. On other days of the winter season, the maxima occur at 10:00 am, with the excess of the concentrations of submicron particles by 1.2 times, and of black carbon, by 1.5 times over the nighttime minima.

A mathematical model is proposed that simulates the acquisition and processing of hyperspectral remote sensing data on subtle fragments of environmental pollution (garbage) comparable in size with the spatial resolution of the observation equipment. Spectral mixing of “objects” with “background” is provided by a special coefficient, which takes into account that the area of each element of a scene template related to the “object” is only partially filled with its spectral characteristic, and the rest of the area, with the background characteristic. The options for calculating the probability of detecting objects depending on the observation conditions specified with the MODTRAN atmospheric model are considered. The difference between the model data and real experimental results is no more than 10%.

The results of synchronous lidar observations of the transfer of atmospheric aerosol fields over Lake Baikal during the summer expedition of 2018 are presented. The experiment was carried out using two lidars, one of which was located on a ship, and the second, at a distance of 732 m at a stationary station. Based on the correlation analysis of the lidar data, the transfer time of atmospheric aerosol heterogeneities between observation points at different altitudes above the mountain basin is estimated. It is found that the transfer time is 5 min 20 s for the altitude range 100-350 m, 7 min 12 s for 1250-1500 m, 5 min 20 s for 2100-2500 m, and 6 min 24 s for the range 4200-4300 m. Such uneven altitude distribution of the transfer time of aerosol objects is due to the complex air flow circulation in the mountain basin.

Changes in the base height of the lower layer cloudiness and cumulonimbus clouds over the territory of Western Siberia are analyzed based on laser data for the period 2010-2021. We established that, in general, there is a decrease in the base height of lower clouds and its increase for cumulonimbus clouds. An increase in the base height of lower cloudiness occurs from north to south. More meridional distribution is obtained for cumulonimbus clouds. The seasonal course of the lower cloudiness and cumulonimbus clouds base height in the south of the territory has a maximum in summer. Two maxima are observed in the center and in the north: for lower cloudiness in summer and spring and for cumulonimbus clouds in winter and summer. The results of the cluster analysis show a significant difference in the base height for cumulonimbus clouds (in comparison with lower cloudiness) at different stations, which is presumably due to differences in earth’s surface characteristics and station height above sea level, as well as regional features of atmospheric circulation and convective processes.

Characteristics of air temperature inversions in the atmospheric boundary layer (frequency of occurrence, intensity, and depth) up to a 1-km height are analyzed based on experimental MTP-5 (meteorological temperature profiler) data obtained in 2020-2022. Air temperature profiles were measured simultaneously at a site with natural landscape (Tomsk suburbs) and over an urban territory (Akademgorodok, outskirts of Tomsk). Temperature inversions were observed in approximately half of the observation period. The statistics of various forms and types of inversions for different seasons is presented. The correlation between the inversion intensity and weather parameters in the surface air layer is considered. A significant effect of the wind direction on the inversion intensity is noted.

The validation of H₂O absorption lines parameters in the modern spectroscopic databases such as HITRAN2016, HITRAN2020, GEISA2020, and W2020 database of H₂O lines is carried out in the visible region 16700-17000 cm^-1. The H₂O transmission spectra were simulated with the spectroscopic databases and compared with laboratory spectra of pure water vapor and H₂O-N₂ mixture ( P = 1 atm), recorded using a Fourier spectrometer with light-emitting diodes of high luminance. The parameters of 65 H₂O absorption lines from HITRAN2020 database were corrected on the basis of the measurements. The positions of 32 lines, intensities of 51 lines, and self-broadening coefficients of 10 lines were improved. The ratio of the HITRAN2020 broadening coefficients to the experimental values is close to 1, whereas the air pressure-induced line shift coefficients in the spectroscopic databases are, on average, two times higher than the experimental values, and therefore, our previously obtained experimental values of N₂ pressure-induced line shift coefficients were used to simulate the transmission spectra of H₂O-N₂ mixture. The difference of the experimental spectra from the spectra calculated with HITRAN2016, HITRAN2020, GEISA2020, and W2020 spectroscopic databases and corrected HITRAN2020cor gives root-mean-square deviations RMS = 1.49E-4, 1.64E-4, 3.96E-4, 3.49E-4, and 1.26E-4 in the case of pure water vapor and RMS = 1.15E-4, 1.1E-4, 2.23E-4, 2.28E-4, and 0.86E-4 for H₂O-N₂ mixture, respectively.

A polarization dielectric mirror on a ZnSe substrate is created for laser systems in the mid-IR range. The film periodic structure was calculated using the Optilayer software. Zinc sulfide (ZnS) and ytterbium fluoride (YbF₃) were used as materials for the interference coating. The optical parameters of the materials used are determined in a wide spectral range. The interference coating of the structure calculated was deposited onto the substrate by the ion-beam sputtering method. The threshold value for laser-induced breakdown of a dielectric mirror by Ho:YAG laser radiation with a wavelength of 2.097 mm was obtained, which was 4 J/cm² at a pulse repetition rate of 10 kHz and a pulse duration at half-height of 30 ns. The mirror was tested in an OPO system based on a ZnGeP₂ single crystal; the conversion efficiency obtained with this mirror reaches 30%.

The results of numerical simulation of the return flux from a sodium laser guide star for atmospheric conditions of astronomical observatories of the North Caucasus are presented. The simulation was performed in accordance with modern concepts of the physics of the interaction of polarized laser radiation with mesospheric sodium atoms. Two cases are considered: the formation of an artificial reference source by laser radiation with circular and linear polarizations. The limitations of the photon flux due to the saturation effect are estimated.

The results of calculations are presented showing how the energy is redistributed and the law of conservation of energy is fulfilled when optical radiation is reflected from mirror surface in a turbulent atmosphere. It is shown that if, as a result of reflection, spatially limited beams of light are formed, then the redistribution of energy in a plane transverse to the direction of propagation occurs near the strictly backward direction in a limited region, the dimensions of which do not exceed several Fresnel zones. In the case of a point reflector, when a spatially unlimited reflected wave is formed, the redistribution of energy occurs on a much larger scale. The increase in the mean intensity of the reflected wave in a limited area with a diameter of two Fresnel zones around the strictly backward direction (backscatter amplification effect) occurs due to the outflow of part of the energy of the reflected wave from the lateral directions from a huge area, several orders of magnitude larger than the area where this energy is accumulated.