Atmospheric and Oceanic Optics最新文献

An approach to increasing the communication channel capacity by amplitude and phase modulation almost reaches its limits. An increase in the information capacity of data communication channels by using the orbital angular momentum (OAM) of laser beams for information encoding is currently an urgent problem. The use of this approach in atmospheric optical communication systems is limited by the distorting effect of atmospheric turbulence, which makes decoding difficult and reduces the data transfer rate. In addition, the intensity distributions of vortex beams with OAMs opposite in sign are identical in a homogeneous medium, which also limits the use of OAM sign for encoding information. This work analyzes fundamental possibility of neural networks for recognizing opposite in sign OAMs of vortex beams in a turbulent atmosphere only by intensity distributions. The study is based on numerical simulation of Laguerre-Gaussian beam propagation in a turbulent atmosphere and use of the derived intensity distributions for training and testing neural networks. It is been shown for the first time that neural networks enables recognizing opposite in sign OAMs of Laguerre-Gaussian beams propagation through a turbulent atmosphere by intensity distributions with an accuracy of more than 90%. The results can be useful for developers and researchers of atmospheric optical communication systems where OAMs of vortex beams are used.

Filamentation of high-power femtosecond pulses in a gas is of great theoretical and practical interest with relation to the study of large-scale spectral and temporal transformations of laser radiation in a medium and generation of extra-wide (supercontinuum) radiation. This radiation is of interest in nonlinear femtosecond diagnostics of environment, optical data transmission through an atmospheric channel, and modern optical material processing techniques. This paper experimentally studies the effect of gas medium (nitrogen) pressure in an optical cell on the characteristics of femtosecond laser radiation propagating under filamentation conditions. It is found that high nitrogen pressure (up to 11 atm) and sharp geometric focusing of femtosecond radiation result in its Kerr self-focusing, which transforms from the single filamentation mode into multiple post filamentation as the gas pressure increases. Due to the phase self-modulation of a femtosecond pulse and plasma generation in the gas, the radiation spectrum is significantly enriched and the pulse spectrum near-linearly broadens with an increase in the gas pressure in the cell. It is ascertained for the first time that the pulse spectrum asymmetrically broadens mainly to the long-wave region while the initial beam focusing sharpness is increasing. The average size of high-intensity post-filaments formed inside a beam decreases as the gas pressure increases in the optical cell and can be fractions of a millimeter.

Energy characteristics of a copper vapor laser (CVL) pumped by a Marx generator are studied. The schematic of the generator is provided; features of its operational are described, since thyratrons are used as switches in the generator. It is shown that a Marx generator enables increasing the upper limit of stable operation of thyratrons (proportional to the number of thyratrons used; up to ∼ 8–10 kV of inverse voltage across the thyratron anodes for two thyratrons) and, hence, ensures active medium pumping parameters unattainable with a single thyratron. The pulse energy is shown to linearly increase with the voltage across a gas discharge tube (GDT) and decrease with the excitation pulse repetition rate. A CVL pumped by a Marx generator is a promising radiation source for high-altitude sensing of the atmosphere and creation of artificial guide stars in adaptive optics devices, active optical systems, and atmospheric bistatic communication channels.

Development of mineral resources in the ocean presents the problem of high-speed communication between two underwater objects. Optical radiation provides the highest transmission rate. However, the turbidity of natural waters is strongly variable; therefore, the study of the effects of different components of water suspension on laser pulse transmission is relevant. In the work, propagation of 2-ns optical pulses at a wavelength of 0.514 μm in water containing only clusters of nanobubbles is simulated. The maximal flux of radiation scattered on nanobubble clusters at the entrance to a receiver is shown to be no higher than 10% of the radiation flux propagated without scattering along a path up to 150 m long; the pulse full width at half maximum decreases by no more than 30%. The restriction on the path length in water containing only clusters of nanobubbles is due to radiation attenuation. Our results can be used for prediction of the solar radiation penetration depth during diving operations in water bodies or analyses of images of underwater objects, as well as for the development and usage of equipment for open underwater optical telecommunication lines. The influence of organic and inorganic suspended matter on the laser radiation propagation in water is planned to be studied further.

Results of solving the problem of determining the temperature dependence of the broadening coefficient of water vapor lines by pressure of different buffer gases are presented. The broadening coefficients γ have been calculated for 18 microwave absorption lines of H₂O molecule broadened by N₂, O₂, CO₂, air, H₂O, CO₂, He, Ar, Kr, and Xe pressure in the temperature range 30 ≤ T ≤ 400 K. The models of rectilinear, parabolic, and exact trajectories of colliding particles are used. It is shown that the calculated dependence γ(T) for T ( lesssim ) 100 K is determined by the calculation method and model of the trajectories of colliding particles; in the case of broadening by monatomic gases, these results strongly depend on the chosen interaction potential. The results of the work can be useful for spectral calculations required by atmospheric applications.

Monitoring of oil pollution of the land surface is one of the pressing ecological issues today. The work is devoted to the experimental study of hyperspectral technique for detecting oil pollution on the land surface in the near-IR. The spectral brightness coefficients of soil samples contaminated with different oil product types are experimentally measured in the 1.6–2.5 μm spectral range. The influence of soil moisture and rainfall on the reflection spectra of soils (several types of sand and soil from forest and park areas) contaminated by oil products (of Moscow and Samara oil processing plants, kerosene, gas condensate, various gasoline brands, motor oils, and diesel fuel) is studied. It is shown that spectral dips near 1.73 and 2.3 μm (typical for soils contaminated with oil products) in most cases remain in the reflectance spectra under conditions of moderately moist soil, moderate rain, and even heavy rain. A specially created neural network shows the probability of detecting oil pollution on the land surface to be more than 99% under conditions of moderately moist soil and moderate rain and more than 88% under conditions of heavy rain and moist soil for 14 spectral channels 10 nm wide in the 1.6–2.4 μm range. The results can be used in the development of pipeline leak remote monitoring systems.

To form plasma antennas in different radio and telecommunication devices it is necessary to increase the relaxation time of laser breakdown centers. To solve this problem, processes running in aerodisperse media with solid microparticles during interaction with laser radiation are considered. The decay time of plasma with aerosol particles under the action of nanosecond and microsecond laser pulses is analyzed. The effect of the electron shell around solid microparticles on the creation of a continuous ionization zone in an aerosol atmosphere formed by overlapping plasma halos around microparticles has been estimated. The conditions necessary for the generation of a long ionized channel by breakdown centers during explosive evaporation of atmospheric microparticles in the zone of action of a nanosecond CO₂ laser pulse and the further maintenance of the generated plasma by microsecond laser radiation are considered. A scheme of an experimental setup for creating a long ionized channel in an aerosol atmosphere is suggested. The results can be used for creation of wireless communication channels in the atmosphere.

In 2023, more than a third of dangerous weather events in the Siberian Federal District were associated with strong wind, which emphasizes the importance of improving the accuracy and timing of its forecasting. Modern numerical simulation and machine learning methods make it possible to improve forecasts; however, the task of direct calculation of wind gusts remains topical due to the limited resolution of models. An original method is proposed for correcting the results of short-term forecast of wind gusts obtained on the basis of mesoscale models of numerical weather forecasting using advance measurements and artificial neural networks. The results show that the proposed correction method makes it possible to improve the forecast of wind gusts by various semiempirical methods. The results can be applied in meteorology, energy engineering, transportation, and other industries to minimize damage from dangerous weather events.

Causes of occurrence of dense non-photochemical haze (smog) over Beijing in winter are still poorly understood. The purpose of the work is to study the catalytic oxidation of sulfur dioxide with molecular oxygen in aerosol particles and origination of dense non-photochemical haze. The rapid accumulation of ({text{SO}}_{4}^{{2 - }}) (tens of micrograms per m³ per h) is shown to occur only at high humidity and moisture acidity in particles (рН = 3.7–4.8) due to a transition of the catalytic (non-photochemical) air oxidation of SO₂ with participation of Fe and Mn ions into a fast degenerate branched mode. Origination of hazard atmospheric haze should necessarily be simulated accounting this catalytic reaction. The results can be used in forecasting the occurrence of dense atmospheric hazes with the aim of minimizing their dangerous consequences for human health and environment.

The NH Earth polar stratospheric vortex significantly varies from year to year in winter, which periodically leads to the occurrence of sudden stratospheric warmings (SSWs). Such events significantly disturb the circulation and chemical composition of the polar stratosphere. Our understanding of the wave processes that are recorded in the stratosphere and are directly involved in the occurrence of SSWs remains incomplete to date. Oscillations of the polar stratosphere of the Northern Hemisphere in the period from 1979 to 2023 are studied based on ERA5 reanalysis data. The method of current spectra is used to study the variations in the periodicity of wave processes in the polar stratosphere for different time intervals. As the main indicator of the wave properties of the stratosphere, we use the field of the vertical component of the wind velocity in the region between 60° and 90° N. It is shown that in some years, oscillations of the stratosphere coincide with or are close to the periods of the main waves of the fortnightly and monthly lunar gravitational tide. The causes and consequences of the oscillatory processes synchronization in the polar stratosphere with the lunar gravitational tide are discussed. The results can be useful for improving the understanding of the mechanisms of occurrence of SSWs, as well as for improving the forecast of such events.