Home – Home – Jornals – Atmospheric and Oceanic Optics 2016 number 4

In this article, we present the results of analysis of the mean intensity, intensity fluctuations, and regular and random wandering of the optical beams crossing a shock wave arising at the supersonic flowing the turret in a turbulent atmosphere. It is shown that with increase of the optical turbulence the impact of the shock wave, arising at the supersonic flowing the turret, is so strong that even at the worst turbulent condition the aero optical impact of the shock wave on the optical beam remains predominant.

The paper discusses airborne lidar sensing of aerosol clusters by a laser beam sent forward in the aircraft flight direction. Numerical simulations are conducted to demonstrate the possibility of observation of the temporal evolution of short-living aerosol clusters with lifetime from few seconds to tens of seconds and horizontal scales from few hundred to few thousand meters. It is demonstrated that, unlike stationary lidars, airborne lidar observations allow the detection of the temporal evolution of aerosol clusters, without involving any additional hypotheses about their spatial and temporal structure.

The methods of analysis of sounding optical beam intensity variations at the nonstationary nonequilibrium path output are presented. The superstatistics and nonextensive statistical mechanics apparatus was used. The connections of the first and the second moments for the experimentally obtained distribution functions of the intensity scintillations inside the subapertures of the propagated beam profile were applied to get the models for nonequilibrium flows as well as the hypotheses about the temperature distributions and aerodynamic flow phase states over the paths.

The processes of rearrangement of structurally stable beams having axial symmetry in the free space data transmitting optical channels are investigated experimentally. The invariants of the structure transformation of the beam as the spatial code bearer are discussed. The estimation of correlation and dispersion parameters of the optical density modulation processes were carried out. The possibility of multiple difference in these characteristics in different directions perpendicular to the beam axis is indicated.

Simultaneous crosswind and strength of atmospheric turbulence are estimated by the classical laser scintillation method and passive optical method from analysis of the light scattered by a natural or man-made topographic objects in natural daylight illumination conditions. The passive sensing method does not require artificial light sources a consists in the formation of incoherent images of topographic objects in the natural sunlight and analysis of image distortions induced by turbulence between the object and the plane of observation. The estimates of integral crosswind and index of refraction structure constant of air were compared in atmospheric experiments at the same measuring optical path by both methods. The comparison with lidar data was made. Optical measurements of integral characteristics were accompanied by independent local acoustic measurements using a sonic anemometer.

The article considers the problem of wind velocity estimation from the statistics of the integral characteristics of the images of incoherent sources in the turbulent atmosphere, namely, the received power and the bias vector of the center of gravity of the image. In the framework of the first approximation of the method of small perturbations, expressions for the mutual correlation functions of these characteristics and the bias vectors for a couple of point sources registered through a couple of receivers are derived. It is shown the correlation maxima are shifted from the origin of coordinates and the shift value depends on the wind velocity. The possibility of estimation of the vector of transverse velocity averaged over the optical path from the shape of correlation functions and shifts of correlation maxima is shown.

Coherent properties of the diffraction-free optical beams propagating in a turbulent atmosphere are studied. The problem analysis is based on solution of the equation for the second-order mutual coherence function of a field of optical radiation. The behavior of the degree of coherence of the diffraction-free (cos and fundamental Bessel) optical beams depending on parameters of the beams and characteristics of the turbulent atmosphere is investigated. It has appeared that fundamental property of diffraction-free beams is the oscillating character of coherence degree of these beams, which is shown at low levels of fluctuations in the turbulent atmosphere. At high levels of fluctuations in the turbulent atmosphere, the degree of coherence of a diffraction-free cos beam becomes closer to the similar characteristic of a plane wave, while a diffraction-free fundamental Bessel beam becomes closer to a spherical wave. The analysis of two spatial scales of degree of coherence of optical beams has shown that the integral scale of coherence degree for diffraction-free beams is more representative characteristic than coherence of radius. The integral scale of coherence degree of diffraction-free beams is practically unequivocally connected with conditions of propagation of optical radiation in a turbulent atmosphere.

Based on the numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field the propagation of a short pulsed Laguerre-Gaussian beam with femtosecond duration was studied. It has been shown that the difraction broadening of the Laguerre-Gaussian beam decreases with the pulse duration in comparison with continuous wave radiation.

In the given paper, using the Pointing vector streamlines, the effective beam width dependence on initial field distribution of axially symmetric laser beam, propagating in the turbulent atmosphere, is investigated. Spatial evolution of effective beam widths of ring-shaped laser beams, such as Laguerre-Gaussian and dark hollow beams was examined in comparison with Gaussian beams under condition that the beam power in transmitter aperture of an atmospheric optical system is the same for all laser beam modes studied in the paper. It was shown that in the case of medium-to-strong turbulence effective beam widths of high-order Laguerre-Gaussian and dark hollow beams can be less than effective beam width of a Gaussian beam in the atmosphere.

Impact of combustion phases of typical Siberian biomass on optical, microphysical, and physical-chemical properties of smoke aerosols were investigated in small-scale fires at the Large Aerosol Chamber (LAC). The comprehensive analysis has revealed the influence of combustion temperature on formation and time evolution of pine and debris emission characteristics. Size distributions and complex refractive indices in the ranges of ultrafine, fine, and coarse particles were determined from polar spectronephelometer measurements of the angular aerosol scattering. In smoldering phases, smoke is found to be weakly absorbing while mixed fires also emit strongly absorbing soot particles produced in open flaming phases. Characteristics of aerosol microstructure such as morphology and composition were analyzed. Group Soot and Organics were identified as micromarkers of Siberian biomass burning in open flaming and smoldering phases, respectively. Carbon fraction (organic and elemental carbon), chemical compounds, and water-soluble ionic fraction exhibit the strong dependence on the combustion phase. Anhydrosugar (levoglucosan) was determined in smoldering fires as the stable molecular marker of Siberian pine burning. A number of chemical compounds were found to act as specific markers of soft wood. At smoke aging in a chamber the condensation of organic and inorganic species leads to transformation of the aerosol surface chemistry and formation of the particle group rich by potassium. Thus, the complexicity and changeability of chemical composition and microstructure of atmospheric aerosol pollution during Siberian wildfires were realized.

The threshold characteristics of lasing in a layer of colloidal solution of dye Rhodamine 6G with plasmon-resonance Au nanoparticles and non-plasmon-resonance Pt nanoparticles excited by a wavelength of 532 nm are experimentally investigated. The spectral dependence of the scattering and absorption cross sections of nanoparticles of gold and platinum are calculated within the Mie theory. It is established experimentally that the addition of nanoparticles to the active medium reduces the lasing thresholds by two orders of magnitude. It is shown that the lasing threshold value is 1.5-2 times lower when adding gold nanoparticles than when adding platinum nanoparticles of the same concentration.

Laboratory experiments with a first-overtone CO laser are performed to simulate a lidar system. The trace remote sensing scheme of atmospheric gases (nitrous oxide and methane) at emission lines of the pulsed first-overtone CO laser is tested using topographic target and receiving telescope. Results of the measurements of absorption of the first-overtone CO laser operating at 20 selected emission lines in gas mixtures with the gases studied at various configurations of the experimental scheme are presented.

To reconstruct the data of hydrophysical parameter observations, a model based on a neural network with the teacher has been suggested. The indices of global climate modes of the ocean-atmosphere system were applied as the model input. The processes of the model teaching and adaptation, which allow one to find the most accurate solution of the problem of modeling, is described. The comparison of modeled monthly average Danube's runoff with data of observation demonstrated their good correspondence. Missed in some years observation data on sea water transparency (depth of white disc visibility) were reconstructed. The proximity of reconstructed and observed depths of white disc visibility was noted. Some features of interannual variability of reconstructed data on sea water transparency caused by both climatic factors during 1950-1962 and changes in the chlorophyll а concentration during 1998-2010 were found.

The methodological issues and theoretical results related to determination of the boundaries of laser-hazard distances (LHD) when eyes are exposed to direct and scattered radiation produced by a laser landing system (LLS) are discussed. LHD calculation algorithms during LLS operation in field conditions are considered. LHD have been calculated for a single and a group of laser sources for a variety of weather conditions. Computer software for laser radiation dosimetry calculation during LLS operation in field conditions is suggested.