A. V. Falits

Numerical simulation of propagation of laser beams formed by multielement apertures in a turbulent atmosphere under thermal blooming

An algorithm for simulating laser beam propagation in a turbulent atmosphere under conditions of thermal blooming for the case where the beam is formed by a multielement aperture is presented. Coherent and incoherent combining of elementary fields of the multielement aperture is considered. Based on numerical simulation, properties of a combined beam are analyzed in comparison with an equivalent Gaussian beam. A complex diffraction pattern is shown to appear upon coherent combinig as a result of superposition of fields formed by individual elements of the initial aperture. Average values of maximum intensity, both of the Gaussian beam and the combined laser beam, little differ from each other when the nonlinearity parameter Nc > 1. Under conditions of strong turbulence and strong nonlinearity, integral radiation characteristics of combined beams are close to characteristics of the Gaussian beam, the effective size of which is determined by sizes of the combined beam. The intensity of combined laser beams in a turbulent atmosphere fluctuates upon incoherent combining of fields to a lesser extent as compared to coherent combining.

Joint radiosonde and doppler lidar measurements of wind in the atmospheric boundary layer

Results of joint measurements of height profiles of wind velocity and direction by the Stream Line pulse coherent Doppler lidar and RS92-SGP radiosonde in Tomsk from 23 to 27 of September, 2013, are presented. It has been established that wind profiles can be retrieved up to heights from 400 to 1100 m depending on the aerosol concentration in the atmospheric boundary layer from lidar data measured at an elevation angle of 45°. It is shown that the coefficient of correlation between lidar and radiosonde measurements of wind velocity and direction is equal to 0.97. The mathematical expectation and standard deviation of the difference between estimates for the wind velocity and direction from the radiosonde and lidar data amount to 0.1 and 0.7 m/s, respectively, for the velocity and 0.8° and 4°, respectively, for the wind direction.

Effectiveness of the subharmonic method in problems of computer simulation of laser beam propagation in a turbulent atmosphere

The results of the analysis of the effectiveness of the subharmonic method for simulating large-scale turbulent inhomogeneities of the refractive index in problems of laser beam propagation in a turbulent atmosphere are presented in comparison with experimental data.

Efficiency of combined beam focusing under thermal blooming

Thermal defocusing of a laser beam leads to a restriction in the power of radiation that can be efficiently transmitted through the atmosphere. Focusing under thermal blooming can be considered as efficient if the minimum radius of the complete radiation interception circumference in the focal plane is less than the radius of the initial aperture of the radiation source. A method for estimating the efficiency of combined beam focusing under conditions of thermal blooming is considered.

Diffraction contraction of short pulses

The mean intensity of partially coherent light pulses propagating in free space under arbitrary diffraction conditions on a transmitting aperture has been calculated. It has been shown that a decrease in the pulse duration leads to a decrease in the diffraction size of the beam compared to continuous-wave beams.

Manifestation of aero-optical effects in a turbulent atmosphere in supersonic motion of a conical body

This paper presents results of the analysis of the mean intensity, intensity fluctuations, and regular and random shifts of optical beams propagating through a shock wave resulting from the supersonic motion of a conical body in a turbulent atmosphere. It is shown that aero-optical effects caused by a shock wave are suppressed with an increase in the optical turbulence. Quantitative data illustrating the degree of the manifestation of aero-optical effects for paths with different geometry and length depending on turbulent conditions of light propagation are presented.

Visualization of the velocity field in a turbulent atmospheric layer from optical radiation passed through the layer

The feasibility of visualizing the 2D velocity field in a turbulent atmospheric layer by the intensity fluctuations of the optical radiation passed through the layer is analyzed. In the scheme considered, the laser radiation passed through a turbulent layer is then scattered at a diffuse surface, and the backscattered radiation is received by a telescope, which forms an image of the illuminated area of the scattering surface. It is shown that the correlative comparison of the large-scale structure of the intensity fluctuations in coherent images of the scattering surface obtained at different times allows for the visualization of the 2D velocity field in the turbulent layer.

Estimation of the turbulence energy dissipation rate in the atmospheric boundary layer from measurements of the radial wind velocity by micropulse coherent Doppler lidar

The accuracy of the method of azimuth structure function for estimation of the dissipation rate of the kinetic energy of turbulence from an array of radial velocities measured by low-energy micropulse coherent Doppler lidars with conical scanning by a probing beam around the vertical axis has been studied numerically. The applicability of the method in dependence on the turbulence intensity and the signal-to-noise ratio has been determined. The method of azimuth structure function was applied for estimation of the turbulent energy dissipation rate from radial velocities measured by the lidar in the experiments on the coast of Lake Baikal. Two dimensional time-height patterns of the wind turbulence energy dissipation rate were obtained. Part of them were obtained in presence of the atmospheric internal waves (AIWs) and low-level jet streams. It is observed that the wind turbulence in the area occupied by jet streams is very weak. In the process of dissipation of AIWs the wind turbulence strength increases.

Structure of aerosol fields of the atmospheric boundary layer according to aerosol and Doppler lidar data during passage of atmospheric fronts

The paper presents the results of complex observations of the atmospheric boundary layer dynamics performed at the Fonovaya Observatory of the Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, in September 2013, with the use of remote sensing facilities, i.e., aerosol and Doppler lidars. The structure of aerosol and wind fields in the period of occurrence of internal buoyancy waves and low-level jet streams in the boundary layer is considered.

Stream Line Doppler lidar measurements of wind speed and direction with the duo-beam method in the surface air layer

The results of retrieval of wind speed and direction from measurements of radial velocity by a Stream Line pulsed coherent Doppler lidar using the duo-beam method and conical scanning are presented. These results are compared with data of a sonic anemometer (point sensor).