V. A. Banakh

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.

Diffraction of short-pulse Laguerre–Gaussian beams

Based on the numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field, the propagation of short-pulse vortex optical beams in a homogenous medium is studied by an example of a Laguerre–Gaussian femtosecond beam. It has been shown that the diffraction spreading of the Laguerre–Gaussian beam decreases with decreasing pulse duration as compared to continuous wave beams.

Estimation of the integral wind velocity and turbulence in the atmosphere from distortions of optical images of naturally illuminated objects

The average crosswind and intensity of atmospheric turbulence are simultaneously estimated by the classical laser scintillation method and by the passive optical method from the analysis of the light scattered by natural or man-made topographic objects in the natural daylight illumination conditions. The passive sensing method does not require artificial light sources, and consists in the formation of incoherent images of sunlit topographic objects and in the analysis of images’ distortions induced by the turbulence between the object and the image plane. Estimates of the integral average crosswind and the structural constant of the air refractive index are compared in atmospheric experiments on the same optical measurement path by both methods. Comparison with lidar data is made. The optical measurements of integral characteristics were accompanied by independent local acoustic measurements using an ultrasonic anemometer.

Study of Turbulent Supersonic Flow Based on the Optical and Acoustic Measurements

Aircraft and missiles moving in the atmosphere with supersonic velocities form air flows of a complicated spatial structure, in which compression shocks of different configurations and intensities arise. Since an air flow is strongly spatially inhomogeneous, the air density in the flow experiences random pulsations much exceeding turbulent pulsations of the air density in the atmosphere. Mean characteristics of supersonic flows are investigated rather well both theoretically and experimentally, but characteristic properties of turbulence in a supersonic flow are studied insufficiently. To study turbulence in supersonic flows, the real-time measurements of the value and spectral composition of pulsations are required. Currently used sensors distort the flow structure and often have the low response rate. The dynamics of fluid or gas flows can also be studied and the turbulent velocity field in fluid and gas flows can be visualized with the use of noncontact optical methods. Among these are speckle photography and speckle interferometry methods (Fomin, 1998), in which the source of information is represented by intensity fluctuations of the laser radiation passed through the flow and a diffuse plate, as well as Doppler methods (laser Doppler anemometers (LDA)) (Abbrecht et al, 2003) and Particle Image Velocimetry (PIV) methods (Raffel et al, 2007) based on the measurement of velocities of microparticles suspended in a flow. LDA and PIV devices are very expensive and difficult in use. They are successfully used mostly for the investigation of fluid flows and subsonic gas flows. In the supersonic gas dynamics, their application is limited owing to such factors as increased requirements to the instrumentation (laser pulse energy, operation rate and sensitivity of recording instruments) and still open problems of velocity relaxation of tracing particles. In the seeding process, the tracing particle sizes are not identical and their concentration is not always uniform in a flow and this inevitably leads to the loss in accuracy of measurements. The widely used methods of shadow visualization (Schlieren photography) do not allow the spatial spectrum of refractive index fluctuations to be determined from the obtained images. Shadow images are integral characteristics of the refractive index in the entire radiation propagation path, and the spatial distribution of the refractive index in different flow layers cannot be reconstructed from them. In this connection, it is interesting to study possibilities

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.

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.

Laser Beam Distortions Caused by a Shock Wave near the Turret of a Supersonic Aircraft

We present results of calculations of the mean intensity of a beam which passes in the beginning of the path through a shock wave which is formed during a supersonic air flow around the turret and propagates further in a homogeneous medium. It is shown that the spatial inhomogeneity of the air refractive index in the region of a shock wave can lead to strong anisotropic distortions of a beam intersecting the wave; the distortions result in focusing and defragmentation of the beam at comparatively short distances from the turret and rapid degradation of the beam in the process of its further propagation.

Propagation of a laser beam reflected from a mirror in the turbulent medium

The paper presents an overview of the results of the authors investigations into the turbulence on the laser beam parameters propagating along double-passage of the correlated (monostatic) and uncorrelated (bistatic) paths. For the conditions of weak fluctuations we considered a variance and mean intensity on an axis of a wave by reflected from a diffraction- limited mirror when illuminating it by a quasi-spherical laser beam. The paper describes the results of the investigations of the turbulence affects on the formation by the receiving optical system of the image of a limited mirror reflector illuminated by a laser beam under conditions of strong fluctuations.

Development of Remote and Contact Techniques for Monitoring the Atmospheric Composition, Structure, and Dynamics

Prototypes of a typical automated station for monitoring the atmospheric composition and state, as well as lidars and sodars, have been designed and manufactured within the project, which are to be the components of monitoring stations. Experimental tests of the instruments confirmed their designed-in specifications and functions. For contact measurements of air parameters, a complex air monitoring station and an aerosol multiwave diffusion spectrometer have been also designed and manufactured in accordance with technical assignment requirements. The measurement results have shown a continuous increase in the concentrations of carbon dioxide and nitrous oxide, as well as a renewed increase in the methane concentration in the layer from 0 to 7 km.