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.

Refractive turbulence strength estimation based on the laser echo signal amplification effect.

Experimental data proving the possibility of lidar measurement of the refractive turbulence strength based on the effect of backscattering amplification are reported. It is shown, for the first time to our knowledge, that the values of the amplification factor correlate with the variance of random jitter of the optical image of an incoherent light source depending on the value of the structure constant of the air refractive index turbulent fluctuations averaged over the probing path.

Method of radial velocities for the estimation of aircraft wake vortex parameters from data measured by coherent Doppler lidar.

The method of radial velocities (RV) is applied to estimate aircraft wake vortex parameters from measurements conducted with pulsed coherent Doppler lidar (PCDL). Operations of the Stream Line lidar and the 2-µm PCDL are simulated numerically to analyze the accuracy of the estimated wake vortex parameters with the RV method. The RV method is also used to estimate wake vortex trajectories and circulation from lidar measurements at Tomsk and Munich airports. The method of velocity envelopes and the RV method are compared employing data gathered with the 2-µm PCDL. The domain of applicability of the RV method is determined.

Laser echo signal amplification in a turbulent atmosphere.

A lidar system for registration of laser return amplification in a turbulent atmosphere due to backscatter amplification effect is considered in this paper. In the system, two receiving channels are used. One of them (axial) coincides with the transmitter channel, while another channel (nonaxial) receives the backscattered radiation at a small angle to the probing beam axis. The power ratio of the echo signal recorded in the axial channel to that recorded in the nonaxial one is a measure of the return amplification. The results of long-duration lidar atmospheric experiments show that the power of the echo signal registered in the axial channel usually exceeds that in the nonaxial one.

Estimation of aircraft wake vortex parameters from data measured with a 1.5-µm coherent Doppler lidar.

A strategy of measurement by a 1.5-µm pulsed coherent Doppler lidar "Stream Line" has been developed, and a method for estimation of aircraft wake vortices from the lidar data has been proposed. The principal possibility of obtaining the information about the vortex situation over an airport airfield with the Stream-Line lidar has been demonstrated.

Optical beam distortions induced by a shock wave.

The mean intensity and the displacement from the initially given propagation direction of the optical beam passed through the shock wave have been calculated. It has been shown that the spatial inhomogeneity of the refractive index of air caused by the shock wave arising in supersonic flow flowing a conical body can cause the focusing of the beam and strong anisotropic distortions of the intensity distribution in its cross section. The angular displacement of the optical beam from the initially given propagation direction owing to the shock wave depends only on the height above the Earth's surface at which the shock wave is formed. As the height increases, the influence of the shock wave on the optical beam propagating through it decreases.

Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere.

Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere have been studied based on numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field by the split-step method. It has been shown that under conditions of strong optical turbulence, the relative variance of energy density fluctuations of pulsed radiation of femtosecond duration becomes much less than the relative variance of intensity fluctuations of continuous-wave radiation. The spatial structure of fluctuations of the energy density with a decrease of the pulse duration becomes more large-scale and homogeneous. For shorter pulses the maximal value of the probability density distribution of energy density fluctuations tends to the mean value of the energy density.

Estimation of the refractive index structure characteristic of air from coherent Doppler wind lidar data.

A technique is proposed for estimating the refractive index structure characteristic of air from data of a coherent Doppler wind lidar. The proposed technique is tested in atmospheric experiments. Time profiles of the structure characteristic in the atmospheric surface layer are obtained and compared with the time profiles of the dissipation rate of the kinetic energy of turbulence obtained from the same lidar data. It is shown in this way that coherent lidars can be used for investigating not only wind turbulence, but also temperature turbulence.

Diffraction-free propagation of a focused delta-pulsed beam.

The propagation of short broadband pulses in a homogeneous medium is analyzed on the basis of the wave equation and in the parabolic approximation of that equation. It is shown that the diffraction spreading of a focused optical pulsed beam does not occur in the limiting case of a δ pulse.

Cross-wind profiling based on the scattered wave scintillation in a telescope focus.

The problem of wind profile reconstruction from scintillation of an optical wave scattered off a rough surface in a telescope focus plane is considered. Both the expression for the spatiotemporal correlation function and the algorithm of cross-wind velocity and direction profiles reconstruction based on the spatiotemporal spectrum of intensity of an optical wave scattered by a diffuse target in a turbulent atmosphere are presented. Computer simulations performed under conditions of weak optical turbulence show wind profiles reconstruction by the developed algorithm.

Wind velocity profile reconstruction from intensity fluctuations of a plane wave propagating in a turbulent atmosphere.

Reconstruction of a wind profile based on the statistics of plane-wave intensity fluctuations in a turbulent atmosphere is considered. The algorithm for wind profile retrieval from the spatiotemporal spectrum of plane-wave weak intensity fluctuations is described, and the results of end-to-end computer experiments on wind profiling based on the developed algorithm are presented. It is shown that the reconstructing algorithm allows retrieval of a wind profile from turbulent plane-wave intensity fluctuations with acceptable accuracy.

Effect of aerosol particle microstructure on cw Doppler lidar signal statistics.

Analysis of signal statistical characteristics is carried out, and estimation errors of the radial wind velocity are calculated by use of numerical simulation of a cw Doppler lidar return, taking into account the atmospheric aerosol microstructure. It has been found that, at small sounded volume, the large particles contribute significantly to the scattered field. As a result the lidar return probability density function distribution can differ significantly from a Gaussian distribution. Neglect of the aerosol microstructure effect results in considerable underestimation of the error of cw Doppler lidar velocity estimates at small sounded volume.

Numerical simulation of the effect of refractive turbulence on coherent lidar return statistics in the atmosphere.

We propose an algorithm and the results of a numerical study of random realizations and statistics of a pulsed coherent lidar return that allow for refractive turbulence. We show that, under conditions of refractive turbulence, the relative variance of the lidar return power can exceed unity by a factor of as much as 1.5. Clear manifestations of the turbulent effect of backscattering amplification have been revealed from simulations of space-based lidar sensing of the atmosphere with coherent lidar. Under conditions of strong optical turbulence in the atmospheric boundary layer, as a result of the backscattering amplification effect, the mean lidar return power can exceed the return power in the absence of turbulence by a factor of 3.

Representativeness of wind measurements with a cw Doppler lidar in the atmospheric boundary layer.

The representativity problem of laser Doppler anemometer wind measurements in the boundary layer under different atmospheric conditions has been investigated theoretically and experimentally. The calculations of the mean wind-velocity measurement errors for the surface layer under different types of thermal stratification and for the boundary layer under neutral conditions have been carried out. The theoretical conclusions are confirmed by the experimental results.

Intensity fluctuations of light in the focal plane of a receiving telescope caused by round-trip propagation through a turbulent atmosphere.

The intensity fluctuations in the focal plane of a receiving telescope of radiation reflected in a turbulent atmosphere have been analyzed. It was found that, when fluctuations of an incident wave are saturated, the focusing can significantly modify the variance of the reflected radiation intensity in comparison with the corresponding value in the aperture plane of the receiving telescope.

Phase approximation of the Huygens-Kirchhoff method in problems of laser-beam propagation in the turbulent atmosphere.

This Letter presents a rigorous mathematical proof of the applicability of phase approximation in the Huygens-Kirchhoff method for the problems of laser-beam propagation in a turbulent atmosphere. The calculated results are in good agreement with experimental data.