The report presents the results of experiments to compensate for the mismatch of the optical axes of the transmitter and receiver based on backscattering of the focused beam radiation. The matching error does not exceed 2.5 arc seconds.
The article presents the results of a series of mesoscale experiments to study wildfires and their impact on the atmosphere. A change in meteorological parameters, a significant increase in fluctuations of the refractive index, speed of sound and temperature in the vicinity of the experiment, which are a reflection of the occurrence of turbulent processes in the atmosphere, were established, experimental data were obtained on changes in the concentration of methane and carbon dioxide as a result of a fire, and data were obtained on the mechanism of occurrence of crown fire.
This article presents the results of experimental studies of the surface layer of the atmosphere in the Baikal coastal zone using four sonic weather stations and a passive video digital meter. In order to study the deviations of the surface layer turbulence from the Kolmogorov model at different stratification, the characteristic daily changes in the Monin - Obukhov number and the index of power of the structural function of turbulent temperature fluctuations were estimated. Data on the dynamics of turbulent parameters of the surface layer are obtained, and data from acoustic and optical measurements are compared.
The results of an experiment on adaptive correction of random initial distortions of the wavefront of a collimated laser beam based on the signal of atmospheric backscattering are presented. The backscattered signal was recorded by a receiver with a limited field of view from an additional source at a different wavelength. A coaxial transmitter receiving scheme with a large transmitting and small receiving apertures was used. The quality of the correction was assessed using the Shack-Hartmann sensor, as well as by the two-dimensional distribution of the intensity on the remote screen. It is shown that after adaptive operation, the divergence of the distorted beam decreases.
The results of an experiment on compensation of random initial distortions of the wave front of an atmospheric backscattering signal from an additional laser source using the aperture sensing method are presented. The quality control of the correction was evaluated using a Shack-Hartmann sensor, as well as the intensity distribution at the end of the propagation path. It was shown that during the operation of the setup, the level of artificially introduced aberrations of the main beam decreased, the focusing quality increased, and the signal at the radiation receiver from an additional source increased.
The paper presents results of an experimental study of the propagation characteristics of grassland fire front, its effect on meteorological parameters and the emission of gaseous combustion products. As a result of the study, it was found that the seat of fire of a small-scale combustion lead to an increase in air temperature by 2-3 degrees and a decrease in relative humidity by 5%. The highest pulsations amplitude of the wind velocity vertical component of 12 m/s was recorded using a weather station installed at a relatively low height. These pulsations are due to the strong inhomogeneous of the upward flow of combustion products.
The concept of an airborne IR differential absorption lidar for the study of methane in the atmosphere (in particular, in the Russian sector of the Arctic) is presented. The description of the main nodes and elements of the transceiver part of the IR lidar is given. The results of calculation of informative methane sensing wavelengths for polar latitudes are presented.
A new method has been developed for estimating the wind turbulence parameters (turbulent energy dissipation rate and radial velocity variance) from measurements with a conically scanning pulsed coherent Doppler lidar (PCDL) for arbitrary values of the parameter μ that is the ratio of the average wind velocity to the linear velocity of the probed volume moving around the base of the scanning cone. The method was tested on data from atmospheric experiment in which a Stream Line PCDL and a sonic anemometer were used. It is shown that, unlike the previously used lidar method, for μ >1 , the new method gives estimates of the dissipation rate, which are in good agreement with the estimates of the corresponding values obtained from measurements with the sonic anemometer.
The results of experimental investigation of the atmospheric boundary layer using coherent Doppler wind lidar Stream Line and temperature profiler MTP-5 are presented. Measurements were carried out in Tomsk and in the coastal zone at the western coast of Lake Baikal near the village Listvyanka. Found that on Baikal stable thermal stratification with the formation of low-level jets almost always was realized, regardless of the time of day. The Richardson number becomes less than the critical number in the area of jet streams and its value can be close to zero. During measurements in Tomsk there was a periodic change of thermal stratification in the boundary layer from stable at night to neutral and weakly unstable during daylight hours.
The task was to create a compact turbulent lidar, working on the backscatter enhancement effect. Initially, it was planned to make a lidar with the spacing of the receiving channels using two small 50 mm Mersenne telescopes collected from off-axis parabolic mirrors. Despite the measures taken, the system did not pass the stability test for prolonged operation. Then we used an optical layout in which the receiving channels were combined. The converted device turned out to be workable, but its sensitivity was slightly lower than that of the channel spacing scheme. Lidar “BSE-4” was successfully used in field experiments in 2017 (Tomsk, Lake Baikal).
Data are presented about the variations in the average power of lidar echo signals with coherent and incoherent receiving over wide range of variations of the refractive turbulence strength in the atmosphere. It is established that in the case of incoherent receiving the backscatter amplification coefficient first increases with increase of the turbulence strength, then saturates at a certain level in the regime of strong turbulence on the probing path and decreases with further refractive turbulence strength increase. The maximum value of the amplification coefficient achievable at a given distance depends on the refractive turbulence strength at the moment of measurement. The time course of the backscattering amplification coefficient is in a good agreement with the temporal changes of the structural constant of turbulent fluctuations of the air refractive index, determined from independent measurements.
The quality of adaptive suppression of initial aberrations of the wave front of a main laser beam with the use of the method of aperture sensing by the signal of atmospheric backscattering of the additional (sensing) laser radiation at a different wavelength has been studied experimentally. It is shown that wavefront distortions of the main laser beam were decreased significantly during the setup operation.
Results of comparative experiments on measurement of the cross (with respect to the given direction) wind by the
correlation method with the prototype of an optical wind meter developed in the IAO SB RAS and the StreamLine
coherent Doppler wind lidar are presented.
Estimates of wind speed and direction obtained from measurements of the radial velocity by a pulsed coherent Doppler lidar with the duo-beam method and the method of conical scanning have been compared experimentally. The obtained experimental results are compared with data of a point meter of wind velocity – acoustic weather station.
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