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Igor Smalikho

Abstract

The results of a theoretical study of the feasibility of wind velocity vector estimation from data, measured with a scanning coherent Doppler lidar, are presented. The estimation techniques considered are (a) the direct sine wave fitting (DSWF) and the filtered sine wave fitting (FSWF), where at first the radial wind velocities are estimated and then the wind vector is estimated from the dependence of the radial velocity versus the azimuth angle of the scanning; and (b) the maximum of the function of accumulated spectra (MFAS) and the maximum likelihood for the wind vector estimation (WV ML), where the wind vector is estimated directly from data measured by a scanning lidar without intermediate estimation of the radial wind velocities.

It has been shown that due to strong averaging of noise fluctuations in accumulated spectra, the WV ML and MFAS techniques allow one to estimate the wind vector with acceptable accuracy at an essentially lower signal-to-noise ratio (SNR) than the methods of the sine wave fitting, where noise can be the source of many spurious estimates of the radial wind velocity.

The ability to find optimal criterion (in the case of MFAS) for acceptance or rejection of the wind vector estimate has been analyzed. The amount of measured data needed for spectral accumulation in order to realize optimal performance has been calculated.

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Friedrich Köpp, Stephan Rahm, and Igor Smalikho

Abstract

The 2-μm pulsed Doppler lidar, already successfully used for wind and turbulence measurements, has been modified for long-range wake-vortex characterization. In particular, a four-stage data processing algorithm has been developed to achieve precise profiles of tangential velocities from which the vortex parameters such as trajectories, core separation, tilt angle, and circulation can be derived. The main advantage of the pulsed lidar is its long-range capability of more than 1 km. This allows for observations over long periods from the moment of wake generation to a progressed state of vortex decay. With the field experiment at Tarbes airfield the potential of the 2-μm pulsed Doppler lidar for full-scale wake-vortex characterization has been demonstrated. Two examples showing the parameters of wake vortices generated by large transport aircraft (LTA)-type aircraft will be presented.

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Igor Smalikho, Friedrich Köpp, and Stephan Rahm

Abstract

Two methods for the estimation of the turbulence energy dissipation rate (TEDR) from data measured by a 2-μm coherent Doppler lidar are described in this paper. Based on data measured at the Tarbes-Lourdes-Pyrénées International Airport in summer 2003, height profiles of TEDR have been retrieved. The results of TEDR estimation both from the Doppler spectrum width and from the velocity structure function are compared. Moreover, the experiment has been treated by numerical simulation and the theoretical results have been used for verification of the described methods.

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Victor A. Banakh, Igor’N. Smalikho, Friedrich Köpp, and Christian Werner

Abstract

The results of a theoretical and experimental study of the feasibility of the turbulent energy dissipation rate ε T measurements with a continuous wave (CW) CO2 Doppler lidar in the atmospheric boundary layer are presented. Three methods of probing ε T are considered: 1) Doppler spectrum width, 2) the temporal spectrum (temporal structure function) of wind velocity measured by the Doppler lidar, and 3) spatial structure function. In these methods, information on the dissipation rate is extracted by means of analysis of the corresponding statistical characteristics of wind velocity in the inertial subrange of the turbulence, taking into account the spatial averaging of the measured wind velocity fluctuations over sounded volume.

In the first and third methods, the spatial structure of the turbulence is analyzed directly. In the second method, to determine ε T from the measured temporal characteristics, it is necessary to use a model for the spatiotemporal correlation function of wind velocity. As a result of the study, it has been shown that in the case of large longitudinal size of sounded volume and weak side wind, Taylor’s hypothesis of “frozen” turbulence cannot be accepted for the correlation function. The strict limitation on the longitudinal size of the sounded volume and therefore sounding height is the main restriction of the first method. The third method is free of such limitations. It allows one to obtain the information on the dissipation rate profile throughout the entire boundary layer. Comparison of the developed theory for statistical characteristics of wind velocity measured by the Doppler lidar with the obtained experimental data has demonstrated their good agreement.

The vertical profiles of the turbulent energy dissipation rate retrieved from Doppler lidar data with the use of the methods described above do not contradict the known experimental results. This fact confirms the feasibility of application of lidar remote sensing methods to the study of the small-scale turbulence in the atmospheric boundary layer.

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Ines Leike, Jürgen Streicher, Christian Werner, Viktor Banakh, Igor Smalikho, Werner Wergen, and Alexander Cress

Abstract

Doppler lidars measure the range-resolved line-of-sight wind component by extracting the Doppler shift of radiation backscattered from atmospheric aerosols and molecules. A virtual instrument was developed to simulate wind measurements by flying virtually over the atmosphere. The atmosphere contains all components that influence the lidar, that is, wind, turbulence, aerosols, clouds, etc. For a selected time period, a dataset of the atmospheric conditions from the global model and the local model was provided by the German Weather Service. Three different Doppler lidar systems were simulated for this report: a coherent airborne conical scanning 10-μm Doppler lidar, a 10-μm and a 2-μm spaceborne system, and a spaceborne incoherent ultraviolet Doppler lidar.

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