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-Pyrenees 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.

Measurement of Atmospheric Turbulence by 2-μm Doppler Lidar

An experimental study of the spatial wind structure in the vicinity of a wind turbine by a NOAA coherent Doppler lidar has been conducted. It was found that a working wind turbine generates a wake with the maximum velocity deficit varying from 27% to 74% and with the longitudinal dimension varying from 120 up to 1180 m, depending on the wind strength and atmospheric turbulence. It is shown that, at high wind speeds, the twofold increase of the turbulent energy dissipation rate (from 0.0066 to 0.013 m2 s−3) leads, on average, to halving of the longitudinal dimension of the wind turbine wake (from 680 to 340 m).

Lidar Investigation of Atmosphere Effect on a Wind Turbine Wake

This study investigates the possibilities and limitations of airborne Doppler lidar for adaptive observations over the Atlantic Ocean. For the first time, a scanning 2-μm Doppler lidar was applied for targeted measurements during the Atlantic “The Observing System Research and Predictability Experiment” (THORPEX) Regional Campaign (A-TReC) in November and December 2003. The DLR lidar system was operated for 28.5 flight hours, and measured 1612 vertical profiles of wind direction and wind speed with a horizontal and vertical resolution of 5–10 km and 100 m, respectively. On average, there were 25 reliable wind values on every profile, which cover 2500 m in the vertical (about one-third of the mean vertical extent of the profiles). A statistical comparison of 33 dropsondes and collocated lidar winds profiles allowed individual estimates of the standard deviation to be assigned to every wind value and to determine threshold values for an objective quality control of the data. The standard deviation ...

/pdf/targeted-observations-with-an-airborne-wind-lidar-2xivgu3r8w.pdf

Targeted Observations with an Airborne Wind Lidar

. Soon after the launch of Aeolus on 22 August 2018, the first ever wind lidar in space developed by the European Space Agency (ESA) has been providing profiles of the component of the wind vector along the instrument's line of sight (LOS) on a global scale. In order to validate the quality of Aeolus wind observations, the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt e.V., DLR) recently performed two airborne campaigns over central Europe deploying two different Doppler wind lidars (DWLs) on board the DLR Falcon aircraft. The first campaign – WindVal III – was conducted from 5 November 2018 until 5 December 2018 and thus still within the commissioning phase of the Aeolus mission. The second campaign – AVATARE (Aeolus Validation Through Airborne Lidars in Europe) – was performed from 6 May 2019 until 6 June 2019. Both campaigns were flown out of the DLR site in Oberpfaffenhofen, Germany, during the evening hours for probing the ascending orbits. All together, 10 satellite underflights with 19 flight legs covering more than 7500 km of Aeolus swaths were performed and used to validate the early-stage wind data product of Aeolus by means of collocated airborne wind lidar observations for the first time. For both campaign data sets, the statistical comparison of Aeolus horizontal line-of-sight (HLOS) observations and the corresponding wind observations of the reference lidar (2  µm  DWL) on board the Falcon aircraft shows enhanced systematic and random errors compared with the bias and precision requirements defined for Aeolus. In particular, the systematic errors are determined to be 2.1 m s −1 (Rayleigh) and 2.3 m s −1  (Mie) for WindVal III and −4.6  m s −1 (Rayleigh) and −0.2  m s −1  (Mie) for AVATARE. The corresponding random errors are determined to be 3.9 m s −1  (Rayleigh) and 2.0 m s −1  (Mie) for WindVal III and 4.3 m s −1  (Rayleigh) and 2.0 m s −1  (Mie) for AVATARE. The Aeolus observations used here were acquired in an altitude range up to 10 km and have mainly a vertical resolution of 1 km (Rayleigh) and 0.5 to 1.0 km (Mie) and a horizontal resolution of 90 km (Rayleigh) and down to 10 km (Mie). Potential reasons for those errors are analyzed and discussed.

/pdf/first-validation-of-aeolus-wind-observations-by-airborne-4suykfjsow.pdf

First validation of Aeolus wind observations by airborne Doppler wind lidar measurements

The air in Alpine valleys is heated faster than over plains due to the smaller air volume in valleys (Steinacker 1984). On days with strong solar radiation this leads to a temperature difference between the foreland and the Alps, and a heat-low builds up in the mountains. The pressure gradient drives a flow from the foreland to the Alps within the boundary layer. This wind transports air and pollutants to the Alps, where they partly reach the free troposphere. The return flow in the troposphere is usually masked by stronger gradient winds (Burger and Ekhart 1937). The Alpine mountain– plain circulation occurs on about 30% of all days between April and September (Lugauer 2003). This study investigates the structure and the mass transports of the circulation on 19 July 2002 using data from an airborne scanning 2 μm Doppler lidar system. The synoptic situation on 19 July 2002 was fairly typical for the development of a mountainplain circulation. The high pressure system “Brian” caused a sunshine duration of up to 10 h, and weak pressure gradients at all levels. The structure and the mass fluxes were compared to numerical simulations with the PennState/NCAR mesoscale model MM5, and the Local Model (LM) of the German Weather Service (DWD). The measurements were taken during the VERTIKATOR campaign (“Vertical Transports and Orography”) in June and July 2002. The objective of the campaign was to study vertical exchange processes above gentle and steep terrain. The target regions were the northern foreland of the Alps and the Black Forest Region in Germany.

/pdf/the-alpine-mountain-plain-circulation-airborne-doppler-lidar-3rw37f710c.pdf

The Alpine Mountain-Plain Circulation: Airborne Doppler Lidar Measurements and Numerical Simulations Using MM5 and LM

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 signalto-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.

Igor Smalikho

Papers

Techniques of Wind Vector Estimation from Data Measured with a Scanning Coherent