 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Enevoldsen, K. (2009).Comparison of 3D turbulence measurements using three staring wind lidars and a sonic anemometer. Meteorologische Zeitschrift, 18(2), 135-140. DOI: 10.1127/0941-2948/2009/0370 Meteorologische Zeitschrift, Vol. 18, No. 2, 135-140 (April 2009 Open Access Article AbstractThe goals are to compare lidar volume averaged wind measurement with point measurement reference sensors and to demonstrate the feasibility of performing 3D turbulence measurements with lidars. For that purpose three pulsed lidars were used in staring mode, placed so that their beams crossed close to a 3D sonic anemometer mounted at 78 m above the ground. The results show generally very good correlation between the lidar and the sonic times series, except that the variance of the velocity measured by the lidar is attenuated due to spatial filtering. The amount of attenuation can however be predicted theoretically by use of a spectral tensor model of the atmospheric surface-layer turbulence. ZusammenfassungDas Ziel ist es, volumengemittelte LiDAR-Windmessungen mit Punktmessungen von Referenzsensoren zu vergleichen sowie die Möglichkeit aufzuzeigen, 3D-Turbulenzmessungen mit LiDAR-Geräten durchzuführen. Zu diesem Zweck wurden drei gepulste LiDAR-Systeme mit fixer Blickrichtung so aufgestellt, dass ihre Strahlen nahe eines 3D-Ultraschall-Anemometers kreuzten, welches 78 müber Grund befestigt war. Die Ergebnisse zeigen im Allgemeinen sehr gute Korrelationen zwischen den Zeitreihen der LiDAR-und Ultraschall-Anemometer, allerdings wird die Streuung der vom LiDAR gemessenen Geschwindigkeit durch räumliches Filtern abgeschwächt. Der Grad der Abschwächung kann jedoch mittels eines spektralen Tensormodells, das die Turbulenz in der atmosphärischen Bodenschicht beschreibt, theoretisch vorausberechnet werden.

A field test with a continuous wave wind lidar (ZephIR) installed in the rotating spinner of a wind turbine for unimpeded preview measurements of the upwind approaching wind conditions is described. The experimental setup with the wind lidar on the tip of the rotating spinner of a large 80 m rotor diameter, 59 m hub height 2.3 MW wind turbine (Vestas NM80), located at Tjaereborg Enge in western Denmark is presented. Preview wind data at two selected upwind measurement distances, acquired during two measurement periods of different wind speed and atmospheric stability conditions, are analyzed. The lidar-measured speed, shear and direction of the wind field previewed in front of the turbine are compared with reference measurements from an adjacent met mast and also with the speed and direction measurements on top of the nacelle behind the rotor plane used by the wind turbine itself. Yaw alignment of the wind turbine based on the spinner lidar measurements is compared with wind direction measurements from both the nearby reference met mast and the turbine's own yaw alignment wind vane. Furthermore, the ability to detect vertical wind shear and vertical direction veer in the inflow, through the analysis of the spinner lidar data, is investigated. Finally, the potential for enhancing turbine control and performance based on wind lidar preview measurements in combination with feed-forward enabled turbine controllers is discussed.

Monitoring of free gas embedded in scattering media, such as wood, fruits, and synthetic materials, is demonstrated by use of diode laser spectroscopy combined with sensitive modulation techniques. Gas detection is made possible by the contrast of the narrow absorptive feature of the free-gas molecules with the slow wavelength dependence of the absorption and scattering cross sections in solids and liquids. An absorption sensitivity of 2.5 x 10(-4), corresponding to a 1.25-mm air column, is demonstrated by measurements of dispersed molecular oxygen. These techniques open up new possibilities for characterization and diagnostics, including internal gas pressure and gas-exchange assessment, in organic and synthetic materials.

Enevoldsen, K. (2009).Comparison of 3D turbulence measurements using three staring wind lidars and a sonic anemometer. Meteorologische Zeitschrift, 18(2), 135-140. DOI: 10.1127/0941-2948/2009/0370 Meteorologische Zeitschrift, Vol. 18, No. 2, 135-140 (April 2009 Open Access Article AbstractThe goals are to compare lidar volume averaged wind measurement with point measurement reference sensors and to demonstrate the feasibility of performing 3D turbulence measurements with lidars. For that purpose three pulsed lidars were used in staring mode, placed so that their beams crossed close to a 3D sonic anemometer mounted at 78 m above the ground. The results show generally very good correlation between the lidar and the sonic times series, except that the variance of the velocity measured by the lidar is attenuated due to spatial filtering. The amount of attenuation can however be predicted theoretically by use of a spectral tensor model of the atmospheric surface-layer turbulence. ZusammenfassungDas Ziel ist es, volumengemittelte LiDAR-Windmessungen mit Punktmessungen von Referenzsensoren zu vergleichen sowie die Möglichkeit aufzuzeigen, 3D-Turbulenzmessungen mit LiDAR-Geräten durchzuführen. Zu diesem Zweck wurden drei gepulste LiDAR-Systeme mit fixer Blickrichtung so aufgestellt, dass ihre Strahlen nahe eines 3D-Ultraschall-Anemometers kreuzten, welches 78 müber Grund befestigt war. Die Ergebnisse zeigen im Allgemeinen sehr gute Korrelationen zwischen den Zeitreihen der LiDAR-und Ultraschall-Anemometer, allerdings wird die Streuung der vom LiDAR gemessenen Geschwindigkeit durch räumliches Filtern abgeschwächt. Der Grad der Abschwächung kann jedoch mittels eines spektralen Tensormodells, das die Turbulenz in der atmosphärischen Bodenschicht beschreibt, theoretisch vorausberechnet werden.