Abstract:The technical aspects of a multi-Doppler LiDAR instrument, the long-range WindScanner system, are presented accompanied by an overview of the results from several field campaigns. The long-range WindScanner system consists of three spatially-separated, scanning coherent Doppler LiDARs and a remote master computer that coordinates them. The LiDARs were carefully engineered to perform user-defined and time-controlled scanning trajectories. Their wireless coordination via the master computer allows achieving and maintaining the LiDARs' synchronization within ten milliseconds. The long-range WindScanner system measures the wind field by emitting and directing three laser beams to intersect, and then scanning the beam intersection over a region of interest. The long-range WindScanner system was developed to tackle the need for high-quality observations of wind fields on scales of modern wind turbine and wind farms. It has been in operation since 2013.
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.
International audienceFollowing the eruption of the Icelandic volcano Eyjafjallajökull on the 14 April 2010, ground-based N2-Raman lidar (GBL) measurements were used to trace the temporal evolution of the ash plume from 16 to 20 April 2010 above the southwestern suburb of Paris. The nighttime overpass of the Cloud-Aerosol LIdar with Orthogonal Polarization onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite (CALIPSO/CALIOP) on 17 April 2010 was an opportunity to complement GBL observations. The plume shape retrieved from GBL has been used to assess the size range of the particles size. The lidar-derived aerosol mass concentrations (PM) have been compared with model-derived PM concentrations held in the Eulerian model Polair3D transport model, driven by a source term inferred from the SEVIRI sensor onboard Meteosat satellite. The consistency between model and ground-based wind lidar and CALIOP observations has been checked. The spatial and temporal structures of the ash plume as estimated by each instrument and by the Polair3D simulations are in agreement. The ash plume was associated with a mean aerosol optical thickness of 0.1{plus minus}0.06 and 0.055{plus minus}0.053 for GBL (355 nm) and CALIOP (532 nm), respectively. Such values correspond to ash mass concentrations of ~400{plus minus}160 and ~720{plus minus}670 µg m-3, respectively, within the ash plume, which was lower than 0.5 km in width. The relative uncertainty is ~75% and mainly due to the assessment of the specific cross-section assuming an aerosol density of 2.6 g cm-3. The simulated ash plume is smoother leading to integrated mass of the same order of magnitude (between 50 and 250 mg m-2
Fiber lasers are becoming new effective sources for coherent lidars, thanks to their spatial and spectral qualities. Allowing operation in continuous, modulated and pulsed modes, their increasing power at eyesafe wavelengths is well suited to anemometry, velocimetry, vibrometry or laser imagery. Requested laser qualities are discussed, concerning wavelength, power, pulse duration and frequency, beam shape and spectral width, and compared to existing fiber source parameters.
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.
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