pulsed doppler lidar wind profile measurement process in complex terrain
DESCRIPTION
Pulsed Doppler Lidar wind profile measurement process in complex terrain. Matthieu Boquet , Bruno Ribstein , Rémy Parmentier, Jean-Pierre Cariou LEOSPHERE SAS – Centre Scientifique d’Orsay - France. Agenda. Pulsed Lidar volume measurement principle Simple & complex terrain - PowerPoint PPT PresentationTRANSCRIPT
23/06/2009 – CLRC 2009
Pulsed Doppler Lidar wind profilemeasurement process in complex terrain
Matthieu Boquet, Bruno Ribstein, Rémy Parmentier, Jean-Pierre CariouLEOSPHERE SAS – Centre Scientifique d’Orsay - France
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Agenda
Pulsed Lidar volume measurement principleSimple & complex terrainCFD modeling exampleOptimizationConclusions
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Pulsed Lidar principleHOW DOES THE WINDCUBETM RETRIEVE WIND VELOCITY VERTICAL PROFILES?
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Volume measurement
Radial velocity along a LOS
Pulse FWHM probed sample
Conically scanningdc=height*tanθ
Sequentially scanning4sec complete rotation
a
v
s = v.cos(a)
qLaser shooting direction
aerosols
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Wind velocity vertical profile
4 radial velocities 3 wind velocity components
Hypothesis:Same wind inside the probed volumeSame wind at the 4 probed domainsStationary atmosphere
Comparison with anemometers point measurement
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Terrain influenceHOW WELL DOES THE WINDCUBETM RETRIEVE WIND VELOCITY VERTICAL PROFILES?
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Flat terrain
Inferior to 1% relative difference between Lidar and cup anemometer
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Forested area and gentle slope
WindCubeTM
Forest
Terrain slope over 10°
About -2% relative difference between Lidar and sonic anemometer
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Mountainous terrain
About -5% relative difference between Lidar and cup anemometer
Intercomparison of Horizontal wind speed at 78mN±40deg
y = 0.9627x - 0.2066
R2 = 0.9911
y = 0.9457x
R2 = 0.9907
0
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12
16
20
0 4 8 12 16 20
Cup Anemometer [m/s]
Win
dc
ub
e L
ida
r [
m/s
]
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CFD Modeling analysisUSING A CFD MODELING OF A COMPLEX TERRAIN TO BETTER UNDERSTAND THE LIDAR AND ANEMOMETER DIFFERENCES?
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CFD modeling
MERCURE/Aria Technologies softwareAdapted to complex topographyFine meshing2x2x1km box~10x10x5m cellsStationary not a time variation studyFair enough to study Lidar wind velocity retrieval process under various local complex flowMatLab analysisLidar measurement process simulation
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Spanish site
Met mast
WindCube
North-West wind
North-West wind
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Wind distribution at 80m height
North-west wind
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Overestimation>5%
Underestimation<-5%
North-West Wind
Lidar vs. cup
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Back to the Lidar equations
Considering first order wind speed variationIntroducing wind speed gradientθ being the zenithal angle, d=height*tanθ is the probed volume to center distanceIn 2D:
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Vertical wind speed gradient dependency
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Geometrical OptimisationHOW CAN WE MODIFY THE LIDAR MEASUREMENT PROCESS TO GET CLOSER TO CUP?
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Reducing the scanning cone
Probing a smaller volume then more homogeneous:
Often but not always trueDifference depends on altitude and vertical wind speed gradientOther issue: smaller horizontal wind speed projection higher noise perturbation No magical scanning
cone angleDangerous below 15° and above 30°
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30° vs. 15°
Intercomparison of Horizontal wind speed at 78mN±40deg
y = 0.9627x - 0.2066
R2 = 0.9911
y = 0.9457x
R2 = 0.9907
0
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16
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0 4 8 12 16 20
Cup Anemometer [m/s]
Win
dcu
be
Lid
ar [
m/s
]
Intercomparison of Horizontal wind speed at 78mN±40deg
y = 0.9457x
R2 = 0.9871
0
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0 4 8 12 16 20Cup Anemometer [m/s]
Win
dcu
be
Lid
ar [
m/s
]
30° 15°
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Multiplying the lines of sight
Consider vertical wind speed linear variationsA line of sight LOSi gives the radial velocity Si:
With
And
Thus
No LOS brings info on Wi
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Conclusion
Point and volume measurementVertical wind speed inhomogeneityScanning cone angle 15°-30°More lines of sight are not more useful infoExperimental set up difficult
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