pulsed doppler lidar wind profile measurement process in complex terrain

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23/06/2009 – CLRC 2009 Pulsed Doppler Lidar wind profile measurement process in complex terrain Matthieu Boquet , Bruno Ribstein, Rémy Parmentier, Jean-Pierre LEOSPHERE SAS – Centre Scientifique d’Orsay - France

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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 Presentation

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Page 1: Pulsed Doppler  Lidar  wind profile measurement process in complex terrain

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

Page 2: Pulsed Doppler  Lidar  wind profile measurement process in complex terrain

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23/06/09 – CLRC 2009

Agenda

Pulsed Lidar volume measurement principleSimple & complex terrainCFD modeling exampleOptimizationConclusions

Page 3: Pulsed Doppler  Lidar  wind profile measurement process in complex terrain

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23/06/09 – CLRC 2009

Pulsed Lidar principleHOW DOES THE WINDCUBETM RETRIEVE WIND VELOCITY VERTICAL PROFILES?

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23/06/09 – CLRC 2009

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

Page 5: Pulsed Doppler  Lidar  wind profile measurement process in complex terrain

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23/06/09 – CLRC 2009

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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23/06/09 – CLRC 2009

Terrain influenceHOW WELL DOES THE WINDCUBETM RETRIEVE WIND VELOCITY VERTICAL PROFILES?

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23/06/09 – CLRC 2009

Flat terrain

Inferior to 1% relative difference between Lidar and cup anemometer

Page 8: Pulsed Doppler  Lidar  wind profile measurement process in complex terrain

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23/06/09 – CLRC 2009

Forested area and gentle slope

WindCubeTM

Forest

Terrain slope over 10°

About -2% relative difference between Lidar and sonic anemometer

Page 9: Pulsed Doppler  Lidar  wind profile measurement process in complex terrain

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23/06/09 – CLRC 2009

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

4

8

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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23/06/09 – CLRC 2009

CFD Modeling analysisUSING A CFD MODELING OF A COMPLEX TERRAIN TO BETTER UNDERSTAND THE LIDAR AND ANEMOMETER DIFFERENCES?

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23/06/09 – CLRC 2009

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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23/06/09 – CLRC 2009

Spanish site

Met mast

WindCube

North-West wind

North-West wind

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23/06/09 – CLRC 2009

Wind distribution at 80m height

North-west wind

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23/06/09 – CLRC 2009

Overestimation>5%

Underestimation<-5%

North-West Wind

Lidar vs. cup

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23/06/09 – CLRC 2009

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:

Page 16: Pulsed Doppler  Lidar  wind profile measurement process in complex terrain

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23/06/09 – CLRC 2009

Vertical wind speed gradient dependency

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23/06/09 – CLRC 2009

Geometrical OptimisationHOW CAN WE MODIFY THE LIDAR MEASUREMENT PROCESS TO GET CLOSER TO CUP?

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23/06/09 – CLRC 2009

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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23/06/09 – CLRC 2009

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

4

8

12

16

20

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

4

8

12

16

20

0 4 8 12 16 20Cup Anemometer [m/s]

Win

dcu

be

Lid

ar [

m/s

]

30° 15°

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23/06/09 – CLRC 2009

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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23/06/09 – CLRC 2009

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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23/06/09 – CLRC 200922

Thank youwww.leosphere.com