Mitigation of Wind Turbine Clutter on the WSD88D Network

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Mitigation of Wind Turbine Clutter on the WSD-88D
Network

• Robert Palmer and Brad Isom
• School of Meteorology
• University of Oklahoma

ROC Presentation 2/10/06
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Gray County Wind Farm

• Located 25 miles SW of Dodge City, Kansas
• 170 towers
• Height of Tower 217 feet (66m)
• Length of Blades 77 feet (23.5m)
• RPM 14-22 (wind variable)
• Tip Velocity 34.5-54 ms-1

Photohttp//www.cimarronkansas.net/WINDMILLFARMPI
CS/WindfarmE200TU-Main.jpg
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Gray County Wind Farm
Photo from.maps.google.com
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Gray County Wind Farm
Photo from maps.google.com
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KDDC Level II Plot
August 4, 2005 1408 UTC
June 19, 2005 1014 UTC
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KDDC Level II Data
August 4, 2005 1408 UTC
June 19, 2005 1014 UTC
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The Doppler SpectrumUnraveling radial velocities

• The Doppler spectrum is a power-weighted
  distribution of radial velocities within the
  resolution volume
• Examples of unique velocity distributions
• Tornados
• Ground Clutter
• Sea Clutter
• Birds
• Wind Turbine Clutter (WTC)

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Simulations Understanding the Expected Doppler
Spectrum

• Study the dynamics of blade rotation
• Approximate Doppler frequency content as a
  function of wind speed, direction, and location
  on blade
• Rough estimation of radar cross-section (RCS)
• Combine to produce simulated Doppler spectrum

Pitch Effects
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Expected Radial Velocity

• Single blade radial velocity as a function of
  distance from hub
• Based on turbine orientation with respect to
  radar. Maximum radial velocity for an angle of
  0o.

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Simulation - Radial VelocitySingle Blade, Three
Positions
Rotating Blades With Time
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Simulation - Radial VelocityThree Blades, Tip
Only
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Simulation - Radial VelocityThree Blades, Three
Positions
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Approximate RCSReturned Power Proportional to RCS
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Approximate RCSThree Blades
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Simulated Doppler Spectrum

• Combine the radial velocity and RCS estimates to
  approximate the expected Doppler spectrum
• Use radial spacing along blades of 10 cm for
  desired velocity resolution
• High pitch angles to simulate third dimension
  (blade thickness)

Extremely Rough Approximation of Doppler Spectrum
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Simulated Temporal Evolution of the Doppler
Spectrum
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Measured Doppler Spectrum From UK

• QinetiQ Radar Study (UK)
• S-band
• PRT0.5 ms
• spotlight mode
• single turbine in resolution volume
• 3.45 km range from turbine
• blade length 30.8 m
• rotation speed 23 rpm

50 m/s
Wind Farm Impact on Radar Aviation Interests,
QinetiQ, September 2003.
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KDDC Level I Experiment September 20, 2005
1400-1600 UTC
Scanning Mode

• VCP 21 and 32
• PRT 1.2 ms and 3.1 ms
• ra 175 km and 466 km
• va 22.17 ms-1 and 8.33 ms-1
• Range Resolution is 250 m

Spotlight Mode

• One azimuth angle 248o
• 6 files each containing 2 minutes of data
• PRT variable from file to file
• Range Mask (10000100001) Range Resolution 1.25
  km

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Conditions During KDDC Level-I Experiment
September 20, 2005 1400-1600 UTC
Wind 4-5 m/s
Ideal for maximum radial velocity
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Spotlight DataApproximate Resolution Volume
Location (range 42.5 km)
Notice multiple turbines in 1.25 km volume
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Spotlight DataTemporal Evolution of Doppler
Spectra

• Periodogram Algorithm
• Non-overlapping 32-pt windows
• Velocity Resolution 1.95 ms-1
• Zero-pad to 128 points
• va 31.05 ms-1

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Spotlight DataTemporal Periodicities
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Spotlight DataTemporal Periodicities
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Spotlight DataTemporal Evolution of Doppler
Spectra
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Next Step in Simulations

• Create an EM scattering model for a wind turbine
  to be placed in the field of view of our Next
  Generation Radar Simulator
• time-series, Doppler spectra
• control over number of turbines, orientation,
  rotation rate, etc.

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Next Step in Experiments

• Collect a new set of Level-I data with recently
  installed RVP8 at KDDC
• Spotlight Mode
• 2-3 azimuth angles
• Shortest possible PRT
• 250 m range resolution (full range mask)
• Simultaneous visual observations of turbine
  orientation, rotation rate, etc.
• Collaboration with wind farm managers?
• Scanning Mode
• Allow more realistic experimental conditions for
  filtering
• Slow radar rotation rate
• Shortest possible PRT
• 250 m range resolution

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Preliminary Conclusions

• Have gained understanding of expected Doppler
  spectrum shape
• Need experimental verification using spotlight
  data with short PRT and 250 m range resolution
• Should visually observe turbines while conducting
  radar experiment contact possible with wind farm
  manager?
• Adapt advanced radar simulator to include turbine
  clutter model
• Explore methods of non-stationary clutter
  mitigation adaptive filtering, sea-clutter
  mitigation, wavelet processing

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backup slides
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Simulation - Radial VelocityThree Blades, Three
Positions, 10o Off
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Simulations Parameters

• ? orientation of blade-face with radar radial
• pitch angle of the blades
• u horizontal wind speed

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Aliasing