14 th Coherent Laser Radar Conference

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Advantage of the High Resolution Doppler Lidar
measurements for nighttime boundary layer study
and wind-energy applications
Y. L. Pichugina1, 2, R. M. Banta2, N. D.
Kelley3, B. J. Jonkman3, W. A. Brewer2, S. P.
Sandberg2, and J. L. Machol1, 2 1 Cooperative
Institute for Research in Environmental Sciences
(CIRES), Boulder, CO 2 Earth System Research
Laboratory, National Oceanic and Atmospheric
Administration (ESRL/ NOAA), Boulder, CO
3National Wind Technology Center/National
Renewable Energy Laboratory (NWTC/NREL) Golden,
CO
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Background

• The 2 mm High Resolution Doppler Lidar (HRDL) of
  NOAA/ESRL can be an important wind-measurement
  tool for wind energy applications.
• During the Lamar Low-Level Jet Project (LLLJP),
  nighttime observations were taken by HRDL to
  obtain detailed information about the periodic
  fluctuations or coherent turbulent structures in
  the wind flow at the rotor heights.
• The project was carried out during the first two
  weeks of September 2003 at a site south of Lamar,
  Colorado which is now a wind farm with more
  than 100 wind turbines.

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Presentation Objectives

• To summarize results of wind measurements
  obtained by HRDL during the Lamar Low Level Jet
  Program
• To demonstrate the ability of the HRDL
  measurements to provide accurate knowledge of
  wind and turbulence characteristics at the
  heights of turbine rotors and above.
• To present the results of a simultaneous
  inter-comparison of wind fields measured by two
  remote sensing technologies and direct
  tower-based measurements.

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Instrumentation
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HRDL measurements
Fixed-beam scans
Vertical-slice (RHI) scans
Conical (PPI) scans
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Available products to monitor flow- examples
Mean wind speed and direction

• Vertical profiles of UH and sU2

On regions such as US Great Plains, wind energy
resource comes from a nocturnal LLJ
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HRDL-sonic anemometers data comparison
N. Kelley et al.Comparing Pulsed Doppler Lidar
with Sodar and direct measurements for wind
assessment Presented at AWEAs 2007 WindPower
conference. Los Angeles, CA, 06/2007

• bias 0.96 0.19 m s-1
• slope 1.017 0.001
• R2 0.96

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HRDL-sodar data comparison
Profiles from HRDL are deeper than from sodar

• A confidence factor is determined by
• consistency of the individual results from
• each of the 10 transmitted frequencies
• returned signal strength
• level of consistency between vertical layers
• (range gates).

• bias -1.06 0.19 m s-1
• slope 1.07 0.01
• R2 0.92

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Relation between HRDL streamwise velocity
variance and LLJ wind speed maxima
LLJ maximum serves as an upper bound to the layer
of strong turbulence.
Shear created turbulence calculated from HRDL
fixed-beam scan and tower-measured coherent
turbulence kinetic energy (CTKE), which is based
on momentum fluxes
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Power law wind speed profile
U2U1(z2/z1)a
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Summary

• Accurate estimates of wind resource potential
  and turbulence structure of the boundary layer at
  the heights of turbine rotors is very important
  as the height reached by commercial wind turbines
  increases up to 200-250 m to take advantage of
  stronger wind speeds at higher altitudes.
• The high temporal and spatial resolution of the
  HRDL data allows investigation of wind and
  turbulence conditions of the stable boundary
  layer, including the atmospheric layer occupied
  by wind-turbine rotors, in finer detail.
• Quantities of interest that can be easily
  monitored using Doppler lidar include -wind
  speed and direction profiles
• -nighttime evolution of the LLJ properties
• -role of the LLJ in generating turbulence below
  the jet
• -estimates of TKE profiles.
• The LLJ maximum serves as an upper bound to the
  layer of strong turbulence.
• Staring mode may be most useful real-time for
  wind energy applications

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Acknowledgements Field data acquisition and much
of the analysis for this research were funded by
the National Renewable Energy Research Laboratory
(NREL) of the U.S. Department of Energy (DOE)
under Interagency Agreement DOE-AI36-03GO13094.
We thank our colleagues from ESRL R. Alvarez,
L. Darby, J.George, J. Keane, B. McCarty, A.
Muschinski, R.Richter, A. Weickmann, and
following from NREL J. Adams, Dave Jager, Mari
Shirazi and S. Wilde. We also wish to
acknowledge NOAA Equal Opportunity Department for
a financial support of our participation in this
conference. THANK YOU!
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EXTRAS
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Obtaining Streamwise LIDAR Wind Profiles Using
Vertical Scan Mode Data

• By design the majority of available data was
  collected in this mode
• Not optimal for obtaining streamwise velocity
  variance due to
• a potential lack of horizontal homogeneity at low
  angles
• sparse spatial sampling at high angles

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Stationary Stare Mode Geometry for Optimal
LIDAR-Sonic Inter-comparison
30-m range gates 6 7
Wind Flow
UH
Uradial
31o
LIDAR
plan view
elevation view
N. Kelley et al. Presented at AWEAs 2007
WindPower conference. Los Angeles, CA, June3-6
2007
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Results of HRDL fixed beam and sonic anemometers
comparisonunder optimal observing conditions

• Sonic UH full vector velocity is projected on to
  the LIDAR UH value for comparison over nominal
  periods of 10 minutes
• The two compare nominally within 0.2 0.3 m/s or
  2.5 over the observed velocity range of 1.0
  to 11.3 m/s
• Compares favorably with similar measurements by
  Hall, et al using a much earlier version of the
  LIDAR at an elevation of 300 m and an observed
  velocity range of 1 to 22 m/s

Hall, et al, 1984, Wind measurement accuracy of
the NOAA pulse infrared Doppler LIDAR. Applied
Optics, 23, No. 15.
N. Kelley et al. Presented at AWEAs 2007
WindPower conference. Los Angeles, CA, June3-6
2007
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Tower, SODAR, LIDAR inter-comparison results
LIDAR Vertical-Scan UH Referenced To All Tower
Sonics UH
LIDAR Vertical-Scan UH Referenced To SODAR UH

• Large bias, -1.02 0.16 m/s
• LIDAR lower at all wind speeds
• Small slope error, 1.023 0.010
• 1s variation, 0.89 m/s
• R2 0.918

• Large bias, -1.35 0.12 m/s
• LIDAR lower at all wind speeds
• Small slope error, 0.984 0.011
• 1s variation, 0.67 m/s
• R2 0.955

N. Kelley et al. Presented at AWEAs 2007
WindPower conference. Los Angeles, CA, June3-6
2007
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Instrument Positions
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120-m Tower Sonic Anemometry

• ATI SAT/3K 3-axis sonic anemometers (7 Hz
  bandwidth, 0.05 sec time resolution)
• Mounted on support arms specifically engineered
  to damp out vibrations below 10 Hz
• Mounted 5 m from edge of 1-m wide,
  torsionally-stiff, triangular tower
• Arms orientated towards 300 degrees w.r.t. true
  north

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Scintec MFAS Phased Array SODAR

• Observed winds between 50 and 500 m
• 20-min averaging period
• 10-m vertical resolution
• Horizontal winds from 8 tilted beams and 10
  frequencies over range of 1816-2742 Hz
• Variable pulse lengths
• Automatic gain control
• Very quiet site

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Relation between HRDL streamwise velocity
variance and LLJ wind speed maxima
LLJ maximum serves as an upper bound to the layer
of strong turbulence.
Shear created turbulence calculated from HRDL
fixed-beam scan and tower-measured coherent
turbulence kinetic energy (CTKE), which is based
on momentum fluxes
CTKE1/2(uw)2(uv)2(vw)21/2
14 th Coherent Laser Radar Conference