The document compares wind measurements from a pulsed Doppler LIDAR, SODAR, and direct tower measurements taken during a field study. It finds that under optimal conditions, the LIDAR achieved a root mean square accuracy of 0.3 m/s or 2.5% compared to tower measurements, while SODAR measurements had a root mean square uncertainty of 0.6-0.7 m/s or 5-6% limited by tower flow distortion. Vertical wind profiles measured by the LIDAR's conical scanning mode provided detailed wind data, but initial vertical profiles from stationary scans showed larger errors compared to tower measurements.

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Comparing Pulse Doppler LIDAR with
SODAR and Direct Measurements for
Wind Assessment
Neil D. Kelley
Bonnie J. Jonkman
George N. Scott
National Wind Technology Center
Yelena L. Pichugina
Cooperative Institute for Research in Environmental Sciences/NOAA
University of Colorado at Boulder

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Background
 The 2001-2003 Lamar Low-Level Jet Project
provided an opportunity to simultaneously compare
the wind fields measured remotely by pulsed LIDAR
and SODAR and directly by tower-mounted sonic
anemometers
 These measurements were taken by NREL/NWTC
and the National Oceanic and Atmospheric
Administration (NOAA) during the first two weeks of
September 2003 south of Lamar, Colorado which is
now the site of the 166 MW Colorado Green Wind
Plant

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We acknowledge the support of this study by
the NOAA Earth System Research
Laboratory (ESRL) and
 Dr. Robert M. Banta
 Dr. W. Alan Brewer
 Scott P. Sandberg
 Janet L. Machol
in particular without whose professional and
scientific dedication the results being
presented today would not have been
possible.
Acknowledgements

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Presentation Objectives
 Present the results of a simultaneous inter-
comparison of wind fields measured by two
remote sensing technologies and direct
tower-based measurements
 Present the results of a longer term inter-
comparison of simultaneous measurements
taken with a SODAR and in-situ instruments

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 Continuous emissions of
infrared energy
 Nominal 200 m range
 Line-of-sight radial wind
speeds made within a single
focused region along the
beam
 Multiple heights measured
by varying position of focal
point and/or elevation angle
 Very narrow beam diameter
 Useful for highly detailed
measurements of a limited
spatial area
 Very short pulses of intense
infrared energy
 Up to 9 km range
 Line-of-sight radial wind
speeds made simultaneously
at up to 300 positions (range
gates) along the beam
 A narrow, highly collimated
beam whose diameter slowly
increases with increasing
range
 Can perform a wide range of
scanning operations for 3D
spatial measurements
BASIC ATTRIBUTES OF EYESAFE
DOPPLER WINDFINDING LIDARS
Continuous Wave (CW) Pulsed

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The Comparison and Inter-Comparison of
Wind Fields Measured by Three Techniques
 In-situ measurements
using sonic anemometry
at heights of 54, 67, 85,
& 116 m
 Scintec MFAS Medium-
Range SODAR (50-500
m)
 NOAA High-Resolution
Doppler LIDAR (HRDL)
120-m tower & four
levels of sonic
anemometry
Scintec
MFAS
SODAR
NOAA
HRDL
LIDAR

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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
 30-70 m pulse lengths
 Automatic gain control
 Very quiet site

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NOAA High Resolution Doppler LIDAR
(as configured for Lamar experiment)
 Research instrument
 Solid State Tm:Lu,YAG laser
 Wavelength 2.02 µm
 Pulse energy 1.5 mJ
 Pulse rate 200/s
 Range resolution 30 m
 Velocity resolution ~ 0.1 m/s
 Time resolution 0.25 s
 Minimum range 0.2 km
 Maximum range 3 km
 Beam width range 6 to 28 cm
vertical
scan
mode
conical
scan
mode
φ
θ
φ
θ
stare
mode

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Inter-comparison of Measured Wind Fields
LIDAR
Sonics
SODAR

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Sources of Flow Distortion Around
Triangular Lattice Tower
 Instrument mounting arm
assemblies
 Aircraft warning beacons
 Tower composed of circular
structural elements:
 1.6 cm main vertical legs
 0.6 cm cross members
 “Star” mount guy wire
connections provide torsional
stiffness
 RESULT: Flow distortion
characteristics vary with height
and wind approach angle

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Tower – SODAR Positions
North
109.05m
Guy Wires
Fenced Area
(Tower and Shed)
AR (including
e panels and
c enclosure)
- Guy Wire Anchor Points (x6)
Tower Coordinates:
37° 40.099N,
102° 39.825W
SODAR Coordinates:
37° 40.059N,
102° 39.879W
Note: SODAR and Tower Coordinates
were measured on June 25, 2002 using
a Brunton Multinavigator MNS GPS
Receiver using Datum WGS84.
guy wires
Fenced Area
(data building)
North
LIDAR
109.1 m
SODAR
instrument
arms
orientation 120-m tower
210o

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116m
-1
-1
-1
-1
0
0
0
1
1
1
2
2
3
-2
-2-2
-3
2
1
Sodar WD (deg)
160 200 240 280 320 360 400 440
SodarUH
(m/s)
2
4
6
8
10
12
14
16
18
20
22
-3
-2
-1
0
1
2
3
40 80
-4
-4
-4
-2
-2
-2
-4
00
0
0
-4
-4
-4
-2
-2
2
4
-4
-4
6
-6-8
8
Sodar WD (deg)
160 200 240 280 320 360 400 440
SodarUH
(m/s)
2
4
6
8
10
12
14
16
18
20
22
-8
-6
-4
-2
0
2
4
6
8
40 80
Estimate of Local Flow Distortion
at 116-m Sonic Anemometer Using High Reliability
SODAR Data As Reference
Horizontal Wind SpeedWind Direction
(deg) (m/s)
instrument arms
azimuth location

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Stationary Stare Mode Geometry for
Optimal LIDAR-Sonic Inter-comparison
31o
Wind
Flow
LIDAR
30-m
range
gates
6 & 7
plan view elevation view
UH
Uradial
Chosen for minimal
flow distortion at the
sonic anemometers
North
109.05m
Guy Wires
Fenced Area
(Tower and Shed)
AR (including
e panels and
c enclosure)
- Guy Wire Anchor Points (x6)
Tower Coordinates:
37° 40.099N,
102° 39.825W
SODAR Coordinates:
37° 40.059N,
102° 39.879W
Note: SODAR and Tower Coordinates
were measured on June 25, 2002 using
a Brunton Multinavigator MNS GPS
Receiver using Datum WGS84.
North
LIDAR
(167 m) 210o

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Results of Stationary Stare Inter-Comparisons
Under Optimal Observing Conditions
 Sonic full vector velocity is projected
on to the LIDAR radial velocity for
direct comparison over nominal
periods of 10 minutes
 The two compare nominally within
0.1 ± 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 CO2 laser version of
the HRDL at height 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.
Mean
Bias
Ulidar –
Usonic
Std
Dev
RMS
(m/s) (m/s) (m/s)
0.14 0.27 0.31
0.34#

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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
horizontal wind speeds due
to
 a potential lack of horizontal
homogeneity at low angles
 sparse spatial sampling at
high angles

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Tower, SODAR, LIDAR Vertical-Scan
Mode Inter-Comparison Results
Tower sonics UH (m/s)
2 4 6 8 10 12 14 16 18 20
SodarUH
(m/s)
2
4
6
8
10
12
14
16
18
20
Sodar UH (m/s)
2 4 6 8 10 12 14 16 18
LidarverticalscanUH
(m/s)
2
4
6
8
10
12
14
16
18
SODAR UH
Referenced
To All Tower Sonics UH
LIDAR Vertical-Scan UH
Referenced
To All Tower Sonics UH
LIDAR Vertical-Scan UH
Referenced
To SODAR UH
• Small bias, +0.12 ± 0.11 m/s
• Tower higher at higher speeds
• Large slope error, 0.921 ± 0.010
• 1σ variation, 0.65 m/s
• R2 = 0.956
Tower sonics UH (m/s)
2 4 6 8 10 12 14 16 18 20
LidarverticalscanUH
(m/s)
2
4
6
8
10
12
14
16
18
20
• Large bias, -1.02 ± 0.16 m/s
• LIDAR lower at all wind speeds
• Small slope error, 1.023 ± 0.010
• 1σ 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
• 1σ variation, 0.67 m/s
• R2 = 0.955

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LIDAR Vertical Wind Profiles Derived
Using Conical Scanning Mode
 More optimal
technique, but
only short
records (~1
min) available
 15 deg
elevation angle
provides 8 m
vertical
resolution
 Used by CW
LIDAR profilers
but only at 5
heights
φ
θ
φ
θ
(1 minute record)

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Long-Term High SNR# SODAR and Tower
Sonics UH Inter-Comparison
 All sonic heights included
 Wind directions of 120 ± 20o
excluded
 14649 records (585 hours)
 Mean bias of -0.5 m/s
 Slope error of 1.035 (sonics
read higher than SODAR)
 R2 = 0.845
 1σ variation of 1.5 m/s
consistent with estimated local
flow distortion magnitudes
# signal-to-noise ratio

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Conclusions
 The achievable RMS accuracy of the pulsed LIDAR under
optimal sampling conditions appears to be in the vicinity of 0.3
m/s or 2.5%
 Tower-induced flow distortion in the vicinity of the sonic
anemometers has limited the precision of the inter-comparisons
with the remote sensing instruments
 The SODAR provided an RMS uncertainty in the range of 0.6 to
0.7 m/s or 5 to 6% under high SNR conditions and is limited by
the local flow distortion at the sonic anemometers
 The pulsed LIDAR, when used in the conical scanning mode,
can provide very detailed vertical wind profiles