comparing pulse doppler lidar with sodar and direct measurements for wind assessment awea windpower...

8/18/2019 Comparing Pulse Doppler LIDAR With SODAR and Direct Measurements for Wind Assessment AWEA WindPower 2007 Los Angeles

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Windpower 2007 – Los Angeles

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. PichuginaCooperative Institute for Research in Environmental Sciences/NOAA

University of Colorado at Boulder


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Windpower 2007 – Los AngelesWindpower 2007 - Los

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Background

The 2001-2003 Lamar Low-Level Jet Projectprovided 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 ofSeptember 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 bythe NOAA Earth System ResearchLaboratory (ESRL) and

Dr. Robert M. BantaDr. W. Alan Brewer

Scott P. Sandberg

Janet L. Machol

in particular without whose professional andscientific dedication the results beingpres

ented today would not have beenpossible.

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 ofinfrared energy

Nominal 200 m range

Line-of-sight radial windspeeds made within a singlefocused region along thebeam

Multiple heights measuredby varying position of focal

point and/or elevation angle

Very narrow beam diameter

Useful for highly detailedmeasurements of a limitedspatial area

Very short pulses of intenseinfrared energy

Up to 9 km range

Line-of-sight radial windspeeds made simultaneouslyat up to 300 positions (rangegates) along the beam

A narrow, highly collimatedbeam whose diameter slowly

increases with increasingrange

Can perform a wide range ofscanning operations for 3Dspatial 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

HRDLLIDAR


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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 armsspecifically 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



8

Scintec MFAS Phased Array SODAR

Observed winds between50 and 500 m

20-min averaging period

10-m vertical resolution

Horizontal winds from 8tilted beams and 10

frequencies over range

of 1816-2742 Hz

30-70 m pulse lengths Automatic gain control

Very quiet site



9

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 armassemblies

Aircraft warning beacons

Tower composed of circular

structural elements: 1.6 cm main vertical legs

0.6 cm cross members

“Star” mount guy wireconnections provide torsional

stiffness

RESULT: Flow distortioncharacteristics vary with heightand wind approach angle


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Tower – SODAR Positions

North

109.05m

Guy Wires

Fenced Area

(Tower and Shed)

R (including

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)

orth

LIDAR

109.1 m

SODAR

instrument

armsorientation 120-m tower

210o


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116

-1-1

-1

-1

00

0

11

1

2

2

3

-2

-2-2

-3

2

1

Sodar WD (deg)

160 200 240 280 320 360 400 440

S o d a r U

H (

m / s )

2

4

6

8

10

12

14

16

18

20

22

-3

-2

-1

01

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

S o d a r U

H (

m / s )

2

4

6

8

10

12

14

16

18

20

22

-8

-6

-4

-2

02

4

6

8

40 80

Estimate of Local Flow Distortion

at 116-m Sonic Anemometer Using High Reliabili ty

SODAR Data As Reference

Horizontal Wind Speed Wind 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)

R (including

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 Coordinateswere measured on June 25, 2002 using

a Brunton Multinavigator MNS GPSReceiver using Datum WGS84.

orth

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 within0.1 ± 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

#

usinga 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 measurementaccuracy of the NOAA pulse infrared

Doppler LIDAR.” Applied Optics, 23, No.

15.

Mean

Bias

Ulidar –

Usonic

Std

DevRMS

(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 obtaininghorizontal 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

S o d a r U H (

m / s )

2

4

6

8

10

1214

16

18

20

Sodar UH (m/s)

2 4 6 8 10 12 14 16 18

L i d a r v e r t i c a l s c a n

U H (

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

• 1 variation, 0.65 m/s

• R2 = 0.956

Tower sonics UH (m/s)

2 4 6 8 10 12 14 16 18 20

L i d a r v e r t i c a l s c a n

U H (

m / s )

2

4

6

8

10

12

14

16

18

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• Large bias, -1.02 ± 0.16 m/s

• LIDAR lower at all wind speeds

• Small slope error, 1.023 ± 0.010

• 1

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

• 1 variation, 0.67 m/s

• R2 = 0.955


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LIDAR Vertical Wind Profiles Derived

Using Conical Scanning Mode

More optimaltechnique, butonly shortrecords (~1min) available

15 deg

elevation angleprovides 8 mverticalresolution

Used by CWLIDAR profilers

but only at 5heights

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 (sonicsread higher than SODAR)

R2 = 0.845

1σ variation of 1.5 m/sconsistent with estimated localflow 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

comparing pulse doppler lidar with sodar and direct measurements for wind assessment awea windpower...

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