#2 outline - ventderaisonventderaison.eu/documents/windturbines_by_prof_van_lil.pdf · gain of...

1

11-062007

Quantising the effects of wind turbines on naval and

aeronautical radarsPrinciples used in Belgium

ESAT – Telemic, K.U.Leuven

Presentation for SET-128

11-062007

#2

Outline

Introduction: Primary Radar

Shadow effectsEffects on accuracyReflections and False EchoesEffects of multiple obstaclesDoppler effects

Secondary RadarEffects on accuracy (monopulse)Reflections and False Echoes

Conclusions

2

11-062007

#3

Introduction

18015010080Tot. Height

60504030Blades

8 x 3 x 45 x 2 x 3Gondola

5432.5Tower top

654.54Tower base

1201006050Tower height

“giant”“large”“small”“mini”Sizes in m

4 standard types of Wind Turbines (aeronautical study)

5 orientations gondola (every 45º)3 orientations blades (every 40º)

Large distances: curvature of Earth (normal atmosphere)

11-062007

#4

Primary RadarsProperties of primary radars

Approach• High beam• Low beam• Brussels,

Liege, …

Enroute• Bertem,

St-Hubert

3634Antenna Gain [dBi]

13002800Frequency [MHz]

21Pulse Width [µs]

1.11.53-dB Beamwidth [º]

-21-26Side Lobe Level [dB]

Horizontal pattern

553-dB Beamwidth [º]

-20-24Side Lobe Level [dB]

1.57/3Main lobe elevation [º]

Vertical pattern

-10Tilt [º]

12060Range [NM]

2500200Transmit Power [kW]

PSR ERPSR AP High/Low

3

11-062007

#5

Primary Radars (cont’d)Patterns: example PSR AP low

−20 −15 −10 −5 0 5 10 15 20−30

−25

−20

−15

−10

−5

0

5

10Relative horizontal pattern of PSR approach radar (low beam)

Angle in degrees

Sig

nal i

n dB

Horizontal Vertical−70 −60 −50 −40 −30 −20 −10 0 10

−80

−60

−40

−20

0

20

40

60

80

Relative vertical pattern of a PSR approach radar (low beam)

Ang

le in

deg

rees

Signal in dB

1000 m

11-062007

#6

Primary Radars (cont’d)Examples of the different rays (Rwr=900 m)

−40

−35

−30

−25

−20

−15

−10

−5

0

5

10

−2000 −1800 −1600 −1400 −1200 −1000 −800 −600 −400 −200−50

−40

−30

−20

−10

0

10

20

30

40

50

x distance in m

Variation of the signal behind a large wind turbine

y di

stan

ce in

m

4

11-062007

#7

PSR Shadow effects

Effects computed with UTDLimited to deep-shadow zone behind the WT: several dBPosition of WT changed

−3 −2 −1 0 1 2 3−30

−25

−20

−15

−10

−5

0

5

Relative signal level of PSR−ER 100 m behind the wind turbine wind turbine at −1.5 degrees

angle in degrees

rela

tive

sign

al le

vel (

dB)

total signal direct signal

−3 −2 −1 0 1 2 3−30

−25

−20

−15

−10

−5

0

5

Relative signal level of PSR−AP (low beam) 100 m behind the wind turbine wind turbine at −0.0 degrees

angle in degrees

rela

tive

sign

al le

vel (

dB)


ApproachEnroute (WT @ -1.5º)

11-062007

#8

PSR Shadow effects (cont’d)

Effects (2):Larger distance: less significant

−3 −2 −1 0 1 2 3−30

−25

−20

−15

−10

−5

0

5Relative signal level of PSR−AP (low beam) 60 nm behind the wind turbine

angle in degrees

rela

tive

sign

al le

vel (

dB)


−3 −2 −1 0 1 2 3−30

−25

−20

−15

−10

−5

0

5Relative signal level of PSR−ER 120 nm behind the wind turbine

angle in degrees

rela

tive

sign

al le

vel (

dB)


Approach: 60 NM

Enroute: 120 NM

5

11-062007

#9


Effects (3):The larger the object the larger the effectExample: naval radar (9.41 GHz) from Marseille port authorities and silo (h 33 m, Ø 41,16 m)

11-062007

#10


Effects (4):Computation of the effect of an existing silo, compared with the shadow of the turbines

6

11-062007

#11

PSR: shadow effects (cont’d)

Probability of detectionFree space:

EPICS: R4 L2 (decay of the signal L > 4πR2)

(Non)Probability of Detection:• Noise: N = kTBF

2

3 4(4 )t t r

fsPG GP

Rσλ

π=

22

2

44 ( )

t t o rr

t t o

PG G GPL PG Gλ πσ

π λ⎛ ⎞

= ⎜ ⎟⎝ ⎠

2 2

22

20

0

/ 2'2

00

( )

22 ' ( ' )

T r

Tr

V V VrN

V NVVN

r

VVNDP Ve I dVN

NDP e V e I V V dVN

+−

− −

=

=

∫

∫

11-062007

#12

PSR: shadow effects (cont’d)Small Values (upper bound):

Approximation:

8.172

r

NDPUPPNDPAPPV

N

=

2 2( )2 2 erfc( ) erfc( )

2 2 2

100

r T rV V Vr T rN N

r

T r

V V VNDPUPP e e VN N N

V VN

π−− − −⎡ ⎤= − + −⎢ ⎥⎣ ⎦

<

7

11-062007

#13

PSR: shadow effects (cont’d)

Probability of detection: example

Alternative representation: change of radar cross section (RCS)Pattern no longer visible

1020.log tot

dir

PP

σ⎛ ⎞

∆ = ⎜ ⎟⎝ ⎠

11-062007

#14

Radar accuracy PSR: distanceRadar resolution

300 m Approach600 m Enroute

EffectDelay ≈ distanceCorrect heightVery small error AP 100 m

ER 120 NM

8

11-062007

#15

Radar accuracy PSR: angleWeighted average of all rays

Viewing angle from radar: 0.14°Perfect symmetry (0°, 0°) zero errorFar from WT smaller angular error

−3 −2 −1 0 1 2 3−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

Angular error (degrees) 1000 m behind a wind turbine for a PSR approach radar

angle in degrees

angu

lar

erro

r in

deg

rees

−3 −2 −1 0 1 2 3−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

Angular error (degrees) 120 nm behind a wind turbine for a PSR enroute radar

angle in degrees

angu

lar

erro

r in

deg

rees

AP 1000 m ER 120 NM

11-062007

#16

Radar accuracy PSR: angle (cont’d)Larger distance (viewing angle 0.07°): Rwr=2000 m

Smaller angular error

Always smaller than viewing angle from the radarAP 1000 m ER 1000 m

−3 −2 −1 0 1 2 3−0.1

−0.08

−0.06

−0.04

−0.02

0

0.02

0.04

0.06

0.08

0.1

Angular error (degrees) 1000 m behind a wind turbine for a PSR approach radar (at 2000 m)

angle in degrees

angu

lar

erro

r in

deg

rees

−3 −2 −1 0 1 2 3−0.1

−0.08

−0.06

−0.04

−0.02

0

0.02

0.04

0.06

0.08

0.1

Angular error (degrees) 1000 m behind a wind turbine for a PSR enroute radar (at 2000 m)

angle in degrees

angu

lar

erro

r in

deg

rees

9

11-062007

#17

Radar accuracy PSR: angle (cont’d)Other WT position

WT at –2ºReflections due to polygonal shape of tower (artifact)

AP 1000 m ER 1000 m

−3 −2 −1 0 1 2 3−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

Angular error (degrees) 100 m behind a wind turbine (at −2 degree) for a PSR approach radar

angle in degrees

angu

lar

erro

r in

deg

rees

−3 −2 −1 0 1 2 3−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

Angular error (degrees) 100 m behind a wind turbine (at −2 degree) for a PSR enroute radar

angle in degrees

angu

lar

erro

r in

deg

rees

11-062007

#18

PSR: Reflections and False Echoes

4 different types of false echoes:Reflection WT – aircraft (types 1 and 2)

Type 2 reflections from aircraft in SLL of antennaVisible behind the WTSame speed as aircraft; until closest position where it

stops and disappears from radar screen

10

11-062007

#19

PSR: Reflections and False Echoes

Reflection aircraft - WT (types 3 and 4)Type 4 reflections from WT in side lobe of antenna

Visible behind the aircraftType 3 moves at twice the speed of the plane ; until

closest position where it stops and disappears from radar screen

11-062007

#20

PSR: False Echoes (cont’d)

Type 1:Only in neighbourhood WTExample: approach (7 km)

2 2 2

41 5 4

. . . ..(4 ) .

TX TX WT MA

RX WR

P GRP R

λ σ σπ

=

Parameters (see next)

11

11-062007

#21


Simulation parameters:Transmitted power:Gain of transmitting antenna = gain of main lobe of receiving antenna: Gain in side lobe of receiving antenna (see types 2 and 4):Frequency = 2.8 GHz (λ = 0.107 m)Minimal detectable level:Radar cross section of a wind turbine, both mono- and bistatic σxW = 400 m2 (no effect of curvature of the Earth was taken into account)Radar cross section of an aircraft, both mono- and bistatic σxA = 1000 m2

200 kWTXP =

34 dBiTXG =

10 dBiRXG =

140 dBWRXP = −

11-062007

#22


Type 2, 3 and 4:

3 different regions for type 2/4 and 3 (on axis):Aircraft further from radar than WT:Aircraft between radar and WT:Aircraft behind radar:

(1)AR WR iR R R= +

(2)AR WR iR R R= −

(3)AR i WRR R R= −

2

2 4 4 2 2(4 )TX TX RX BW BA

RX WR AR

P G GR RP R R

λ σ σπ

= =2 2 2

43 5 4(4 )TX TX BA MW

RX AR

P GRP R

λ σ σπ

=

12

11-062007

#23

PSR: False Echoes (cont’d)Type 3: PSR-AP

2 2 2

43 5

( )3 3

(4 )

2 5120

TX TX BA MW

RX

crit

P GKP

R K m

λ σ σπ

=

= =

(1) 33 2

3

(2) 33 2

3

2(3)3 3

24

24

2 2

WR WR

WR WR

WR WR

KRR R K

KRR R K

R RR K

=+ +

=± −

⎛ ⎞= − + +⎜ ⎟⎝ ⎠

11 km

5.1 km

11-062007

#24

PSR: False Echoes (cont’d)Type 2/4: PSR-AP

2

2 40

( ) 32 / 4 2

(4 )

4 10673

TX TX RX BW BA

crit

P G GKP

R K m

λ σ σπ

=

= =

All types simultaneously!!

(1) 22/ 4 2

2

(2) 22 / 4 2

2

2(3) 22 / 4

2 /4 /

2 /4 /

2 2

WR

WR WR WR

WR

WR WR WR

WR WR

WR

K RRR R K R

K RRR R K R

R R KRR

=+ +

=± −

⎛ ⎞= − + +⎜ ⎟⎝ ⎠

14 km

10.7 km

13

11-062007

#25


At/below ‘critical’ distance:Whole zone between radar and WTBehind WT much smaller zone (2-4 km)

Modification for cylindrical towerScattering: 6 dB decrease of signal

1 0 1

1 1 2cos( )l rρ θ

= +

11-062007

#26


0 ( ) ( )

( )0 ( )

( ) 0

ww t gon gon

t

g wg w gon

g

w g

hh Dhh h

h h Dh

h h D

σ σ σ σ

σ σ

σ

> ⇒ = − +

+− < < ⇒ =

< − ⇒ =

2 2

3.4.

4 2.sin ( / 2)3 cos( ) 17. 6

a

w t a t

DR

Dh h R he

θ

θθ

=

= − ≈ −

Large distances: curvature of EarthVariation of radar cross section

14

11-062007

#27


Examples of false echo sizes (curved surf.):

PSR-AP PSR-ER

11-062007

#28

−80 −60 −40 −20 0 20 40 60 80−60

−40

−20

0

20

40

60

80

rada

r cr

oss

sect

ion

in d

Bsm

angle in degrees

Monostatic and bistatic radar cross−section of a 20 x 10 m plate at −45 degrees and 1.3 GHz

monostaticbistatic

Flat plate


RCS extremelyvariable

WT

Aircraft

2

2

4 ( )abπλ

22 abπλ

15

11-062007

#29


Vertical cross section:

11-062007

#30


Fortran routine, provided to BelgocontrolProgram inputVariation of regions with respect to distance radar – wind turbineVertical cross section if only 1 distance is requested

INPUT

16

11-062007

#31


The zones can be put on a marine/land chart

11-062007

#32


Example on a digital display

17

11-062007

#33

PSR: Multiple obstacles4 case studies:

Parallel case: WT’s on line with radarPerpendicular case: line WT’s perpendicularWT’s on line at 45º (not in this presentation)Minimal distance between 2 obstacles (Vert. Pol.)?

Remarks:Blocks 6 x 6 x 200 m3 @ intermediate distance of 400 mRadar at 1000 m; trajectory = circle of 10 km radiusOmni-directional antenna (dipole), thus all WT illuminated

the same way (≠ radar pattern)Change radar cross section

11-062007

#34

PSR: Multiple obstacles (cont’d)

Parallel case (enroute radar, h= 35 m)Very little effectOnly deep shadowing behind the line

−3 −2 −1 0 1 2 3−40

−35

−30

−25

−20

−15

−10

−5

0

5

Change Radar Cross Section (enroute) cut at h=1000m

angle (degrees)

chan

ge r

adar

cro

ss s

ectio

n (d

B)

1 block 5 blocks 10 blocks20 blocks

18

11-062007

#35

PSR: Multiple obstacles (cont’d)

Perpendicular case:Obstacles visible at angles: Height of obstacles:

400arctan1000n

nα ⎛ ⎞= ± ⎜ ⎟⎝ ⎠

2 2

100002001000 (400 )

nhn

=+

11-062007

#36

PSR: Multiple obstacles (cont’d)Minimal distance between 2 obstacles?

Varied between 10 and 100 m

Cylinder (heptadecahedron) Extension smaller

19

11-062007

#37

PSR: Multiple obstacles (cont’d)Large parks can be handled taking only into account tower

11-062007

#38

PSR: Doppler effectsDoppler of the blades:

Doppler shift varies between ± maximal value• Max. speed value = (ω = 15 rev./min)• Combination of relative Doppler shifts• ca. 1750 Hz for PSR-AP; ca. 800 Hz for PSR-ER

wl ω

0

v2Df c∆ ≈

20

11-062007

#39

PSR: Doppler effectsMakes rotating blades visible on primary radar

Example: Enroute radar of St. Hubert windmill park of St. Ode (sometimes initiating false tracks on Belgocontrol’s ATC systems):

11-062007

#40

PSR: Doppler effects (cont’d)

Doppler obstacle behind WTObstacle can become visible due to Doppler shiftVery low Doppler shifts (some Hertz; Rwo= 2 km; )Filtered out (30 dB) with simple MTI filter

21

11-062007

#41

Secondary Surveillance RadarsRadar parameters

Max. power = ± 1.685 º3 3 dB-BW = 2.3 º3 dB-BW = 12 º

SLL = -30 dBSLL = -28 dBSLL = -15 dB

Gain = 2.13 dB below sumGain = 28 dBiElevation = 8º

Horizontal Difference patternHorizontal Sum patternVertical pattern

−5 −4 −3 −2 −1 0 1 2 3 4 5−35

−30

−25

−20

−15

−10

−5

0

5

Relative horizontal sum and difference pattern of a secondary radar

angle in degrees

rela

tive

sign

al le

vel (

dB)

sum signal diff signal

−70 −60 −50 −40 −30 −20 −10 0 10

−80

−60

−40

−20

0

20

40

60

80

Relative vertical pattern of a SSR radar

Ang

le in

deg

rees

Signal in dB

11-062007

#42

Secondary Radar (cont’d)

Link budget (without antenna gains)

Effect on radar pattern:Shadowing behind WTLarger distance: less significantChanged WT position (right)

-133.5-132.01Allowed Losses

-115-99Receiver sensitivity [dBW]

18.533.01Transmit Power [dBW]

Reply @ 1090 MHzInterrogation @ 1030 MHz

22

11-062007

#43

Variation SSR pattern

Shadowing effects:

−3 −2 −1 0 1 2 3−30

−25

−20

−15

−10

−5

0

5

Relative SSR signal level 100 m behind the wind turbine wind turbine at −0.0 degrees

angle in degrees

rela

tive

sign

al le

vel (

dB)

total sum signal direct sum signal total diff signal direct diff signal

−3 −2 −1 0 1 2 3−30

−25

−20

−15

−10

−5

0

5

Relative SSR signal level 100 m behind the wind turbine wind turbine at −1.0 degrees

angle in degreesre

lativ

e si

gnal

leve

l (dB

)

total sum signal direct sum signal total diff signal direct diff signal

11-062007

#44

Radar accuracy SSR: distance

EffectDelay ≈ distanceCorrection for heightVery small error

100 m

1000 m

23

11-062007

#45

Radar accuracy SSR: angle

Angular error (monopulse, else see PSR)Iteratively from

• Where γ, β and α are parameters of the radar pattern

MIGHT BE LARGER THAN ACCURACY OF SYSTEMMIGHT BE LARGER THAN ACCURACY OF SYSTEM

2

.sin( . )cos ( . )γ β ϕ

α ϕ∆=

Σ

100 m 120 NM

−2 −1.5 −1 −0.5 0 0.5 1 1.5 2−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

angle in degrees

angl

e er

ror

in d

egre

es

Angular error (degrees) 100 m behind the wind turbine (h = 20 m)

−2 −1.5 −1 −0.5 0 0.5 1 1.5 2−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

angle in degrees

angl

e er

ror

in d

egre

es

Angular error (degrees) 120 nm behind the wind turbine (h = 20 m)

11-062007

#46

Radar accuracy SSR: angle (cont’d)

Larger distance between radar and WT (Rwr=2 km)Smaller angular error

100 m 120 NM

−2 −1.5 −1 −0.5 0 0.5 1 1.5 2−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

angle in degrees

angl

e er

ror

in d

egre

es

Angular error (degrees) 100 m behind the wind turbine (h = 20 m)

−2 −1.5 −1 −0.5 0 0.5 1 1.5 2−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

angle in degrees

angl

e er

ror

in d

egre

es

Angular error (degrees) 120 nm behind the wind turbine (h = 20 m)

24

11-062007

#47

ConclusionsPSR:

Accuracy: angular error angle ≤ WT seen from the radarShadowing effect:

• No effects if

• Visible if Da > D & False Echoes : • Everywhere between radar and WT if distance ≤ ‘critical’ distance• Large distances 2 separate volumetric regions

Effects of N obstacles in all cases ≤ N times the effect of one obstacle and in most cases = effect of one obstacleDoppler shift of reflections very small

2 2

6

3( ) ( )8 17.10t r gt tg gr r

a

D Dh h h h h hR

′ ′− = + − + ≤ =

2 2

6 2( )17.10

a aa r t r

t

D Dh h h hD

′ ′ ′ ′≤ − ≤ −

11-062007

#48

Conclusions (cont’d)

Secondary Radar:Shadowing effect: like PSR, but smaller (half the dB value, 1-way communication system)Accuracy: angular error might be ≥ accuracy of system & viewing angleFalse Echoes: • Type 3 = less strict one• Type 4 = much smaller than PSR (smaller gain of

transponder)

25

11-062007

#49

Poetic views of wind turbines

11-062007

#50

Questions?

#2 outline - ventderaisonventderaison.eu/documents/windturbines_by_prof_van_lil.pdf · gain of...

Documents