1 11-06 2007 Quantising the effects of wind turbines on naval and aeronautical radars Principles used in Belgium ESAT – Telemic, K.U.Leuven Presentation for SET-128 11-06 2007 #2 Outline Introduction: Primary Radar Shadow effects Effects on accuracy Reflections and False Echoes Effects of multiple obstacles Doppler effects Secondary Radar Effects on accuracy (monopulse) Reflections and False Echoes Conclusions
25
Embed
#2 Outline - ventderaisonventderaison.eu/documents/windturbines_by_prof_van_lil.pdf · Gain of transmitting antenna = gain of main lobe of receiving antenna: Gain in side lobe of
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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)
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
PSR: False Echoes (cont’d)
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
PSR: False Echoes (cont’d)
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
PSR: False Echoes (cont’d)
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
PSR: False Echoes (cont’d)
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
PSR: False Echoes (cont’d)
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
PSR: False Echoes (cont’d)
RCS extremelyvariable
WT
Aircraft
2
2
4 ( )abπλ
22 abπλ
15
11-062007
#29
PSR: False Echoes (cont’d)
Vertical cross section:
11-062007
#30
PSR: False Echoes (cont’d)
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
PSR: False Echoes (cont’d)
The zones can be put on a marine/land chart
11-062007
#32
PSR: False Echoes (cont’d)
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
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