Radar Impact AssessmentUK Offshore Wind 2003, 26-27 March 2003Dr John G Gallagher

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Contents

1 The radar impact

2 Approach

3 Computer model

4 Radar trials

5 Validation

The radar impactSection 1

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The problem• Important for Offshore and On-shore wind farms

– radar used for maritime navigation and safety

– land-based radar

– ship-based radar

– Air Traffic Control radar

• Associated electromagnetic issues

– Communications (HF, VHF to microwave)

– GPS, DGPS

– AIS

– Radar beacons (racons)

– SSR

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The radar problem

• Safety at sea and airspace safety

• Wind turbine interaction with radar affects

– Marine radar both land-based and ship-based radar

– Air Traffic Control primary radar and SSR

• by

– giving rise to false targets on radar

– obscuration of wanted targets as a result of radar shadows cast behind turbines

– corrupts information on the radar waveform

ApproachSection 2

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Need

• There is a need to understand the operational impact of siting wind turbines near radar and other electromagnetic systems

– Radar cross-section (measure of energy scattered)

– propagation of radar energy

• Who are the main stakeholders and what systems do they operate that may be affected by the wind farm

• Determine the key interaction parameters that affect the radar and other electromagnetic systems

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Approach

• DTI Renewable Energy Programme funded model

• Generate detailed electromagnetic scattering predictions of wind turbines

• In the case of radar systems configure computer model to simulate the effects of wind turbines on radar

• Carry out a trial to collect measured data of a turbines and relate it to the turbine state (pitch, yaw, RPM)

• Validate computer model using the measured data

Computer modelSection 3

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Computer model

• Modular components allow configuration for offshore and on-shore environments

– Transmission from radar

– Propagation over terrain to turbines

– Complex scattering from turbines

– Return of complex echo to radar

– Radar processing • target discrimination in range and bearing

• (MTI / Threshold Etc.)

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Radar cross-section predictions

• CAD models made from data supplied from manufacturers

• Meshed appropriately for input to RCS code

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Radar cross-section predictions• Results show RCS of complete turbine to be

generally between 10dbsm -30dBsm (10m2 - 1000m2)

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Computer model

• Display

– Takes time history data files from prediction files and displays them on the PPI display

• The computation is run on QinetiQ high performance computer facility

Radar TrialSection 4

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Radar Trials

• The QinetiQ MPR instrumentation radar measures the radar signature of a wind turbine

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Measured RCS of wind turbine

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 30

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10

15

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25

30

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Time (s)

RC

S (

dB

)

RCS from SWT008

Time (secs)

RCS (dBsm)

• 23 RPM

• 40° Yaw

19Doppler spectrum for three revolutions

-80

-60

-40

-20

0

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Time (s)

Doppler(Hz

)

0 1 2 3 4 5 6 7 8

-1000

-500

0

500

1000

1500

20A radar PPI display

ValidationSection 5

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Validation• Simulation

– CAD model of turbine– Propagate electromagnetic wave– Predicted wind turbine RCS;– Radar signal process model through to PPI display

• Measurement– Gathered wind turbine truth data– Measured the RCS of a wind turbine– Collected video of a real PPI display showing a wind farm

• Compare measured data with the predicted data for validation

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RCS validation

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Display validation

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Validation

• The RCS predictions reproduce the peaks and basic

trend of the measurement data;

• The simulation agrees well with the recorded PPI

display for single turbine configurations;

• The model is shown to be between 93% and 98%

accurate for several configurations of a single

turbine.