East Anglia ONE Offshore Windfarm - Planning Inspectorate · East Anglia ONE Offshore Windfarm Environmental Statement ... vessels operate in the vicinity of the East Anglia ONE site

East Anglia ONE

Offshore Windfarm

Environmental Statement

Volume 2 Chapter 16 Telecommunications and Interference Appendices

Document Reference – 7.3.11b Appendix 16.1 APFP Regulation - 5(2)(a) Author – Environmental Resources Management Ltd Date – Nov 2012 Revision History – Revision A

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Environmental Statement Volume 2- Offshore.

Appendix 16.1

Marine Radar

Stefanie.Pini

Text Box

1.1 INTRODUCTION

Commercial passenger ferries, fishing boats, piloting activities and cargo

vessels operate in the vicinity of the East Anglia ONE site. All of these vessel

types use marine radar systems for the primary purposes of navigation and

collision avoidance.

Wind turbines are large structures and will affect marine radars in a similar

way as other large objects such as container vessels and port buildings. The

impacts are well documented through experimental trials (QinetiQ and MCA

2004; MCA, 2005, BWEA and MCA, 2007). Mariners will typically be aware of

the potential impacts of large objects on the operation of their radar system. In

this Appendix the main impacts are discussed. Illustrations are given

assuming a 12-foot long S-band (approximately 3GHz) radar system typical of

those used by cargo vessels.

This Appendix is supported by the following Figures

• Figure 1 - Layout A (172 7.0MW Wind Turbines).

• Figure 2 - Layout B (325 3.6MW Wind Turbines).

• Figure 3 - Radar Display Simulation for Layout A (gravity base or

suction caisson foundations).

• Figure 4 - Radar Display Simulation for Layout A (jacket foundations).

• Figure 5 - Radar Display Simulation for Layout B (gravity base or

suction caisson foundations).

• Figure 6 - Radar Display Simulation for Layout B (jacket foundations).

• Figure 7 - Zones where two-way shadow loss is 3dB or more for Layout

A using jacket foundations.

• Figure 8 - Zones where two-way shadow loss is 3dB or more for Layout

B using gravity base or suction caisson foundations.

1.2 DETECTABILITY

The appearance of the wind turbines on marine radar displays will depend on

the size of the reflected radar signals. The reflections in turn will depend on

factors such as the radar frequency, the material, size and shape of the wind

turbine and its foundations, and the distance of the radar from the wind

turbine.

In a marine environment, reflections from the wind turbine and foundations

are likely to dominate impacts. Reflections from the blades will typically be

smaller. The foundation options being considered for the East Anglia ONE

windfarm are jackets, gravity bases and suction caissons.

Illustrative scattering predictions were made of the different foundation types

being considered. Diagram 1 shows the typical scattering behaviour from the

gravity bases and suction caisson options, whose dimensions are similar. The

tapered tower scatters energy mostly above the sea surface and the vertical

section of the gravity base scatters signals mostly back in the direction of the

radar.

Diagram 1 Illustration of Scattering from Wind Turbine and Gravity Base and

Suction Caisson Foundation Options (the colour indicates the bistatic RCS in units of

dBsm)

Diagram 2 shows the corresponding results for the jacket foundations, now

assuming tubular legs with an estimated taper angle of seven degrees and a

diameter of three metres. In this case, both the tapered tower and tapered

jacket legs reflect signals predominantly above the sea surface. In this case, the

strength of interfering signals due to reflections from the wind turbine for

vessels on the sea surface is smaller than the case for the gravity base or

suction caisson foundations.

Diagram 2 Indicative Illustration of Scattering from Wind Turbine and Jacket

Foundation option (the colour indicates the bistatic RCS in units of dBsm)

The results shown in Diagram 1 and Diagram 2 are only indicative, as the

precise dimensions of the wind turbines are not yet finalised and the results

only hold for an S-band radar at the distance and antenna height shown in the

illustrations. Several assumption about the radar configuration have been

made. However, the trends for other radar frequencies and configurations are

likely to be the same.

1.3 SIDE LOBE BREAKTHROUGH

The energy from a radar antenna radiates out in a narrow azimuth beam to

capture as much detail as possible for every bearing. Antennas, however, are

not perfect, and consequently the main beam has several side beams (known

as side lobes) associated with it, albeit at a much lower power level. A

representative S-band radar azimuth beam is shown in Diagram 3.

Diagram 3 Illustration of Azimuth Beam Pattern for an S-band radar

It is desirable for reflections from objects to only be detected through the main

lobe, making the objects appear on the radar display as small arcs of

approximately two degrees or less. If the size of a reflection from an object is

large enough it may be detected through the antenna's side lobes, causing the

size of the arc to increase. This effect is called side lobe breakthrough. In the

extreme, where the object is detected through all of the side lobes, it may

appear as a complete ring around the radar. This effect is called ring around.

For illustration, the appearance of the radar display was modelled for a vessel

at a distance of 1.0NM from the closest wind turbines. This distance was

chosen according to the design criteria for the East Anglia ONE windfarm

where a set back buffer of 1.0NM has been applied to the International

Maritime Organisation (IMO) Deep Water Route to the east of the project

boundary. At this stage it is not known whether the worst case will be a layout

with the largest (most reflective) turbines, or for a layout with the smallest

inter-turbine spacing. Accordingly, tTwo illustrative worst case layouts are

considered:

• Layout A - consists of 172 7.0MW wind turbines distributed evenly

throughout the East Anglia ONE site. This is the worst case in terms of

individual turbine size

• Layout B - consists of 325 3.6MW wind turbines distributed in the

middle of the site. This is worst case in terms of smallest inter-turbine

spacing.

Layouts A and B are shown in Figure 1 and Figure 2 respectively. These

figures also show the location of the IMO Deep Water Route and the example

radar location. The initial position and direction of a small vessel is also

shown in the figures. The small vessel is assumed to have a representative

RCS of 10dBsm.

The radar display simulation for Layout A using a gravity base or suction

caisson foundation is shown in Figure 3. Wind turbine plots are shown in

white and the plots from the small vessel are shown as dark blue. There is

considerable side lobe breakthrough for the wind turbines closest to the radar.

However, this decreases at greater ranges from the radar. All of the wind

turbines are detectable and a significant area of clutter is generated. In this

illustration the side lobe breakthrough does not affect the detection of other

vessels in the traffic route. The radar operator could have significant

difficulties detecting or tracking the small vessels operating within the

windfarm.

It is noted that radar operators often use sensitivity time control (STC), which

is a technique to reduce the radar sensitivity at close ranges to the vessel

normally to reduce the effects of sea clutter. The modelled results shown in

Figure 3 assume a worst case where STC has not been used and the radar is

operating at maximum sensitivity. The use of STC would reduce the extent of

the clutter shown in the figure, although the probability of detection of vessels

would also be reduced.

For comparison, the modelling results assuming a jacket foundation are

shown in Figure 4. Again the scattering levels are only representative, the

reflections from the jacket foundation are smaller and the extent of the side

lobe breakthrough is less. The clutter will be less of a distraction to the radar

operator and the inter-turbine visibility is better, meaning the small vessel

within the windfarm can be detected more easily. A similar effect is likely to

be achievable with the use of STC.

For comparison, the same analysis was carried out for Layout B using the two

foundation models. Figure 5 shows the display for gravity base or suction

caisson foundations, Figure 6 shows the results for jacket foundations. Layout

B is worst case in terms of the local density of wind turbines and thus the

wind turbine clutter.

Figure 5 shows that a radar operator would again have difficulties tracking

the small vessel through the windfarm. Figure 7 shows that the jacket

foundation option, assumed here to have a lower reflectivity, makes it

possible to track the small vessel as it exits the windfarm. Again, a similar

effect could be achieved using STC, albeit at the risk of reducing the

detectability of smaller vessels.

In the worst case there will be five collector/convertor stations and one met

mast within the project. At shorter ranges the impact of the

collector/convertor stations is likely to be similar to a turbine with a jacket

foundation. At longer ranges, the impact may be greater as a result of large

reflections from the structure of the stations. The impact will be similar to the

impacts from similar offshore stations or large flat sided vessels. The impact

from the met mast will be no greater than that from a turbine with a gravity

base foundation.

1.4 SHADOWING

Wind turbines are physical obstructions and will block radar signals casting a

shadow behind them. The shadow is not complete, however, as at radar

frequencies a significant amount of energy diffracts around obstacles. The

amount of signal loss will depend on the size of the obstruction, its distance

from the radar and the frequency.

Single wind turbines do not tend to generate significant shadowing losses by

themselves, although it is possible, in principle, to affect the detection of small

vessels immediately behind wind turbines. More significant shadowing losses

are possible where wind turbines line up and losses are compounded but

these cases only affect detection across the entire windfarm. This is potentially

significant for large vessels operating on either sides of a windfarm.

Because they are likely to present less of a physical obstruction close to the sea

surface, jacket foundations are likely to have a smaller impact on shadowing

than the gravity base of suction caisson foundations. The extent of any benefit

will depend on the jacket design and the antenna height above sea level.

To illustrate the potential differences in impact, illustrative shadowing

modelling was carried out to determine the impact on the detection of the

small vessel. The less dense Layout A with less obstructive jacket foundations

was modelled as the best case. The denser Layout B with the more obstructive

gravity base or suction caisson foundations was modelled as the worst case. It

is judged that two-way shadow losses of 3dB or less have a small impact on

vessel detection. Accordingly, the areas where the two-way cumulative

shadow loss is 3dB or more are shown in Figure 7 for Layout A and Figure 8

for Layout B.

The modelling results give qualitative estimates of the fraction of the small

vessel's path that will be potentially affected by shadowing within the

windfarm. In Figure 7 the small vessel could have had reduced detectability

for around one tenth of the time. In Figure 8 this rises to around one third of

the time.

It is stressed that the shadowing results shown are indicative, and will depend

on the vessel sizes and locations, the radar frequency, and the alignment and

density of wind turbines. The impact of collector/convertor stations and the

met mast is likely to be similar to those from the turbines. The impact from the

collector/convertor stations could be more significant if the main structure

blocks the signal, but impacts will be comparable with those from similar

existing offshore platforms.

1.5 FALSE PLOTS (GHOSTING)

Ghosting is caused when returns from an object are received via a reflection

from secondary reflective object. Ghosting may be caused by reflections from

large structures such as port buildings, oil and gas platforms, large vessels

wind turbines, or from reflectors on the observing vessel's own structure.

Operationally, in terms of persistence and severity, the most significant impact

is the ghosting due to reflections from the vessel's structure (BWEA and MCA,

2007).

Diagram4 shows the typical appearance of ghosting on the radar of a vessel

passing within 2km (approximately 1NM) of the boundary of an operational

windfarm (BWEA and MCA, 2007). The ghosting is due to reflections from

structure onboard the observing vessel.

Diagram 4 Illustration of typical ghosting produced on a passing vessel 1NM (2km)

from the wind farm boundary.

At any instant, ghosting due to reflections from vessel structures could occur

at all bearings, between ranges R1 and R2, where:

• R1 is approximately the distance between the radar vessel and the

closest turbine;

• R2 is approximately the distance between the radar vessel and the

furthest turbine.

The area where ghosting can arise due to reflections from structure on the

observing vessel is illustrated in Diagram 5. Ghost images are more likely to

appear behind the observing vessel’s than forward, due to installation

regulations on where radars are placed relative to vessel structures (BWEA

and MCA, 2007; Brown, 2007). However, items such as badly placed

containers, cranes, derricks and antennas could cause ghosting forward of the

vessel (Brown, 2007).

Diagram 5 Area where ghosting due to reflections from structures on the observing

vessel could occur. Because the wind farm is an extended object, its direct returns and

the ghost image can also overlap.

Genuine targets within the ghost targets may not be detected. The impact can

potentially be mitigated through gain control, but this may also reduce the

probability of detection of vessels or structures. Mitigation can also be through

ensuring separation of the ghost targets with other objects:

• ensuring separation from other vessels is not practical; and

• ensuring separation from other windfarms is practical, with a separation

distance based on the maximum range at which ghosting is likely to be

observed and the separation between vessels and turbines (if a vessel

will not sail within A km of any turbine in a windfarm, and significant

ghosting due to reflections from the radar vessel structure can be

observed at a maximum range of B km, then a separation distance of

A+B should be maintained between the windfarm and any other

turbines, to ensure ghosting does not overlap any other development.

The value of B will depend on factors such as turbine RCS and the

shape, size and position of the vessel reflector). This topic is being

researched by NOREL, to determine the necessary windfarm separation

distances and navigation channel widths through individual windfarms.

1.6 SATURATION

The variation in received signal strength for any radar system can be huge.

This means that the dynamic range in radar’s receiver (which is the largest

measurable signal divided by the smallest) must be very large. The smallest

signal detectable by the radar receiver is defined by the noise that is inherent

in any electrical system. The minimum discernible signal (MDS) for a radar

system is set up to ensure that the probability of getting a false detection from

this noise is low enough that it is not detrimental to radar performance, yet

allowing maximum sensitivity in the receiver.

If signal levels exceed the dynamic range of the receiver, it can become

saturated, leading to a possible loss of sensitivity behind the saturating object.

This is depicted in Diagram 6which shows the radar beam intersecting the

saturating object and affecting the radar's sensitivity, or its ability to detect

objects. The sensitivity takes a defined amount of time to return to normal

levels, causing a blind zone behind the saturating object of up to 0.5NM in

some instances.

Diagram 6 Plan View (top) of the Radar Beam Intersecting the Saturating Object

(and how that affects the radar’s sensitivity to detect objects (bottom) causing a blind

zone behind the object)

The severity of any saturation impacts due to the East Anglia ONE windfarm

is not likely to be significantly different from that caused by large vessels

operating in the area. The 1.0NM separation between the windfarm boundary

and the traffic route partially mitigates any impacts. For vessels closer to the

wind turbines the impacts are likely to be the same as those caused by other

large structures, such as container vessels. The jacket foundation option is

likely to have a smaller reflectivity than other foundation choices, and so its

impact on saturation is likely to be less.

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5 S

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6 B

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2°50'0"E

2°50'0"E

2°40'0"E

2°40'0"E

2°30'0"E

2°30'0"E

2°20'0"E

2°20'0"E52

°20'0

"N

52°2

0'0"N

52°1

0'0"N

52°1

0'0"N

52°0

'0"N

52°0

'0"N

Ref:

Datum: WGS84Projection: UTM31N

Rev Date By CommentA 20/04/12 AG First Issue.

© East Anglia Offshore Wind Limited 2012Wind turbine data provided by Qiniteq

NA ALayout Dwg No.Date Rev

0 1 2 km

0 1 nm

Illustrative Layout A (172 7.0 MW Wind Turbines)

East Anglia Offshore Wind

Figure 1Volume 02Original A4

Plot Scale

2°50'0"E

2°50'0"E

2°40'0"E

2°40'0"E

2°30'0"E

2°30'0"E

2°20'0"E

2°20'0"E

52°2

0'0"N

52°2

0'0"N

52°1

0'0"N

52°1

0'0"N

52°0

'0"N

52°0

'0"N

Ref: Rev Date By CommentA 20/04/12 AG First Issue.

© East Anglia Offshore Wind Limited 2012Wind turbine data provided by Qiniteq


0 1 2 km

0 1 nm

Illustrative Layout B(325 3.6 MW Wind Turbines)



Plot Scale6115-500-PE-1346115-500-PE-13310/07/20121:250,000 1:250,000 10/07/2012

© ESRI


© ESRI

LegendEast Anglia ONE Windfarm SiteEast Anglia Zone

Vessel Radar Position

Target Vessel Position

Illustrative wind turbine positionIMU Shipping Lane

LegendEast Anglia ONE Windfarm SiteEast Anglia Zone


Target Vessel Position

Illustrative wind turbine positionIMU Shipping Lane

B 10/07/12 AG Figure change, amendments B 10/07/12 AG Figure change, amendments

2°40'0"E

2°40'0"E

2°30'0"E

2°30'0"E

2°20'0"E

2°20'0"E52

°20'0

"N

52°2

0'0"N

52°1

0'0"N

52°1

0'0"N

Ref:



Contains Ordnance Survey data © Crown Copyright and database right 2012.

© East Anglia Offshore Wind Limited 2012Radar data provided by Qinetiq


0 1 2 km

0 1 nm

Radar Display Simulation for Layout A (gravity base or suction caisson foundations)



Plot Scale

2°40'0"E

2°40'0"E

2°30'0"E

2°30'0"E

2°20'0"E

2°20'0"E

52°2

0'0"N

52°2

0'0"N

52°1

0'0"N

52°1

0'0"N



© East Anglia Offshore Wind Limited 2012Radar data provided by Qinetiq


0 1 2 km

0 1 nm

Radar Display Simulation for Layout A (jacket foundations)



Plot Scale6115-500-PE-1426115-500-PE-14110/07/20121:200,000 1:200,000 10/07/2012

© ESRI


© ESRI

LegendEast Anglia ONE windfarm siteEast Anglia Zone Turbine Radar EchoesVessel Radar Echoes10 km buffers


Vessel Starting Position

IMO Shipping Lane




IMO Shipping Lane


2°40'0"E

2°40'0"E

2°30'0"E

2°30'0"E

2°20'0"E

2°20'0"E52

°20'0

"N

52°2

0'0"N

52°1

0'0"N

52°1

0'0"N

Ref:




© East Anglia Offshore Wind Limited 2012Qinetiq


0 1 2 km

0 1 nm

Radar Display Simulation for Layout B (gravity base or suction caisson foundations)



Plot Scale

2°40'0"E

2°40'0"E

2°30'0"E

2°30'0"E

2°20'0"E

2°20'0"E

52°2

0'0"N

52°2

0'0"N

52°1

0'0"N

52°1

0'0"N



© East Anglia Offshore Wind Limited 2012Qinetiq


0 1 2 km

0 1 nm

Radar Display Simulation for Layout B (jacket foundations)



Plot Scale6115-500-PE-1446115-500-PE-14310/07/20121:200,000 1:200,000 10/07/2012

© ESRI


© ESRI




IMO Shipping Lane




IMO Shipping Lane


2°35'0"E

2°35'0"E

2°30'0"E

2°30'0"E

2°25'0"E

2°25'0"E52

°15'0

"N

52°1

5'0"N

52°1

0'0"N

52°1

0'0"N

Ref:



© East Anglia Offshore Wind Limited 2012Shadow Loss data provided by Qinetiq


0 1 km

0 0.5 nm

Zones where two-way shadow loss is 3dB or more for Layout A using jacket foundations



Plot Scale

2°35'0"E

2°35'0"E

2°30'0"E

2°30'0"E

2°25'0"E

2°25'0"E

52°1

5'0"N

52°1

5'0"N

52°1

0'0"N

52°1

0'0"N


© East Anglia Offshore Wind Limited 2012Shadow Loss data provided by Qinetiq


0 1 km

0 0.5 nm

Zones where two-way shadow loss is 3dB or more for Layout B using gravity base or suction caisson foundations



Plot Scale6115-500-PE-1466115-500-PE-14420/04/20121:70,000 1:70,000 20/04/2012

© ESRI


© ESRI

Proje

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Small vessel path

Proje

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Small vessel path

LegendEast Anglia ONE Windfarm SiteEast Anglia Zone Illustrative wind turbine positionsShadow Loss



IMO Shipping Lanes

LegendEast Anglia ONE Windfarm SiteEast Anglia Zone Illustrative wind turbine positionsShadow Loss



IMO Shipping Lanes


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East Anglia ONE Offshore Windfarm - Planning Inspectorate · East Anglia ONE Offshore Windfarm Environmental Statement ... vessels operate in the vicinity of the East Anglia ONE site