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1 INTRODUCTION
In the area of Ławica Słupska, several Offshore Wind
Farms OWF are planned to be built and they are to
cover an area of about 10 nautical miles wide and 50
nautical miles long. The mainstream of ship’s traffic
through the shoal leads in the W-E direction to the
south of the planned investments, but there will also be
designated passages in the N-S direction between
individual OWF. Activities related to safety at sea are
corrected by the Maritime Office, but they are agreed
with the Navy and Border Guard, as well as with the
sea rescue service. The requirements of these
institutions will change as the period considered is 30
years or more.
The issue of the impact of OWF on the safety of
navigation should be considered in two aspects.
Shipping near OWF and inside the wind farm. Each of
these issues should be related to three stages:
− power plant construction,
− operation and exploitation,
− demolition.
During the construction phase, the offshore wind
farm area is closed to navigation and the investor is to
secure this area. Inside, there are ships servicing
investments, and in exceptional cases, the navy, SAR
ships. Wind turbines are being built larger and larger
and their blades reach a height of over 250 m and
observation should be carried out to at least this height.
The construction phase, which will last until
approximately 2030. Then the current National
Maritime Safety System will be technically obsolete.
Until then, broadband Internet will probably be
operational in the coastal zone at sea. This will result in
a significant increase in the support of the ship by land
services in the field of safe ship operation, unmanned
ships supervised from the shore will appear, and the
traffic of recreational vessels may also increase.
Merchant ship traffic, if it increases, is not much. A
rapid development of fisheries should not be expected,
if it comes to the example of Norway, i.e., fish farming
at sea. The traffic of the ships servicing investments at
sea will increase, their cruise routes will cross shipping
routes.
The Impact of the Offshore Wind Farm on Radar
Navigation
T. Stupak & P. Wilczyński
Gdynia Maritime University, Gdynia, Poland
ABSTRACT: Offshore wind farms can improve safety at sea because they are clearly visible landmarks at sea.
Although they limit the sea area available to sailors and ships, they will increase the scope of observation of the
sea traffic from land, constitute additional landmarks and, thanks to the installation of additional devices in their
waters, expand the area of communication between ships and land services, and increase the scope of information
on sea traffic available to the services. They also practically do not limit the possibility of observation through the
farm's reservoir.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 16
Number 4
December 2022
DOI: 10.12716/1001.16.04.06
648
One OWF is up to two hundred wind turbines. The
distance between them is several hundred meters to
over a kilometre. The wind turbine is a foundation
slightly protruding above the water, a concrete pillar
with a diameter of several meters and a height of over
100 m. On it there is a generator the size of a large
single-family house (10 m x 30 m) and propellers with
a length of up to 100 m each. One wind turbine covers
an area of several dozen hectares. During construction,
ships must deliver a huge number of materials,
specialized ships will operate on site. Cables should be
laid between the wind turbines and the control center
(one or more), the main power cable to the shore.
In a few years, after the construction of part of the
OWF, the construction will continue at the same time
and the transmission of electricity to land will begin.
After the construction of the investment is completed,
there will be an exploitation phase lasting 20-30 years,
if in the meantime we do not withdraw energy
production from this source in favour of another
technology, e.g., hydrogen energy.
The last stage is the demolition of the OWF and the
reclamation of the reservoir. It is difficult to predict
anything about this, because by then the farms
currently in operation will be decommissioned and the
technologies and regulations regulating this process
will be developed. It will resemble the construction
phase. It will be necessary to use heavy equipment and
specialized ships equipped with cranes, as well as
ships transporting rubble and other materials to shore.
It is highly probable that the construction and
demolition phases will be costly, and much attention
will have to be paid to protecting the marine
environment. Currently, cables and pipelines are
usually left behind after the end of the operation. They
will have to be removed, because by then there will be
a lot of them, and ecologists are setting their growing
demands. Therefore, in the design phase, the length of
power cables should be reduced as far as possible, so
that there is less to clean up at the end.
When laying the cables, a 12 or 24 core optical fibre
should also be laid, because the farm area is to be
monitored, the generators are remotely controlled, the
power plant is to be marked, illuminated, monitored,
the movement of units outside the farm is to be
observed and supervised and all these data must be
sent to farm control center and onshore to the National
Maritime Safety System center in Ustka for other
services. During the operation of the OWF, there may
be a need to install new devices, so it is better to ensure
remote control and data transmission between the
power plants and the control center at the initial stage.
The fibre optic network is to ensure data exchange,
observation, and control of individual generators.
2 CHARACTERISTICS OF THE RESEARCH AREA
OWF must be marked from the beginning, marked on
nautical charts, and the ships are to be kept informed
about the ongoing works. The National Maritime
Safety System monitors the movement of ships in the
Polish Economic Zone. One of the centres is located in
the port of Ustka.
It can transmit local navigational warnings about
the OWF using the AIS or live messages via VHF
radiotelephone, if justified.
2.1 Navigational markings of OWF
The requirements of the Maritime Administration will
be presented for the OFW markings. At the initial
stage, the investment area is to be marked with
navigation lights placed on buoys to indicate the
boundaries and vertices of the investment. The buoys
can be easily moved when the work area increases. In
addition, the Maritime Office in Gdynia may require
the marking of the water area with RACONs to identify
navigational marks on the radar. They will be placed
on the same buoys. The area is also to be marked with
AIS devices.
Information on sea charts is provided by the
Hydrographic Office of the Polish Navy. It also
transmits navigational information to other countries.
The investor is to provide data on constructions
constituting obstacles to navigation. During the
construction phase, wind turbine structures must be
built, generators installed and power cables between
the generators and the switchgear, fibre optic cables
from the generators to the control center and the main
power cable and fibre optic cable from the farm to the
shore networks.
2.2 OWF’s monitoring
Currently, one transmitting device is used for this
purpose, which can generate several AtoN characters
for, for example, marking the control center as real and
the extreme vertices as virtual characters. The real
AtoN sign transmits the real-time determined position
of the mark on which it has been mounted. The virtual
mark data is sent from elsewhere and its current
position can be monitored by another system (GPS), or
the mark position can be sent regardless of its current
position, or the beacon itself can be taken down.
OWF also requires remote monitoring, so CCTV
will be installed there. Monitoring around all
investments should be carried out comprehensively. If
all planned investments are implemented in Ławica
Słupska, there is no justification for installing radars,
AIS devices, radiotelephones, hydro-meteorological
stations separately for the Maritime Office, Border
Guard and Navy on each OWF.
The radars working at KSBM are Terma 2001i, a
very reliable and high-class device, the Border Guard
had older Terma 2000 devices in stock, also very good
and proven at VTS Zatoka Gdańska, which were
replaced with the 2001i model. Their price is
proportional to the technical parameters. Currently, it
is planned to replace them with an even newer model.
The works inside the OWF take place in a closed
area and can be organized efficiently and without
collisions, while the laying of cables ashore will at some
stage cross the TSS, and then it is especially important
to ensure current information for ships navigating
there. In addition to the warnings provided by the
shore services, the assistance of the supervising vessel
is required, which informs the vessels approaching the
place of laying the cable on an ongoing basis about the
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activities carried out and, if necessary, intervenes,
forcing the vessel to change course.
Vessels employed for the construction and
operation of the OWF should be equipped with AIS
devices. This device informs about the presence of
other units and facilitates establishing communication
with them. The OWF area is marked with traditional
navigation marks. Once the constructions of the
offshore wind turbines are built, they are properly
painted and illuminated (red flashing light), which
ensures their very good visibility.
On the radar, OWFs are shown from distances
exceeding 20 nautical miles as polygons consisting of
many point echoes. Problems with the radar
observation occur during heavy precipitation when the
detection range decreases drastically.
Surveillance inside the OWF is carried out by the
owner and includes supervision of the works carried
out there and protection against unauthorized
intrusion, and the tracking of vessels passing in its
vicinity. For this purpose, remotely controlled optical
cameras are used, which will provide much more
information than radar. In addition, there may be
infrared cameras that enable observations also in
limited visibility.
The range of the camera is related, so you need to
choose the right compromise. The cameras are
remotely controlled from the farm control center. The
image from the cameras can be made available to land
services. During the SAR operation, the image of the
cameras can be very helpful for the rescue services. The
procedure to be followed in different scenarios should
be agreed with the relevant institutions. The use of
radar to observe the situation inside the OWF does not
seem advisable. Currently, land services use Danish
Terma radars (type 2000i).
The radar allows to track vessels at sea and
automatically determine their movement parameters
and detect the risk of collision with the OWF elements
early. Therefore, they should be used to control traffic
near OWF. In relation to small vessels that manoeuvre
quickly, this device does not work. But the collision of
a yacht or a motorboat with the structure of the
offshore wind turbines will not cause damage to the
power plant and pollution of the sea. OWF, similarly to
the Baltic Beta & Petrobaltic platforms, can be a station
for the installation of the devices of the Maritime
Office, Border Guard or Navy to extend the traffic
monitoring area along the Polish coast and/or in the
Polish Economic Zone.
The scope of the activities should be agreed
between the institutions concerned. The fibre optic
network built by the investor enables the transmission
of data and images and connecting it to the fibre optic
bus along the coast, which is at the disposal of the
maritime administration.
The AIS base station will increase the range of
marine traffic monitoring around the OWF. The cost of
the AIS base station is low and will significantly
increase the range of the system. Installing one or two
stations (north and south sides, or tops) for each farm
is expedient.
The OWFs are located mainly close to Ławica
Słupska, north of the TSS traffic separation zone. Table
1 shows their distances from important points.
Each of the discussed OWFs occupies an area of
several dozen square kilometres. One radar installed at
a height of 20-30 meters can cover the entire area, but
the construction of wind turbine will create radar
shadow sectors, which may result in missing small
targets. Therefore, the concept of installing two devices
should be applied, one on the southern side of the OWF
to improve the observation of traffic on the TSS and the
other on the northern side of the OWF to increase the
radar monitoring area in Polish Economic Zone.
Table 1 – Distances of the selected facilities from OWF
(Baltic II & Baltic III)
________________________________________________
Objects BS II [Nm] BS III [Nm]
________________________________________________
1 Wymiar WE 6,00 9,60
2 Wymiar NS 7,20 5,00
3 Lane NE 13,50 1,10
4 Lane SE 16,00 5,50
5 Lane NW 7,00 11,60
6 Lane SW 11,40 13,00
7 Lth. Czołpino 19,20 – 27,50 13,30 – 19,50
8 Lth.Łeba 25,00 – 33,50 12,500 – 19,5
9 Lth. Ustka 26,00 – 32,60 26,00 – 34,00
________________________________________________
2.3 Presentation of OWF on the navigation devices
Currently, electronic chart and navigational
information systems - ECDIS (Electronic Chart Display
and Information System) or integrated systems INS or
IBS are commonly installed on ships. They allow the
presentation of multiple data on the indicator or
different sets of data on different screens. OWF areas
are very well marked on navigation charts, but excess
data on one screen is a bad idea. Some examples are
shown below.
Figure 1. OWF on ECDIS screen
Figures 1 shows an image of an electronic map with
two wind farms located in German waters on the
Pomeranian Bay. The position of each wind turbine
and the routing of the submarine cables are marked.
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Figure 2 shows the image on the screen of the
ECDIS.A radar image overlay (the echoes marked by
red) and data from the AIS system (the ship is marked
with an isosceles triangle) have been applied to the
nautical chart background. The distance of the ship on
which the photo was taken from the farm exceeds 3
nautical miles. The image of the echoes is clear, and it
is easy to identify which echo comes from which object.
Figure 2. OWF on ECDIS screen with AIS
The range of 24 nautical miles of the radar operation
corresponds approximately to the chart scale of
1:200,000. Figure 3 shows the image of the same farm
as in Figure 2, but the SAM Electronic integrated bridge
indicator shows the night image. It is illegible, due to
the wrong colour palette, the radar image is lost. The
radar echoes are red, but the black background and the
excess of white symbols make this image unusable.
Figure 3. OWF on ECDIS screen with night mode, range 24
nautical miles
Figure 4 shows the image after correcting the color
palette. The radar echoes of OWF are easy to recognize,
but the echoes of small objects such as a fishing boat or
a yacht remain invisible in the radar image
superimposed on the map background.
Figure 5 shows the same image as before, but with
a working range of 12 nautical miles. The number of
symbols shown has been reduced, making the image
more usable. There is a radar echo to the south of the
home ship and an AIS symbol delayed to it. It is likely
that the ship is moving at a slow speed and the AIS data
is transmitted less frequently. (A small boat with a class
B AIS device transmits every 30 seconds). Many
soundings are displayed on the screen, which makes
the radar image very poorly visible.
Figure 4. OWF on ECDIS screen with night mode
Figure 5. OWF on ECDIS screen with night mode, range 12
nautical miles.
Figure 6. OWF on radar’s screen
Figure 6 shows the same situation as in Figure 3 - 5,
but only the radar image is presented on the indicator
on the integrated bridge and the planned route of the
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ship has been marked. The presented AIS symbols are
also shown. The echoes of two OWFs are shown in the
upper right of the screen. The adjustment of the image
on the screen and the appropriate selection of the
amount of information presented on the screen are
very important.
Figure 7 shows an image of OWF along with the
routes of the submarine cables. AIS symbols are also
shown.
Figure 7. OWFs with power cables connections on ECDIS
screen
On Figure 8, in the upper right corner, other wind
farms operating in this area are shown along with the
ranges of the lights working on the farms. On the same
Figure 8 several ships equipped with AIS devices
operate inside the construction site. Trade ships can
pass between two buildings. Probably in the future, the
entire area may be occupied by one large OWF. The
OWF is marked with buoys and AIS signs.
Figure 8. OWF under construction
Figure 9 shows the information about the OWF that
we will get on the screen of the electronic chart of the
ECDIS system. The name of the OWF, position and
designation of the offshore wind turbine, its type and
light characteristics are given.
In Figure 10, available information on the ECDIS
screen, concerning the marked OWF using the real sign
of the Automatic Identification System. Typically, the
real AIS sign is installed at the farm headquarters (it
broadcasts its position determined by means of a GPS
receiver). The same device can send data about virtual
characters pointing to farm vertices.
Figure 9. Offshore wind turbine information
Figure 10. Real AIS AtoN information
Figure 11. OWF with N cardinal buoy
Figure 11 shows the marking of the northern edge
of the OWF with a cardinal buoy.
Figure 12. OWF on the German Bight
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Figure 13. OWF on the German Bight
Figures 12 and 13 show the OWF located on the
German Bight, all pictures were made by the authors
on board ship Dar Młodzieży in 2021 during onboard
training.
3 RESEARCH STUDIES
The computer program CARPET 2.0 (Computer Aided
Radar Performance Evaluation Tool), developed by
TNO Physics and Electronics Laboratory, was used to
carry out the simulations. CARPET 2.0 is an extensive
computer program that allows to simulate the
propagation conditions in which marine radar, and
land devices are used, as well as those installed on e.g.,
airplanes or helicopters, and define the objects they
detect.
The purpose of the simulations is to assess the
possibility of detecting an offshore wind farm by ship
radar depending on the parameters of the radar
antenna, weather conditions as well as the dimensions
of the wind turbines. Table 2 presents typical
parameters of the ship radar used for simulations.
Table 2. Raytheon NSC34 pulse radar parameters
________________________________________________
Parameter Value Units
________________________________________________
Radar band X [-]
The horizontal width of the characteristic 1,2 [°]
The vertical width of the characteristic 23 [°]
Gain 29 [db]
Polarization horizontal [-]
Frequency 9410 [MHz]
Pulse length 1,00 [µs]
Pulse frequency 3000 [Hz]
Bandwidth 20 [MHz]
Peak power 25 [kW]
________________________________________________
The radar installed to monitor traffic around
offshore wind farms is to be remotely controlled and
provide relevant data compatible with the system.
They are standard because the ship's radar image is
transmitted to the electronic charting and navigational
information system ECDIS from various
manufacturers. However, some manufacturers make
exceptions. A composite signal can be used (trigger
pulses, analogy, digital, trigger video signals in one
package) and an interface that will separate them must
be attached. Signals are transmitted between
navigation devices using the NMEA standard. The
signals are to comply with the IEC 61162-1 standard. It
was also issued by the Polish Committee for
Standardization - Table 2. The signals are sent via the
RS-232c serial link.
This standard allows for free presentation of the
data from various devices on any indicators. However,
it should be remembered that new versions of this
standard are created, but each subsequent version
removes all older ones, but older versions may not
work with newer ones. That is, the new radar will
receive data from the older GPS receiver, but the older
radar will not receive the position from the new GPS
receiver.
Table 3. Detailed list of the formatters using in navigational
equipment [1]
________________________________________________
Formater Explanation
________________________________________________
ALM Data from the GPS almanac
DPT Depth
GLL Geographical position, lat/long geographical
HDG Ship heading, deviation, and magnetic variation
HDT True Course
HTD Direction/route control data
MWD Direction & speed of the wind
MWV Speed & angle of the wind
OSD Own Ship Data
ROT Course Change Speed
RSD Radar System Data
RTE Routes
TLL The latitude and longitude of the object
TTM Message about the tracked object
VBW speed through the water & over ground
VDR Direction & speed of the current
VHW Speed & course of ship through the water
VLW Distance made good through the water
VTG Course & speed over the ground
WCV Waypoint approach speed
WNC Distance from waypoint to waypoint
WPL Waypoint location
XTE Cross track error
XTR Cross track error, navigation reckoning
ZDA Hour and date
ZDL Time and distance to the moving point
ZFO UTC and time from the starting waypoint
ZTG UTC and time to destination waypoint
________________________________________________
Table 4. Detailed list of the RSD Radar System Data –
example [1]
________________________________________________
$ - - RSD - Radar System Data
________________________________________________
x.x the distance of the starting point
x.x Bearing of the starting point
x.x VRM 2, distance
x.x EBL 2 degree
x.x Cursor distance from own ship
x.x Cursor bearing degrees clockwise from 0°
x.x Distance scale used
a Distance units K= kilometre, N = nautical miles,
S = land miles
a*hh Image rotation:
<CR> <LF> C- oriented relative to true course, course
relative to the ground, degrees
N - oriented to the north, north is true 0°
H - oriented relative to the bow, the direction
(Centre line) of the vessel 0°
________________________________________________
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4 SIMULATION DATA PROCESSING
The results of the simulation are presented in the form
of graphs of the signals received from objects and
disturbances, the probability of the detection as a
function of the distance from the object. The probability
shows how many times the echo is on the screen, e.g.,
80% means that the echo is shown in 4 times by 5 turns
of the antenna.
The graph showing the signals received by the
radar antenna shows:
− thermal noise in blue,
− useful signal in green,
− signal scattered by the surface of the sea in red,
− purple signal reflected by precipitation.
The computer program used for the simulations
defines the effective reflecting surface RCS (Radar
Cross Section) as the amplification of the radar signal
corresponding to the real value of the reflecting object
placed in the center of gravity of the tested object. The
useful detection range of an object is defined as the
probability of the detecting an object and for marine
radars, the probability of correct detection is assumed
to be 0,995 and the probability of a false alarm of 10-6,
which corresponds to a signal to noise ratio of 20.
In the simulations carried out, an exemplary
offshore wind farm was used, the effective reflection
surface of which is 350,0 m2. The assumed reflection
surface of the power wind turbine is quite small, so the
given values of the detection distance may be larger. In
all simulations, there is rainfall over 5 - 15,00 km
(approx. 2,70 to 8,00 nautical miles).
Because the watch officer most often conducts
observations in the range of 12,00 nautical miles, it was
assumed in the simulations that the radar transmitter
works on a long pulse.
Figure 14. The detection signals of the ship by shore radar in
Darłowo
Figure 14 shows a signal for a ship whose effective
reflection area is estimated at 300,0 m
2
and its height is
11,00 m. The level of the signal reflected from the ship
exceeds the level of the signal reflected from the sea
surface by more than 20 dB. The simulation was carried
out for sea state 7, i.e., high disturbance. A similar level
of disruption is also caused by rainfall.
Figure 15 shows the probability of the detecting a
fishing boat using the radar of the KSBM system in
Darłowo for sea state 2. Detection with a probability of
80% is achieved at 13,40 nautical miles, but for smaller
distances the object disappears from the screen.
The signal disappears at 5,00 to 7,00 miles from the
radar and about 3,00 nautical miles, and short duration
dips occur above 1,00 nautical miles. Despite the large
detection range of a small object, it is difficult to track
it, while the weather conditions are not bad.
Figure 15. The probability of detecting a fishing boat by shore
radar
The diagrams below (Figures 16 – 23) show the
possibility of observing offshore wind farms with the
use of a ship's radar. Its detection capabilities are lower
than those of the shore radars. The study was
conducted for three different situations, which are as
follows:
− height of the center of the surface 50,00 m, height of
the radar antenna 12,00 m, precipitation 4 mm/h,
− height of the center of the surface 75,00 m, height of
the radar antenna 20,00 m, precipitation 4 mm/h,
− height of the center of the surface 50,00 m, height of
the radar antenna 12,00 m, precipitation 20 mm/h.
A radar antenna height of 12,00 m corresponds to
the conditions on a small vessel and 20,00 m on a
medium-sized vessel. The higher-mounted antenna
allows you to increase the detection range. A rainfall of
4 mm/h is a light rain, and 20 mm/h is a heavy rain.
Figure 16. The probability of detecting an offshore wind
turbine for the center of the reflection surface at a height of
50,00 m and the height of the radar antenna 12,00 m above
sea level, sea state 1
Figure 16 above shows the distribution of the
probability of the detecting an offshore wind turbine
recorded on a small vessel (e.g., a fishing boat) when
the radar antenna is 12,00 m above sea level. For the
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calculations of the signal reflected from the offshore
wind power plant, shown in Figure 16, the
precipitation zone occurring at 5 to 15 km from the ship
was assumed.
In this zone, the offshore wind farm's reflected
radar signal is weakened. In the presented example, it
is not important for observing the offshore wind
turbine echo on the radar screen. Up to 3,00 nautical
miles from the radar antenna, the power plant gives a
very good signal, then fluctuations occur causing
signal decay caused by interference of the direct signal
with the reflected one from the sea surface. The signal
disappears at about 18,00 nautical miles, which is over
33,0 km.
Figure 17. The probability of the detecting an offshore wind
turbine, state of the sea 3
A deterioration in detectability can be seen in an
area where there is rainfall. It can be assumed that the
probability of detecting a wind farm during
precipitation, but the maximum detection range is
large and amounts to about 18,00 nautical miles. If the
ship is closer than 800,00 m from the offshore wind
turbine, the antenna illuminates only part of the
structure.
Figure 18. The probability of detecting an offshore wind
turbine, state of the sea 7
The probability shown in Figure 18 is for the same
offshore wind turbine seen in the previous two cases,
but this time at a high sea level of 7. During such a high
sea level and rainfall, the radar detects the power plant
much weaker. Already at less than 3,00 nautical miles
from the radar antenna, interference caused by sea
waves reduces the probability of the detecting an
offshore wind turbine to less than 80%. Outside the
fallout zone, the object is clearly visible up to about
17,00 nautical miles, although at about 12,00 nautical
miles, the echo signal weakens.
Figure 19 shows the probability of the detecting an
offshore wind turbine 50% taller and observed from a
larger ship whose radar antenna is placed at a height of
20,00 m. At 1,60 nautical miles, a slight decrease in the
probability of the detection to about 90% can be
observed. Fluctuations caused by rainfall are small at
the beginning and up to about 3,50 nautical miles the
probability of detection remains above 80%. Further in
the fallout zone, frequent power plant echo signal
disappearances occur. A several-fold decrease in
detection at distances from the radar of approx. 12 - 19
nautical miles can be seen outside the precipitation
area.
Figure 19. The probability of the detecting an offshore wind
turbine for the center of the reflection surface at a height of
75,00 m and the height of the radar antenna 20,00 m above
sea level, sea state 1
Increasing the height of the offshore wind turbine
by 50% slightly increased the maximum observation
range estimated at 90% probability of detection.
(increase by about 0,40 nautical miles), while in the
precipitation zone the probability is lower by about
10% than in the previous scenario. For the same
simulations during a higher sea state 3, the same
practical results as shown in Figure 6 are achieved.
Figure 20. The probability of detecting an offshore wind
turbine, state of the sea 7
Figure 20 shows the distribution of the probability
of the detecting the offshore wind turbine during
precipitation and high sea level. Compared to Figure 5,
the turbine observation conditions deteriorated. The
reason is mainly the increase in the height of the radar
antenna on the ship, which resulted in a greater level
of signal reflected from sea waves.
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From the smallest distance from the antenna, we
observe a rapid decrease in the probability of detecting
a wind farm and already at 1,00 nautical miles, the
probability of the detection drops to 80%. Due to
precipitation, the chance of detecting a windmill drops
from 55% at approx. 2,70 nautical miles to nearly 25%
at the final border of the area where it is raining (8,00
nautical miles). Further, the probability of the detection
remains above 80%, except for two deep drops at 16,00
and 19,00 nautical miles. The signal disappears again
around 25,00 nautical miles, which means that with a
long pulse, both the state of the sea and atmospheric
precipitation do not have a significant impact on the
maximum detection range, but the occurrence of both
phenomena at the same time complicates the radar
observation.
Figure 21. The probability of the detecting an offshore wind
turbine during heavy rainfall, sea state 1
Figure 21 shows the probability of the detecting a
offshore wind farm during heavy rainfall, which
occurs at a distance from the radar antenna of 5,00 to
15,00 km. Heavy rainfall makes it virtually impossible
to observe the offshore wind farm in the rainfall zone.
The detectability up to 2,70 nautical miles is at 100%,
after which it drops drastically below 20%. Outside the
rainfall zone, the offshore wind farm is quite well
detected, up to 20,00 nautical miles, although due to
the large drop above 15,00 nautical miles, the
probability of the detecting it is at the level of 50%. The
level of the detection outside the heavy precipitation
zone is lower than when the precipitation was lighter.
If the state of the sea increases slightly, the
distribution of the probability of the detection will
practically change very little.
Figure 22. The probability of the detecting an offshore wind
turbine, state of the sea 7
In the graph above, Figure 22, the probability of the
detecting the offshore wind turbine during a storm and
heavy rainfall is practically impossible. It will be even
worse on a large ship. If there is no heavy rainfall, the
offshore wind farm is visible on the radar screen very
well. because more and more wind turbines are being
built, they are better visible from a slightly greater
distance. The new radars are equipped with software
that analyses radar signals and can reduce the impact
of hydro-meteorological disturbances, thanks to which
ships and marine structures can be tracked in any or
almost any conditions.
Figure 23. The probability of detecting an offshore wind
turbine by the S band radar
Two radars are to be installed on the ships of more
than 3 000 gross tonnage. If one of them works in the S-
band, the detection range of the offshore wind farm
will be greater (26,00 nautical miles) and the signal will
be less disturbed by the precipitation and waves. This
is shown in Figure 23.
5 SUMMARY
An offshore wind farm is an investment of very large
dimensions, which is clearly visible visually and
detected by ships’ radar even from very long distances,
thanks to which it can be treated as a navigational aid.
Note, however, that it may also generate false echoes
or mask other objects, obstacles, or navigational
markings. Restrictions on the visibility of the
navigation marks, including RACON, around wind
farms should be considered.
The OWF has a significant impact on the ship's
radar systems. It creates new problems related to the
regulation and interpretation of the radar image.
Similar problems occur on the radar regardless of the
band in which it works. This is due to the high
construction height of the wind generator turbines and
the metal structure, which makes the effective
reflection area large. It causes multiple and sidelobe
indirect echoes, but also generates shadow sectors. As
a result, it is difficult to detect other units operating
around the farm, but also behind it. Navigating around
the farm requires a different adjustment of the radar
image, which may result in other units not being
detected. Detection of the signals from units operating
in the farm area is not always possible. Tracking units
by ARPA also poses problems if they are in the vicinity
of the wind turbine structure. Also, reducing the gain
656
of the radar signal may result in the loss of
navigationally important echoes by ARPA.
Due to the many echoes present on the radar screen,
there may be interference with the tracking of ship
echoes, the same as in other areas where there are many
echoes. In this case, if two echoes pass close, ARPA
may swap the echoes or get lost from tracking. Auto-
acquisition should not be used in this area as indirect
echoes will be introduced into the trace, which will
then be lost and a lot of operators distracting alarms
will be generated.
The farm is detected by ship radar from more than
12,00 miles away. At short distances from the farm (less
than 1,00 nautical miles), ship’s X-band radar is more
useful than S-band radar due to higher antenna
parameters. Large ships passing near the offshore wind
farm are observed on the radar without problems with
detecting their signals. Due to the large dimensions
and good reflecting properties, the echo coming from
the offshore wind turbine has larger dimensions than it
results from its dimensions and radar properties. At
distances below 6 nautical miles from the farm, the
possibility of the false reflections from the farm objects
should be expected.
If the radar antenna is much higher on a larger
vessel, the detection range is slightly greater than on a
smaller vessel. On the other hand, heavy precipitation
reduces the detection range significantly even by 20%.
Intense precipitation can completely prevent radar
observation, but also optical. The AIS (Automatic
Identification System) is less sensitive in these
conditions because it uses ultra-short waves.
In conclusion, offshore wind farms, like all other
constructions in the open sea, are a danger to
navigation. Due to the fact that they are usually placed
in the coastal areas, they can additionally obscure other
objects important for the sea navigation, such as
lighthouses. Their presence affects the availability of
the space when approaching ports, although shipping
routes are usually marked out in their vicinity. These
structures are very well marked, visible from a distance
both during the day and at night. Unfortunately, visual
observation and attempts to determine the position
using optical bearing may be unsuccessful due to
problems with identifying individual offshore wind
turbine in the farm.
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