301
1 INTRODUCTION
At the beginning of the 21
st
century a major shift
occurred in the field of naval navigation. The
navigatorwasnowinpossessionofdatapertainingto
ships in their vicinity which was previously
unavailable. Utilizing the Automatic Identification
Systemshipstransmittheirname,size,etc.aswellas
current navigational readings. This opens new
possibilities
of situation assessment and allows for
direct radio communications. One can obtain more
precisedataaboutothervesselsthantheonegivenby
anon‐boardradar,but,atthesametime,theycanbe
blocked or incorrect. As a result of that, the
comparativeresearchofresultprecisionbetweenship
radar and the Automatic Identification System was
undertaken. It was conducted within Gdańsk Bay
using radars installed in AM laboratories and on‐
boardcommercialvessels.
2 TRACKINGPRECISIONREQUIREMENTS
On the 6th of December 2004 the Maritime Safety
Committee adopted a new resolution entitled
Adoption of the Revised Performance
Standards for
Radar Equipment[2, which pertains to the radar
equipmentinstalledon‐boardseavessels starting on
1stJuly2008.Thisdocumentstatestherequirements
for radar tracking devices and the precision with
which object parameters must be presented during
acquisition and tracking. The International
Electrotechnical Union presented a norm which
preciselystatesinwhatwaythisequipmentmustbe
tested. It is the IEC 60872‐1 norm: Maritime
navigationandradio‐communicationequipmentand
systems–Part1:Shipborneradar‐AutomaticRadar
PlottingAids‐Performancerequirements.Methodsof
testingandrequiredtestresults[1].
Automatictracking is basedonthe relative
radar
echo position measurement and inner vessel
movement parameters. Other available sources of
informationmaybeusedasasupportintheprocess
ofautomatictracking.Echoesclearlyvisiblefor5out
of 10 concurrent cycles of antenna rotation, or a
period equal to that, should be tracked. For vessels
travelling
with real speeds up to 30 knots, the
tracking device should give results with error
marginsnotgreaterthanthosegivenintable1(with
95%probability):
The Assessment of Drafting Ship Movement
Parameters Using Radar and the Automatic
Identification System
T.Stupak
GdyniaMaritimeUniversity,Gdynia,Poland
M.Wąż
PolishNavalAcademy,Gdynia,Poland
ABSTRACT:ThisarticlepresentsthemovementvectorresearchconductedintheradarlaboratoryofGdynia
MaritimeUniversityandduringvesselcruises.Theprecisionofdesignatingthevesselsʹlocation,course,speed
andCPAwereresearchedusingon‐baordradarsandAISdata.Itisconcludedthatthe
precisionofdesignating
theresearchedparametersisgreaterthantheInternationalMaritimeOrganizationrequires.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 12
Number 2
June 2018
DOI:10.12716/1001.12.02.10
302
Table1.Trackingdeviceprecision(for95%probability)[2]
__________________________________________________________________________________________________
TimeofsetRelative Relative Closestpoint Timeofclosest Real Real
trackingprocess course speedofapproach pointofapproach course speed
Minutes
Degrees KnotsNauticalmile MinutesDegrees Knots
__________________________________________________________________________________________________
1
111.5or10%
1
 1.0‐‐‐
330.8or1%
1
 0.30.550.5or1%
1
__________________________________________________________________________________________________
relative movement tendencies of the echo in one
minutetrackingintervals,
movementparametersoftheechointhreeminute
trackingintervals.
The trackingprocess isset whenown vesseland
the tracked object do not manoeuvre and the
precisionsareasfollows:
radarmeasurementsare
within2oand50mor+/‐
1% observational range (bigger margin of error
decides),
the information about movement parameters is
lesssufficientthanthatrecommended by IMOin
resolutions.
Device testing leading to vessel installation is
performed on a simulator, which allows the
introductionofechoeswiththerequiredparameters.
Those parameters are kept with precision, so the
objectmovementconditionsarestableandunchanged
instableenvironmentalconditions
3 VESSELMOVEMENTVECTORTESTINGIN
GDAŃSKBAY
Systematic surveillance of vessel movement in
Gdańsk Bay isperformed usingequipment installed
in the radar laboratory. Data given by the
radars is
compared with data given by the Automatic
Identification System, through which vessels send
current navigational parameters obtained from their
equipment.Inaddition,vesselsmovewithinGdańsk
Bay on designated waterways and thus their real
courses are known. Measurement conditions are
better than on open sea because the ships
ʹ own
movementdoesnotplayarole.
TheAutomaticIdentificationSystemdeliversdata
from ship equipment, and allows for source
information gathering, the same information the
shipʹsofficer obtains.Thisisthebestsource of data,
howevernotalways.WecanswitchtheAISoffwhen
it endangers our
safety. It being deactivated means
thevesselisnolongervisiblewithinthesystem.We
obtain one‐time data from a given device (GPS
receiver,gyrocompass)inregularintervalsdependent
ontheshipʹsspeed.However,theradiotransmission
isnotalwaysreceivedandouractionscancausethe
data sent
to be invalid. That is why the main
information source for manoeuvre planning is the
radar.In the AISsystem theposition ofthe receiver
antenna is transmitted, while the echo is created
where themicrowave signal is reflected (thehull or
otherelementsofthevesselsconstruction)andsuch
a
signalisprolongedwiththeradarstransmittedsignal
and widened by the radar antenna radiation angle.
That is why the shift between both positions will
occur.Duetothefactthatthedataiscalculatedfrom
subsequentpositions,differencesinotherparameters
willoccur,thatisthecourseofthe
trackedvessel,its
CPA and TCPA speed. Measurements are recorded
everyminute.Everyvesselisusuallysurveilledfora
periodofseveralminutestoonehour.[3]
Radars with the X Raytheon Mk2 i NSC34, and
Decca AC 1659 spectrums were used in the
laboratory. Both Raytheon radars worked with one
transmitter,butthesamesignalwhichcanbeseenon
the diagram, was calculated differently due to
differentsoftware.
On Gdańsk Bay about 100 vessel cruises were
recorded. The radar measures the distance and
direction of the echo. The CPA, the time it has
achieved,aswellasthecourse
andspeedofthevessel
arecalculatedbasedonthefollowingmeasurements.
Distancemeasurementsinthe10Nmrangeare95%
probable to within a circle of 0.03 Nm in diameter.
The distances between radar echo position and that
obtained through AIS are within a 0.03 to 0.06 Nm
range.
Thevaluesarewithinthewidthrangeof0.5o
(from0.2oto0.7o).Devicesfromdifferentproducers
calculatethoseparametersdifferently.TheARPAby
Raytheon always showsa greater distance than that
showedonECDIS300byTransas,mostoftenby0,04
Mm.
The AIS sends temporary values of the course,
whichwereearlierobtainedfromthememorybuffer
of the device. The tracking system in the radar
calculatesitonthebasisofconcurrentmeasurements
of distance and direction. The course presented by
different devices can differ up to a couple degrees.
The lowest fluctuations can be found in the
AIS
systems.ThehighestintheDecca systems,andabit
lower in Raytheon. This is the result of different
trackingalgorithms.[5]
For radar surveillance performance it is essential
todesignateacourseandspeedofanothervesseland
the closest point of approach and time of its
achievement. The distance
and direction
measurementdependsontheradarʹsprecisionandin
practice, due to the fact that tracked vessels give a
strongreflectedsignal,thesemeasurementsaremore
precisethanthenormsrequire.Therestofthedatais
averaged fromconcurrent measurements and
depending on thealgorithms assumed, the
calculationsmaygivedifferentresults.Dataobtained
from different devices differs form one another. At
sea the vessel is always under the influence of
different ever‐changing forces, thatʹs why its speed
and course is constantly but ever‐slightly changing.
The radar signal is also changing due to condition
changes
and the changes of surface calculations of
trackedobjects.Thismeansthattheconcurrentradar
signalsilluminatedifferentpartsofthevesselandas
suchtheparametersobtaineddiffer.[4]
303
The CPA calculations performed based on data
receivedfromtheAISshowalmostdoubletheerrors
than when calculated using ARPA equipment. It is
the result of the fact that ARPA averages data of
constantsurveillanceandAISarediscreetvalues.The
average CPA errors calculated by the radar were
below 0.1 Nm, and those from the AIS were on the
level of 0.15Nm. All results were within the norms,
whichstatetheprecisionmustbeunder0.3Nm.Time
forTCPAwasnotcalculated.
As an example. the course (pic. 2) and speed
(pic.3) of one vessel registered in
typical weather
conditions are shown. Itwas an LPG tanker 99m in
lengthand20minwidthwith4954tonnage–pic.1.It
wastravellingonthewatersofGdańskBaytowards
theNorthPort.Duringthemeasurementtherewas a
west wind with the force of 4B. The M/V
GAS
FLAWLESSmeasurementsessionwas60minutes.
Figure1.M/VGASFLAWLESS
Figure2.CoursediagramforM/VGASFLAWLESS
Duringthemeasurementsessiontheobjectwason
a constant course up until minute 22. Between
minutes 22 and 33 the M/V GAS FLAWLESS
manoeuvredchangingcoursefrom206/207startingto
227/228 andfinally finishing with a course of about
240 degrees. All measurement equipment readings
werealmostidentical,withthe
exceptionofDECCA,
which recorded bigger changes in course with a
delay. A the beginning of the measurement the
difference was about 1,5 degrees. In the following
minutes the difference is about 1 degree. After the
manoeuvre the radars show a greater fluctuation in
thecalculatedcourse.Themeasurementsended
when
theradarsignalbegantovanish.
Thevesseltravels withaconstantspeedof13,1kn
betweenminutes1and26andthenreducesthespeed
betweenminutes27and45toavalueof9,5kn.Inthe
following minutes the vessel travelled at a constant
speed as measured
by Raytheon and VTS. The
differenceinspeedbetweenvesselandshoreradaris
insignificant.
Figure3.SpeeddiagramM/VGASFLAWLESS
The momentary speed values of the vessel
received from the AIS and calculated by the radars
differbylessthan0,5knandshowsimilartendencies,
which means that they rise or fall in in the same
periods. It shows that the speed changes were not
createdbyaccidentalerrorsand
arearesultofslight
changes in speed caused by waves, wind and are
connected with the ship steering precision. Usually
the DECCA radar gives a slightly higher speed
readingsthanRaytheon.
4 RESEARCHONBOARDAVESSEL
Radarsurveillanceperformedduringshipmovement
is burdened by input data about
own course and
speed.Iftheshiptravelsinastablemannerandthe
influenceofwaveandwindisminimal,theinfluence
is not important, and it is additionally lowered by
radar data filtration. Those can, however, play a
greater role in calculating data for AIS systems,
because momentary ship
data is being transmitted
andcomparedtoownvectordesignatedinadifferent
time period. [6] The measurements were also
performed during research cruises, where about 20
vesselswererecorded.Inthisreportoneofthemwas
recorded,thatofMVNicola.Itisageneralcargoship
with gross
tonnage of 9611 t. The Sperry Marine
BridgeMmaster E 340 radar worked within the X
spectrum.The presented researchwas conductedon
9th October 2015 on the Pacific Ocean. The
meteorologicalconditionswereasfollows:seastatus
4,windinBeaufortscale5,winddirectionSW,dead
wave1.7mSW.
Figure4.Oriondata
304
Figure5.Theregisteredcourseofthevessel.
At the beginning of the measurement the
difference is about 1,5 degrees. In the following
minutesthedifferenceisabout1degree.Fromminute
5to7ofthesurveillance,ascalculatedbyARPA,the
course is unchanged, than it is slightly lowered.
According to the AIS, the vesselʹs course
is slightly
fluctuating,andthesystemsʹreadingsarehigherthan
those of the radar. Average errors in both devicesʹ
readingsareabout1degree.
Figure6.Registeredspeedoftheregisteredvessel.
Duringthesurveillancetheresearchvesselskepta
constant speed. The values obtained using the AIS
showonlyslightfluctuations,theiraveragebeingjust
0.1 kn. Speed calculations performed using a radar
showmuchbiggerchanges,andtheiraverageistwice
ofthosebytheAIS,atthesametimestill
beingvery
smallandnotover1kn.Theradar‐signalledchanges
of thetracked echoesʹ speedare possibly a result of
echosignalfluctuation.
5 CONCLUSION
ThedataobtainedbytheAISgivethenavigatornew
possibilities. It offers not only movement data on
othervesselswithmuchhigher
precisionandshorter
delaythan inthe case ofthe radar, butalso enables
directinformationexchange.
On the basis of the performed observations, one
can state that the measurements of distance using
radar are performed with high precision. The
calculationsofshipdistanceperformedwiththeAIS
(fromthedifference
inGPSpositionofownandalien
vessel) are also precise. The differences in
measurements between both systems are constant
during all operations, which proves that they are
caused by different software and different
measurement methods. The course calculated by
ARPA is done by subsequent measurements of
distance.Theechoʹ
sspeediscalculatedwithprecision
and each measurement series shows the stability of
this measurement. The shipʹs course is designated
with less precision and shows fluctuations in the
rangeofafewdegrees.Theradarsignaliscalculated
differently by different devices and higher
fluctuationsare shownby ARPA
Raytheonthan the
ECDISconnectedwithsuchradar,andtheRaytheon
is quicker to detect the echoʹs change course
manoeuvre.
Theresearchshowsthat none of thenavigational
devices gives full certainty as far as the presented
data isconcerned. The differences between readings
of distance, position, speed and
especially course of
the echoes show that navigation utilizing only one
devicecanbe risky.However, eachof thediscussed
systems presents valuable data for the navigator.
Comparing readings from different sources is
conducive to safe cruises, that is why bridges on
many modern vessels are equipped with all the
devices
mentionedabove.
All the obtained results, both laboratory and on
board, are in line with the MSC.192(79) resolution.
Measurementsatseahavea slightly lower precision
than those registered in a laboratory, which is the
resultofdelaysinthegyrocompass’s transmissionof
coursechange.Thisinfluenceismarginal,because
the
researchwasdoneon‐boardalargevesselwithgood
hydro‐meteorological conditions. During a storm,
when the ships works on waves the readingsof the
movementvectorandCPAwillbelessprecise.
REFERENCES
[1]IEC 60872‐1 Maritime navigation and radio‐
communication equipment and systems – Part 1:
Shipborne radar‐ Automatic Radar Plotting Aids‐
Performance requirements Methods of testing and
requiredtestresults,London,2004.
[2]Rezolucja MSC.192(79) Adoption of the Revised
PerformanceStandardsforRadarEquipment,London
[3]Stupak T.: Wykorzystanie Systemu Automatycznej
identyfikacji dla poprawy bezpieczeństwa jachtów
żaglowychnamorzu.Autobusy12/2016,pp430‐434.E‐
ISSN2450‐7725.
[4]StupakT.,WążM.: Amplitudedetectionofweakradar
signal, 5th International Congress on Marine
TechnologicalInnovationsandResearch,Departmentof
Nautical Science and Engineering Technical University
ofCatalonia,Proceedings,Barcelona2007,
pp677‐682.
[5]WawruchR.,StupakT.:RadarDetectionofSmall Sailing
Yachts. 2nd Microwave & Radar Week in Poland,
International Radar Symposium „IRS2006”, Kraków
2006, Telecommunications Research Institute, German
Institute of Navigation,Warsaw University of
Technology, Hamburg – Harburg University of
Technology, Proceedings, IEEE Catalog Number:
06EX1284, ISBN:
83‐7207‐621‐9, Warsaw 2006, pp. 523‐
526.
[6]Wawruch R., Stupak T.: Verification of the Radar
Visibility of Small Objects. 2nd Microwave & Radar
Week in Poland, International Radar Symposium
„IRS2006”,Kraków2006,TelecommunicationsResearch
Institute, German Institute of Navigation, Warsaw
University of Technology, Hamburg – Harburg
University of
Technology, Proceedings, IEEE Catalog
Number:06EX1284,ISBN: 83‐7207‐621‐9,Warsaw2006,
pp.405‐408.
[7]http://jproc.ca/rrp/rrp2/kingston_bmaster340.jpg