439
1 INTRODUCTION
AccordingtotheResolutionMSC.192(79)“Adoption
of the revised performance standards for radar
equipment” adopted by the International Maritime
Organisation(IMO)on6
th
ofDecember2004,inradar
installed on sea going vessels on or after 1
st
of July
2008,ifthetargetdata fromautomaticidentification
system (AIS) and radar tracking are both available
andtheassociationcriteria(position,motion,etc.)are
fulfilledsuchthattheAISandradarinformationare
consideredasconcerningonephysicaltarget,thenas
a default condition, the AIS target symbol
and the
alphanumerical AIS target data should be
automaticallyselectedanddisplayed[1].
But at the same time, according to the
recommendationsofthesubsequentIMO Resolution
A.1106(29) „Revised guidelines for the operational
use of shipborne automatic identification systems
(AIS)”adoptedon2
nd
ofDecember2015,theAISmay
be recommended as an anti‐collision device in due
timeanditsintroducinghasnotimpactontheRule19
“Conduct of vessels in restricted visibility” of the
InternationalRegulationsforthePreventingCollision
at Sea (COLREG) and its interpretation. The ship’s
masterand
watchkeepingofficers(OOW)shouldnot
relyonAISasthesoleinformationsystem,butshould
makeuseofallsafety‐relevantinformationavailable.
Ingeneral,datareceivedviaAISimprovesthequality
oftheinformationavailabletotheOOW onboard a
ship. AIS is a useful source of supplementary
informationtothatderivedfromnavigationalsystems
includingradar.It may be used to assist incollision
avoidancedecision‐makingasanadditionalsourceof
informationwhichsupportsradarandradartracking
aids,byassistingin[2]:
Identification of targets by name, call sign, ship
typeandannavigational
status;
Presentationoftargetsheading;
Immediate identification of manoeuvres
performedbytargets;and
Moreaccurate presentation of the targets courses
andspeedsovergroundandrateofturn.
Itmeans,introducingofAISonseagoingvessels
changes significantly possibility of maintaining a
proper look‐out and assessment
of the meeting
Comaparative Study of the Accuracy of AIS and ARPA
Indications. Part 1. Accuracy of the CPA Indications
R.Wawruch
GdyniaMaritimeUniversity,Gdynia,Poland
ABSTRACT:AccordingtotheIMOrecommendationwhenthetargetdatafromradartrackingandAISareboth
availableandtheassociationcriteriaarefulfilledsuchthattheradarandAISinformationareconsideredasfor
one physical target, then as a default condition in radar equipment
should be automatically selected and
displayedthe AIS target symbol and the alphanumerical AIS target data only. The articlepresents research
conductedinrealsea conditionsonthereliabilityofinformationpresentedbytheshipʹsAISandARPAabout
thepassingdistancewiththeothervesseltrackedbyradar
equipmentandfittedwithAIS.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 12
Number 3
September 2018
DOI:10.12716/1001.12.03.02
440
situation with other vessel, particularly in restricted
visibility.
Twobasicparametersneededtoassesstheriskof
collisioninmeetingsituationbetweentwovesselsat
sea are passing distance and passing time called
respectivelyclosestpointofapproach(CPA)andtime
totheclosestpointofapproach(TCPA).IECStandard
61993‐2 presenting performance standards for AIS
required that if AIS display equipment provides
facilities for the calculation of CPA and TCPA then
thefacilitiesshouldcomplywiththerelevantclauses
of the IEC Standard 62388 “Shipborne radar –
Performance requirements, methods of testing and
requiredtestresults”[3].This
standardspecifies the
minimumoperationalandperformancerequirements
conformingtoperformance standards notinferior to
thoseadoptedbyIMOintheResolutionMSC.192(79)
[4]. According to that standard, accuracy of radar
trackingshallbeaspresentedinTable1[1,4].
In maritime navigation are officially used as the
units of distance
and speed nautical miles (M) and
knots (kn). ARPA and AIS present values of the
distance, CPA and speed in these units and due to
that,theyarepresentedinthispaperrespectivelyin
nauticalmilesandkilometresandinknotsandm/s(1
M=1852m;1knot
=1M/h0.514m/s).
Mentioned in Table 1 time of steady state means
radartrackinga target, proceeding atsteady motion
[1,4]:
aftercompletionoftheacquisitionprocess;or
withoutamanoeuvreoftargetorownship;or
withouttarget swap or any disturbance.
There are available some publications
comparing
the accuracy of the position, course and speed
presentedbytheAISandradartracking[5].Butitis
stillanopen question the accuracyand reliability of
informationaboutCPAindicatedbyAISascompared
withtheaccuracyofitsvaluecalculatedonthebasis
of radar tracking by
automatic radar plotting aid
(ARPA)andautomatictrackingaid(ATA).
The measurements reported in this article were
carriedouttofindtheanswertothisquestion.
2 DESCRIPTIONOFTHEMEASUREMENTS
The measurements were conducted in real (not
simulated)conditionsduringtheseavoyagesofships
listedinTable2
andpresentedinFigures1,2 and3,
using installed on these vessels AIS and radar
equipment mentioned in this table too. JRC is the
abbreviation of Japan Radio Company Ltd. Weather
conditionsduringthetests describes the stateof the
sea,expressedindegreesoftheDouglasscaleinthe
lastcolumnofTable3.
Tests were carried out during more than 100
meetingsituationswithothervessels.Inthisarticle,to
calculate accuracy of the CPA indication were
analysedonly55meetingsituationslistedinTable3
duringwhichbothships(ownandopposite)didnot
take any manoeuvres
and were proceeding with
steadycoursesandspeeds.
Figure1.Bulkcarrier“MagdalenaOldendorff”[9]
Figure2.LPGcarrier“Pampero”[10]
Figure3.Multipurposevessel“ESLAfrica”[11]
Table1.Trackedtargetaccuracy(95%probabilityfigures)[1,4]
__________________________________________________________________________________________________
Timeofsteady Relative RelativeCPATCPA True Truespeed
statetracking[min] course[
o
] speed[kn/m/s][M/km][min] course[
o
] [kn/m/s]
__________________________________________________________________________________________________
1min:trend111.5/0.8or10%1.0/1.85‐‐‐
(whicheverisgreater)
3min:motion30.8/0.4or1%0.3/0.560.550.5/0.3or1%
(whicheverisgreater)(whicheverisgreater)
__________________________________________________________________________________________________
441
Table2.Shipsonwhichtestswerecarriedout[6,7,8]
__________________________________________________________________________________________________
Ship’snameMagdalenaOdendorffPamperoESLAfrica
__________________________________________________________________________________________________
Ship’stypeBulkcarrierLPGtankerMultipurposevessel
Grosstonnage1068844678911864
Length[m]299.9m226.0m143.0m
Servicespeed[kn/m/s] 15.6/8,016.7/8,613.2/6.8
UtilisedradarandARPA JMA‐9132‐SA,JMA‐9172‐SA,GR3017(X‐Band),
equipment/manufacturer
 JMA‐9122‐9XA/JRCJMA‐9122‐9XA/JRCGR3018(S‐Band),
ARPAMultipilot1100/SAM
ElectronicsGmbH
UtilisedAIS/manufacturer JHS‐183/JRCJHS‐183/JRCDEBEG3400/SAM
ElectronicsGmbH
__________________________________________________________________________________________________
Table.3.Observedships[6,7,8,12]
__________________________________________________________________________________________________
No Ship’snameT L[m] Speed[kn/m/s] Distance[M/km] Seastate
__________________________________________________________________________________________________
1 AlexandraCS 270 17.5/9.02.5‐2.2/4.6‐4.12
2 BelgianExpressC 180 13.0/6,71.0‐0.7/1.9‐1.34
3 CelticAmbasador CS 889.1/4.713.4‐12.4/24.8‐23.0 5
4 ChinaPeaceB 289 0/016.8‐14.5
/31.1‐26.9 3
5 ChristopherCS 171 15.1/7.81.8‐1.6/3.3‐3.05
6 CoralMeandraT 9111.1/5.71.5‐1.4/2.8‐2.64
7 CorcovadoCS 207 0.5/0.318.9‐15.8/35.0‐29.3 1
8 CSCLJupiterCS 366 18.2
/9.43.6‐2.6/6.7‐4.83
9 F.D.GennaroAurilia B 225 12.0/6.214.1‐13.2/26.1‐24.4 3
10 FlinterAlandCS 132 10.7/5.57.9‐7.1/14.6‐13.14
11 HeinrichT 114 11.9/6.118.6‐18.1/34.4‐33.5 2
12
 HistriaIvoryT 179 10.8/5.617.1‐17.0/31.7‐31.5 6
13 HyundaiUnityC 294 13.3/6.89.3/17.23
14 LenaRiverT 290 0/06.7‐3.4/12.4‐6.32
15 NavinKestrelCS 116 10.2/5.35.2‐4.4/
9.6‐8.13
16 OceanTraderCS 180 11.1/5.719.8‐19.6/36.7‐36.3 4
17 PacificHeronSP 884.8/2.59.0‐7.8/16.7‐14.41
18 PantherCS 207 16.1/8.311.4‐10.9/21.1‐20.2 3
19 RegioMarFV218.0/
4.16.5‐3.0/12.0‐5.62
20 SuezVasilisT 274 14.0/7.22.0‐1.8/3.7‐3.34
21 TianZhuFengB 225 10.8/5.616.8‐16.4/31.1‐30.4 7
22 UnionRangerCS 185 11.7/6.018.7‐18.4/34.6‐34.1 1
23 VarvaraCS 225 11.2/5.85.7‐5.1/10.6‐9.43
24 APLVancuverC 328 19.2/9.918.4‐13.1/34.1‐24.3 4
25 AraAntwerpenCS 145 11.2/5.89.2‐3.0/17.0‐5.64
26 BeatrizBCS 159 12.9/6.619.0‐12.9
/35.2‐24.0 6
27 BomarResoluteCS 232 15.4/7.97.0‐1.8/13.0‐3.31
28 CoscoJinggangshanB 177 10.0/5.113.1‐6.6/24.3‐12.2 5
29 EkenT 135 12/6,24.7‐2.0/8.7‐3.72
30 GasPashaCS 96
9.3/4.814.1‐8.4/26.1‐15.6 3
31 HoeghShanghaiCS 229 9.2/4.717.1‐11.3/31.7‐20.9 2
32 HSCB 289 11.6/6.07.6‐5.7/14.1‐10.63
33 JacamarArrowB 199 14.0/7.25.5‐1.3/10.2‐2.45
34
 MaerskCapeCoast C 249 15.0/7.76.5‐2.6/12.0‐4.81
35 NYKAltairC 333 14.1/7.312.5/23.24
36 PortShanghaiB 190 10.0/5.17.7‐2.5/14.3‐4.65
37 RomeTraderCS 179 14.4/7.419.5‐12.6
/36.1‐23.3 2
38 RomeTraderCS 179 14.4/7.410.1‐3.4/18.7‐6.32
39 ThorcoLegionCS 132 12.35/6.413.5‐6.8/25.0‐12.6 3
40 VaramoC 166 25.3/13.06.9‐1.2/12.8‐2.24
41 AbisCalaisCS 115 9.4
/4.816‐13.7/29.6‐25.4 4
42 ArklowCadetCS 8710.6/5.46.7‐4.3/12.4‐8.03
43 BulkSwitzerlandB 289 9.5/4.920.0‐18.0/37.0‐33.3 5
44 CapSanMarcoC 333 20.0/10.34.3‐2.7/8.0‐5.0
4
45 CarnivalValorP 292 18.2/9.43.4‐2.9/6.3‐5.44
46 CoralLopheliaT 109 13.4/6.917.1‐16.3/31.7‐30.2 5
47 FreeNeptuneCS 185 11.5/5.914.2‐11.5/26.2‐21.3 2
48 HorncapC 153 14.5/7.55.6
‐2.9/10.4‐5.43
49 IlyasEfendiyevCS 140 8.4/4.39.6‐4.9/17.8‐9.12
50 JSColumbiaB 199 14.4/7.416.7‐12.8/30.9‐23.7 2
51 MSCRacheleC 334 19.5/10.023.4‐17.5/43.3‐32.4 5
52 NCCDanah
T 183 13.5/6.95.6‐3.3/10.4‐6.17
53 OOCLKoreaC 366 15.8/8.15.7‐1.6/10.6‐3.07sw
54 RiodeJaneiroExpress CS 260 13.4/7.419.5‐15.4/36.1‐28.5 2
55 SpiritofBritainF 213 23.5/12.1
9.1‐8.3/16.9‐22.43
__________________________________________________________________________________________________
442
ThetermsandabbreviationsusedinTable3mean:
Name‐nameoftheobservedvessel;
T‐typeoftheshipindicatedbyAIS:
B‐bulkcarrier;
C‐containervessel;
CS‐cargoship;
F‐ferryboat;
FV‐fishingvessel;
P‐passengership;
SP–specialpurposeship;and
T‐tanker;
L‐thelengthofthevesselpresentedontheweb‐
site;
Distance‐distancetotheobservedshipduringthe
measurement;and
Sea‐seastateexpressedindegreesoftheDouglas
scale,swmeansswell.
In each test were
recorded, simultaneously every
30 seconds, following parameters of the observed
vesselindicatedbyARPAandAIS:bearing,distance,
truecourse,truespeed,CPAandTCPA.
Inallcases, observedshipwastrackedbyARPA
for at least 5 minutes before the start of registration
andbothvessels(ownandopposite)did
nottakeany
manoeuvres at this time and later during the
registration.
3 DISCUSSIONOFTESTSRESULTSAND
CONCLUSIONS
Described tests were conducted in order to check
whether,whendatafromAISandradartrackingare
bothavailableandtheassociationcriteriaarefulfilled,
the person in command and manoeuvring
the ship
(captain or watch keeping officer) can rely on CPA
value of other vessel available from AIS only. The
amount of the measurements is small and makes it
impossible to determine any statistical relationships
butallowstoformulatesomegeneralobservations.
TherewereobservedbyAIS andtrackedbyARPA
shipsofdifferentsizes,fromthesmallfishingvessel
tolargecontainershipsandtankers,proceedingwith
differentspeedsindifferentmeetingsituationsandin
different weather conditions, including stormy
weather. They were passing own ship at different
CPA, between, according to the data received from
ARPA, 0.36 M (0.67
km) and 17.18 M (31.82 km).
Results of conducted tests are presented in Table 4.
ErrorsoftheCPAindicationgreater than their limit
value defined in the mentioned IEC standard and
IMOresolutionareprintedinthisTableinboldand
underlined,σ–standarddeviation.
Table4.Testsresults(95%probabilityfigures)
_______________________________________________
No CPA(ARPA)CPA(AIS)
Meanvalue 2σMeanvalue 2σ
[M/km][M/km][M/km][M/km]
_______________________________________________
Parallelcourses‐overtaking
_______________________________________________
1 2.11/3.91 0.16/030 2.07/3.83 0.18/0.33
2 0.69/1.28 0.04/0.07 0.67/1.24 0.04/0.07
3 2.29/4.24 3.04/5.63 2.15/3.98 1.42/2.63
4 4.50/8.33 1.74/3.22 4.38/8.11 0.74/1.37
5 1.54/2.85 0.24/0.44 1.44/2.67 0.42/0.78
6 1.17/2.17 0.20/0.37 1.21/2.24 0.20/0.37
7 2.70/5.00 0.42/0.78 2.65/4.91 0.36/0.67
8 1.62/3.00 0.48/0.89 1.56/2.89 0.56/1.04
9 6.72/12.45 5.82/10.78 7.66/14.19 1.60/2.96
10 2.65/4.91 1.20/2.22 2.83/5.24 0.70/1.30
11 11.31/20.95 5.24/9.70 11.17/20.69 3.94/7.30
12 15.71/29.09 4.64/8.59 15.27/28.28 4.52/8.37
13 9.25/17.13 0.06/0.11 9.18/17.00 0.06/0.11
14 0.68/1.26 0.02/0.04 0.69/1.28 0.04/0.07
15 2.39/4.43 0.64/1.19 2.41/4.46 0.28/0.52
16 17.18/31.82 5.20/9.63 15.71/29.09 6.12/11.33
17 6.81/12.61 0.22/0.41 6.79/2.58 0.16/0.30
18 4.70/8.70 3.42/6.33 4.68/8.67 2.54/4.70
19 2.65/4.91 0.14/0.26 2.58/4.78 0.12/0.22
20 1.64/3.04 0.18/0.33 1.45/2.69 0.16/0.30
21 11.31/20.95 8.68/16.08 9.99/18.50 7.04/13.04
22 8.47/15.69 7.52/13.93 9.21/17.06 9.32/17.26
23 0.47/0.87 0.82/1.52 0.32/0.59 0.34/0.63
_______________________________________________
Reciprocalcourses
_______________________________________________
24 9.76/18.08 1.14/2.11 9.81/18.17 0.20/0.37
25 1.22/2.26 0.18/0.33 1.17/2.17 0.16/0.30
26 3.38/6.26 0.94/1.74 3.35/6.20 0.26/0.48
27 1.64/3.04 0.42/0.78 1.64/3.04 0.12/0.22
28 3.34/6.19 0.38/0.70 2.95/5.46 0.22/0.41
29 0.36/0.67 0.06/0.11 0.36/.670.04/0.07
30 1.45/2.69 0.22/0.41 1.54/2.85 0.16/0.30
31 1.83/3.39 0.82/1.52 1.98/3.67 0.28/0.52
32 5.55/10.28 0.12/0.22 5.48/10.15 0.08/0.15
33 1.11/2.06 0.04/0.07 1.11/2.06 0.08/0.15
34 2.13/3.94 0.10/0.19 2.05/3.80 0.08/0.15
35 11.13/20.61 4.54/8.41 6.13/11.35 6.48/
12.00
36 2.38/4.41 0.04/0.07 2.19/4.06 0.18/0.33
37 1.36/2.52 0.60/1.11 1.36/2.52 0.42/0.78
38 1.36/2.52 0.32/0.59 1.37/2.54 0.10/0.19
39 2.27/4.20 0.64/1.19 2.39/4.43 0.12/0.22
40 1.15/2.13 0.04/0.07 1.28/2.37 0.16/0.30
_______________________________________________
Crossingcourses
_______________________________________________
41 4.43/8.20 1.86/3.44 4.33/8.02 0.42/0.78
42 3.72/6.89 0.14/0.26 3.71/6.87 014/0.26
43 17.18/31.82 0.76/1.41 17.19/31.84 0.50/0.93
44 2.60/4.82 0.04/0.07 2.54/4.70 0.10/01.9
45 2.90/5.37 0.02/0.04 2.79/5.17 0.04/0.07
46 13.12/24.30 6.44/11.93 14.30/26.48 0.32/0.59
47 9.43/17.46 1.22/2.26 9.48/17.56 0.16/0.30
48 2.84/5.26 0.04/0.07 2.70/5.00 0.12/0.22
49 2.44/4.52 0.58/1.07 2.41/4.46 0.20/0.37
50 5.92/10.96 0.52/0.96 5.30/9.82 0.32/0.59
51 3.85/7.13 4.64/8.59 3.65/6.76 0.30/0.56
52 2.97/5.50 0.26/0.48 2.92/5.41 0.22/0.41
53 1.51/2.80 0.12/0.22 1.47/2.72 0.16/0.30
54 0.76/1.41 0.66/1.22 0.77/1.43 0.32/0.59
55 8.28/15.33 0.06/0.11 8.25/15.28 0.06/0.11
_______________________________________________
Table5presentsthenumbersofmeetingsituations
where the CPA indications by AIS and ARPA had
errorsgreaterthantheirallowablevaluespecifiedin
the standards. Measurements have shown that the
problem with accurate determination of CPA values
occurs mainly during overtaking. In this meeting
situationbothARPAandAIS
indicatedCPAwithan
443
errorgreaterthanacceptablein14casesfor23tested
(in61%ofmeetingsituation).In12meetingsituations
problemswithaccurateindicationofCPAvaluehad
bothARPAandAIS.Inothermeetingsituations,AIS
showedmorefrequentlyCPAvalueswithacceptable
accuracythanARPA.ARPAerrorsexceededthe
limit
value in more than half the meeting situations (in 9
outof17forshipsonreciprocalcoursesandin8out
of 15 for crossing courses). AIS errors exceeded the
limitvaluein2outof17meetingsituationsforships
onreciprocalcoursesandin5out
of15situationsfor
crossingcoursesonly.
Table5. The number of meeting situations where CPA
errors were greater than their allowable value (for 95%
probability figures)
_______________________________________________
TypeofNumberofmeetingsituations
meetingTotal WithCPAerrorgreater
situationthanacceptable
ARPA AIS
_______________________________________________
Parallelcourses‐23  1414
overtaking
Reciprocalcourses 17  92
Crossingcourses15  85
_______________________________________________
Total55  3121
_______________________________________________
No clear correlation was found between the
magnitudeoftheCPAerrorsandthestateofthesea.
TheCPAindicationsinAISandARPAexceededthe
allowablevaluesforallseastatesfrom1to7degrees
intheDouglasscale.
The number of described in this paper
measurements carried
out on ships during their sea
voyages is too small to formulate on their basis
general conclusions about the accuracy of the CPA
indicationsbyARPAandAIS,buttheyallowforthe
followinginitialconclusions:
1 OnboardAIS,likeradartrackingaids(ARPAand
ATA),maydisplaythe
CPAvalueoftheopposite
vesselunstableandinaccurateinallstatesofsea.
2 Due to the possible instabilities and inaccuracies
mentioned in the first conclusion, a systematic
observation of the CPA value of opposite vessel
indicatedbybothAISandARPA(ATA)shouldbe
recommended.
3 Attention of the
AIS and ARPA manufacturers
should be paid on the problem identified in the
firstconclusion.
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