673
1 INTRODUCTION
As emphasized in part 1 of the article titled
“ComparativestudyoftheaccuracyofAISandARPA
indications.Part1.AccuracyoftheCPAindications”
published in The International Journal on Marine
Navigation and Safety of Sea Transportation
“TransNav”, Vol. 12, No 3 [1], according to the
recommendations of the Resolutions: MSC.192(79)
“Adoptionof the revised performance standards for
radarequipment”adoptedbyInternationalMaritime
Organization (IMO) on 6
th
of December 2004 and
A.1106(29) „Revised guidelines for the operational
use of shipborne automatic identification systems
(AIS)” adopted by the same organization on 2
nd
of
December2015,AISmaybeusedtoassistincollision
avoidance decision‐making process as an additional
sourceofinformationwhichsupportsradarandradar
trackingaids,byassistingin[2,3]:
Identification of targets by name, call sign, ship
typeandanavigationalstatus;
Presentationoftargets
heading;
Immediate identification of manoeuvres
performedbytargets;and
Moreaccurate presentation of the targets courses
andspeedsovergroundandrateofturn.
IfthetargetdatafromradartrackingandAISare
both available and their association criteria are
fulfilled, then as a default condition of radar
equipmentinstalledon sea going vessels on or after
1
st
of July 2008, the AIS target symbol and the
alphanumerical AIS target data should be
automatically selected and displayed only [2]. This
meansthatiftheassociationcriteriaarefulfilled,the
radardisplayunitdoesnotshowinthedefaultmode
of work the data calculated by the radar tracking
systems(ARPAodATA).
IEC Standard 61993‐2 on AIS required that on
board AIS shall calculate and display value of the
closestpointofapproach(CPA)withtheaccuracynot
inferiortothoseadoptedforradarequipmentbyIEC
intheStandard62388onshipborneradarandbyIMO
in
theResolutionMSC.192(79)[4,5].Accordingtothat
Comaparati
v
e Study of the Accuracy of AIS and ARPA
Indications. Part 2. Accuracy of the Opposite Vessel
True Course and True Speed Indication
R.Wawruch
GdyniaMaritimeUniversity,Gdynia,Poland
ABSTRACT: The article presents analysis of the automatic radar plotting aid (ARPA) and automatic
identification system (AIS) indications reliability performed on the base of the results of measurements
conductedonmerchantvesselsatsea.Inthefirstpartofthearticletitled“Comparativestudyofthe
accuracyof
AISandARPAindications.Part1.AccuracyoftheCPAindications”aredescribed:vesselsonwhichthetests
werecarriedout,AISandradarequipmentinstalledonthem,observedmeetingsituationsandaccuracyofthe
CPAindication.Inthisarticlearediscussed,forthesamemeetingsituations,accuracyof
theinformationon
truecourseand truespeed oftheopposite vesselpresented byARPAandAISandcorrelationbetweenthis
accuraciesanderrorsoftheCPAindication.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 12
Number 4
December 2018
DOI:10.12716/1001.12.04.04
674
requirements, accuracy of radar tracking and CPA
indication by AIS shall be as described in Table 1
presentedinthefirstpartofthisarticleandrepeated
thereonly[1,2,3,4].
On board AIS transmits automatically the actual
valuesofthetruecourseandtruespeedoftheshipon
which
itisinstalled,receivedfromtheconnectedtoit
GNSS receiver, currently mainly the GPS or DGPS
receiver. Due to that listed IMO recommendations
and IEC standards contain requirements regarding
the accuracy of the presentation of these two
parametersbyARPAonly,notbyAIS.
The analyses described in this
paper have been
performedtoverifythatARPAindicationsoftracked
vessel true course and true speed in real sea
conditions meet the specified accuracy requirements
andtoclarifythereasonsfortheerrorsinthecorrect
CPA values presentation by both ARPA and AIS.
They were carried out as a
part of the statutory
research No. 440 conducted at the Navigation
DepartmentoftheMaritimeUniversityinGdynia.
2 DESCRIPTIONOFTHEMEASUREMENTS
The measurements were performed in real (not
simulated)conditionsduringtheseavoyagesofthree
merchantshipsdescribedin[5]:
Bulk carrier “Magdalena Odendorff” (gross
tonnage
106884);
LPGtanker“Pampero”(grosstonnage46789);and
Multipurpose vessel “ESL Africa” (gross tonnage
11864).
The ships, their AIS and radar equipment used
during research as well as observed meeting
situations are also described in the first part of the
article[5].
As already mentioned, on board AIS retransmits
onlydataonthetruecourseandtruespeedreceived
from the GNSS receiver connected to it, so
internationalstandardsandrecommendationsdonot
specify with what accuracy these data should be
transmitted and then presented by AIS on the other
ship. Nevertheless, for each series of measurements,
themean
valuesandstandarddeviationsofthetrue
motion vector parameters were calculated to verify
theirstabilitypotentiallyaffectingtheaccuracyofthe
radar tracking and the calculation of the CPA value
byARPAandAIS.
The presented analysis was done for 55 meeting
situationslistedinthe table3in the
first partofthe
article [5]. As noted in this article, in all tests,
observedvesselfittedwithAISwastrackedbyARPA
for at least 5 minutes before the beginning of
registration and own and opposite ships were
proceeding with steady courses and speeds during
thistimeandlater
duringtheregistration.Therewere
recorded, simultaneously every 30 seconds, all
elements of a radar report about the vessel being
observedandtrackeddisplayedbyARPAandAIS.
3 DISCUSSIONOFTESTSRESULTSAND
CONCLUSIONS
The exact numerical values of the average true
courses and average true speeds of the vessels
observed and tracked during the individual
measurement series and doubled va lues of their
standard deviations are presented in Table 5
publishedinProceedingsfromthe19thInternational
Radar Symposium (IRS) [6].
Table 2 summarizes
this information and presents the
number of
meetingsituationswheretruecourseandtruespeed
indication errors (ARPA) or dispersion (AIS) were
greater than their allowable values for a probability
equalto95%.
Table1.TrackedtargetaccuracyaccordingtotheIECStandard62388(95%probabilityfigures)[4]
__________________________________________________________________________________________________
Timeof Relative RelativeCPA TCPA TrueTrue
steadystate course speedcourse speed
[min] [
o
][kn/m/s][M/km] [min] [
o
] [kn / m/s]
__________________________________________________________________________________________________
1 min: trend 111.5/0.8or10%1.0/1.85 - - -
(whicheverisgreater)
3 min: motion 3 0.8/0.4or1%0.3 / 0.56 0.5 5 0.5/0.3or1%
(whicheverisgreater)(whicheverisgreater)
__________________________________________________________________________________________________
Table2.Thenumberofmeetingsituationswheretruecourseandtruespeedindicationserrors(ARPA)ordispersion(AIS)
weregreaterthantheirallowablevaluesforaprobabilityequalto95%
__________________________________________________________________________________________________
TypeofNumberofmeetingsituations
meetingsituationTotal Witherrorgreaterthanacceptable
ARPAAIS
TC+TSp TCTSp TC+TSp TCTSp
__________________________________________________________________________________________________
Parallelcourses‐overtaking 23  43 6‐4‐
Reciprocalcourses17  23 5‐‐‐
Crossingcourses15  6‐5‐3‐
Total55  126 16‐7‐
__________________________________________________________________________________________________
AbbreviationsusedinTable2means:
TC+TSp‐truecourseandtruespeed;
TC‐truespeed;and
TSp‐truespeed.
675
Results of the measurements of the accuracy of
ARPA and AIS indications presented in Table 5 in
Proceedings from 19th IRS (the accuracy of the
presentation of true motion parameters) [6] and in
Table4inthefirstpartofthisarticle(theaccuracyof
theclosestpointofapproach(CPA)
presentation)[1]
aresummarizedinTable3.Thistableshowswhether
or not the accuracy requirements have been met by
values of the true course, true speed and CPA of
opposite ship displayed by the on board ARPA and
AIS. Information that the presented data does not
meet the accuracy
requirements is marked in bold
andunderlined.Thelastcolumnindicatesthestateof
theseaduringtheparticularseriesofmeasurements
expressedindegreesoftheDouglasscale.
AISpresentedinallmeetingsituationsmeanvalue
oftheoppositeship’struespeedwiththesatisfactory
accuracy (with doubled value of
the standard
deviation less than 0.5 knots or 1% of the speed). It
meansthattheinstabilityduringmeasurementsofthe
instantaneous values of the speed of observed and
tracked ships should not affect the accuracy of their
CPA calculation. Values of the current true course
indicated by AIS had
unacceptable errors (the
variationbiggerthan5
o
)in7meetingsituationsfor55
tested.Forallthese7situationsARPAhadproblems
withthetruecoursecalculationtoo.Generally,ARPA
presented true motion parameters (true course, or
truespeed,ortruecourseandtruespeed)witherrors
greaterthanacceptablein34meetingsituationsfor55
tested
(61% of all situations). No relationship was
found between the magnitude of errors in the
determinationoftruemotionvectorandCPAandthe
typeofmeetingsituationandthestateofsea.
ThemeasurementsshowthatbothARPAandAIS
canindicatetheCPAva lueoftheradartracked
vessel
fitted with AIS with accuracy smaller than that
required by the regulations. Analysis of the tests
results does not clearly explain the causes of these
errors.InterestingaretheresultsofmeasurementsNo
5, in which was tracked, at sea state 5
o
, overtaken
cargoshipʺCristopherʺproceedingonparallelcourse
atthedistances1.8‐1.6M(3.3‐3.0km)withthespeed
of15.1knots(7.8m/s).BothARPAandAISindicated
the true parameters of its motion with the required
accuracy. The accuracy requirements also met the
CPAvalueshownby
ARPA.Theunacceptableerror
hadonlyCPAindicatedbytheAIS(Figures1,2and
3).
Table3. Compliance with accuracy requirements for a
probabilityequalto95%
_______________________________________________
Number Compliancewithaccuracyrequirements State
ofmeetingTruecourse Truespeed CPAofthe
situation ARPA AIS ARPA AIS ARPA AIS seas
_______________________________________________
Parallelcourses‐overtaking
1Yes Yes Yes Yes Yes Yes 2
2Yes Yes Yes Yes Yes Yes 4
3NoYes Yes Yes NoNo 5
4NoNo NoYes NoNo 3
5Yes Yes Yes Yes Yes No 5
6Yes Yes Yes Yes Yes Yes 4
7NoNo Yes Yes NoNo 1
8Yes Yes NoYes NoNo 3
9NoYes NoYes NoNo 3
10Yes Yes Yes Yes NoNo 4
11Yes Yes NoYes NoNo 2
12Yes Yes NoYes NoNo 6
13Yes Yes NoYes Yes Yes 3
14NoYes Yes Yes Yes Yes 2
15Yes Yes Yes Yes NoYes 3
16NoNo NoYes NoNo 4
17Yes Yes Yes Yes Yes Yes 1
18Yes Yes Yes Yes NoNo 3
19Yes Yes Yes Yes Yes Yes 2
20Yes Yes Yes Yes Yes Yes 4
21NoNo NoYes NoNo 7
22Yes Yes NoYes NoNo 1
23Yes Yes NoYes NoNo 3
Reciprocalcourses
24NoYes NoYes NoYes 4
25Yes Yes NoYes Yes Yes 4
26Yes Yes NoYes NoYes 6
27NoYes NoYes NoYes 1
28NoYes Yes Yes NoYes 5
29Yes Yes NoYes Yes Yes 2
30Yes Yes NoYes Yes Yes 3
31NoYes Yes Yes NoYes 2
32Yes Yes Yes Yes Yes Yes 3
33Yes Yes Yes Yes Yes Yes 5
34Yes Yes Yes Yes Yes Yes 1
35Yes Yes NoYes NoNo 4
36Yes Yes Yes Yes Yes Yes 5
37Yes Yes Yes Yes NoNo 2
38Yes Yes Yes Yes NoYes 2
39NoYes Yes Yes NoYes 3
40Yes Yes Yes Yes Yes Yes 4
Crossingcourses
41Yes Yes NoYes NoNo 4
42Yes Yes Yes Yes Yes Yes 3
43NoNo NoYes NoNo 5
44Yes Yes Yes Yes Yes Yes 4
45Yes Yes NoYes Yes Yes 4
46NoYes NoYes NoNo 5
47NoYes NoYes NoYes 2
48Yes Yes Yes Yes Yes Yes 3
49NoYes NoYes NoYes 2
50Yes Yes NoYes NoNo 2
51NoYes NoYes NoYes 5
52Yes No Yes Yes Yes Yes 7
53Yes Yes NoYes Yes Yes 7sw
54Yes Yes NoYes NoNo 2
55NoNo NoYes Yes Yes 3
_______________________________________________
676
Figure1. True course values of the ship “Christopher”
(meetingsituation5)presentedbyARPAandAIS[7]
Figure2. True speed values of the ship “Christopher”
(meetingsituation5)presentedbyARPAandAIS[7]
Figure3. CPA values of the ship “Christopher” (meeting
situation5)presentedbyARPAandAIS[7]
Another interesting example are the results of
measurements No 22, in which was tracked, at sea
state 1
o
, overtaken cargo ship “Union Ranger”
proceeding on parallel course at the distances 18.7‐
18.4M(34.6‐34.1km)withthespeedof11.7knots(6.0
m/s).AISindicatedthetrueparametersofitsmotion
with the required accuracy. The accuracy
requirementsalsometthetruecoursevalueshownby
ARPA.
The unacceptable error had CPA indicated
bothbytheARPAandAIS(Figures4,5and6).
1
Figure4. True course values of the ship “Union Ranger”
(meetingsituation22)presentedbyARPAandAIS[7]
Figure5. True speed values of the ship “Union Ranger”
(meetingsituation22)presentedbyARPAandAIS[7]
Figure6.CPAvaluesoftheship“UnionRanger”(meeting
situation22)presentedbyARPAandAIS[7]
Figures7‐9show,forexample,thevaluesofthetrue
course, true speed and CPA as a function of the
measurementtimeforthemeasurementseriesNo.1,
in which all parameters were presented with the
requiredaccuracy both by AIS and by ARPA. There
was tracked, at sea state
2
o
, cargo ship “Alexandra”
proceedingonparallelcourseatthedistances2.5‐2.2
M(4.6‐4.1km)withthespeedof17.9knots(9.0m/s).
677
Figure7. True course values of the ship “Alexandra”
(meetingsituation1)presentedbyARPAandAIS[7]
Figure8. True speed values of the ship “Alexandra”
(meetingsituation1)presentedbyARPAandAIS[7]
Figure9. CPA values of the ship “Alexandra” (meeting
situation1)presentedbyARPAandAIS[7]
Anexampleofoneofthethreesituationsinwhich
all parameters, with the exception of the true speed
indicatedbyAIS,werepresentedwithtoolargeerrors
was the meeting situation 16. There was tracked, at
seastate4
o
,cargoship“OceanTrader”proceedingat
the distances 19.8‐19.6 M (36.7‐36.3 km) with the
speedof11.1knots(5.7m/s).Graphsforthismeeting
situationarepresentedinFigures10,11and12.
Figure10. True course values of the ship “Ocean Trader”
(meetingsituation16)presentedbyARPAandAIS[8]
Figure11. True speed values of the ship “Ocean Trader”
(meetingsituation16)presentedbyARPAandAIS[8]
Figure12.CPAvaluesoftheship“OceanTrader”(meeting
situation16)presentedbyARPAandAIS[8]
The number of described in this paper
measurements carried out on merchant ships at sea
and the number of tested equipment of different
manufacturers are too small to formulate on their
basis general conclusions about the stability of the
oppositevesseltruecourseandtruespeedindications
byAISandaccuracies
oftheircalculationsbyARPA
andcorrelationbetween these stability and accuracy
of the CPA indications by ARPA and AIS, but they
allowforthefollowinginitialconclusions:
1 As expected, AIS is really a much more accurate
source of information about the opposite vessel
truemotionvectorthanARPA.
678
2 No clear relationship was found between the
accuracy and stability of the opposite vessel true
motion vector indication and the accuracy of its
CPAvaluedisplayedbothbyARPAandAIS.AIS
displayedobservedvesseltruevectorwithtoolow
stabilityin7meetingsituationsanditsCPAwith
unacceptableerrorin21situations(foratotalof55
investigatedmeetingsituations).
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the automatic identification system (AIS) –
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