95
1 BACKGROUND
The Automatic Identification System (AIS) is in fact
the system for broadcasting specific information
concerningtheshiptoothershipsandshorestations.
Ingeneralitconsistsof:
Groupofconstantdata,e.g.thenameofshipand
Callsign;
Groupofdynamicdata,e.g.position,headingand
speedoftheship;
Groupofinformat
ionconcerningthetripi.e.port
ofdestinationandETA.
InformationprovidedbyAISareextremelyuseful
forautomatictrackingsystems,vesseltrafficservices.
In addition it makes bridge watchkeeping duties
more comfortable. According to many expertises,
since its introduction in2004, the system has pla
yed
an important role in improving safety at sea. The
introductionofthesystemintoshippingindustryhas
been oriented mainly on VTS and monitoring of the
traffic on busy waters. However, other aspects of
maritime security in vicinity of different threats, e.g.
with the piracy or for environments are equally
import
ant.
Itseemsevidentthatthesystemplays avitalrole
in search operations on the sea as the source of the
informationwithregardtothepositionofvictims,but
thepracticeprovedthatAIScouldbeveryusefulalso
insearchandrescueoperationsasatoolforresource
coordination.Inthi
scontext,itispropertoremember
that the system assures the communication not only
between ships, but also with aircrafts. In addition,
recent years revealed how useful can be AIS‐data
registered in the system of shore‐base stations for
accidents investigations, since it provides accurate
informat
ion concerning positions, headings, courses,
rates‐of‐turn and speeds of all participants of
accident,exactlycoordinatedinrelationtothetime.
The Integrity of Information Received by Means
of AIS During Anti-collision Manoeuvring
A.Felski&K.Jaskólski
PolishNavalAcademy,InstituteofNavigationandHydrography,Gdynia,Poland
ABSTRACT: Radar and ARPA feat
ure certain efficacy limitations due to weather conditions and target
manoeuvres.Therefore,itappearsrationaltosupplementtheinformationderivedfromradarwithadditional
information.AsystemwhichisclaimedtobetailoredtoperformthistaskisAISdeliveringproperinformation
automaticallyandcontinuously. However,incertainusersopinion,int
egrityofAISdataisstillinsufficient.In
this paper, discussion concerning incompleteness and integrity of this type of data is presented. To prove
effectiveness of AIS dynamic data in collision avoidance, detailed investigations have been conducted.
AnalyseddataoriginatefromtheGulfofGdansk,datingbacktotheyears2006‐2012.Accordingtotheresearch
results,thereareexceptionalsituations,whentheinformat
ioncomingfromthesensorscooperatingwithAISis
incomplete.ThisproblemconcernsinformationrelatedtoHDGandROT,especially,whenthevesselsarenot
“ontheway”.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 7
Number 1
March 2013
DOI:10.12716/1001.07.01.12
96
Innovative,andtosomeextentnotfoundedbythe
architectsofthesystem,istheuseofAISpositiondata
indifferentgeographicinformationsystemsavailable
ontheInternet.
Thisuse,asopposedtoabovementionedexamples,
wakes however certain provisions either on the part
of IMO or usual users, as
the potential threat for
internationalmaritimetransport.
2 COLLISIONAVOIDANCE
OneofthemostimportantfieldofapplicationofAIS
data planned on the beginning stage of the system
was collisions avoidance, especially between large
vesselsatseathatarenotwithinrangeofshore‐based
systems. However this use
is still marginal and
controversial. It results from the fact that AIS
transponder is typically connected to the bridge
equipment and is gathering data from a Global
Navigation Satellite System (GNSS) receiver,
gyrocompass or heading indicator device and a rate
ofturnindicator.Suchsetofinformationissufficient
for the
planning of avoidance maneuvers.
Additionally,datadeliveredbyAISprovetobemore
exact and more recent than these, which is collected
bymeansofARPA.Thisisespeciallyimportantwhen
ships are not keeping the heading or speed. In such
situation,dataprovidedbyARPAarenotsufficiently
reliable.
Conversely, due to significant limitations,
AIS cannot be recognized as the main tool for the
collisionavoidance.Primarylimitationisthefactthat
not all vessels are equipped with AIS devices. In
addition, the constraints of VHF radio
communicationsplayanimportantrole,butthemost
troublesome is the common opinion
of the mariners
with regard to the system and the insufficient
confidencetotheAISinformation.Itisafactthatthe
systemwasintroducedhurriedlyandfirstyearsofits
use resulted in many examples of its incorrect
operation.CommonuseofAIScausedtheopinionon
theimperfections
ofthesystem,relatedtothelackof
transmission or the transfer of not integrated
information, emerged. However some signs of
improvement of the situation can be found in the
analysis of accessibility of one of base stations
situatedatthePolishshore[Felski,JaskólskiEJN].
Figure1. Availability of AIS transmission channel. Base
StationHEL.[ownstudy]
As an example of users opinion concerning the
AIS, this information can be used in the results of
opinionpollconductedbytheauthorsofthispaperin
November2011 on the groupof deck officers witha
professional experience from 5 to 15 years on their
position. The question was:
“what kind of
information delivered by AIS can be useful for
collision avoidance?” All participants of the
investigation pointed the ship name as the most
usefulinformationforthistask. It seems that among
investigated officers the prevailing method of the
avoidanceofcollisionsisbymeansofexplanationsof
mutualintentionsbyradio.Insuchcase,AISdelivers
theimportantinformationaboutthenameoftheship,
what gives no radaar, and is indispensable for
establishingthecommunicationviaVHF.Suprisingly,
only 70‐80% investigated staff members perceive
advantages from gaining of the information
broadcasted by nearby ship concerning its
heading
andspeed.
Figure2.UsefulnessofAISinformation[ownstudy]
Overall studies on the incompleteness and
integrity of AIS information published to date are
generally linked to message No. 5 (Static & voyage
related data). This problem was also analysed by
[Harati‐Mokhtari A. et all, 2007a] and [Bailey N.,
2005],[DrozdW.,etall,2007],[Harati‐MokhtariA.et
all,
2007b],[HoriA.,etall,2009].However,literature
studies revealed that there is no publications
concerning quality of the dynamic information,
particularly the one that is important in the analysis
ofanti‐collisionmanoeuvring.
This paper is limited to presenting the results of
the integrity of AIS dynamic information. An
assessment of the integrity was performed on the
basisofAISsignalsrecordedintheyears2006,2007,
2010,2011,2012.Thisenabledademonstrationofthe
variabilityofthemeasurednavigationcharacteristics.
3 DEFINITIONOFINTEGRITY
In respect to maritime navigation, the integrity is
widely referenced to the radio navigation
system. It
appeared in 2001, when (Federal Radio navigation
Systems,2001)defineditasasystemabilitytotimely
inform deck officers about the AIS unfitness for its
97
use in the navigation process. Since 2005, (Federal
RadionavigationPlan, 2005) the term is defined as a
measure of confidence in the accuracy of the
information provided by the system. The same
document adds that integrity implies the ability of
radionavigation system for the timely alerting the
user when the
system should not be used for
navigation.
PerceivingAISasanavigationsystemisdebatable.
Thisisessentiallyaradiobroadcastchannel.Forthis
reason, it does not provide information about its
improperwork.
Theauthorsconsidertheintegrityasameas ureof
confidence in derived information and the degree
of
correctness of received AIS messages. This measure
willbeexpressedbystatisticalmethods.
4 DATASETSANDRESEARCHAREA
The studies of AIS integrity were performed on the
basisofrecordedmessagesintxtfiles.Thestudywas
conducted in the Gulf of Gdansk. Each information
recordedtoafileis
treatedasaseries.Analyzesused
only 24‐hour recordings, which were made on the
basisofstatisticalanalysisforevery7days.Datawere
recorded from 4 April 2006 to 08 January 2012
(selected 54 weeks‐378 days). Assessment of the
dynamic information integrity may be carried in a
message group 1, 2 and 3. Message No. 1 provides
information concerning the status navigation,
position, SOG, COG, ROT, HDG. Summary of the
range of valid data and the value indicating
incompletedataareshowninTable1.
Table1.Summaryofrangesofcorrectandincorrectdatain
themessageNo.1[ITUR.M.1371,1998]
Componentsofdynamic
data
Correct
value
Incorrect
value
LONGITUDE ±180 181
LATITUDE ±90 91
SOG [0,1022] 1023
COG [0,3599] 3600
TRUEHEADING [0,359] 511
RATEOFT
U
RN ±127 128
Figure3. Graph of AIS dynamic information integrity
during24hours[ownstudy]
Figure4. Graph of AIS dynamic information integrity
during1hour[ownstudy]
On the basis of research criterion authors have
developedaresearchtooltoevaluatetheintegrityof
dynamic information. The results from a single
sessionareshowninFigure3andFigure4.
Theauthorssuggestedtworesearchapproachesto
conductastudyofAISinformationintegrity.Itwasa
ʺ
criterionoflinesʺ,referringtothenumberoflinesof
information transmitted and theʺcriterion of ships”
corresponding information for the state of
incorrectness.
5 STATISTICALSUMMARYOFRESULTS
According to the methodology, the following
componentsofPositionReportwereevaluated:
trueheading;
rateofturn;
position;
speedoverground;
courseoverground.
5.1 Integrityoftrueheading
The analysis of study results leads to the conclusion
that the integrity of HDG is below requirements in
each of the 7‐day test series. This is a problem for
ʺcriterion of vesselsʺ andʺcriterion of lines
ʺ.
Maximumfactorsare:0,86(ships)and0,92(lines).
Inte
g
rit
y
of T rue Headin
g
. Lines criterion.
54 stud
y
attem
p
ts
(
weeks
)
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
date
0,70
0,72
0,74
0,76
0,78
0,80
0,82
0,84
0,86
0,88
0,90
0,92
0,94
factor
Figure3.GraphoftheintegrityofTrueHeading,„criterion
oflines”[ownstudy]
98
Inte
g
ri t
y
of True Headin
g
. Shi
p
s criterion.
54 stud
y
attem
p
ts
(
weeks
)
date
factor
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
0,70
0,72
0,74
0,76
0,78
0,80
0,82
0,84
0,86
0,88
Figure4.GraphoftheintegrityofTrueHeading,„criterion
ofships”[ownstudy]
Detailedanalysisoftheinformationexcludedfrom
further study the information transmitted by ships
standing in port and at anchor if the SOG was less
than4knots.Resultsofthestudyarepresentedbelow
(Fig 5, Fig 6) through the filtering data used for
integrityanalysis.
Integrity of True Heading (criterion of ships)
54 study attempts (weeks)
Mean; Box: Mean±SE; Whisker: Mean±SD
Mean
Mean±SE
Mean±SD
2006‐04‐03/09
2006‐04‐24/30
2006‐11‐27/03
2007‐01‐22/28
2007‐07‐23/29
2010‐12‐20/26
2011‐01‐17/23
2011‐02‐14/20
2011‐03‐21/27
2011‐04‐18/24
2011‐08‐29/04
2011‐10‐10/16
2011‐11‐21/27
2011‐12‐19/25
date
0,82
0,84
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00
1,02
1,04
factor
Figure5.IntegrityofTrueHeadingafterfiltrationprocess,
„criterionofships”[ownstudy]
Integrity of True Heading (criterion of lines)
54 study attempts (weeks)
Mean; Box: Mean±SE; Whisker: Mean±SD
Mean
Mean±SE
Mean±SD
2006‐04‐03/09
2006‐04‐24/30
2006‐11‐27/03
2007‐01‐22/28
2007‐07‐23/29
2010‐12‐20/26
2011‐01‐17/23
2011‐02‐14/20
2011‐03‐21/27
2011‐04‐18/24
2011‐08‐29/04
2011‐10‐10/16
2011‐11‐21/27
2011‐12‐19/25
date
0,80
0,82
0,84
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00
1,02
1,04
1,06
factor
Figure6.IntegrityofTrueHeadingafterfiltrationprocess,
„criterionoflines”[ownstudy]
During research, it was observed that lower
coefficientswereobservedfortheʺcriterionofshipsʺ.
5.2 Integrityofrateofturn
Themaximumvalueoftheintegritycoefficientofthe
seriesamountedto0.880forʺcriterionofvesselsʺand
0.930 forʺcriterion of linesʺ. This problem has been
presented,
interalia,by(BanyśP.,et.all,2012),where
theresearchwasconductedinapproachestotheport
ofRostock,andontheBalitcSeabetweenArkonaand
Treleborg.Theinvestigationresultswerepresentedat
European Navigation Conference 2012. In this case,
the coefficient on the ROT integrity in the
harbour
area was at the level of 0.716. In the coastal area,
correctness was at the level of 0.948. Preliminary
resultsofROTintegritywerepresentedbelow.
Inte
g
rit
y
of Rate of Turn. "Lines criterion"
54 stud
y
attem
p
ts
(
weeks
)
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
date
0,64
0,66
0,68
0,70
0,72
0,74
0,76
0,78
0,80
0,82
0,84
0,86
0,88
0,90
0,92
0,94
factor
Figure7. Graph of the ROT integrity, „criterion of lines”
[ownstudy]
Integrity of True Heading. "Ships criterion"
54 study attempts (weeks)
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
date
0,64
0,66
0,68
0,70
0,72
0,74
0,76
0,78
0,80
0,82
0,84
0,86
0,88
factor
Figure8. Graph of the ROT integrity, „criterion of ships”
[ownstudy]
Detailedanalysisoftheinformationwereexcluded
from further examination of the information
transmittedbyshipsstandinginportandatanchorif
the SOG was less than 4 knots. Below the results of
thestudy,obtainedthroughthefilteringdatausedfor
integrity analysis, are presented (mean values,
standarddeviations
andstandarderrors).
Onthebasisoftheintegritygraphofinformation
concerningROT(Fig.9,Fig.10),theimprovementof
informationqualityhasbeenobservedforthesession
ofDecember2010.UptoDecemberof2010theresults
take much larger values of standard deviations and
standarderrorsof
parameters.
99
Inte
g
rit
y
- rate of turn
(
shi
p
s criterion
)
(
54 stud
y
attem
p
ts
)
Mean; Box: Mean±SE; Whisker: Mean±SD
Mean
Mean±SE
Mean±SD
2006‐04‐03/09
2006‐04‐24/30
2006‐11‐27/03
2007‐01‐22/28
2007‐07‐23/29
2010‐12‐20/26
2011‐01‐17/23
2011‐02‐14/20
2011‐03‐21/27
2011‐04‐18/24
2011‐08‐29/04
2011‐10‐10/16
2011‐11‐21/27
2011‐12‐19/25
date
0,74
0,76
0,78
0,80
0,82
0,84
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00
1,02
1,04
factor
Figure9.GraphoftheintegrityROTafterfiltrationprocess,
„criterionoflines”[ownstudy]
Integrity - rate of turn (lines criterion)
(54 study attempts)
Mean; Box: Mean±SE; Whisker: Mean±SD
Mean
Mean±SE
Mean±SD
2006‐04‐03/09
2006‐04‐24/30
2006‐11‐27/03
2007‐01‐22/28
2007‐07‐23/29
2010‐12‐20/26
2011‐01‐17/23
2011‐02‐14/20
2011‐03‐21/27
2011‐04‐18/24
2011‐08‐29/04
2011‐10‐10/16
2011‐11‐21/27
2011‐12‐19/25
date
0,84
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00
1,02
factor
Figure10. Graph of the integrity ROT after filtration
process,„criterionofships”[ownstudy]
5.3 Integrityofgeographicalposition
The results of integrity of information for the
geographicalpositionareshownbelow.
Inte
g
rit
y
of
g
eo
g
ra
p
hical
p
osit ion. Lines crit erion.
54 st ud
y
attem
p
ts
(
weeks
)
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
date
0,978
0,980
0,982
0,984
0,986
0,988
0,990
0,992
0,994
0,996
0,998
1,000
1,002
factor
Figure11. Graph of the integrity position, „criterion of
lines”[ownstudy]
Theresultsforʺcriterionoflinesʺandʺcriterionof
shipsʺindicateahighcoefficientforpositionintegrity.
Theincreaseincompletenessofgeographicalposition
canbeobservedfromDecember2010.
Integrity of geographical position. Ships criterion.
54 study attempts (weeks)
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
date
0,91
0,92
0,93
0,94
0,95
0,96
0,97
0,98
0,99
1,00
1,01
factor
Figure 12. Graph of the integrity geographical position,
„criterionofships”[ownstudy]
5.4 Integrityofspeedoverground&courseoverground
Preliminary results of SOG and COG integrity were
presentedbelow(Figure13,Figure14).
Inte
g
ri t
y
of SOG & COG. "criterion of lines"
53 stud
y
attem
p
ts
(
weeks
)
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
date
0,965
0,970
0,975
0,980
0,985
0,990
0,995
1,000
1,005
factor
Figure13.GraphoftheSOGandCOGintegrity„criterionof
lines”[ownstudy]
Integrity of SOG. Ships criterion.
53 study attempts (weeks)
2006-04-03/09
2006-11-06/12
2007-01-01/07
2007-03-26/01
2007-07-30/05
2010-12-27/02
2011-01-24/30
2011-02-28/06
2011-03-28/03
2011-08-08/14
2011-09-05/11
2011-10-17/23
2011-11-28/04
2011-12-26/01
date
0,84
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00
factor
Figure14.GraphoftheSOGandCOGcorrectness„criterion
ofships”[ownstudy]
According to the research results concerning the
SOG and COG integrity, since December 2010 the
increaseofcoefficientswasobserved.
100
6 SUMMARY
This paper presents the results of AIS integrity
dynamicdata. The research studies of dynamic data
integrityprovidesinformationwithregardtoabilities
of the AIS information to supplement radar and
ARPA information. The results of a measurement
experiment indicate a high level of dynamic data
integrity. The
smallest value of variable integrity
concerns ROT (0.9755). The highest value of the
coefficient applies to geographical position (0.9986).
The accuracy of the parameters is associated with
accurate indications of GNSS receivers and gyro‐
compasses. The results of AIS integrity information
arepresentedintable2.
Table2. The results of AIS integrity information [own
study]
Variable X*
Xmax*** Xmin****
Integrityofheading–
“criterionoflines”
0,9783 0,0118 0,9921 0,9378
Integrityofheading–
“criterionofshi
p
s”
0,9436 0,0214 0,9675 0,9122
IntegrityofROT–
“criterionoflines”
0,9755 0,0125 0,9894 0,9379
IntegrityofROT–
“criterionofshi
p
s”
0,9316 0,0246 0,9552 0,8911
Integrityofposition–
“criterionoflines”
0,9986 0,0011 0,9996 0,8649
Integrityofposition‐
“criterionofshi
p
s”
0,9867 0,0074 0,9953 0,9765
IntegrityofSOG&COG‐
criterionoflines”
0,9964 0,0028 0,9993 0,9724
IntegrityofSOG&COG‐
“criterionofshi
p
s”
0,9576 0,0149 0,9775 0,9390
*X–mean,**standarddeviation,***Xmax‐maximum
value,****X
min
‐minimumvalue
Accordingtoresearchpresentedinthetable2,the
mostreliablevariables is: position– “the criterionof
lines” (0.9986), “the criterion of ships” (0.9867),
whereasthelowestratewasobtainedforintegrityof
ROT–“criterionofships”(0.9316).Morethan84.98%
ofthecommunicationscamefromvesselsmovingat
a
speed of less than 1 knot in the harbour area for
15.84%ofallmessageswithunreliableinformationon
thetrueheading. This stateisrepresentedby80.17%
ofvesselstransmittingincompleteinformationinthe
harbourareawithSOGlessthan1knotto20.49%of
all vessels in
the Gulf of Gdansk transmitting
incompletedtrueheading.Itwasfoundthat17.3%of
all messages with incomplete ROT comes from
85.67%ofships,tothemaximum.Thespeedwasless
than 1 knot and they were located in the harbour
area. This state is represented by 77.56% of the
vessels.
Theymeetthepreviouslyspecifedcriteriafor
the position and velocity of 21.74% of all vessels
transmittingunreliablemessagesonROTintheGulf
of Gdansk. Graphical presentation of the studies has
been illustrated in Figure 11. During the studies of
dynamicinformation(HDG&ROT),whenSOGwas
less
than 4 knots, the information from the harbours
area have been omitted. The number of vessels
transmitting unreliable messages is not equal to the
number of unreliable messages. It results from the
timeintervaloftransmitteddatabytheon‐boardAIS.
These differences can be observed in Table 2 and
in Figure 11 These factors present a synthetic
summaryoftheintegrityofinvestigatedvariables.
Summar
y
of AIS D
y
namic Data Inte
g
rit
y
54 stud
y
attem
p
ts
(
weeks
)
Mean Mean±SE Mean±SD
T.HDG. komunikaty
T.HDG. statki
ROT komunikaty
ROT statki
POS. wiersze
POS. statki
SOG& COG wi ers z e
SOG& COG s tatki
variable
0,88
0,90
0,92
0,94
0,96
0,98
1,00
1,02
factor
Figure11. Summary of the results for the selected
components of The Integrity Position Report (selected
variables)[ownstudy]
*T.HDG komunikaty – True Heading “criterion of lines”,
T.HDG statki‐True Heading “criterion of ships”, ROT
komunikaty–RateOfTurn”criterionoflines”,ROTstatki–
Rate Of Turn “criterion of
ships”, POS wiersze‐
Geographical Position “criterion of lines”, POS statki‐
Geographical Position “criterion of ships”, SOG&COG
wiersze – Speed Over Ground & Course Over Ground
“criterionlines,andships”.
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