183
1 INTRODUCTION
Automatic Identification System (AIS) refers to the
technology working on the Very High Frequency
(VHF) radio wave that enables the ship’s various
information such as name, position, type, speed,
course, cargo, destination etc. to be automatically
exchanged between ship to ship as well as between
shiptoshoreinreal ti
me.Sinceitsintroductioninto
the various sectors of the shipping industry, the
significant role AIS has played in ensuring the
navigationalsafety,maritimesecurity,marinesearch
and rescue and environmental protection at sea and
onshorehasbeenwellacknowledged.Nowadays,the
utilization of shore‐based AIS station network to
capture the ship’s informat
ion transmitted from the
onboardAISequipmentinordertotrackandmonitor
those ships close to shore has become a standard
practice of the vessel monitoring service for the
maritimeauthoritiesin many nations.However,this
so‐called shore station‐based AIS ship monitoring
systemisst
illlimitedtosatisfytheneedsofglobally
identifyingtheshipsduetothelimitationoftheVHF
horizontalrange(approximately20nmand100nmfor
onboardAISequipmentandshore‐basedAISstation,
respectively).
In recent years, the serious situation at sea
pertaining to the unlawful acts of piracy, arm
ed
robbery and port attack by utilizing ships as a
weaponhasalreadydrawnmanycostalstatestoput
the long‐range or global ship monitoring system on
the top agenda in order to effectively track and
identify the ships in the wider horizon and at the
earliertimeevenintherealti
me.Asaresult,theship
monitoring system combining the AIS powerful
information capacity and the satellite global range
detection has been prompted and continued in the
progresssincethebeginningofthiscentury.
Satellite-based AIS and its Comparison with LRIT
Y.Chen
ShanghaiMaritimeUniversity,Shanghai,China
ABSTRACT: The sat
ellite‐based Automatic Identification System (AIS) system has continuously been
developedbytheshippingindustryinrecentyears.Thispaperintroducesthesatellite‐basedAISincludingthe
concept,thesystemstructure,thedevelopmentanditsnewapplications.TheLongRangeIdentificationand
Tracking(LRIT) system,whichismandatorytoberequiredoncertainclassesofshipsengagedonint
ernational
voyagesto reporttheirposition atleast every sixhoursusingonboard communication meanshowever, has
similarkindoffunctionofshipmonitoringwiththesatellite‐basedAISsystem.Basedonthebasicintroduction
oftheLRITsystem,thispaperpresentsthecomprehensivecomparisonbetweensat
ellite‐basedAISandLRITin
termsoftheship’scost,thecommunicationscheme,themonitoringcoverage,theinformationdetailsandthe
informationcreditability.Theconclusionthatthesatellite‐basedAISshouldbeencouragedtoeffectivelyplaya
complementroletotheLRITsystemisadvancedinthepa
per.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 8
Number 2
June 2014
DOI:10.12716/1001.08.02.02
184
2 SATELLITE‐BASEDAIS
2.1 Conceptandsystemarchitecture
Thesatellite‐basedAIS,alsoreferredtoasthespace‐
basedAIS,iscreatedanddevelopedasaglobalship
surveillancesystemthatusessmallloworbitsatellites
carrying the AIS transponders to receive the ship’s
AIS information from space and then relay them to
the ground station. Consequently similar to other
sat
ellite communication and navigation systems, the
satellite‐based AIS system consists of five
components, i.e. small low orbit satellites in space,
shipborne AIS equipment, ground station, user and
communicationlink,seeFigure1.
Figure1.Satellite‐basedAISarchitecture
While the ship’s information is automatically
exchanged between AIS‐equipped ships via VHF
communication link, the satellite on which the AIS
transponder is installed running on the low earth
orbitatthesametimeisabletoreceivetheVHFsignal
transmitted for the ship’s AIS equipment since the
VHF radio wave with the significant signal strength
has been proven to be ab
le reach the altitude up to
1000kmfromtheearthground.Thesatellitetransfers
the received VHF signal to the ground station in
charge of controlling the whole system. The ground
stationthereforecandistributetheship’sinformation
transferredbytheAISsat
ellitetotheauthorizeduser.
The communication links between the satellite and
the ground as well as between the ground and the
user are bi‐directional whereas the communication
link from the ship to the satellite is uni‐directional.
Consequently, the satellite‐based AIS is capable of
globallymonitoringtheship’smovementinrealti
me
ifthenumberofthesatelliteandthegroundstationis
satisfied.Cain&Megerhasshownoneofthesatellite‐
based AIS operational results to globally track the
shipsinthetheirpaper[1].
2.2 Development
The concept of satellite‐based has continuously
a
ttractedNorway,theUnitedStatesandCanadaetc.
tomakeeveryefforttocarryouttherelativeresearch
withthe great investment sinceitsinception in 2003
[2].TheSubcommitteeonRadiocommunicationsand
Search and Rescue (COMSAR) of the International
Maritime Organization (IMO) made its debut to
receivetheproposalregardingthesat
ellite‐basedAIS
in 2005. Subsequently, the IMO Maritime Safety
Committee (MSC), Navigation (NAV) subcommittee
and COMSAR subcommittee have usually remained
thespacetodiscussthesatellite‐basedAIStopicinthe
varioussessions.
In addition, some military units, commercial
companies and research institutions have gradually
and successfully conducted the sat
ellite‐based AIS
activities as well as provided the ship’s AIS
monitoringservicebasedonthesatellites.
In 2007, the US Air Force Research Laboratory
(AFL)launchedtheAISsatelliteofTacSat‐2inorder
toverifytheconceptofthesatellite‐basedAISforone
year[3].
InApril2008,theSpaceFlightLaboratory(SFL)of
Toronto University under the sponsorship of
Ca
nadian COM DEV Company has successfully
launched the AIS satellite of NTS (Nano‐satellite
Tracking Ships) after 7‐month effort. The exactEarth
Company affiliated in the Canadian COM DEV
Company has become the first commercial unit for
providingtheserviceofsat
ellite‐basedAISdatainthe
world[4].
InJune2008,theUSORBCOMMCompanyandthe
United States Coast Guard (USCG) jointly launched
the AIS satellite of M2M (Machine‐to‐Machine), but
which was out of operation at the end of 2010. In
2011, ORBCOMM successfully launched two AIS
sat
ellitesmanufacturedbytheLuxSpaceCompanyof
Luxemburg. ORBCOMM has planned to 17 AIS
satellites by the end of 2014 in order to establish a
complete satellite AIS management system, together
withthecurrent16groundstations[5].
In July 2009, the US SpaceQuest Company
launched the two AIS sat
ellites, but both of which
were incorporated into the exactEarth Company
systemsinceJuly,2010[6].
In September 2009, an AIS satellite named as
PathFinder2 manufactured by the LuxSpace
Companywaslaunched,whichenabledthiscompany
tobecomethefirstcommercialunitforprovidingthe
serviceofsatellite‐basedAISdatainEurope[7].
In September 2009, the AIS sat
ellite of
SumbandilaSat jointly developed by University of
Stellenbosch South Africa, Council for Scientific and
Industrial Research (CSIR) and Kenya SunSpace
Companyhasbeensuccessfullylaunched[8].
In October 2010, under the guidance of Norway,
the AISSat‐1 satellite designed and ma
nufactured
jointlybyNorwegianDefenceResearchEstablishment
(FFI)andCanadianSpaceFlightLaboratoryhasbeen
launched.AndNorwayhasdecidedto launchedthe
AISSat‐2bythe2014andthemorepowerfulAISSat‐3
bythe2015[9].
InMay2012,JapanAerospaceExplorationAgency
(JAXA) has successfully launched the SDS‐4 AIS
sat
ellitetoshowtheresearchoutcomeinaspectofthe
Satellite‐basedAIS[10].
In July 2012, the Canadian exactEarth Company has
successfully launched the EV‐1 AIS satellite, which
enableditssatellite‐basedAISsystemofexactView™
tobecomethelargestsystemforprovidingtheservice
ofsat
ellite‐basedAISdataintheworld[11].
185
Table1.DetailedinformationregardingtheAISsatellites
__________________________________________________________________________________________________
AISsatellite
LaunchtimeInstituteinchargeWeight Orbitalheight Operationstatus
__________________________________________________________________________________________________
TacSat‐2
2007USAFL370kg 410kmoutofoperation
NTS2008.4CandianCOMDEV 8kg630km inoperation
M2M2008.7 USORBCOMM80kg775kminoperation
Aprize‐3&42009.7USSpaceQuest12kg565/677km inoperation
PathFinder22009.9LuxemburgLuxSpace 8kg865kminoperation
SumbandilaSat 2009.9CSIR,SunSpace84kg500kminoperation
AISSat‐12010.7NorwegianFFI6kg630kminoperation
SDS‐42012.5JapaneseJAXA50kg680kminoperation
EV12012.12CanadianexactEarth 98kg817kminoperation
AAUSAT32013.2DMA 0.8kg800kminoperation
__________________________________________________________________________________________________
In February 2013, the AIS satellite of AAUSAT3
fundedbytheDanishMaritimeAuthority(DMA)but
designed by the Aalborg University has been
successfullyputintoservice[12].
The detailed information regarding the AIS
satellitesissummarizedintheTable1.
Furthermore,tomeettherapiddevelopmentofthe
Satellite‐based AIS service required by the maritime
commercial community, the International
Telecommunication Union (ITU) have allocated two
specific VHF Channels (75 and 76) and defined the
new Message 27 for the application of the satellite‐
based AIS in order to solve the technological
difficulty regarding the time slot collision for
the
shipborne AIS Class A equipment working on the
principle of Self‐Organized Time Division Multiple
Access (SOTDMA) scheme according to the ITU‐R
M.1371‐4[13].ThisnewVHFChannelsallocationfor
the marine AIS denotes that the shipborne AIS
equipment will be upgraded to support the
functionality of
transmitting the signals to the
satellites in the coming years. It is hence estimated
that the service provided by the satellite‐based AIS
will widely accepted by the industry and make the
greater contribution in the ship long‐range
monitoringinfuture.
2.3 Newapplications
Theinitialpurposebasedonthe
AISsatellitedatais
thattheshorecantrack,identifyandmonitortheAIS‐
equippedshipsintheglobal forthe enhancementof
ships safety and security. Many commercial
applications have proven that the AIS satellite data
hasplayedtheessentialroleinthisregard.However,
therecentresearchhas
demonstratedthatthefunction
of the AIS satellite data is more than this. For
example,thiskind ofdataisarelativelyreliabledata
sources for assessing the world shipping efficiency
[14];thiskindofdataisalsoabletobeappliedinthe
analysisofnavigationalfeasibilityoftheroutes
inthe
polarwaters [15].Thereforeit isanticipated that the
databasedupontheSatellite‐basedAISwillbecomea
basicbut mostvaluable data for theglobal shipping
commercialapplicationandresearch.
3 LRITSYSTEM
3.1 Mandatoryrequirement
The Regulation V/19‐1 of the International
Conventionforthe
SafetyofLifeatSea(SOLAS)1974
effective on January 1 2008 was amended and
adopted by the IMO in 2006 mandating that ships
engaged on international voyages, including all
passengerships,highspeedcrafts,cargoshipsof300
gross tonnages and above and mobile offshore
drilling units are requested
to bear the obligation to
automatically transmit the LRIT information
includingtheiridentity,positionanddate/timeofthe
position to the Flag States at 6‐hourly intervals or
uponpollrequestsforanon‐demandpositionreport
at the interval to a frequency of a maximum of one
every15minutes.
Itisquiteobvious thatthepurpose
ofLRITsystemisofprovidingtheFlagStatewiththe
globalidentificationandtrackingofships.
3.2 Systemarchitecture
The complete LRIT system is comprised of the
shipborneLRIT informationtransmittingequipment,
the Communication Service Provider(s), the
Application Service Provider(s), the LRIT
Data
Centre(s), including any related Vessel Monitoring
System(s), the LRIT Data Distribution Plan and the
International LRIT Data Exchange. The LRIT system
architecture is illustrated in the IMO Resolution
MSC.263(84)[16].
EachFlagState isrequiredto establishorselect a
LRIT Data Centre to directly collect the LRIT
informationtransmitted
fromtheshipsentitledtofly
itsflag. The LRITinformationis always availableto
theship’sFlagStatewhiletheDataDistributionPlan
developed by the IMO in accordance with the Flag
State’s routing rules and connected with the
International LRIT Data Exchange provides the
scheme to another Flag
State for the valid access of
the LRIT information of the ships concerned. The
CommercialServiceProviderandApplicationService
Providerplaytheroleofenablingthecommunication
betweenthesatelliteandthedatacentre.
It is also acknowledged that “a robust
internationalschemeforLRITofshipsisanimportant
and integral element of maritime security” and “an
active and accurate LRIT system also has potential
safetybenefits,mostnotablyformaritimesearchand
rescue”[17].
186
4 COMPARISONBETWEENSATELLITE‐BASED
AISANDLRIT
4.1 Ship’scost
The shipborne terminal for the satellite‐based AIS is
undoubtedlyoftheAISequipmentonboard.Thereis
thereforenoadditionalcosttheshipshouldcurrently
incurtomaintainthenormaloperationofthesatellite‐
basedAISaslongas
theAISequipmenthasalready
been installed onboard and operated in normal
condition. However, if the new AIS equipment to
supportthenewVHFchannelallocationfortheuseof
the satellite‐base AIS is required in future, the ship
should pay extra expense to upgrade the AIS
equipment.
For
the LRIT shipborne terminal, the technical
means are not specified and it can be any
communication terminal on board the vessel that is
capable of automatically and onreceiptof a specific
request from the shore transmitting the ship’s LRIT
information. In practice, the satellite‐based
communication mean probably existing Global
Maritime Distress and Safety System (GMDSS)
equipmentsuchasInmarsatCterminalwiththedata‐
pollingserviceandShipSafetyAlertSystem(SSAS)is
widelyappliedastheLRITshipborneterminalonthe
shipsengagedoninternationalvoyages.Eventhough
the cost of establishing the LRIT system is mainly
borne
bytheContractingGovernment,thereisstilla
cost regarding GMDSS equipment upgrading or
standalone equipment installation and testing that
shipsshouldincurinensuringtheLRITequipmenton
boardtheshipcanrespondtotheLRITrequirements.
4.2 Communicationscheme
Subject to the communication scheme between the
satellite and the
ship, the satellite‐based AIS is
designed as an uni‐directional monitoring system
while the LRIT system is maintained as a bi‐
directional monitoring and communication system.
AnAISsatelliteisabletosimultaneouslycaptureall
AISinformationtransmittedfromtheshipswithinits
footprintbutitcannotsendany
signalinstructionto
any shipborne AIS equipment within its footprint
since there is no communication downlink from the
satellite to the ship. From this perspective, the
satellite‐basedAISisdefinitelyamonitoringsystem.
In contrast, as in most cases the majority of the
LRIT shipborne terminals is based on the
Inmarsat‐
satellite mean, each Flag State data center is
designatedtolink to Flag State ship’s terminals and
vice versa via Inmarsat satellites. In other words, a
LRIT ship terminal is able to automatically send
informationasrequiredto theFlagStatedata center
and the Flag State data center
can send signal
instruction to a ship beca use one of most important
characteristics for the LRIT system is that the
shipborne terminal is able to receive the request
instructiontransmitted from shore‐based datacenter
and make the corresponsive response. The LRIT
systemisthereforeamonitoringandcommunication
system.
4.3
Monitoringcoverage
As the low‐earth‐orbit satellites are utilized in the
satellite‐based AIS, in theory, the satellite‐based AIS
canglobally,includingthepolarwaters,monitorand
tracktheship’sinformationinrealtimeifthenominal
number of the satellites and the ground stations is
satisfied.That
iswhythecurrentsatellite‐basedAISis
able to draw the global ship monitoring picture but
stillhave alittle time delay dueto too fewsatellites
andgroundstationsinoperation.
As for the LRIT system mainly depending upon
the Inmarsat Geostationary Orbit satellites for
tracking the ocean‐going
ships, the monitoring
geographicalcoverageislimitedtotherangebetween
two latitudes of 76° due to the Inmarsat‐satellites
nominalfootprint.Hence, theLRIT systemisunable
fullytoidentifyandtracktheshipssailingbeyondthe
rangebetweentwolatitudesof76° suchasthepolar
waters.
4.4 Informationdetails
ComparedtotheLRITsystemwhichonlythreetypes
ofships’information,i.e. theiridentity,position and
date/time of the position are available, the satellite‐
based AIS has enjoyed quite rich ship’s information
available since its received information is directly
emanated from the any types of onboard
AIS
equipment. Taking Class A AIS equipment as an
example, this equipment is able to exchange four
categoriesofmessage,static,dynamic,voyage‐related
and safety‐related including more than 20 types of
ship’s details. Even for the AIS Message 27, it still
includes the ship’s identifier, position and its
accuracy, navigational status, speed and course etc.
Moreship’smonitoringinformationisavailable,more
choice is also available for more users to manage
ships. Moreover, the theoretical capability of the
satellite‐basedAISreceivingtheship’sinformationin
real time is also advantageous to the information
refresh interval from 15 minutes
to 6 hours of the
LRITsystem.
4.5 Informationcreditability
The LRIT system is established by the international
organizationandtheContractingGovernments from
the beginning in order to enhance the navigational
safety,securityandmarineenvironmentalprotection.
According to the LRIT performance standard, the
LRIT information is provided to
Contracting
GovernmentsandSearchandRescueservicesentitled
to receive the information, upon request, through a
system of National, Regional, Cooperative and
InternationalLRITDataCenters.Therefore, theLRIT
information can only be used by the governmental
organs for maritime security, safety and marine
environmental protection. The confidentiality and
sensitivityof
theLRITinformationarehighlystressed
byContractingGovernmentsandnotsharedwithany
commercialentities.TheLRITinformationisofhigh
creditability. However, the satellite‐based AIS is
launchedanddevelopedbysomeprivatecompanies
andtheship’sinformationmaybewidelysharedby
thecommercialuserswhopay.
187
5 CONCLUSION
Itisobviousthatthesatellite‐basedAISandtheLRIT
system are developed to provide the service of the
shipdetectionandidentificationinthelongrangein
ordertoenhancethemaritimesafety,security,marine
environmental protection and the efficient shipping.
However, both also deserve the
pros and cons. The
satellite‐basedAIS seemsto experience the meritsof
the ship’s global monitoring coverage in theory and
the powerful information categories available in
contrast to the LRIT system. Nevertheless, the LRIT
system is designed as a navigation and
communication system and organized by the
Contracting Government
so that it is able to have a
bilateral link between the shore and the ship and
enjoy the better information creditability.
Additionally, the ship should bear the extra fee to
upgrade the current AIS equipment onboard to
effectivelysupporttheuseofthesatellite‐basedAIS.
Thereforethesatellite‐based
AIS does not supersede
the LRIT system as the LRIT system is more
governmental but the satellite‐based AIS is focusing
on more commercial. And the information provided
by the satellite‐based AIS is indeed welcome by the
industry to promote the efficient shipping, so the
satellite‐based AIS should
be encouraged and
developedinordertoeffectivelypla y acomplement
roletotheLRITsystem.
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