581
1 INTRODUCTION
Thebasicmethodofincreasingthenavigationsafety
isto ensure precision shippositioning by setting up
navigation marking systems, including radio
navigation systems accessible to all vessels
[Czaplewski, K., 2018; Czaplewski, K., Goward, D.,
2016; Jang, W.S. et al., 2018; Specht, C. et al., 2016].
The Differential
Global Positioning System (DGPS)
system in its marine version is the basic positioning
system for coastal navigation and it is also widely
used in hydrography, both marine and inland
[Stateczny, A. et al., 2018], meeting all categories of
requirements laid down in the International
Hydrographic Organization (IHO) S‐44 standard
[IHO, 2008]. Moreover, DGPS system also has other
applications,includingoffshoreactivities[Baptista,P.
etal.,2008].
At the same time, methods of positioning
improvement are applied both by such technical
solutions as alternative positioning systems [Kelner,
J.M.etal.,2016;Sadowski,J.,Stefański,J.,2017],radar
positioning [Stateczny, A.
et al., 2019] and multi‐
GNSS (Global Navigation Satellite System) solutions
[Specht, C. et al., 2019a; Yang, C. et al., 2016] using
Kalmanfiltering[Xinchun,Z.etal.,2016].
Unlike various alternative positioning solutions
mentionedhere,themarineDGPSsystemdominated
the vessel positioning process due to the following
operational
features:
Polish DGPS System: 1995-2018
–
Studies of Reference
Station Operating Zones
C.Specht,M.Specht&P.S.Dąbrowski
GdyniaMaritimeUniversity,Gdynia,Poland
ABSTRACT: The operating zone of a radio navigation system is one of its main operating features. It
determinesthesizeofawaterbodyinwhichthesystemcanbeused,whileguaranteeingvessels’navigation
safety.
TheDGPSsystemintheLF/MFrangeisnow
thebasicpositioningsystemincoastalwatersaroundtheworld,
whichguaranteesnotonlymetrepositioningaccuracy,butitisalsotheonlyonetoprovidenavigatorswith
signalsonpositioningreliability.
ThispaperdescribesandsummarisesovertwentyyearsofstudiesdealingwiththeoperatingzoneofthePolish
DGPS
referencestationnetwork.Thispaperisthefifthinaseriesofpublicationswhoseaimwas topresentin
detailtheprocessofinstallation,testingandlong‐termevaluationofthenavigationalparametersofthePolish
DGPS system, launched in 1995. This paper includes the theoretical foundations of determination of
the
DziwnówandRozewieDGPSreferencestationoperatingzonesintheyears1995‐2018.Moreover,itpresents
the measurement results for the signal levels and the results of their analyses, which determine the station
operatingzones.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 13
Number 3
September 2019
DOI:10.12716/1001.13.03.13
582
referencestationsareplacedatthesamelocations
whereradiobeaconsusedtooperate,whichmade
it possible to use the existing transmission
infrastructure,
atypicalrangeofareferencestationisapprox.100
km,whichmakesitpossibletocovermostwaters
ofcoastalstates,
thepositioningaccuracyofapprox.1m(p=0.95)
guarantees high navigation safety for vessels
approaching ports, which is competitive against
other commonly accessible systems [Specht, C. et
al.,2019b],
the ability of the DGPS system to transmit
positioningreliabilitysignalsisuniqueamongall
thepositioningsystemsworldwide.
Being a combined system, the marine DGPS
system requires that the operating zone should be
definedasaspatialproductoftheGlobalPositioning
System(GPS)operatingzoneandtheDGPS
reference
station operating zone. The GPS system operating
zone is by definition regarded as global, but due to
the dynamics of the satellite constellation system
movementandavariablenumberofsatellitesvisible
above the required topocentric altitude, it can be
alternativelydefinedasafunctionoftime[Specht,C.
et
al.,2015].Inthiscase,itacquiresaspatial‐temporal
dimensionratherthanbeingonlywaterbody‐related.
The availability of individual satellites in an area
[Specht, C., Dąbrowski, P., 2017], their average
number in a global approach and their geometric
configuration, and in pa rticular their constellation
within a
specific period of time, can be predicted
analytically.
Thefollowingaretheproposedprecisedefinitions
ofbothterms:
a GPS operating zone is the percentage of time
relative to its predefined interval, during which
the required number of satellites is above the
required topocentric altitude, thereby enabling
users to determine position with a permissible
error,atanypointonorabovetheEarth,
a DGPSreferencestationoperatingzoneisaspace
referred to geographic coordinates of the DGPS
reference station (
, , h), in which telemetric
transmission can be received with required
reliability.
Thispaperpresentsthetheoreticalfoundationsof
the DGPS operating zone determination and shows
thefindingsofresearchonthePolishDGPSsystemin
theyears1995‐2018.
2 THEDGPSSYSTEMOPERATINGZONE–
THEORETICALFOUNDATIONS
Sending radio
signals, associated directly with the
systemrangeandcoverage,dependsonanumberof
factors and circumstances. Propagation conditions
vary depending on the place, time and frequency
range. However, although the radio wave
propagation theory is well developed, calculation
resultsbasedonformulasandtheoreticalcurvesoften
deviate from reality
[Enge, P. et al., 1992]. This is
caused by an insufficiently strict approach to highly
complex propagation phenomena, their insufficient
explanation and practically unavoidable
simplifications. Therefore, theoretical considerations
regarding the coverage of an area by a radio
navigation system must be verified practically, and
theplanneddeploymentofaDGPSreference
station
shouldtakeintoaccounttherealresultsofoperating
systemsofthistype.
Characteristic features of 300 kHz radio waves
include different propagation conditions during the
dayandnight,whichiscausedbytheoccurrenceof
thesurfacewaveandtheskywaveatnight.Theycan
cause undesired interference
(Figure 1), resulting in
even signal disappearance. The DGPS‐related
experience so far shows that the effect of this
interference is not significant (over distances under
consideration)[Specht,C., 1997], although obviously
it has to be considered at boundary ranges and its
occurrencemustbepredictedevenduringthedayin
winter [Huuhka, E., Lehtoranta, V., 1995]. For this
reason, radio wave propagation at this frequency
shouldbeconsideredmainlyfromthepointof view
of the surface wave propagation, particularly taking
intoaccounttheeffectofthegroundandinterference.
Figure1. Thesignalstrength‐E[dBμ] (blue) of a Hoburg
DGPSreferencestationandthemeanpositioningerror‐M
(p=0.95)(red)asafunctionoftime.Recording:24‐05‐1995
11:50 UTC – 25‐05‐1995 04:50 UTC, Gdynia, measurement
frequency:1minute[Specht,C.,1997].
It is noteworthy that interference of the surface
wave and skywave at night results in fluctuation of
the Signal‐to‐Noise Ratio (SNR), which causes
changes in the Bit Error Rate (BER) and, ultimately,
damages Radio Technical Commission for Maritime
(RTCM) messages. This results in increasing of the
Age of Corrections
(AoC) and, further, mean
positioningerror (M).Accordingtotherequirements
for telemetric transmission of the DGPS system, the
minimumSNRis7dB,withBERof10
‐3
.Itshouldbe
acceptedthatapartfromtherequiredsignalstrength
(34 dBμ), the required SNR value is another factor
which determines the DGPS reference station
operatingzone.
ADGPSreferencestationtransmitssignalswithin
the range of: 283.5‐325 kHz with Minimum‐Shift
Keying(MSK),atatransmission
speedof(R):50,100,
200bd.Inpractice,itisacceptedthattheradiosignal
at distances larger than 70 Nm from a broadcasting
antennaneartheEarthsurfaceisafieldconsistingof
twotypesofwaves:surfaceandionospheric.Signals
sentfromaDGPS referencestationbasically reach
a
useronasurfacewave.Thesignalstrengthdepends
mainly on the radio beacon transmitter power, the
receiver‐station distance and conductivity of the
groundabovewhichtheradiowavepropagates.The
received signal strength for the ground of the ideal
conductivitycanbeexpressedwiththeformula:
583
5
10 10
310
20 log 10 log
1000
P
E
d
, (1)
where:
E
– signalstrength[dBμ],
P –radiatedpower[kW],
d –distancefromtransmitter[km].
This equation also describes approximate
propagationconditionsabovethemediumofvariable
conductivity,butitistrueonlyforsmallranges.With
respecttotherealconditions,thesignalstrengthcan
becalculatedfromthefollowingformula:
5
0
310 P
EF
d
, (2)
where:
0
E
– signalstrength[μV/m],
F
– dampingfactor[‐].
The value of
F
for routes of non‐uniform
conductivity is calculated by the Millington method
taking into account the electric properties of
individualsectionsoftheroute.Ifarouteconsistsof
twosectionsofdifferentelectricproperties,then:
11 2 2
21
21 12
,,
,,
,,
Fd F d
F
Fd Fd
Fd Fd
, (3)
where:
11
,
F
d
– dampingfactorcalculatedforauniform
routesectionofconductivity
1
andlength
1
d [‐],
d –sumofdistances
1
d
and
2
d
[m].
The damping factor for routes of uniform
conductivity can be calculated from Burrows graphs
orfromanapproximateformula:
2
20.3
20.6
d
dd
x
F
x
x
, (4)
where:
22
22
'1 60
'60
d
d
x
, (5)
assumingthat:
d
x
– distancenumber[‐],
d
– distancefromthestation[m],
'
– relativepermittivity[ ‐],
– wavelength[m],
– groundconductivity[mS/m].
Another method of the surface wave signal
strength determination uses Comité Consultatif
International des Radiocommunications (CCIR)
curves.
SkywaveisanothersignalwhichreachesaDGPS
receiver, especially at night. A radio wave from the
DGPS station transmitter antenna reaches the
ionosphere layer D, from which it
is reflected and
interfereswiththesurfacewave,creatingionospheric
interference.TheconditionoftheionosphericlayerD
is a function of: time of day and time of year,
geomagneticlatitude.Duringtheday, the sunisthe
basicionizationsource,creatinganeffectivereflection
surfaceat70km(thesun
atitszenith)and75km(at
sundown). Solar ionization disappears at night and
theeffectivereflectionsurfaceincreasesto80‐90km.
Thesignalstrengthinashortverticalantennacan
bedescribedas:
52
310 cos
s
jtr
sky
PRDFF
E
s
, (6)
where:
s
ky
E
– signalstrengthofskywave[μV/m],
– anglebetweenthedirectionofpropagationand
thehorizon[rad],
s
R
– ionosphericreflectioncoefficient[‐],
j
D
– ionosphericconditioncoefficient[‐],
t
F
– a coefficient characterising the transmitter
antenna[‐],
r
F
– acoefficientcharacterisingthereceiverantenna
[‐],
s
– totallengthofskywave[km].
Assuming the spherical shape of the Earth, the
valueofscanbeexpressedas:
1
2
2
2
22cos
2
EEEE
sRhRRRh
, (7)
where:
R
E–Earthradius[km],
h–effectivereflectionaltitude[km],
– central angle between the transmitter and the
receiver[rad],
therefore:
2sin
2
cos
E
Rh
s
. (8)
Figure 2 presents signal strength curves. The
signalstrengthforthesurfacewaveandskywaveasa
functionofthetimeofdayandtimeofyear,distance
from the reference station for the frequency of 300
kHzandEPRof1kW.
Figure2. The signal strength for the surface wave and
skywaveasafunctionofthetimeofdayandtimeofyear,
distancefromthereferencestationforthefrequencyof300
kHz and EPR of 1 kW. The red line denotes the signal
strengthforthesurfacewave[IALA,
1996].
584
3 TESTINGTHEPOLISHDGPSSYSTEM
OPERATINGZONE
3.1 Studyintheyears:1995‐1996
The implementation work conducted during the
processoflaunchingthePolishDGPSsystemin1995‐
1996focusedonestablishingtwobasiccharacteristics
ofthesystem:positioningaccuracyandtheoperating
zone. Since no software for
determining the system
operating zone was available, it was decided to
conduct the measurements directly in the sea. The
energymeasurements(signalstrength)fortheDGPS
referencestationwereconductedmultipletimes and
simultaneouslywithothersystemstudiesinsummer
andwinter(1995‐1996).
Figure 3 shows the operating zones
– signal
strengthforbothDGPSreferencestations(Dziwnów
andRozewie).
Figure3. The Dziwnów and Rozewie DGPS reference
stationoperatingzonesin1996[Specht,C.,1997].
The signal level of 50μV/m is regarded as the
operating zone border value, which means that the
PolishDGPSsystemoperatingrangewas60and100
km for the Dziwnów and Rozewie DGPS reference
stations.
Table1showstheplannedandreal(basedonthe
measurements) operating zones for both
DGPS
referencestations(DziwnówandRozewie).
Table1.Radiatedpowermeasurementsresultswithsource
dataforPolishDGPSsystems[Specht,C.,1997].
_______________________________________________
Station Geographic Nominal Nominal ERP
name coordinates rangerange[W]
(50μV/m) (50μV/m)
source actual
data[km] data[km]
_______________________________________________
Dziwnów 54˚01’N 90550.1
14˚44’E120*0.5*
Rozewie 54˚49’N 901000.4
18˚20’E
_______________________________________________
*forsimulateddata
3.2 Studyafter systemmodernisationin2002
Opinions on the need to use the DGPS system
appearedintheliteratureinthelate1990s.Itturned
outthattheclose(local) monitoringdoesnotmeetthe
system users’ expectations. There were situations in
which the DGPS system was not available at
a
considerable distance from the reference station
(several dozen kilometres) and the local monitoring
didnotgenerateanalarm.Therefore,itwasdecided
to set up additional monitoring stations in the most
dangerousareasfornavigation.Amonitoringstation
inthePortofGdynia waslaunched forthe Rozewie
DGPS
referencestation,andoneinSzczecin–forthe
DziwnówDGPSreferencestation.
In2002,underanagreementbetweenthemaritime
offices, a decision was taken to hand over the
technical infrastructure of the Dziwnów DGPS
referencestationtotheMaritimeOfficeinGdynia.It
resultedinasystemwhichis
controlledbyonestation
inGdynia.ReconnectingthesystemsofDziwnówand
Rozewie DGPS reference stations and handing over
thecoordinationofrunningthewhole DGPSsystem
should be regarded as justified and in line with
international standards. The essence of the
modernisationlayinreplacementofthetransmitting
antennas
inbothstations,resultinginaconsiderable
increase in the system operating range. Figure 4
shows the new transmitting antennas in the station.
Replacement of the antenna in the Dziwnów DGPS
reference station was of particular importance
because its grounding failed to meet the required
technicalstandards.
Figure4. The transmitting antennas in the Dziwnów (left)
andRozewie(right)DGPSreferencestations,modernisedin
2002.
Thesechangesresultedinaconsiderable increase
in the operating range of both stations. Tests
conductedin2002showedthattheoperatingrangeof
theRozewieDGPSreferencestationwas300km,and
thatoftheDziwnówDGPSreferencestation–150km.
The operating ranges of both stations are shown
in
Figure5.
585
Figure5. The Dziwnów and Rozewie DGPS reference
stationoperatingzonesin2003[Specht,C.etal.,2016].
3.3 Studyafter systemmodernisationin2007
Thesystemmodernisationstartedin2007.Thefirstto
be modernised by the Gdynia Maritime Office was
theRozewieDGPSreferencestationandtheCentral
Control Station (CCS) in Gdynia. The modernisation
workattheDziwnówDGPSstationwascompletedin
July2008,and
attheRozewieDGPSstation–inApril
2011[Dziewicki,M.,Specht,C.,2009].
As part of the National Maritime Safety System,
thorough modernisation of the Polish DGPS system
wascompletedinApril2011.Itiscurrentlypartofthe
integratednavigationmarkingsystemoftheMaritime
Office in Gdynia.
Owing to a subsidy from the
EuropeanUnion(EU),wornequipmentandsoftware
at the DGPS stations was replaced with a new
generation of devices; it included old systems of
antenna masts and GPS receivers. The new system
organisationisshowninFigure6.
Figure6.OrganisationofthePolishDGPSsystemafterthe
modernisationin2007‐2011[Specht,C.,2011].
The aim of the DGPS transmitting infrastructure
modernisationplanwasmainlytoimprove thestate
of maritime safety; it was developed for the coastal
navigation and navigation marking services,
hydrographic services, search services, marine
engineering, etc. Operation of both stations is
monitored from Gdynia. Now each station has two
modernreceivers
andtwotransmitters,whichreactto
changes in atmospheric conditions, adjusting the
radiatedpoweraccordingly.Theold,run‐downAGA
antennas,madeofsteel,hadbeeninusefor50years
andthemastguywiresabsorbedpartoftheradiated
energy. They were replaced with modern, effective
and durable,
plastic rod antennas. This unique
solution was implemented by Elecom‐Mastertech of
Gdynia as the last stage of the comprehensive
modernisation of the National Maritime DGPS
Network. The Rozewie DGPS reference station
operatingzoneisshowninFigure7.
Figure7. Signal strengthlevel in dBμV/mfor the Rozewie
DGPSreferencestation[Specht,C.,2011].
Basedonthe signal strength level measurements,
ERPwascalculatedasa4.02Wforthetransmitterof
the Rozewie DGPS reference station. Presented
coverageofthemodernisedRozewieDGPSreference
station (Figure 7) guarantee maximum range for the
systemas200km(for34dBμV/m).
4 CONCLUSIONS
ThePolish
DGPSsystemisnowthemainpositioning
systeminthewaterbodiesoftheRepublicofPoland.
It is used mainly to ensure navigation safety for
vesselsandinhydrography.Intermsofitstechnical
equipment,thePolishDGPSsystemisatthehighest
level.Owingtotheequipmentmodernisation
in2002‐
2003 and in 2007‐2011, the operating range has
increased two‐fold and the positioning accuracy has
increased nearly five‐fold. These modernisation
workswere taken in accordance with the guidelines
for e‐Navigation [Urbański, J. et al., 2008], whose
principleswereformulatedbyInternational Maritime
Organization(IMO)
andareimplementedbycarrying
out the Efficient, Safe and Sustainable Traffic at Sea
(EfficienSea)projectco‐financedfromthefundsofthe
InterregBalticSeaRegionProgramme.
REFERENCES
Baptista, P., Bastos, L., Bernardes, C., Cunha, T., Dias, J.
(2008).MonitoringSandyShoresMorphologiesbyDGPS
–APracticalTooltoGenerateDigitalElevationModels,
JournalofCoastalResearch,Vol.24(6), pp.1516‐1528.
Czaplewski, K. (2018). Does Poland Need eLoran?,
Proceedings of the 18
th
International Conference on
TransportSystemTelematics(Kraków,Poland),pp.525‐
544.
Czaplewski, K., Goward, D. (2016). Global Navigation
Satellite Systems – Perspectives on Development and
Threats to System Operation, TransNav, the
586
International Journal on Marine Navigation and Safety
ofSeaTransportation,Vol.10,No.2,pp.183‐192.
Dziewicki, M., Specht, C. (2009). Position Accuracy
Evaluation of the Modernized Polish DGPS, Polish
MaritimeResearch,Vol.16(4),pp.57‐61.
Enge, P., Levin, P., Hansen, A., Kalafus, R. (1992‐1993).
Coverage of DGPS/Radiobeacons,
NAVIGATION, the
JournaloftheInstituteofNavigation,Vol.39(4),pp.363‐
380.
Huuhka, E., Lehtoranta, V. (1995). Study of Night‐Time
CoverageofDGPSRadiobeaconsinFinland,Document
preparedforFinnishMaritimeAdministration,Tuusula.
IALA (1996). IALA RNAV 5/3.5/2, GNSS and DGNSS
SubmissionfromUSCG.
IHO (2008). IHO Standards
for Hydrographic Surveys,
SpecialPublicationNo.44,5
th
Edition.
Jang, W.S., Park, H.S., Park, S.G. (2018). Analysis of
PositioningAccuracyofPPP, VRS, DGPSin Coast and
InlandWaterAreaofSouthKorea,In:Shim,J.‐S.,Chum,
I.,Lim,H.S.(eds.),Proceedingsofthe15
th
International
CoastalSymposium(Busan,RepublicofKorea),Journal
ofCoastalResearch,SpecialIssueNo.85,pp.1276‐1280.
Kelner, J.M., Ziółkowski, C., Nowosielski, L., Wnuk, M.
(2016). Reserve Navigation System for Ships Based on
Coastal Radio Beacons, Proceedings of the 2016
IEEE/ION Position, Location and Navigation
Symposium(Savannah,USA),
pp.393‐402.
Sadowski, J., Stefański, J. (2017). Asynchronous Phase‐
Location System, Journal of Marine Engineering &
Technology,Vol.16(4),pp.400‐408.
Specht, C. (1997). Multicriterial Analyses of DGPS in
ContextofRadionavigationServiceontheSouthBaltic,
Doctoral Thesis, Polish Naval Academy, Gdynia (in
Polish).
Specht, C. (2011).
Accuracy and Coverage of the
Modernized Polish Maritime Differential GPS System,
AdvancesinSpaceResearch,Vol.47(2),pp.221‐228.
Specht, C., Dąbrowski, P. (2017). Runaway PRN11 GPS
Satellite, Proceedings of the 10
th
International
Conference „Environmental Engineering“ (Vilnius,
Lithuania),pp.1‐6.
Specht,C.,Dąbrowski,P.,Pawelski,J.,Specht,M.,Szot,T.
(2019a). ComparativeAnalysis of Positioning Accuracy
ofGNSSReceiversofSamsungGalaxySmartphonesin
Marine Dynamic Measurements, Advances in Space
Research,Vol.63(9),pp.3018‐3028.
Specht, C., Mania,
M., Skóra, M., Specht, M. (2015).
AccuracyoftheGPSPositioningSystemintheContext
of Increasing the Number of Satellites in the
Constellation,PolishMaritimeResearch,Vol.22(2),pp.
9‐14.
Specht, C., Pawelski, J., Smolarek, L., Specht, M.,
Dąbrowski, P. (2019b). Assessment of the Positioning
Accuracy of DGPS
and EGNOS Systems in the Bay of
Gdansk Using Maritime Dynamic Measurements, The
JournalofNavigation,Vol.72(3),pp.575‐587.
Specht, C., Weintrit, A., Specht, M. (2016). A History of
MaritimeRadio‐NavigationPositioningSystemsUsedin
Poland,The Journal of Navigation,Vol. 69(3), pp. 468‐
480.
Stateczny, A.,
Kazimierski, W., Burdziakowski, P., Motyl,
W., Wisniewska, M. (2019). Shore Construction
Detection by Automotive Radar for the Needs of
Autonomous Surface Vehicle Navigation, International
JournalofGeo‐Information,Vol.8(2),pp.1‐19.
Stateczny,A.,Włodarczyk‐Sielicka,M.,Grońska,D.,Motyl,
W. (2018). Multibeam Echosounder and LiDAR in
Process
of 360‐Degree Numerical Map Production for
RestrictedWaters with HydroDron, Proceedings ofthe
2018 Baltic Geodetic Congress (Gdańsk, Poland), pp.
288‐292.
Urbański, J., Morgaś, W., Specht, C. (2008). Perfecting the
Maritime Navigation Information Services of the
European Union, Proceedings of the 1
st
International
Conference on Information Technology (Gdańsk,
Poland),pp.1‐4.
Xinchun,Z.,Ximin,C.,Dongkun,Y.(2016).Applicationof
Modified Kalman Filtering Restraining Outliers Based
on Orthogonality of Innovation to Track Tester,
Proceedings of the 2016 IEEE International Conference
on Mechatronics and Automation (Harbin, China), pp.
171‐175.
Yang,
C.,Mohammadi,A.,Chen,Q.W.(2016).Multi‐Sensor
FusionwithInteractionMultipleModelandChi‐Square
TestTolerantFilter,Sensors,Vol.16(11),pp.1835.
