International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 2
Number 3
September 2008
229
EGNOS Status and Performance in the Context
of Marine Navigation Requirements
J. Cydejko
Gdynia Maritime University, Gdynia, Poland
ABSTRACT: The current status of EGNOS (December 2006) is described as Initial Operations Phase and the
EGNOS Open Service is just about to be formally declared as available for non-safety of life service. In
meanwhile the EGNOS Signal in Space is provided almost in its nominal level and delivering, when
available, the nominal system performance. New positioning technologies, such as EGNOS in Europe, create
a new quality in marine navigation and bring further improvement of the maritime transport safety. It may be
expected that very soon EGNOS will find significant interest among the maritime community serving as the
augmentation system in the maritime transport applications of GNSS. The paper discusses the EGNOS status
and the expected EGNOS performance in the context of marine navigation requirements. The system
performance analysis is backed with the study of the various field tests results where the EGNOS positioning
performance was verified by author in the experimental way.
1 EGNOS STATUS
European Geostationary Navigation Overlay Service
(EGNOS) is designed to provide in Europe the
regional augmentation to GPS and GLONASS
systems. The main objective of the implementation
such an augmentation is to improve the performance
of existing satellite positioning systems in the
context of accuracy, integrity, availability, and
continuity.
The EGNOS will be available for users in the
form of three services:
− The Open Service, consisting of provision of
unrestricted access to the signal in space (SIS)
without any guarantee of service.
− The Safety of Life (SoL) Service, consisting of
the provision of access to the SIS with a
guarantee of service regulated by a service-level
agreement and by specific requirements on user
terminal and the intended navigation operations.
− The Commercial Service, consisting of provision
of controlled access to the SIS and data regulated
by a commercial agreement.
On 28
th
of July 2005 EGNOS entered its Initial
Operations Phase (IOP). The main objectives of the
IOP are: to gradually increase operating efficiency
and performance, and to ensure that appropriate
resources are in place to guarantee the EGNOS
operation. The IOP consists of three phases:
rumping up, stabilization and qualification. Each
phase was planned to last six months. The end of
stabilisation phase supposed to be marked by
Operations Definition Review (ODR) and at this
stage EGNOS Open Service could be declared at the
discretion of the authorising bodies (specifically the
GNSS Supervisory Authority and European
Commission). After the ODR the qualification phase
to be conducted leading to Operation Qualification
Review (OQR), at which point EGNOS will be
capable of supporting safety-of-life operations. The
IOP is conducted by ESA contractor called ESSP
(European Satellite Service Provider), which is a
consortium of European companies, lead by Alcatel
230
Space. Following the OQR, the technical operation
of the EGNOS should be directly controlled by the
Galileo Concessionaire under formal management of
the GNSS Supervisory Authority (Ventura-Traveset
at el. 2006).
In spite of the established schedule, at the time of
writing (March 2007) none of the official bodies did
declared the EGNOS to be in its Open Service. The
latest major system modifications took place in July
2006 when the EGNOS Test Bed (ESTB) operation
was ceased and the full transition from ESTB to
EGNOS was concluded. The actual EGNOS SIS
status is as follows:
− The signal broadcast by the EGNOS satellites
IOR-W (PRN 126) and AOR-E (PRN120) is used
for EGNOS Initial Operations.
− The EGNOS ESA ARTEMIS satellite (PRN 124)
is currently used by industry to perform various
tests on the system.
Since July 2006 the operational EGNOS signal
broadcast on PRN126 and PRN120, is using the
MT0/2 and Band 9 of the Ionospoheric grid. The
addition of MT0/2 into the system has a big
significance in the development of EGNOS for users
of non-safety of life services. MT0/2 will allow all
receiver units, at their own risk, to process and use
the corrections broadcast by EGNOS for multimodal
non-safety of life applications. The provision of
Ionospheric Band 9 should improve the EGNOS
performance in the Northern European latitudes. The
EGNOS signal on PRN124, currently used for
testing, will broadcast in MT0/0 configuration
(EGNOS website). At the moment it can be assumed
that IOP phase will last till early 2008 when the SoL
service will start finally. In meanwhile, the
declaration of Open Service and Commercial
Service opening can be expected during year 2007.
Together with resolving certain legal issues the
technical infrastructure of EGNOS will evolve as
well. The technical objectives of future EGNOS
development include: extension system coverage to
the North Africa region, implementation Message
Type 0/2, enhancement of EGNOS RIMS to monitor
GPS L1/L5, Galileo and GLONASS (EGNOS News
2006).
2 EGNOS AND MARITIME TRANSPORT
REQUIREMENTS
In the maritime transport, the improvement of the
performance parameters of the satellite positioning
allows to extend the applicability of this method of
positioning to operations with high safety
requirements and in general improve the safety of
navigation. The framework of maritime transport
requirements for radionavigation systems
performance is formed by two IMO resolutions:
A.915(22) “Revised Maritime Policy and
Requirements for a Future GNSS” and A.953(23)
“World-Wide Radionavigation System”. First of
those documents must be viewed as guidance for
future developments of GNSS. Resolution
A.915(22) is very valuable in the context of defining
the operational requirements of various types of
maritime operation but in general is addressed to the
future satellite navigation systems such as: Galileo
or the second generation GPS. EGNOS as the
augmentation system of currently existing satellite
systems has to be analyzed in the context of
requirements set forth in the other document – IMO
Resolution A.953(23).
This document gives the formal requirements for
qualifying a radionavigation system as acceptable
and safe enough for current needs of the maritime
transport operations and in its general concept refers
to existing systems showing the direction towards
improvement of the actual performance and quality
of positioning based on radionavigation services.
The operational performance requirements for
maritime radionavigation systems stated in the IMO
Resolution A.953(23) are summarised in Table 1.
Table 1. Performance requirements for radionavigation systems
according to IMO Resolution A.953(23) adopted 5th December
2003.
Parameter
Area of navigation
Harbour entrances, harbour
approaches and coastal waters
Ocean waters
High volume
of traffic
and/or a
significant
degree of risk
Low volume
of traffic
and/or a less
degree of risk
Position
accuracy
(horizontal,
95%)
≤ 10 metres ≤ 10 metres ≤ 100 metres
Coverage
adequate to provide position-
fixing throughout this phase of
navigation
Global
Update rate
(computed
and displayed
position)
≤ 10 seconds ≤ 10 seconds ≤ 10 seconds
Update rate
(if used for
AIS,
graphical
display or
direct control
of ship)
≤ 2 seconds ≤ 2 seconds ≤ 2 seconds
Availability
≥ 99.8%
(2 years
period)
≥ 99.5%
(2 years
period)
≥ 99.8%
(30 days
period)
231
Continuity
≥ 99.97%
(3 hours
duration)
≥ 99.85%
(3 hours
duration)
NA
Time-to-
alarm
10 seconds 10 seconds
as soon as
practicable
by Maritime
Safety
Information
(MSI)
systems.
The required operational performance of EGNOS
is defined in the terms of the civil aviation needs and
it is expected that EGNOS SIS (Signal in Space) will
at least fulfil requirements of APV-II (Approach
with Vertical Guidance) operation:
− position accuracy: horiz. – 16 m, vert. – 8 m;
− integrity: time-to-alarm – 6 s; integrity risk –
1÷2 × 10-7/150 s; alarm limit – 20 m vert., 40 m
horiz.;
− availability: 99.9% ÷ 99.999%;
− continuity risk: 1÷8 × 10-6/15 s (equivalent of
0.72÷5.76 × 10-3/3hours) – (highest requirement
in maritime transport 3 × 10-2/3hours).
Above aviation requirements are stricter in every
aspect than those set forth in IMO Res. A.953(23).
It is worth to explain that with GNSS or any its
augmentation it is much easier to achieve the better
horizontal position accuracy than vertical, so by
complying to 8 meter vertical position accuracy
requirement EGNOS has to bring the horizontal
position accuracy well below 10 metres level.
Additionally, the APV-II requirements describe
expected EGNOS performance by some additional
parameters, such as integrity risk and alarm limits,
which are not stated in Res.A.953(23) but have been
defined as the maritime transport requirements for
future GNSS and set forth in IMO Res.A.915(22).
In this context EGNOS potentially fulfils the
maritime transport requirements not only as
component of the current World-Wide Radio-
navigation System (Res.A.953(23)) but as “Future
GNSS” (Res.A.915(22)) as well.
The final performance of EGNOS in the aspect of
integrity, continuity and availability will be achieved
after the service reaches its full SoL (Safety–of-Life)
application operability. So this is, why in the further
part of paper the actual EGNOS performance in
various areas is mainly characterized in the aspect of
the positioning accuracy.
3 EGNOS PERFORMANCE ON THE POLISH
COAST
When a new positioning system appears, it always
raises questions about that how good is it and is it
good enough for various applications. These
questions become worthy to answer especially while
talking about the Wide Area DGPS solution, which
is highly dependent on the errors modelling over
large areas. In this context, the verification of the
EGNOS performance in various regions becomes the
important issue. Along The Polish Coast, EGNOS
may find many potential users serving as the
augmentation of the positioning in the general and
coastal navigation or during the port operations. This
region, however, is located on the eastern edge of
nominal EGNOS coverage and there is a possibility
that the EGNOS accuracy in this region may be
somehow degraded than that what is observed in the
areas better covered by RIMS network.
Below the results of the tests of satellite
positioning with using EGNOS signal are presented.
The tests were conducted in the period after EGNOS
had been declared to be in its Initial Operations
Phase. In its main approach, the conducted
experiments were focused on the verification of
EGNOS performance in the context of maritime
applications of the system. So this is why, the
EGNOS accuracy is referred to maritime DGPS
performance and the tests took place on the Polish
Coast.
The results of conducted tests are presented in
figures below. In Figures 1-3 the horizontal position
error (HPE) or vertical position error (VPE) obtained
during positioning for various systems (EGNOS,
DGPS, GPS) or for different test sites (Gdynia;
Dziwnów) is compared in several ways. Figure 1
presents and compares all-day position scatter plots.
In Figure 2 the epoch-to-epoch HPE comparison of
selected systems is given. The graphs included in
Figure 2 show the distribution of points defined by
two HPEs observed in the same time in two different
receivers. The percentage of points located closer to
one of two axes visualizes a quantity of epochs,
while one receiver was giving less HPE than the
other. Figure 3 summarizes the statistical parameters
describing the accuracy of positioning observed with
different systems or for different test sites during
selected day periods and for whole day
measurements. During tests, in both sites, the
positioning was performed in static conditions with
the antennas of the receivers located in known,
precisely surveyed positions.
Having access to the EGNOS performance
monitoring data, published on Internet, for Warsaw
RIMS, the field measurements obtain in Gdynia
could be referred to those, which were observed, at
the same time, in the closest EGNOS monitoring
station in Warsaw. The graph, presented in Figure 4
compares the EGNOS HPE observed during field
tests in Gdynia to the EGNOS HPE logged during
the same day in Warsaw RIMS.
Finally the Figure 5 gives the comparison of
EGNOS performance parameters observed in
232
various monitoring stations across Europe. This
summary was based on information collected from
ESA website. The sites chosen for analysis have
been selected with the intension to compare the
EGNOS performance in some extreme locations at
the edge of the nominal service coverage (Tromso,
Warsaw, Madrid) with those observations, which are
obtained in the core of the service (Brussels,
London). The Figure 5 compares the following
performance parameters: Horizontal Position Error
(HPE), Horizontal Protection Level (HPL), Vertical
Position Error (VPE), Vertical Protection Level
(VPL) and daily service availability for APV-I and
APV-II operations. Protection Levels calculated
within EGNOS describe the level of guarantee,
which may be given by service that the positioning
accuracy stays below the certain value. The data
presented in the graph are the averages of the daily,
95% confidence level values of the each individual
parameter logged at the end of every day in the
period between 26th and 31st March 2007.
Fig. 1. Position scatter plots for GPS, EGNOS, DGPS observed during all-day measurements referred to “true” position
Fig. 2. Epoch-to-epoch comparison of HPE and VPE value between various methods of positioning or between various locations
Horiz. Error(95%)
2.13 m
Horiz.
Error(95%)
Horiz. Error(95%)
1.66 m
Horiz. Error(95%)
3.42 m
Bias:
1.00 m North
0.15 m East
Bias:
1.08 m North
0.05 m East
Bias:
0.06 m North
-0 09 m East
Bias:
0.66 m North
0.40 m East
Epoch-to-Epoch HPE comparison
various systems and locations
48%
35%
52%
65%
HPE
EGNOS(Dziwnów)
bigger than
HPE
EGNOS(Gdynia)
HPE
EGNOS(Gdynia)
bigger than
HPE
GPS
233
Fig. 3. Summary of position accuracy statistics obtained during experiment for various positioning methods, various locations and
various periods of the day
Fig. 4. EGNOS HPE observed in Gdynia compared to HPE and Horizontal Protection Level (HPL) logged, in the same time, in
RIMS Warsaw – all day measurements (EGNOS website)
234
Fig. 5. EGNOS performance across Europe. Average daily values of HPE, HPL, VPE, VPL and APV availability observed in
various EGNOS monitoring stations between 26sh and 31st March 2007(EGNOS website)
4 CONCLUSIONS
The horizontal EGNOS position accuracy in the area
of experiment estimated during the all-day static test
has reached the following values:
− horizontal error (95%) referred to true position –
2.13 to 2.17 meters;
− average position offset (bias) from true position –
1.1 meters to North;
− maximum single position HPE - not higher than
6 meters.
The performance of EGNOS is stable and at the
same level during various day periods (daylight,
night, sunrise, sunset) and the observed magnitude of
the single HPEs and statistical errors in both test
sites on the two edges of Polish Coast are similar.
The accuracy of EGNOS observed during field
tests on the Polish Coast is worse than the accuracy
obtained during the same time in the closest
(~350 km away) RIMS station in Warsaw but the
differences are not big (approx. 0.5m of horizontal
error (95%)) and explainable by field nature of the
tests conducted in Gdynia.
The EGNOS at the current stage of development
delivers the comparable positioning accuracy as the
maritime DGPS service. Slightly better absolute
(referred to true position) accuracy of DGPS,
expressed by lower values of 95% horizontal
position error, can be considered as the result of
lower offset (bias) of position estimates (lower offset
of DGPS average position). This fact can be
considered as the obvious advantage of Local Area
DGPS over Wide Area DGPS, especially while close
reference station is used (Rozewie ~40 km away).
The EGNOS performance may differ in various
locations and may be degraded in the areas located at
the edge of the nominal system coverage (Fig.5,
Tromso and Warsaw). This service degradation is
not so big in the context of positioning accuracy but
exists mostly in the aspect of predictable service
reliability (protection levels, availability).
Summarizing, it may be stated that the results of
EGNOS Initial Operations Phase positioning
presented in the paper show that this system is able
to deliver users the service, which gives the
comparable positioning accuracy as the maritime
DGPS actually utilized in maritime transport.
However, having in mind that EGNOS is providing
to users the integrity channel and improves the
satellite positioning availability, there are no doubts,
that implementing EGNOS into the maritime
transport applications is a good step towards the
creation of the new quality of the navigational safety
at sea.
REFERENCES
EGNOS website – EGNOS for Professionals
http://esamultimedia.esa.int/docs/egnos/estb/egnos_pro.htm
EGNOS News. 2006 Volume 6, Issue 1, EGNOS Project
Office ESA, May.
IMO Resolution A.915(22). Revised Maritime Policy and
Requirements for a Future GNSS adopted on 29th
November 2001. London.
IMO Resolution A.953(22). Revised World-Wide Radio-
navigation System adopted on 5th December 2003. London.
Ventura-Traveset J. & Flament D. et al. 2006. The European
Geostationary Navigation Overlay System – A cornerstone
of Galileo. ESA Publications. SP-1303.
