GNSS Integrity in the Arctic

Full text

GNSS Integrity in
The Arctic
Tyler G. R. Reid, Todd Walter, Juan Blanch, & Per K. Enge
Stanford University
BIOGRAPHY
Tyler G. R. Reid is a Ph.D. candidate in the GPS
Research Laboratory working under the guidance of
Professor Per Enge and Dr. Todd Walter in the
Department of Aeronautics and Astronautics at Stanford
University. He received his B. Eng. in Mechanical
Engineering from McGill University in Canada in 2010
and his M.Sc. in Aeronautics and Astronautics from
Stanford University in 2012. He has also worked as a
software engineer for Google’s Street View.
Todd Walter is a senior research engineer in the GPS
Research Laboratory in the Department of Aeronautics
and Astronautics at Stanford University. He received his
Ph.D. from Stanford in 1993 and has worked extensively
on the Wide Area Augmentation System (WAAS). He has
received the Thurlow and Kepler awards from the
Institute of Navigation (ION). In addition, he is a fellow
of the ION and has served as its president
Juan Blanch is a senior research engineer in the GPS
Research Laboratory in the Department of Aeronautics
and Astronautics at Stanford University. He graduated
from École Polytechnique in France in 1999 and received
his M.Sc. in Aeronautics and Astronautics from Stanford
University in 2000. He completed both a M.Sc. in
Electrical Engineering and a Ph.D. in Aeronautics and
Astronautics at Stanford in 2004. He has worked
extensively on integrity algorithms for Space-Based
Augmentation Systems as well as Receiver Autonomous
Integrity Monitoring.
Per K. Enge is a Professor of Aeronautics and
Astronautics at Stanford University, where he is the
Vance and Arlene Coffman Professor in the School of
Engineering. He has received the Kepler, Thurlow, and
Burka Awards from the Institute of Navigation. He also
received the Summerfield Award from the American
Institute of Aeronautics and Astronautics (AIAA) as well
as the Michael Richey Medal from the Royal Institute of
Navigation. He is a fellow of the Institute of Electrical
and Electronics Engineers (IEEE), a fellow of the ION,
and a member of the National Academy of Engineering.
He received his Ph.D. from the University of Illinois in
1983.
ABSTRACT
Growing activity in the Arctic calls for high integrity
navigation in this region. Since 1980, the summer Arctic
sea ice has decreased by more than 50%. This now
accessible Arctic Ocean has attracted many industries to
the region such as oil and gas, fishing, and tourism. There
is also the prospect of new shorter shipping routes,
bypassing the Suez or Panama Canals in favor of the now
open Arctic Ocean. This harsh environment and remote
reaches necessitate the highest levels of safety both at sea
and in the air. This secluded setting has limited
infrastructure, lending itself to a space-based architecture
for achieving navigation safety based on Global
Navigation Satellite Systems (GNSS).
GNSS integrity can be achieved via Satellite Based
Augmentation Systems (SBAS) as well as Advanced
Receiver Autonomous Integrity Monitoring (ARAIM).
Here we examine both in the context of aviation and
maritime navigation requirements. SBAS relies on
ground-based and space-based infrastructure. ARAIM,
planned for 2029, is more self-contained and will rely on
the multitude of frequencies and core constellations
coming in the future. Single frequency GPS-only SBAS is
available today in North America, Europe, Japan, and
India but falls short in the Arctic. By 2021, more systems
are expected to come online, enabling service in Russia,
South Korea, and China. It is 2026, which brings multi-
frequency and multi-constellation to SBAS, that holds the
key to enabling service in the Arctic. The existing ground
infrastructure was found to be sufficient, though the
geostationary (GEO) space segment was not. GEOs have
a coverage limit of 72oN, falling short in the Arctic.
Here we propose the Japanese Quasi-Zenith Satellite
System (QZSS) to deliver SBAS corrections to the Arctic.
With such a link in place, SBAS can enable aircraft
precision approach and even precise maritime operations
such as mapping. ARAIM was also found able to support
aircraft precision approach and autonomous ice
navigation at sea, but falls short of the precision maritime
requirements. Thus, depending on the application at hand,
ARAIM or SBAS may present the better option, though
both have their individual merits in the Arctic.

INTRODUCTION
The once inaccessible Arctic Ocean has gained economic
attention as a result of the recession of the Arctic sea ice.
As shown in Figure 1, the summer Arctic sea ice extent
has decreased by more than 50% since 1980 [1]. This
decline is projected to continue and the Arctic is likely to
be ice free in the summer months sometime between 2030
and 2080 [2]. This decrease in sea ice coverage has
triggered the expansion of many industries in the Arctic,
some prospective and others very real and rapidly
expanding.
Figure 1. Summer minimum Arctic sea ice extent.
The United States Geological Survey (USGS) has
estimated the Arctic to contain 30% of the world’s
undiscovered natural gas and 13% of its undiscovered oil
[3]. As a result of this, the U.S. government has recently
approved the first Arctic drilling off the shores of Alaska
in May of 2015 [4]. This and other natural resources are
attracting commercial activity in the form of exploration
and exploitation. Industries such as fishing and tourism
have seen the largest growth in the Arctic in the last
decade [5]. Furthermore, some project that the Arctic
Ocean could be used for alternative shipping routes,
offering shorter distances than the traditional routes of the
Suez or Panama Canals [6-9]. It is essential that all these
activities be done sustainably and safely and providing
navigation integrity is tantamount to their success.
Maritime traffic in the Arctic is on the rise [7, 10]. Traffic
along the Northern Sea Route along the coast of Russia
has increased 20% per year between 2009 and 2013 [10].
Traffic in the Canadian Arctic nearly doubled between
2005 and 2010 with voyages through the Northwest
Passage more than tripling [7]. The maritime activities
being undertaken here vary both in scope and in their
navigation requirements. Open water requirements in this
region are similar to elsewhere on Earth. However, in
regions overrun by ice, navigation requirements are more
stringent. Figure 2 shows vessels navigating through ice-
infested waters by means of a track carved out by
icebreaker. For ships to safely and autonomously operate
in the ice without assistance, they need to be able to find
these tracks and follow them. Navigation requirements are
stricter still for precision operations such as drilling and
mapping. Mapping is especially important in the Arctic as
it is known that existing charts are unreliable in this
region [11].
Figure 2. Ships navigating through ice via a path carved out previously
by icebreaker (source: Finnish Transport Agency).
Figure 3 shows the existing airports in the Arctic Circle
which are mostly small to medium sized. This family of
airports is that which benefits most from a GNSS-based
precision approach, as they typically are not equipped
with ground infrastructure for instrument landing. Figure
4 shows the many transpolar routes that pass though the
Arctic Circle. These would benefit greatly from improved
horizontal guidance as well as having the option for a
precision approach to one of many Arctic airports in the
event of an emergency. Figure 5 shows that there are also
many flights whose destination is the Arctic. As
commerce in this region grows, it is likely that the
number of flight destinations and their traffic will
increase, further showing the need for navigation integrity
in this region.
Figure 3. Airports in the Arctic Circle (based on data from
openflights.org and ourairports.com).

Figure 4. Transpolar flight routes (based on data from openflights.org).
Figure 5. Destination flights in the Arctic Circle (based on data from
openflights.org).
The sparse and limited infrastructure in the Arctic makes
it ideal for space-based architectures for navigation.
Navigation integrity can be achieved using Global
Navigation Satellite Systems (GNSS) in conjunction with
Satellite Based Augmentation Systems (SBAS) or
Advanced Receiver Autonomous Integrity Monitoring
(ARAIM). SBAS requires both ground-based and space-
based infrastructure to achieve integrity. ARAIM is more
self-contained and achieves integrity algorithmically by
leveraging the multitude of core constellations and signals
coming in the near future. Single frequency GPS-only
SBAS is in service today in many regions for aircraft
precision approach. Service is available in North America
through The Wide Area Augmentation System (WAAS),
in Europe through the European Geostationary Navigation
Overlay Service (EGNOS), in Japan through the Multi-
functional Satellite Augmentation System (MSAS), and in
India through the GPS Aided GEO Augmented
Navigation system (GAGAN). By 2021, more systems are
scheduled to come online which include the Russian
System for Differential Corrections and Monitoring
(SDCM), the South Korean Augmentation Satellite
System (KASS), and the Chinese BeiDou SBAS. The
future also holds the completion the Galileo and BeiDou
constellations as well as the availability of two civil
frequencies for use in ionospheric correction. As a result
of this, multi-frequency multi-constellation SBAS is
slated to be available by 2026, offering an increased level
of service. ARAIM will also leverage these
modernizations and is expected to be in service by 2029.
ARAIM will rely on multiple frequencies for ionospheric
correction and on the many core constellations online by
this time to enable integrity.
The ultimate goal is to get ahead of the growth in the
Arctic and get safety standards in place early before bad
practices are adopted and become the norm. The
usefulness of SBAS for precision approach in aviation has
already been demonstrated in the northernmost airports of
Alaska [12, 13]. In addition, many have advocated for the
use of SBAS in Arctic for navigation safety [14, 15].
Previous work has examined single frequency GPS-only
SBAS in the Arctic for aviation and determined it to be
very difficult to achieve precision approach in this region
[16]. Additional work has shown the potential of multi-
frequency multi-constellation EGNOS in the Arctic for
both aviation and maritime applications in the high
latitude regions of Europe [17].
Results presented here show that the planned ground
infrastructure and standards of SBAS and ARAIM allow
for all levels of service for both maritime and aviation
applications in the Arctic. This does not require the
sharing of SBAS reference stations, just the ability to
switch between the various systems. However, the
geostationary (GEO) satellites employed to deliver SBAS
corrections today do not reach much of the Arctic. Here,
the Quasi-Zenith Satellite System (QZSS) is examined as
a potential candidate for the near term as it is found to fill
much of the gap left by GEOs. QZSS is already partially
in place with one satellite on orbit delivering
augmentation over Japan. QZSS is also planned to deliver
an SBAS-like service known as the L1-SAIF (Sub-meter-
class Augmentation with Integrity Function) [18].
Furthermore, the next generation SBAS Minimum
Operational Performance Standards (MOPS) to be
broadcast on L5 will support its highly elliptical orbit
(HEO) [19].
SBAS AND ARAIM IN THE ARCTIC
SBAS is comprised of ground-based and space-based
infrastructure. Ground stations monitor GNSS signals
over their particular service region which are in turn used

to generate satellite corrections. These corrections are
then broadcast to the user via a bent pipe communications
link based on the GEO satellite space segment. Single
frequency GPS-only SBAS is available today in North
America, Europe, Japan, and India. By 2021, more
systems will be coming online, extending this service to
Russia, South Korea, and China. By 2026, dual frequency
multi-constellation SBAS is planned to come online,
offering an increased level of service than that available
today.
Figure 6. SBAS ground segment: reference stations of all current
systems and those under construction.
In the Arctic Circle, SBAS will rely heavily on high
latitude reference stations. Figure 6 shows the SBAS
ground-segment for the existing WAAS, EGNOS, MSAS,
and GAGAN, as well as SDCM, KASS, and BeiDou
SBAS under construction. This shows that there are many
high latitude reference stations, particularly in the areas
around Russia, Northern Europe, and Alaska. Figure 7
shows the SBAS space-segment consisting of GEO
satellites at the equator. Table 1 shows the details of these
augmentation satellites and Figure 8 shows their coverage
area as viewed from the Arctic. Clearly, there is a large
gap in the Arctic Circle. This coverage assumes a 5o
elevation mask, giving a theoretical limit of 76oN.
However, in practice it is known that GEOs are
problematic even around 72oN, approximately the latitude
of the northernmost airport supported by WAAS located
at Point Barrow Alaska (71.29oN). In fact, approach
maneuvers are restricted at this airport to ensure visibility
of SBAS GEOs. Tests of the European Geostationary
Overlay Navigation System (EGNOS) have shown similar
difficulties at the edge of GEO coverage [20].
ARAIM is meant to operate more autonomously and will
rely on multi-frequency and multiple core constellations
to gain sufficient information for integrity. As such, it is
slated to become operational by 2029. ARAIM will make
use of a long latency Integrity Support Message (ISM)
which need only be updated every 30 days [21]. This
message is expected to be broadcast in the spare bits of
the GPS constellation. The ISM will be built up over time
using a ground reference network which can be very
much like that of the International GNSS Service (IGS).
This network need not be devoted or real time like that of
SBAS. As such, ARAIM requires no additional
infrastructure than is planned to operate in the Arctic. In
fact, symmetry of the circular orbits of the core
constellations ensures the same performance in the
southern hemisphere around Antarctica.
Table 1. Operational and proposed GNSS augmentation satellites.
System
Satellite Name
PRN
Longitude
On
Orbit?
WAAS
AMR
(AOR-W)
133
98.0
o
W
Y
CRW
(Galaxy 15)
135
133.0
o
W
Y
CRE
(ANIK F1R)
138
107.3
o
W
Y
EGNOS
AOR-E
(Inmarsat 4F-2)
120
15.5
o
W
Y
IOR-W
(Inmarsat 4-F2)
126
25.0
o
E
Y
SES-5
(Astra 4B)
136
5.0
o
E
Y
MSAS
MTSAT-1R
129
140.0
o
E
Y
MTSAT-2
137
145.0
o
E
Y
GAGAN
GSAT-8
127
55.0
o
E
Y
GSAT-10
128
83.0
o
E
Y
GSAT-15
-
93.5
o
E
N (2015)
SDCM
LUCH 5A
140
167.0
o
E
Y
LUCH 5B
125
16.0
o
W
Y
LUCH 5V
144
95.0
o
E
Y
KASS
-
150
143.5
o
E
N (2016)
BD SBAS
BeiDou G6
141
80.0
o
E
Y
BeiDou G3
142
110.5
o
E
Y
BeiDou G1
143
140.0
o
E
Y
QZSS
QZS-1
193
135.0
o
E
Y
QZS-2
194
135.0
o
E
N (2016)
QZS-3
195
135.0
o
E
N (2017)

Figure 7. SBAS space segment: SBAS GEO groundtracks and
combined availability.
Figure 8. SBAS space segment as viewed from the Arctic. This shows
the combined availability of the SBAS GEOs as well as their theoretical
and practical latitude limits.
SBAS DATA LINK TO THE ARCTIC
The previous section demonstrated that the SBAS GEO
space segment is inadequate for the Arctic. As such, a
number of alternate systems have been proposed. The
Iridium constellation (shown in Figure 9) consisting of 66
LEO satellites has been suggested [16]. Best known for
satellite phone service, these spacecraft are placed in
polar orbits, providing excellent coverage at the poles.
The satellite-based Automatic Identification System (AIS)
used to track ship traffic is being built by Orbcomm
(shown in Figure 10) and has also been proposed [17].
Dedicated systems based on highly elliptical orbits (HEO)
have also been proposed to support both communications
and SBAS at high latitudes [15, 22]. The highly eccentric
nature of the orbit allows satellites to spend most of their
time at high elevations over the northern hemisphere,
making them ideal for coverage in the Arctic. These types
of orbits have been used to deliver reliable satellite
communications to high latitude regions of Russia since
the dawn of the space age.
Figure 9. The Iridium constellation (October 2014).
Figure 10. The Orbcomm constellation (October 2014).
Figure 11. Dedicated system for communications and SBAS in the
Arctic based on Molniya (12 hour period HEO) orbits.
QZSS for SBAS in The Arctic
Here we propose a GNSS augmentation system already
under development to deliver SBAS integrity data to the
Arctic: the Japanese Quasi-Zenith Satellite System
(QZSS). This system is designed for augmentation over
Japan, offering an additional navigation satellite at high
elevation angles (near zenith) over this region at all times.
This aids in urban canyons where tall skyscrapers can
block GNSS signals low on the horizon [23]. There is
currently only one QZSS satellite in service, QZS-1,

located in a geosynchronous HEO orbit inclined at 43o to
match the latitude of Japan. This on its own is not enough
to provide constant coverage over the Arctic, but the with
the three QZSS satellites of the full constellation design,
this could fill the gaps left by GEO satellites. Figure 12
shows the existing SBAS GEOs, the GPS constellation, as
well as the completed QZSS constellation. From this
picture alone, it is easy to see why QZSS has better
visibility of the Arctic compared to the geostationary belt
at the equator. QZSS has the added benefit of being an
existing system, already proven and delivering
augmentation over Japan. Furthermore, it is scheduled to
deliver an SBAS-like service via its L1-SAIF signal [24].
Figure 12. The GPS constellation, current SBAS geostationary
satellites, and the future completed QZSS constellation.
Figure 13. Availability of the completed QZSS constellation consisting
of QZS-1, QZS-2, and QZS-3.
Figure 13 shows the coverage of the complete QZSS
constellation. Even though the constellation is designed to
give optimal coverage over Japan, it has fairly good
coverage in the Arctic Circle. Figure 14 shows that
combining this with the SBAS GEOs gets pretty good
coverage in the Arctic. Though this is not perfect, it
demonstrates that QZSS could be used to broadcast
corrections in the near term or perhaps as an experimental
platform in this region. Unfortunately, the current L1
SBAS Minimum Operational Performance Standards
(MOPS) do not support orbits other than GEO. However,
the next generation MOPS to be broadcast on L5 will
support a multitude of orbit classes including the HEO
orbit of QZSS [19, 25-28].
Figure 14. Combined availability of the SBAS GEOs and the completed
QZSS constellation.
Case Study: Svalbard Airport, Longyear
To showcase the capabilities of QZSS in the Arctic, we
will examine its value added at the northernmost public
airport located at Longyearbyen in Svalbard at 78.25oN. It
has daily flights to several destinations and is listed as a
diversion airport for many polar route flights in the event
of an emergency. Figure 16 shows the location of the
airport. Not only is the Svalbard Airport outside of the
current EGNOS coverage, it is also outside of the
coverage of its GEO satellites. Figure 15 shows the
elevation angles to all SBAS GEOs in the vicinity as well
as to the full QZSS constellation throughout a period of
24 hours. Indian Ocean Region – West (IOR-W) is the
only SBAS GEO visible for any period of time above an
elevation of 5o. In contrast, the QZSS constellation always
has a satellite above an elevation of 8.3o.
Figure 15. Elevation angles to SBAS GEOs and QZSS from the runway
at the Svalbard Airport, Longyear.

Figure 16. Location of the NYA2 (Ny-Ålesund, Svalbard, Norway) and
KIRU (Kiruna, Sweden) IGS-MGEX stations; the only ones which
report QZSS measurements in the Arctic Circle.
The Svalbard Airport is plagued with mountainous terrain
which further limits the visibility of augmentation
satellites. Figure 17 shows the lines of sight to IOR-W
and the QZSS satellites. Figure 18 shows that the line of
sight to IOR-W is always blocked by terrain to the south.
Figure 19 shows that the terrain is more favorable for the
QZSS constellation to the north though it doesn’t need to
be as the satellites are relatively high in the sky.
Figure 17. Lines of sight to IOR-W and the QZSS constellation at the
Svalbard Airport in Longyear.
Figure 18. Line of sight to the EGNOS GEO IOR-W blocked by terrain
on the runway at the Svalbard Airport in Longyear.
Figure 19. Lines of sight to QZS-1, QZS-2, and QZS-3 on the runway at
the Svalbard Airport in Longyear.
Unfortunately, we were unable to visit Svalbard to take
measurements of QZSS. Instead, we turned to data
collected by the IGS network, specifically those part of
the Multi-GNSS Experiment (MGEX) [29]. There are
currently only two IGS stations in the Arctic Circle which
report QZSS measurements: the KIRU station located in
Kiruna, Sweden at 67.86oN and the NYA2 station in Ny-
Ålesund, Svalbard at 78.86oN. The location of these sites
is given in Figure 16. The NYA2 station is located near
the airport of interest at Longyearbyen and as such was
used as a proxy.
Figure 20 shows the signal to noise ratio (SNR) of
satellites observed at the NYA2 site. The light
background traces represent the observed GPS satellites
and the dark foreground trace is that of QZS-1. With this
and the known orbits of QZS-2 and -3, we can infer what
the SNR of these future satellites would look like and they
are included on this plot. We see that we would always
have good visibility of a QZSS satellite at this location.
The closest SBAS GEO of EGNOS is always low on the
horizon and the receiver is never able to track it.
Figure 20. Observed signal to noise ratio (SNR) of satellites viewed by
the NYA2 IGS station in Ny-Ålesund, Svalbard, Norway at 78.86o N.
QZS-1 Data from October 27, 2014.
37#
QZSS

AVIATION GNSS INTEGRITY
In this section, we turn to SBAS and ARAIM
performance for aviation, specifically GNSS-based
precision approach in the Arctic. Table 2 shows the
navigation requirements for Localizer Performance with
Vertical guidance (LPV). Especially of interest are the
strict requirements needed to bring the aircraft down to a
decision height of 200 feet (61 meters) (LPV 200). This
requires an integrity bound known as the Vertical Alert
Limit (VAL) of 35 meters and represents the degree to
which knowledge of the aircraft altitude must be
protected.
Table 2. Aviation navigation requirements.
Horizontal
Alert
Limit
(HAL)
[m]
Vertical
Alert
Limit
(VAL)
[m]
Time
to
Alarm
[sec]
Continuity
Integrity
Risk
LNAV
556
-
10
99.99%
per hour
10-7 per
hour
LNAV /
VNAV
556
50
10
99.945 %
per 15 sec
2×10-7
per
approach
(150 sec)
LPV
40
50
6.2
99.992%
per 15 sec
2×10-7
per
approach
(150 sec)
LPV 200
40
35
6.2
99.992%
per 15 sec
2×10-7
per
approach
(150 sec)
Figure 21. Groundtracks of the GPS constellation.
GPS satellite geometry in the Arctic poses a fundamental
difficulty with vertical guidance. Figure 21 shows the
groundtracks of the GPS constellation which are limited
by the 55o inclination of their orbit. This orbital
inclination coincides with the highest latitude where they
can be seen overhead. In the Arctic, this results in
satellites being low on the horizon though more can be
seen due to visibility of more orbital planes at once. This
yields geometry that is good for horizontal positioning
(HDOP) but poor for vertical (VDOP). This is shown
pictorially in Figure 22. Figure 23 shows that the situation
improves by adding more core constellations though most
of the gain seen here comes from GLONASS. All systems
are inclined at 55o with the exception of GLONASS at
64o. GLONASS was designed at this higher inclination to
better support the high latitude regions of Russia.
Figure 22. Dilution of Precision (DOPS) in the Arctic.
Figure 23. Groundtracks of all GNSS core constellations.
The performance of SBAS and ARAIM in the Arctic was
simulated using the MATLAB Algorithm Availability
Simulation Tool (MAAST) developed at Stanford
University [30]. This tool is available for free download
on the Stanford GPS Lab website. To achieve precision
approach, we require a Vertical Protection Level (VPL)
less than the specified VAL of 50 meters. To get down to
a decision height of 200 feet (61 meters), this must be
below 35 meters. Figure 24 shows the VPL achieved
today by the operational WAAS, EGNOS, MSAS, and

GAGAN. This result represents single frequency GPS-
only SBAS. By 2021, SDCM, KASS, and BeiDou SBAS
are expected to come online. This offers more areas of
coverage as shown in Figure 25. From this we see that
precision approach is achievable in many areas such as
Northern Europe, Alaska, Northern Canada, as well as
much of the Russian coastline. However, there is not
much coverage in the rest of the Arctic.
By 2026, it is expected that dual frequency will be
introduced into SBAS. This was found to yield a
substantial improvement in service. In addition, some
systems plan to add multi-constellation to SBAS by this
time. WAAS, MSAS, GAGAN, and KASS plan to
maintain GPS-only operation. EGNOS plans to use GPS
+ Galileo, SDCM GPS + GLONASS, and BD SBAS GPS
+ BeiDou. The coverage of the planned 2026 system is
given in Figure 26. Here we see the importance of adding
non-GEO satellites to deliver SBAS corrections to the
Arctic. The large area with no coverage comes entirely
from a lack of communication to this region. Figure 27
shows the same situation with a reliable Arctic
communication link. Planned service for 2026 achieves
precision approach in the Arctic Circle as long as there is
a means of getting SBAS data there reliably. Figure 28
shows the level of service that can be achieved by the
addition of another constellation to each system. In this
scenario, a performance better than LPV 200 is achieved
in all of the Arctic Circle.
We now turn to ARAIM in 2029. Figure 29 shows the
level of service provided by dual-frequency GPS +
Galileo ARAIM. This gives precision approach in all of
the Arctic. Figure 30 shows that LPV 200 can be achieved
if GPS + Galileo + GLONASS were used. SBAS is
ultimately limited in service area by the reference stations
given in Figure 6. ARAIM requires no such infrastructure
and has the added benefit of delivering the same level of
service in both the northern and southern hemisphere.
Figure 24. VPL for single frequency GPS-only SBAS for WAAS,
EGNOS, MSAS, and GAGAN (2015).
Figure 25. VPL for single frequency GPS-only SBAS for WAAS,
EGNOS, MSAS, GAGAN, SDCM, KASS, and BD SBAS (2021).
Figure 26. VPL for dual frequency multi-constellation SBAS (2026).
Figure 27. VPL for dual frequency multi-constellation SBAS (2026)
with an Arctic communications link.

Figure 28. VPL for dual frequency multi-constellation SBAS (2026)
with an Arctic communications link plus an additional constellation
being used by each system.
Figure 29. VPL for dual frequency GPS + Galileo ARAIM (2029).
Figure 30. VPL for dual frequency GPS + Galileo + GLONASS
ARAIM (2029).
MARITIME GNSS INTEGRITY
In this section, we turn to maritime navigation in the
Arctic. Maritime navigation requirements are strict for
horizontal positioning due to the ship’s knowledge of
being at sea level. These requirements are given in Table
3. The integrity bound, known as the Horizontal Alert
Limit (HAL), is 25 meters for open water operations.
Precision applications such as drilling and mapping
require an order of magnitude better protection at 2.5 – 5
meters. These requirements are long standing and have
been agreed upon by the International Maritime
Organization (IMO) [31]. The requirements for
autonomous ice navigation have yet to be strictly defined.
Ice navigation has traditionally been a field which relies
heavily on the experience of mariners [5]. Even today, the
most reliable way to detect and classify dangerous ice is
not by radar or infrared camera, but by experienced
human lookouts [5]. As standards modernize, allowing for
better communication of ice conditions, ships will be
required to find safe tracks on their own without
icebreaker assistance. In order to find and follow tracks
previously carved out by icebreaker, ships need to find
these tracks to within half a boat width. This is where the
10 – 12 meter requirement comes from in Table 3.
Table 3. Maritime navigation requirements [31].
Horizontal
Alert Limit
(HAL)
[m]
Time
to
Alarm
[sec]
Continuity
per 3 hours
Integrity
Risk
(per 3
hours)
Ocean
25
10
N/A
10-5
Coastal
Ice Navigation
10 - 12
10
99.97%
10-5
Hydrography
2.5 - 5
10
99.97%
10-5
Port
2.5
10
99.97%
10-5
Exploration /
Drilling
These simulations were again run using MAAST [30].
However, MAAST was developed with aviation, not
maritime, requirements in mind. As such, we need to first
determine what parameters are equivalent in aviation and
maritime and adjust those that are not. Let’s begin with
the integrity risk. Table 2 shows that aviation precision
approach requires a Probability of Hazardously
Misleading Information (PHMI) of 2×10-7 per approach (a
duration of 150 seconds). In the maritime world, this is
defined as 10-5 over a period of 3 hours. Converting this
to a period of 150 seconds gives:
PHMI =10−5
3 hours
1 hour
3600sec150sec
=1.38×10−7per 150 sec
(1)

This is very close to the aviation requirement and is
roughly equivalent for the purposes of this simulation.
The same is true for continuity. In general, assuming the
integrity and continuity requirements for aviation in the
context of ships at sea is more conservative than is likely
needed because of the strict timescales in aviation. Thus,
results shown here will be somewhat conservative.
In order to use SBAS for maritime, a few of the aviation
MOPS parameters need to be adjusted, as the focus is
now on protecting in horizontal rather than vertical. This
amounts to changing allocation in the MOPS KH
parameters used in the computation of the Horizontal
Protection Level (HPL). For aviation, the K parameters
are defined as follows [32]:
KH,PA =6.0
KH,NPA =6.18
KV=5.33
(2)
where KH,PA is the value used to compute HPL for
precision approach, KH,NPA is the value used for en route
or non-precision approach, and KV is the value used to
compute the VPL. In this scenario, the assumption will be
that we are always in the SBAS service area and thus will
always be in precision approach mode. Furthermore, with
the focus on horizontal protection, we adjust the precision
approach value for KH to match that of KV :
KH,PA =5.33
(3)
Similarly, allocations for ARAIM need to be adjusted as
well. At sea, most of the integrity and continuity budget
will be moved from to horizontal. By default, the
following allocation is given for aviation [33]:
PHMI =10−7
PHMIVERT =9.8×10 −8
PHMIHOR =2×10−9
P
FA =4×10−6
P
FA,VERT =3.9 ×10−6
P
FA,HOR =9×10−8
(4)
Here we see the total ARAIM budget for the Probability
of Hazardously Misleading Information (PHMI) as well
as that for the Probability of False Alarm (PFA). These are
the budgets for integrity and continuity, respectively. For
aviation, most of these are allocated to for vertical. As
maritime cares about horizontal, these allocations will be
swapped:
PHMIVERT =2×10−9
PHMIHOR =9.8 ×10−8
P
FA,VERT =9×10−8
P
FA,HOR =3.9 ×10−6
(5)
Figure 31 shows the performance of single frequency
GPS-only SBAS today given the operational WAAS,
EGNOS, MSAS, and GAGAN. Figure 32 shows the
improvement in 2021 when SDCM, KASS, and BD
SBAS are expected to come online. Figure 33 shows the
service provided in 2026 once dual frequency has been
introduced into SBAS. As previously mentioned, some
systems also plan to incorporate additional constellations
by this time. WAAS, MSAS, GAGAN, and KASS all
plan to maintain GPS-only operation whereas EGNOS
plans GPS + Galileo, SDCM GPS + GLONASS, and BD
SBAS GPS + BeiDou. This is reflected in the simulations
shown here. As with aviation, dual frequency adds a huge
benefit in the Arctic. Again, the area of missing coverage
is due to the limitations of the SBAS GEOs. Figure 34
shows what is attainable with an SBAS data link to the
Arctic. In this scenario, the requirements for open water
and ice navigation are met in most areas but not all.
Interestingly, the areas without this service are those
covered by land or by the summer sea ice and would
likely not be areas of significant sea traffic in the near
future.
Figure 35 shows the level of service that can be attained if
an additional constellation were added to each system. In
this scenario, requirements for ice navigation are met and
exceeded. Furthermore, some regions give service levels
needed for some precision applications. Most areas are at
the 7.5 meter protection level which some indicate as
being useful for some restricted use purposes [17].
Adding two constellations to each system gives the
performance shown in Figure 36. Now, we begin to
approach the levels required for precision applications in
all of the Arctic Circle.
We now turn to ARAIM in 2029. Figure 37 shows the
level of service provided by dual frequency GPS +
Galileo. Here we see that open water requirements are
met and ice navigation requirements are met only near the
pole. The increased service near the pole is the satellite
geometry at work. Horizontal geometry is better closer to
the poles due to many satellites visible low in the sky.
This effect is not visible in SBAS as the user is required
to switch between systems. This results in making use of
only a subset of all satellites visible in the sky and hence
we do not get this geometrical benefit. Figure 38 shows
the service for dual frequency GPS + Galileo +
GLONASS. This meets the requirements for ice
navigation as well as allows for some restricted use
applications at the 7.5 meter level. Figure 39 shows the
result for dual frequency GPS + Galileo + GLONASS +
BeiDou. This shows that ARAIM reaches a limit and does
not get down to the level of service provided by SBAS.
As such, it appears that precision applications require
SBAS and that others may only require ARAIM. This is
an interesting trade space to consider in the future.

Figure 31. HPL for single frequency GPS-only SBAS for WAAS,
EGNOS, MSAS, and GAGAN (2015).
Figure 32. HPL for single frequency GPS-only SBAS for WAAS,
EGNOS, MSAS, GAGAN, SDCM, KASS, and BD SBAS (2021).
Figure 33. HPL for dual frequency multi-constellation SBAS (2026).
Figure 34. HPL for dual frequency multi-constellation SBAS (2026)
with an Arctic communications link.
Figure 35. HPL for dual frequency multi-constellation SBAS (2026)
with an Arctic communications link plus an additional constellation
being used by each system.
Figure 36. HPL for dual frequency multi-constellation SBAS (2026)
with an Arctic communications link plus two additional constellation
being used by each system.

Figure 37. HPL for dual frequency GPS + Galileo ARAIM (2029).
Figure 38. HPL for dual frequency GPS + Galileo + GLONASS
ARAIM (2029).
Figure 39. HPL for dual frequency GPS + Galileo + GLONASS +
BeiDou ARAIM (2029).
CONCLUSION
Safe navigation both at sea and in the air can be achieved
in the Arctic through GNSS integrity systems. Here, both
SBAS and ARAIM were examined for maritime and
aviation applications in this region. Dual frequency multi-
constellation SBAS as it is intended for 2026 can meet
many of the aviation and maritime navigation needs.
Localizer Performance with Vertical guidance (LPV) can
be achieved, allowing for GNSS-based aircraft precision
approach. In addition, autonomous ice navigation
requirements can be attained at sea. Realizing this,
however, requires a reliable communication link to the
Arctic. This is an impossibility with the SBAS GEOs in
service today which have a latitude limit of 72oN. The
next generation of SBAS standards allow for other, more
suitable orbits to be considered for the Arctic [19]. As
such, the Quasi-Zenith Satellite System (QZSS) was
proposed. Its constellation of three HEO orbits fills much
of the gap left by GEOs and will be available in the near
future. Dual frequency multi-constellation ARAIM,
planned for 2029, can also support many activities in the
Arctic. GPS + Galileo ARAIM can attain aircraft
precision approach as well as enable autonomous ice
navigation in much of the Arctic Circle.
Both SBAS and ARAIM can achieve even stricter
requirements and support more activities if more core
constellations are utilized. Currently, only EGNOS,
SDCM, and BD SBAS have plans for two constellations.
It was found that utilization of all four core constellations
allows SBAS to support an aviation service better than
LPV 200 as well as precision applications at sea such as
mapping. Similarly, ARAIM allows for autonomous ice
navigation for ships as well as LPV 200 for aircraft.
ARAIM does approach a limit and does not reach the
service level required for precision drilling and mapping.
Thus, depending on the particular application, SBAS or
ARAIM may be more desirable and certainly both have
their place in the Arctic.
Safe navigation practices in the Arctic are of utmost
importance as industries expand into this region. This can
be achieved by providing high integrity navigation
services through SBAS and ARAIM. Making them
available is key to industries adopting safe practices in the
Arctic early while growth in this region is still in its
infancy and standards are being established. The ultimate
goal is to attain the highest levels of safety to avoid
accidents resulting in severe loss of life or environmental
disasters.
ACKNOWLEDGMENTS
The authors would like to gratefully acknowledge
Lockheed Martin, The Boeing Company, and the National

Science and Engineering Research Council of Canada
(NSERC) for supporting this work.
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