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Challenges of Positioning in the Arctic
NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
• Introduction to the Arctic
• Offshore Positioning - Summary of issues
• Surface Positioning - DGNSS
• Subsea Positioning - Acoustics
• Surface Positioning - Heading
• Inertial Positioning Systems
• Summing up
Overview
Introduction to the Arctic
NAUTRONIX
Where is the Arctic?
Area north of the Arctic circle
• 66° 33′ 44″
Average temperature for July is <10 °C
Consists of:
• Arctic Ocean
• Canada
• Russia
• Denmark (Greenland)
• Norway
• United States (Alaska)
• Sweden
• Finland
• Iceland
Arctic Overview
A U.S. Geological
Survey estimated that areas
north of the Arctic Circle have:
• 90bn barrels of undiscovered,
technically recoverable oil
• Estimated 13% of the global
undiscovered oil
• 44bn barrels of natural gas
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Canada Canada (Arctic Ocean) Norway Russia (FSU) Russia (FSU) (Sakhalin) USA (Alaska)
Statoil 35%
Gazprom 18%
ExxonMobil 11%
North Atlantic
8%
Rosneft BP 6%
Husky 5%
Gazprom Shell Mitsubishi Mitsui
5%
Eni 4% Shell
3%
ConocoPhillips 2%
BP 1%
Other 2%
Data Courtesy of Infield Systems
Arctic Field Locations
Arctic Offshore Positioning –
Some of the issues
NAUTRONIX
• Various methods of positioning offshore, the majority fall under
the following two categories:
• Satellite Positioning (surface)
• Acoustic Positioning (subsea)
• An additional positioning method is to provide an Inertial
Navigation System solution aided by either of the above
• Positioning is not just about position...
– Heading and attitude are also critical
Offshore Positioning
Surface Positioning -
Satellites
NAUTRONIX www.nautronix.com
• Global – Collectively known as GNSS
– GPS – USA
– GLONASS – Russia
• Regional
– India – IRNSS
– China – Beidou
• In development...
– Europe – Galileo
– China - COMPASS
Satellite Positioning
• Contributing factors generally exaggerated versions of known
low elevation or harsh environment issues
• Many factors affect the quality of satellite positioning
– Multipath from sea and land surface
– Icing on antennae – attenuation of satellite signals.
– Vessel motion causing loss of signal lock
– Signal scintillation due to the effects of solar activity
– Coverage of satellites limited
– Sources of differential corrections
– Attenuation of signals due to ionospheric conditions & weather
• Affects signal path length
Arctic GNSS issues
Solar effects
• Sunspots create solar storms
• Interference with radio signals
• GNSS suffers
• Current focus is on tropics due to
existing oil and gas activity
• Also an issue in the arctic
Combined constellations
• GLONASS + GPS best 2 constellations
• GLONASS orbits have higher orbit inclination – better for high
latitudes
• Better again with additional constellations
GNSS options
• Correction signals generally from equatorial orbiting
geostationary satellites (Inmarsat & VSAT)
Theoretical maximum coverage 81.3° North
Little or no Arctic coverage (70°+ ‘dodgy’)
Low elevation angles make them more vulnerable to external
influences
Differential GNSS
• IMCA-S-015 – Guidelines for GNSS Positioning in the Oil & Gas
Industry - 4.1.3 Geographic Operating Region –
“The geostationary communication satellites used to deliver GNSS
correction data can typically be used up to latitudes of 75-78° north
or south. In work areas above the latitude horizon of the
communication satellites they may no longer be used for correction
data delivery.
In these instances alternative means of delivering correction data will
be required.”
Differential GNSS
• Iridium satellite constellation
• Complete coverage of the earth including the polar regions.
• Largest constellation in (above!) the world - 66 low earth
orbiting (LEO) satellites
• Over-the-pole Iridium orbits ensures very good satellite
visibility at high latitudes
• Data transfer through internet connection
Alternative correction sources
Subsea Positioning -
Acoustics
NAUTRONIX www.nautronix.com
• Many Acoustic Positioning Solutions
– USBL – Ultra-Short Baseline
– SBL – Short Baseline
– LBL – Long Baseline
• Various ‘standard’ potential issues
– Environmental Noise
– Seabed Topography
– Water Depth
– Water Temperature
– Limited User Capability
Acoustic Positioning
• Surrounding Ice Sheets may cause
Multipath of the signals
– Increased acoustic noise and potential for
interference
• Melting ice can cause rapid changes to
the water column, affecting speed of
sound
– Impact on positioning accuracy
• Temperature & Thermoclines
– Surface waters are heated by the sun
– Wind & Ocean currents churn the warm water
with the colder water below
– The Temperature/Depth ratio changes more
rapidly than it does in the layers above or
below it
Subsea Acoustics in the Arctic - operational
Sound Velocity Profiles
Arctic Salinity
Arctic VOS
Arctic Temp
North Sea
Salinity
North Sea VOS
North Sea Temp
Raybending Arctic
North Sea
• You may have to get transponders through ice...
• Cold water reduces battery capacity
• Cold water also increases attenuation of acoustic signal,
requiring more power
– more frequent battery change
• Acoustic transducers become brittle in extreme cold
– Susceptible to impact damage
• Arctic water has higher oxygen content
– Increases corrosion
Subsea Acoustics in the Arctic - practical
Direction and relative
positioning
NAUTRONIX www.nautronix.com
• Multiple Norths
– True North – Geographical location
of North Pole (rotation axis)
– Magnetic North – North Pole of
Earth’s magnetic field
– Grid North – Direction northwards
along grid lines of a map projection
Surface Positioning - Heading
Magnetic Compass
• Aligns itself with the Earth’s magnetic field
• Points in the direction of the magnetic
north pole
• Affected by ferromagnetic materials &
variations in the earths magnetic field
• Becomes ineffectual at high latitudes
Heading Sensors
Gyrocompass
• Uses the Gyroscopic effect
• Senses the rotation of the Earth about its axis (15° in 1 hour)
• Use the horizontal component of the Earth’s rotational rate to
determine north
• Unaffected by ferromagnetic materials or variations in Earth’s
magnetic field
• Earth’s spin rate becomes less at higher latitudes
• Gyros cease to function at the north and south geographic poles
• Dynamic error is dependent on latitude
secant latitude (1/cosine)
accuracy reduces with latitude
Heading sensors
Heading sensors
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90
Seca
nt
of
lati
tud
e (m
ult
iplie
r)
Latitude (degrees)
Plot of 'secant latitude' multiplier against latitude
Equator
N.Pole
• GNSS Compass
– Two GNSS antennas forming a dynamic baseline
• Not subject to the ‘sec lat’ scaling issue
• Doesn’t require differential corrections
• Does require reasonable GNSS coverage
Heading Sensors
• Offers an additional positioning solution
• Increases position update rates & relative accuracy
• Not an absolute positioning system on its own
• Absolute accuracy is limited to host positioning system
• 3 gyros
monitor rotation and speed in X, Y & Z axis
• 3 accelerometers
measure acceleration (>> speed >> motion) in 3 axis
• Powerful electronic / firmware package
calculates its position in real time + heading, pitch, roll, heave,
etc…
Inertial Navigation Systems
Inertial Navigation Systems in the Arctic
• Why is it more difficult to navigate with
inertial systems close to the pole ?
– Mainly because the poles are singular points
– When travelling in a straight line, heading
may vary very fast
– Longitude instability : pole is the converging
point of all meridians
– Heading determination is more difficult :
horizontal component of Earth rotation rate
becomes smaller and smaller
Slide courtesy of
Heading Changes while in a straight line
Slide courtesy of
Example of trajectory at constant speed
Slide courtesy of
• True heading representation as a function of time on previous
trajectory
Navigation close to the pole
0
20
40
60
80
100
120
140
160
180
200
0 200 400 600 800 1 000 1 200
He
ad
ing
(d
eg
ree
s)
Time (seconds)
Slide courtesy of
Navigation close to the pole
• Solution: use “wander angle” :
• Instead of choosing the North as a reference when
developing the differential equations, the reference will be
the first direction of the X axis of the INS
• Vehicle azimuth is provided with respect to this initial
reference and “wander angle” the rotation angle requested
to face North directions is provided as an additional
parameter.
Slide courtesy of
• Wander angle representation as a function of time on previous
trajectory
Navigation close to the pole
-200
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
20
0 200 400 600 800 1 000 1 200
Azi
mu
th (
de
gre
es)
Time (seconds)
Slide courtesy of
Instability on longitude
Slide courtesy of
• Standard representation with latitude and longitude !!
Instability on longitude
89.965
89.97
89.975
89.98
89.985
89.99
89.995
90
90.005
0 50 100 150 200 250 300 350 400
Lati
tud
e
Longitude
Slide courtesy of
How to Solve this?
Slide courtesy of
How to Solve this?
Virtual
pole
Slide courtesy of
Trajectory representation using new virtual pole
-0.030
-0.025
-0.020
-0.015
-0.010
-0.005
0.000
0.005
0.010
0.015
-0.025 -0.015 -0.005 0.005 0.015
Latitude (degrees)
Longitude (degrees)
Slide courtesy of
Summing up
NAUTRONIX www.nautronix.com
You can position in the arctic
But it’s not as easy as on the equator!
The effect of extreme latitude needs to be considered and
assessed for all sensors
As does the reliability of equipment in the harsh environment
Look out for #1 - take a good set of thermals...
In conclusion
Thanks for Listening
Aberdeen Houston Rio
NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Questions?