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

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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

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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

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• 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

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• 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

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• 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

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• 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

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Seca

nt

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lati

tud

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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

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He

ad

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Time (seconds)

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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

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Azi

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de

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Time (seconds)

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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

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89.995

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90.005

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Lati

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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

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-0.025 -0.015 -0.005 0.005 0.015

Latitude (degrees)

Longitude (degrees)

Slide courtesy of

Summing up

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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?