Challenges of Positioning in the Arctic

Transcription

1 NAUTRONIX MARINE TECHNOLOGY SOLUTIONS Challenges of Positioning in the Arctic

2 Overview Introduction to the Arctic Offshore Positioning - Summary of issues Surface Positioning - DGNSS Subsea Positioning - Acoustics Surface Positioning - Heading Inertial Positioning Systems Summing up

3 NAUTRONIX Introduction to the Arctic

4 Where is the Arctic? Area north of the Arctic circle Average temperature for July is <10 C Consists of: Arctic Ocean Canada Russia Denmark (Greenland) Norway United States (Alaska) Sweden Finland Iceland

5 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 7,000 6,000 5,000 4,000 3,000 2,000 1, Canada Canada (Arctic Ocean) Norway Russia (FSU) Russia (FSU) (Sakhalin) USA (Alaska) Eni ConocoPhillips 4% Shell 2% Gazprom Shell 3% Mitsubishi Mitsui 5% BP 1% Other 2% Husky 5% Statoil 35% Rosneft BP 6% North Atlantic 8% ExxonMobil 11% Gazprom 18% Data Courtesy of Infield Systems

6 Arctic Field Locations

7 NAUTRONIX Arctic Offshore Positioning Some of the issues

8 Offshore Positioning 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

9 NAUTRONIX Surface Positioning - Satellites

10 Satellite Positioning Global Collectively known as GNSS GPS USA GLONASS Russia Regional India IRNSS China Beidou In development... Europe Galileo China - COMPASS

11 Arctic GNSS issues 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

12 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

13 GNSS options Combined constellations GLONASS + GPS best 2 constellations GLONASS orbits have higher orbit inclination better for high latitudes Better again with additional constellations

14 Differential GNSS 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

15 Differential GNSS IMCA-S-015 Guidelines for GNSS Positioning in the Oil & Gas Industry Geographic Operating Region The geostationary communication satellites used to deliver GNSS correction data can typically be used up to latitudes of 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.

16 Alternative correction sources 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

17 NAUTRONIX Subsea Positioning - Acoustics

18 Acoustic Positioning 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

19 Subsea Acoustics in the Arctic - operational 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

20 Sound Velocity Profiles Arctic VOS Arctic Salinity North Sea VOS North Sea Salinity Arctic Temp North Sea Temp

21 Raybending Arctic North Sea

22 Subsea Acoustics in the Arctic - practical 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

23 NAUTRONIX Direction and relative positioning

24 Surface Positioning - Heading 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

25 Heading Sensors 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

26 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

27 Secant of latitude (multiplier) Heading sensors 100 Plot of 'secant latitude' multiplier against latitude N.Pole Equator Latitude (degrees)

28 Heading Sensors 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

29 Inertial Navigation Systems 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

30 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

31 Heading Changes while in a straight line Slide courtesy of

32 Example of trajectory at constant speed Slide courtesy of

33 Heading (degrees) Navigation close to the pole True heading representation as a function of time on previous trajectory Time (seconds) Slide courtesy of

34 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

35 Azimuth (degrees) Navigation close to the pole Wander angle representation as a function of time on previous trajectory Time (seconds) Slide courtesy of

36 Instability on longitude Slide courtesy of

37 Latitude Instability on longitude Standard representation with latitude and longitude!! Longitude Slide courtesy of

38 How to Solve this? Slide courtesy of

39 How to Solve this? Virtual pole Slide courtesy of

40 Trajectory representation using new virtual pole Latitude (degrees) Longitude (degrees) Slide courtesy of

41 NAUTRONIX Summing up

42 In conclusion 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...

43 NAUTRONIX MARINE TECHNOLOGY SOLUTIONS Thanks for Listening Questions? Aberdeen Houston Rio