Pieter Toor Veripos


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Presentation Pieter Toor gave during the Hydrographic Society Benelux workshop about the z-axis positioning with Veripos.

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Pieter Toor Veripos

  1. 1. Real-time Tidal Observation using High-Accuracy GPS Positioning Pieter Toor Research & Development Manager VERIPOS Hydrographic Society Benelux, Dordrecht 7 th May 2008
  2. 2. Company Information <ul><li>VERIPOS </li></ul><ul><ul><li>A product line within Subsea 7 </li></ul></ul><ul><ul><li>Established in 1989 </li></ul></ul><ul><ul><li>Providing precise navigation & positioning services </li></ul></ul><ul><ul><li>Global business </li></ul></ul><ul><ul><li>Specialising in marine operations in offshore oil & gas sector </li></ul></ul>
  3. 3. Corporate Structure Subsea 7 Inc. Construction / IRM VERIPOS i-Tech Drill Rig Support Oslo S.E.
  4. 4. VERIPOS Background <ul><li>FORMED 1989 – JV BROWN & ROOT AND ORMTEC </li></ul><ul><li>1992 – BRS SOLD TO SUBSEA OFFSHORE </li></ul><ul><li>1994 – OSIRIS ENTERED VERIPOS ALLIANCE </li></ul><ul><li>1995 – CGG (TOPNAV) ACQUIRES OSIRIS </li></ul><ul><li>2002 – FUGRO ACQUIRES TOPNAV – VERIPOS 100% SUBSEA 7 </li></ul><ul><li>2003 – FUGRO ACQUIRES THALES GEOSOLUTIONS </li></ul><ul><li>2005 – EXPANSION PLAN FORMULATED </li></ul><ul><li>2008 – VERIPOS +/- 75 people </li></ul>
  5. 5. Overview <ul><li>Advances in Positioning Technologies </li></ul><ul><li>Overview of Tides </li></ul><ul><li>Using High-Accuracy GPS to Determine Tide </li></ul><ul><li>Veripos Implementation </li></ul><ul><li>Benefits and Applications </li></ul><ul><li>Future </li></ul>
  6. 6. Advances in Positioning Technologies <ul><li>Positioning is essential technology for offshore operations </li></ul><ul><ul><li>Satellite Navigation technology can now be considered a mature and accepted technology </li></ul></ul><ul><li>Augmentation data from service providers allows a higher level of accuracy & precision over standalone GPS </li></ul><ul><ul><li>Services offered range in accuracy from the metre level to the decimetre level </li></ul></ul><ul><li>Satellite navigation will remain a key technology for offshore operations </li></ul>
  7. 7. Advances in Positioning Technologies <ul><li>Positioning techniques can now deliver position solutions at the decimetre level </li></ul><ul><ul><li>Future enhancements will see new satellite constellations and modernisation of the current systems </li></ul></ul><ul><ul><li>Will see developments with new position solutions </li></ul></ul><ul><ul><ul><li>Different levels of accuracy </li></ul></ul></ul><ul><ul><ul><li>Different combinations of satellite signals </li></ul></ul></ul><ul><ul><li>High-Accuracy positioning systems allow use in new applications </li></ul></ul><ul><ul><ul><li>One area is the determination of Tidal information </li></ul></ul></ul>
  8. 8. What is Tide? <ul><li>Tide is the periodic rise and fall of the sea level under the gravitational pull of the moon and sun </li></ul><ul><li>Tides cause periodical variations in the ‘equilibrium’ sea level called Mean Sea Surface </li></ul>
  9. 9. Tidal Trend in High-accuracy Positions <ul><li>Veripos Ultra DGPS (PPP) system offers 10-20cm vertical accuracy </li></ul><ul><ul><li> High correlation between tides and DGPS heights after removing antenna motion relative to waterline </li></ul></ul>Ultra PPP Height and Predicted Tide
  10. 10. GPS to Vertical Reference - Offsets <ul><li>Reduce GPS antenna height via a few basic steps: </li></ul><ul><li>reduce WGS84 height of antenna reference point to vessel’s CRP </li></ul><ul><ul><li>inputs: antenna offsets, pitch & roll and heading, heave </li></ul></ul><ul><li>reduce vessel CRP to waterline </li></ul><ul><ul><li>inputs: draft, squat </li></ul></ul><ul><li>correct for additional local effects to finally derive the waterline in WGS84 (optional) </li></ul><ul><ul><li>e.g. currents, atmospheric pressure </li></ul></ul>Geoid: T1 = h – H + D – N Chart datum: T2 = h – H + D – L Ellipsoid: T3 = h – H + D
  11. 11. Veripos Tides Implementation <ul><li>Reduce the effect of heave, pitch and roll by averaging the Ultra high-accuracy heights </li></ul><ul><ul><li>ensure that the position used is an accurate Ultra position (not Standard DGPS or converging) using QC tag to Error Ellipse/SD threshold of less than 0.1m </li></ul></ul><ul><li>After 39hrs de-tide the heights by using the Doodson filter </li></ul><ul><li>Leave actual tidal reduction to client, i.e. antenna offsets, draft & squat </li></ul>
  12. 12. Doodson Filter <ul><li>The Doodson X0 filter is a simple filter designed to damp out the main tidal frequencies </li></ul><ul><li>It takes hourly values, 19 values either side of the central one </li></ul><ul><li>A weighted average is taken with the following weights (1010010110201102112 0 2112011020110100101)/30 </li></ul><ul><li>‘ Ultra Tide ’ estimate only available after initial 39hrs of observation </li></ul><ul><li>Secondary instantaneous tide value, ‘ Geoid Tide ’, is based on the deviation from the EGM96 geoid model </li></ul>
  13. 13. Ultra Tide vs. Geoid Tide 39 hrs 0 hrs Doodson X0 Ultra Tide <ul><li>Ultra Tide can only be calculated after 39 hours </li></ul><ul><ul><li>Unbiased but long initialisation </li></ul></ul><ul><li>Geoid Tide can be calculated instantaneously by using EGM96 Geoid Model as an approximate of mean sea level </li></ul><ul><ul><li>Instantaneous but biased </li></ul></ul>EGM96 Geoid Tide
  14. 14. Ultra Tide vs. Geoid Tide 39 HOURS 1010010110201102112 0 2112011020110100101/30 Geoid Tide Ultra Tide = Avg. Ultra Height – Doodson X0 output Geoid Tide = Avg. Ultra Height – EGM96 (Earth Gravitational Model 1996) Tide Value Availability Ultra Tide Start of Ultra positioning 39 hours
  15. 15. Application Level <ul><li>Tidal estimation is available in the Verify-QC positioning & QC software application </li></ul>$UltraTide,20070827,12:20:00,989,600,600,5708.8614,N,00057.7000,E,20.76,0.06,1.17,18.98,22.45,20.62,0.14,-0.36,21.13,46.43,EGM96*08 $UltraTide,20070827,12:30:00,990,600,600,5708.9052,N,00057.7425,E,20.80,0.06,0.97,19.28,22.21,20.62,0.18,-0.33,21.13,46.43,EGM96*06 $UltraTide,20070827,12:40:00,991,600,600,5708.9503,N,00057.7887,E,20.83,0.06,1.02,19.47,22.18,20.62,0.22,-0.29,21.13,46.43,EGM96*0A $UltraTide,20070827,12:50:00,992,600,600,5708.9828,N,00057.8221,E,20.83,0.07,1.06,19.26,22.27,20.62,0.21,-0.29,21.13,46.43,EGM96*08 <ul><li>Output average height and associated quality information to ASCII file </li></ul>
  16. 16. Validation Against Predicted Tides <ul><li>Comparison of Veripos Tides against predicted tide (SHM159a v2.00) in Singapore </li></ul><ul><li>C-O showed Standard Deviation of 11cm and a Mean of 1cm </li></ul>
  17. 17. Validation Against Tide Gauge <ul><li>Comparison of Veripos Tide observation against tide gauge close to work site </li></ul><ul><ul><li>Conducted over a three day period in United Kingdom </li></ul></ul><ul><ul><li>Comparison of both the Geoid Tide and Ultra Tide at 10 minute intervals </li></ul></ul><ul><ul><li>C-O for the Ultra Tide showed a Standard Deviation of 10 cm and a Mean of 5 cm </li></ul></ul><ul><ul><li>C-O for the Geoid Tide (EGM96) showed a Standard Deviation of 8 cm and a Mean of 12 cm </li></ul></ul>
  18. 18. Comparison Against Tide Gauge
  19. 19. Comparison Against Tide Gauge
  20. 20. Comparison Against Tide Gauge
  21. 21. Validation on Subsea Vessel <ul><li>Comparison of Veripos Tide observation against tide gauge close to work site </li></ul><ul><ul><li>Subsea 7 ‘ Kommandor Subsea ’, in Aberdeen </li></ul></ul><ul><ul><li>Comparison of both the Geoid Tide and Ultra Tide at 10 minute intervals </li></ul></ul><ul><ul><li>C-O for the Ultra Tide showed a Standard Deviation of 13 cm and a Mean of 2 cm </li></ul></ul><ul><ul><li>C-O for the Geoid Tide (EGM96) showed a Standard Deviation of 12 cm and a Mean of 50 cm </li></ul></ul>
  22. 22. Validation on Subsea Vessel Results highlight biases in EGM96 Geoid Model (accurate to +/- 1m)
  23. 23. Performance & Verification <ul><li>Veripos tide solution has ability to observe tide at different locations with different sea state conditions </li></ul><ul><li>Figure below is tide observations recorded during transit from Scotland to Cyprus </li></ul>
  24. 24. Applications & Benefits <ul><li>Real-time observation of tidal variations using high-accuracy GPS offers many advantages over conventional methods </li></ul><ul><ul><li>Cost and time savings if deployment of tide gauges not required </li></ul></ul><ul><ul><li>Correct bathymetric data in real-time removing need for post-processing </li></ul></ul><ul><ul><li>Better representation of tides compared to model based predictions since it includes tidal variations at a much higher frequency </li></ul></ul><ul><ul><li>Used for tidal current prediction especially if tidal range is very high </li></ul></ul><ul><ul><ul><li>Current at minimum during peak or trough of tide and strongest current during the tide rise or fall </li></ul></ul></ul><ul><ul><ul><li>Useful when conducting critical operations </li></ul></ul></ul>
  25. 25. Future Activities <ul><li>Further improvement with the inclusion of pitch and roll data </li></ul><ul><li>During vessel operations (loading, unloading, crane movement, etc.) will affect the vessel draft which can impact tidal observations </li></ul><ul><ul><li>Investigate how these values can be incorporated </li></ul></ul><ul><li>Any improvement in positioning accuracy will immediately benefit the tide observation process </li></ul><ul><ul><li>Future enhancements to Satellite Navigation </li></ul></ul><ul><li>Improved MSS / Geoid models will aid in linking GPS height (ellipsoidal) to MSS </li></ul><ul><ul><li>New MSS anticipated with greater resolution than EGM96 but more importantly higher accuracy </li></ul></ul>
  26. 26. Positioning for Success Thank you for your attention ? QUESTIONS