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Comparison of Network and State Space DGPS Services

Comparison of Network and State Space DGPS Services Real Time Tidal Monitoring for Seismic Data Collection Applications Richard Barker and Dariusz Lapucha Fugro Chance Inc. OVERVIEW. DGPS Positioning Services The Big Solar Event of Cycle 23 in 2003 Tidal Determination Using dDGPS

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Comparison of Network and State Space DGPS Services

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  1. Comparison of Network and State Space DGPS Services Real Time Tidal Monitoring for Seismic Data Collection Applications Richard Barker and Dariusz Lapucha Fugro Chance Inc.

  2. OVERVIEW • DGPS Positioning Services • The Big Solar Event of Cycle 23 in 2003 • Tidal Determination Using dDGPS • Normand Tonjer Seabed Mapping and Cable Route Survey Project at 71 Degrees N • 3D Seismic Data Processing With and Without Tidal Compensation

  3. GPS ACCURACY • Stand Alone GPS: +/- 10m • No Augmentation • Differential GPS (DGPS): Sub meter - 3m • Code Error Computation • Decimeter dDGPS: 10 - 15cm H, 15 – 45cm V • GPS Carrier Phase • Network or State Space Solutions • Real Time Kinematic: cm at short range • RTK Integer Resolution

  4. WHY DIFFERENTIAL GPS Differential GPS – DGPS / dDGPS • Increased level of position accuracy over stand alone or autonomous GPS by use of satellite range corrections from a reference receiver at a known location • Common error sources between reference and remote or user receiver are removed (e.g. iono, tropo, clock) • Remain subject to spatial (distance) and temporal (time) decorrelation (e.g. orbit errors and S/A) • .01 to 3 meter positioning possible depending on range and method (Integer RTK, Float RTK or standard DGPS)

  5. Trim 212 Lafayette (30°13'12.501 "N 92° 3'19.685 "W) STAND ALONE GPS PERFORMANCE

  6. Trim 212 W 750 RTCM Lafayette (30°13'12. 501 "N 92° 3‘ 19.685 "W) SINGLE SITE DIFFERENTIAL

  7. STARFIX / SkyFix dDGPS SERVICES • Starfix GSS / SkyFix XP • Uses JPL Reference Network and Data Stream • Broadcast of Orbit and Clock corrections • Valid Globally • GSS/XP must separate Orbits/Clocks correctly, account for Earth Tide, Ocean Loading, Satellite Phase Windup etc… • Starfix HP • Independent Service From GSS/XP • Service Region Network Solution • Higher Vertical Accuracy

  8. CHARACTERISTICS OF FUGRO HIGH ACCURACY PHASE BASED dDGPS SYSTEMS • GPS Code and Phase are Independent Observables • Code More Susceptible To: • Multipath • Reacquisition errors, e.g. during scintillations • State Space – Orbits and Clocks • Reference station independence • Less sensitivity to ionospheric problems • Network Solution • Higher Accuracy: Un modeled error reduction

  9. JPL REFERENCE NETWORK DISTRIBUTION 30 Reference Stations

  10. 85 Reference Stations HP NETWORK SERVICEDEPLOYMENT 50 HP Stations World Wide

  11. STARFIX HP LAFAYETTE 1 Sigma East = 3cm, North = 2cm, Vertical = 6cm

  12. STARFIX GSS LAFAYETTE 1 Sigma East = 7cm, North = 5cm, Vertical = 8cm

  13. SkyFix XP LAFAYETTE 1 Sigma East = 13 cm, North = 10 cm, Vertical = 14cm

  14. OSLO STARFIX HP SOLUTION HP dDGPS Oslo NO (58°48‘38.0486"N 5°40’23.9901"E) 1 Sigma East = 4cm, North = 4cm, Vertical = 10cm

  15. 1 Sigma East = 4cm, North = 6cm, Vertical = 18cm OSLO STARFIX GSS SOLUTION

  16. RMS = 4 cm East, 3 cm North, 8 cm Vertical JPL RTG PROCESSED DATA

  17. UNIVERSITY OF SOUTHERN MISSISSIPPI TEST RESULTS(FROM ION GPS GNSS 2003) • Long Term Static Tests July 25 - August 7, 2003

  18. http://science.msfc.nasa.gov/ssl/pad/solar/images/ssn_predict_l.gifhttp://science.msfc.nasa.gov/ssl/pad/solar/images/ssn_predict_l.gif SOLAR CYCLE 23

  19. SOLAR EVENT OCTOBER 28/29, 2003 http://www.sec.noaa.gov/ftpmenu/plots/kp.html

  20. IONOSPHERIC DELAY CALCULATION ct=f22/(f12- f22 )*(PR2-PR1)  Iono=tREF- tMOB Ionosphere tREF Ref Stn Single Frequency System: tREF and tMOB ionospheric delay calculated from a model (Klobuchar) Dual Frequency System: tREF and tMOB delay calculated from dual frequency GPS measurements (Delay=40.3 *TEC/c*f2) tMOB Mobile

  21. DIFFERENTIAL GPS WORKS BECAUSE … • Modern GPS receivers have high measurement precision and accuracy providing consistency between reference and rover receivers • At short ranges (< 50 km) most errors are correlated and canceled (Kinematic GPS cm level positioning) • At long ranges (> 500 km) many errors can be removed by DGPS / dDGPS Network and State Space (Orbit / Clock) methodology providing meter to decimeter level accuracies • With a “GOOD” GPS constellation the DGPS solution is statistically robust and reliable Any changes to the operating environment which adversely impacts the fundamentals will limit operational success.

  22. OSLO SINGLE BASELINE HP OCT 29 AND NOV 4

  23. OSLO NETWORK HP OCT 29 AND NOV 4

  24. WAAS PERFORMANCE DURING OCT 29 EVENT

  25. WAAS PERFORMANCE DURING OCT 29 EVENT

  26. WAAS PERFORMANCE DURING OCT 29 EVENT

  27. DISCOVER SEVEN SEAS IN RIO NOV 10, 2003

  28. BASELINE PLOT BELEM-RECEFE OCT 30, 2003 (1700 KM) Single Frequency DGPS : 12.8 m 95%Horizontal Starfix Plus: 1.2 m 95%Horizontal

  29. Real Time Tidal Monitoring for Seismic Data Collection Applications

  30. TIDAL DETERMINATION To Compute Real Time Observed Tide You Need: • Accurate vertical GPS ellipsoid height measurement • Mean Sea Surface (MSS) model relative to ellipsoid • Position of GPS antenna reduced to vessel reference • Heave and Draft correction to produce ‘Calm Sea’ height Difference between MSS and Calm Sea is observed tide Advantages: • More accurate than predicted tides • Repeatable reference to MSS • No offshore tide gauge and accompanying support

  31. HPel = HP antenna Height Hel = Vessel Reference Point Height CSHel = Calm Sea Height MSSel = Mean Sea Surface OT = Observed Tide AVO = Average Vertical Offset PT = Predicted Tide HPel = HP antenna Height Hel = Vessel Reference Point Height CSHel = Calm Sea Height MSSel = Mean Sea Surface HPel = HP antenna Height HPel = HP antenna Height Hel = Vessel Reference Point Height CSHel = Calm Sea Height HPel = HP antenna Height Hel = Vessel Reference Point Height Height Calm Sea Wave Motion Predicted Tide GPSel Hel OT CSHel PT MSS Model (MSL) Geoid MSSel Gel Ellipsoid Time 12 hours AVO TIDAL DETERMINATION

  32. TIDAL DETERMINATION • GPS measures Ellipsoid heights • Reduced to reference point and wave-movement removed • Mean Sea Surface (MSS) model applied to get sea level reference • MSS models are available • Geoid differ from MSS by 1m GPSel = GPS Antenna Height Hel = Vessel Reference Point Height CSHel = Calm Sea Height MSSel = Mean Sea Surface OT = Observed Tide AVO = Average Vertical Offset PT = Predicted Tide • Predicted tide used to calculate Average Vertical Offset (AVO) • If no predicted tide is available, the AVO is the tide

  33. MSS (CLS98) vs GEOIDE (EGM96)

  34. NORMAND TONJER PROJECT AT SNØHVIT 71 DEGREES NORTH Seabed Mapping and Cable Route Survey, June 2002

  35. NORMAND TONJER PROJECT 100 km From: ”The Use of GPS Heights for Offshore Charting Purposes” Arne E. Ofstad – The Norwegian Hydrographic Service Jan Didrik Andersen – DeepOcean AS Havbunnskartlegging og inspeksjon, Geilo, February 2003

  36. RAW DATA HEIGHT COMPARISON • 2 - Meter Change in Ellipsoid Height in 100 km • Between about 23rd June 19:00 UTC and 24th June 02:00 UTC, the vessel sailed more than 100 km from the Snøhvit field towards Hammerfest, this is reflected in the drop of 2 m in the ellipsoid height measured by dDGPS • dDGPS Raw Height • The difference in the point to point real time raw data agree to within 0.28 m (95%) (35 hours data) in height with independent water level estimates using tidal gauges • Use of Tidal Gauges • The difference between using and not using offshore tidal gauges amounts to about 0.5 m in the accuracy of height determination in this region

  37. dDGPS Height above Sea level and Starfix MSS calculation dDGPS Height Starfix MSS External Tide Data NORMAND TONJER PROJECT

  38. dDGPS MSS versus External Tidal Data NORMAND TONJER PROJECT

  39. PROCESSED DATA COMPARISON • Real Time Tide Determination • Using a real time tide determination SW (here in replay mode), the difference in the point to point real time tide data agree to within 0.22 m (95%) in height with independent water level estimates using tidal gauges • Inaccuracies in External Tidal Information? • Some of the differences are likely to be due to inaccuracies in the externally estimated tide. GPS derived tidal information is independent of external data • Mean Sea Surface • In this project the geoidal data was based on the NKG96 Geoidal Model (Norwegian Mapping Authority). There are worldwide Mean Sea Surface models based on satellite altimetry available today, that can be used to reference measured ellipsoidal heights to the sea level

  40. Static Shift Seismic Data Processing by Veritas DGC Ltd., London 3D SEISMIC SURVEY SPRING 2002JOB1 NEAR OFFSET CUBE TIMESLICE

  41. Reduced Static Shift Seismic Data Processing by Veritas DGC Ltd., London JOB1 NEAR OFFSET CUBE TIMESLICE WITH TIDAL CORRECTIONS

  42. Static Shift Seismic Data Processing by Veritas DGC Ltd., London 3D SEISMIC SURVEY SPRING 2002 WITHOUT TIDAL CORRECTIONS

  43. Reduced Static Shift WITH TIDAL CORRECTIONS Seismic Data Processing by Veritas DGC Ltd., London

  44. Seismic Data Processing by Veritas DGC Ltd., London Static Shift 3D SEISMIC SURVEY SPRING 2002 JOB 1 NEAR OFFSET CUBE CROSSLINE 5440

  45. Seismic Data Processing by Veritas DGC Ltd., London Reduced Static Shift JOB 1 NEAR OFFSET CUBE CROSSLINE 5440 WITH TIDAL CORRECTIONS

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