Fugro Chance Inc. 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 –Normand Tonjer Seabed Mapping and Cable Route Survey Project at 71 Degrees N –3D Seismic Data Processing With and Without Tidal Compensation

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

Fugro Chance Inc. 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)

Fugro Chance Inc. STAND ALONE GPS PERFORMANCE Trim 212 Lafayette (30°13' "N 92° 3' " W)

Fugro Chance Inc. SINGLE SITE DIFFERENTIAL Trim 212 W 750 RTCM Lafayette (30°13' "N 92° 3‘ " W)

Fugro Chance Inc. 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

Fugro Chance Inc. 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

Fugro Chance Inc. JPL REFERENCE NETWORK DISTRIBUTION 30 Reference Stations

Fugro Chance Inc. HP NETWORK SERVICE DEPLOYMENT 50 HP Stations World Wide 85 Reference Stations

Fugro Chance Inc. STARFIX HP LAFAYETTE 1 Sigma East = 3cm, North = 2cm, Vertical = 6cm

Fugro Chance Inc. STARFIX GSS LAFAYETTE 1 Sigma East = 7cm, North = 5cm, Vertical = 8cm

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

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

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

Fugro Chance Inc. JPL RTG PROCESSED DATA RMS = 4 cm East, 3 cm North, 8 cm Vertical

Fugro Chance Inc. UNIVERSITY OF SOUTHERN MISSISSIPPI TEST RESULTS (FROM ION GPS GNSS 2003) Long Term Static Tests July 25 - August 7, 2003 System TypeHor Acc 95%Vert Acc 95% Fugro HPNetwork SkyFix XPSDGPS

Fugro Chance Inc. SOLAR CYCLE 23

Fugro Chance Inc. SOLAR EVENT OCTOBER 28/29,

Fugro Chance Inc. IONOSPHERIC DELAY CALCULATION Mobile Ref Stn  t REF Single Frequency System:  t REF and  t MOB ionospheric delay calculated from a model (Klobuchar) Dual Frequency System:  t REF and  t MOB delay calculated from dual frequency GPS measurements (Delay=40.3 *TEC/c*f 2 ) Ionosphere c  t=f 2 2 /(f f 2 2 )*(PR 2 -PR 1 )  t MOB  Iono=  t REF -  t MOB

Fugro Chance Inc. DIFFERENTIAL GPS WORKS BECAUSE … Any changes to the operating environment which adversely impacts the fundamentals will limit operational success. 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

Fugro Chance Inc. OSLO SINGLE BASELINE HP OCT 29 AND NOV 4

Fugro Chance Inc. OSLO NETWORK HP OCT 29 AND NOV 4

Fugro Chance Inc. WAAS PERFORMANCE DURING OCT 29 EVENT

Fugro Chance Inc. WAAS PERFORMANCE DURING OCT 29 EVENT

Fugro Chance Inc. WAAS PERFORMANCE DURING OCT 29 EVENT

Fugro Chance Inc. DISCOVER SEVEN SEAS IN RIO NOV 10, 2003

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

Fugro Chance Inc. Real Time Tidal Monitoring for Seismic Data Collection Applications

Fugro Chance Inc. 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

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

Fugro Chance Inc. 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 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 TIDAL DETERMINATION GPS measures Ellipsoid heights –Reduced to reference point and wave-movement removed Predicted tide used to calculate Average Vertical Offset (AVO) –If no predicted tide is available, the AVO is the tide Mean Sea Surface (MSS) model applied to get sea level reference –MSS models are available –Geoid differ from MSS by 1m

Fugro Chance Inc. MSS (CLS98) vs GEOIDE (EGM96)

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

Fugro Chance Inc. 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

Fugro Chance Inc. RAW DATA HEIGHT COMPARISON 2 - Meter Change in Ellipsoid Height in 100 km –Between about 23 rd June 19:00 UTC and 24 th 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

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

Fugro Chance Inc. NORMAND TONJER PROJECT dDGPS MSS versus External Tidal Data

Fugro Chance Inc. 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

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

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

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

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

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

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