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Real-Time and Near Real-Time GPS Products and Services from Canada. Y. Mireault, P. Tétreault, F. Lahaye, P. Collins, M. Caissy Geodetic Survey Division, Natural Resources Canada (GSD/NRCan) http://www.geod.nrcan.gc.ca IGS Analysis Center Workshop 2008 June 2-6, 2008

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Real-Time and Near Real-Time GPS Products and Services from Canada


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    1. Real-Time and Near Real-TimeGPS Products and Services from Canada Y. Mireault, P. Tétreault, F. Lahaye, P. Collins, M. Caissy Geodetic Survey Division, Natural Resources Canada (GSD/NRCan) http://www.geod.nrcan.gc.ca IGS Analysis Center Workshop 2008 June 2-6, 2008 Miami Beach, Florida, USA

    2. Outline • NRCan Ultra Rapid Products (EMU) • CSRS Precise Point Positioning Service (CSRS-PPP) • Canadian RT GPS Tracking Network • Canadian High Precision RT GPS Wide-Area Correction Service (GPS·C) • Final Notes

    3. 1. NRCan Ultra Rapid Products (EMU) 1.1 Description • Orbits and clocks for RT/NRT usage • Covers 48h, i.e. 24h estimated and 24h predicted • Produced every hour • ~1h delay for orbits and ~1.5h delay for clocks • Submission to IGS every 6h • Predicted orbits used inGPS·C • Estimated orbits and 30-sec satellite clocks used in NRT PPP

    4. 1.2 Some Highlights

    5. 1.3 Precision* • (*) Orbit and Clock Median RMS when compared to IGS Rapid (IGR) • (a) Orbits and clocks are used in NRT PPP • (b) Orbits are used in GPS·C

    6. A Web based global positioning service for single GNSS datasets (currently GPS only; GLONASS planned) Initiated in the Fall of 2003 as next-day service (17h delay) Delay reduced to 90min (May 2008) using NRCan Ultra Rapid orbits and 30sec clocks Process static or kinematic (both with single or dual frequency data) Use of IGS IONEX grids for single frequency processing 2. CSRS Precise Point Positioning (PPP) 2.1 Description

    7. 2.2 CSRS-PPP Usage

    8. 1.4 EMU (30sec) 1.2 IGR (5min) 1 IGS 5min IGS 30sec 0.8 Mean Differences (cm) 0.6 0.4 0.2 0 -0.2 Ellipsoidal height Latitude Longitude -0.4 2.3 CSRS-PPP Static Positioning Corrections(wrt IGS05) Statistics based on processing of 30 secs data from 24 hour files for ALGO DRAO RESO SASK STJO for GPS Week 1470

    9. EMU (30sec) 25 IGR (5min) IGS 5min 20 IGS 30sec 15 Mean position variations (cm) 10 5 0 Latitude Longitude Ellipsoidal height 2.4 CSRS-PPP Kinematic Positioning Variations (wrt IGS05) Statistics based on processing of 30 secs data from 24 hour files for ALGO DRAO RESO SASK STJO for GPS Week 1470

    10. 3.Canadian RT GPS Tracking Network

    11. Pseudorange & Phase Processing from IGS-RT + RT-CACS Stations P3 = r(Xsta,Xsat) + c · ( dtsta – dtsat ) + dtrop + e L3 = r(Xsta,Xsat) + c · ( dtsta – dtsat ) + dtrop + lN + e Xsat provided by EMU (1h cycle) || IGU (6hr cycle) predictions dtsta, dtsat,dtrop,N estimated in real-time Enhancement of the current code-based system 4.GPS·C: Canadian High Precision RT GPS Wide-Area Correction Service 4.1 Description (1/2)

    12. Modeled Effects • Earth & ocean tides • Station & satellite absolute PCV • Relativity • ITRF station velocity • Phase wind-up • Parameters Estimated • Station and satellite clocks (white noise parameters wrt VRC) • Station troposphere ZPD (random-walk) • Constant (float) ambiguities • RT High Precision Correction Stream • Xsat-BRD @ 120sec (linear over 240sec) • dtsat-BRD @ 2sec 4.1 Description (2/2)

    13. 4.2 GPS·C Results

    14. 4.3 GPS·C Development • Status • Access to 50+ real-time stations globally • Finalizing stress-tests & application robustness improvements • IOC targeted for Fall 2008  Pilot Project / ESS activities • Further Refinements to the Phase-based Algorithm & Models • YAW model (Kouba, GPS Solutions (online)) • Un-differenced integer ambiguity resolution with decoupled clocks • Define BRD-independent orbit messages • Define messages for troposphere-mapping grid, satellite DCB’s • Define messages required for PPP ambiguity resolution

    15. 4.4 Day-Boundary Clock Jumps / Decoupled Clocks

    16. 5. Final Notes • IGS Ultra Rapid Combination • Push it to a 3h cycle? Ultimate goal of 1h cycle? • Reduce delay from 3h to 2h? • Need more AC clock solutions to improve precision and accuracy! • Global RT GPS Tracking Network • Would provide faster data for Ultra Rapid orbits/clocks turnaround • Need for 30sec satellite clocks for Rapid and Ultra Rapid products (NRT users such as PPP)

    17. Information on decoupled clocks • “Isolating and Estimating Undifferenced GPS Integer Ambiguities”, Paul Collins, GSD, NRCan • Presented at the Institute of Navigation, NTM 2008, San Diego, January 28-30 2008, session D3. • Look also for the corresponding paper in the ION TNM proceeding.

    18. Statistics based on processing of 5 min data from 24 hour files for ALGO for GPS Week 1470

    19. Statistics based on processing of 5 min data from 24 hour files for ALGO for GPS Week 1470

    20. 6 EMU (30sec) Latitude 5 EMU (30sec) Longitude 4 EMU (30sec) Ellip. Height 3 IGS 30sec Latitude IGS 30sec Longitude 2 IGS 30sec Ellip. Height 1 Mean corrections (cm) 0 0 2 4 6 8 10 12 14 16 18 20 22 24 -1 -2 -3 -4 -5 2.5 CSRS-PPP Static Positioning Corrections (wrt IGS05) Hours Statistics based on processing of 30 secs data from 24 hour files for ALGO DRAO RESO SASK STJO for GPS Week 1470