1. Estimating COMPASS Orbits And Clocks And Applying To Real-Time Precise Positioning Services Maorong Ge(maor@gfz-potsdam.de), Hongping Zhang, Xiaolin Jia, Shuli Song, and Jens Wickertmaor@gfz-potsdam.de German Research Centre for Geosciences GNSS Research Center, Wuhan University Xi’an Research Institute for Surveying And Mapping Shanghai Astronomical Observatory Munich Satellite Navigation Summit, 13-16 March 2012, Munich, Germany

2. Motivation COMPASS Constellation WHU Tracking Network EPOS-RT Software Precise Orbit And Clock Estimation Applying to Positioning And GPSMET Real-time Precise Positioning Service Summary Contents

3. Three Phases: Phase I :Demonstration System, 2000 Phase II: Regional System, 2012 Phase III: Global System, 2020 What Can Be Achieved With Current COMPASS Constellation? Motivation

4. COMPASS Constellation Five GEOs: Inclination 0º,longitudes: 60ºE to 160ºE, Altitude 36,000 km. 27 MEOs: In 3 orbital planes, Inclination 55.5º, Altitude 21,500 km. Three IGSOs.

5. COMPASS Constellations Space Segment (Constellation) Phase II: 5 GEOs + 5 IGSOs + 4 MEOs Phase III: 5 GEOs + 3 IGSOs + 27 MEOs Current Constellation (Sept. 2011) 3 GEOs + 4 IGSOs (Data available)

6. Tracking Network (Wuhan Uni) A Global GNSS Network Dedicated To COMPASS Scientific Research Data Available At Stations: Beijing, Wuhan, Chengdu, Lasha, Shanghai, Urumuqi and Xi’an, Singapore and Perth Australia

7. Tracking Network (Wuhan Uni)

8. UR240 UA240 BD/GPS 四频 OEM 接收机 Recevier And Antenna

9. Data Availability

10. EPOS-RT Software  Multi-Technology GNSS SLR VLBI …  Multi-Function Real-time/Post-mission; Static/Kinematic/Dynamic

11. EPOS-RT: Structure  Left Side: Post-Processing. Right Side: Real-Time

12. Data Processing  POD& PTD  Real-Time PPP service

13. Dynamical Models ParameterCOMPASS Satellite GravityEIGEN GRACE02S 12 x 12 Point massEarth, Sun, Moon and Planets TidesSolid Earth tides Pole tides Ocean tide Relativistic effectsYes Solar radiationBern model with 9 model parameters Velocity BreaksOnly for maneuver modelling Satellite Attitude: As GPS PCO/PCV: Not Available

14. Observation Models ParametersModelConstraint ObservationLC and PCL1 0.02cycle, P1 1.0m Sampling rate60 seconds Cutoff elevation7 degree WeightElevation dependentelev > 30 o, 1; else 2*sin(elev) PCO/PCVNot available Phase wind-upYes Tropospheric delaySaastamoinen model + process10cm + 5 mm/sqrt(hour) Ionospheric delayEliminated by using LC and PC Satellite clockBroadcast + Wite noise300 m Receiver clockRange estimating + White noise300 m Station displacement Solid earth, pole tide, ocean loading Station coordinateConstraint to GPS derived valueAccordingly AmbiguityEstimated and fixed to integer Relativistic effectsYes ERPSolve for x-pole y-pole and rates and LOD Almost fixed

15. Three-Day Solution  Three-Day Sliding Window With One-Day Step-size.  Orbit Overlap 48 h, Sol. 1 and 2, or Sol 2 and 3 24 h, Sol. 1 and 3, or Sol 2 and 4 1 h, Sol. 1 and 4 (Blue parts) Estimation (Green), Predicted (Blue) Sol. 1 2 3 4

16. Orbit Comparison  RMS increases along with time-lag  GEO has significant larger RMS  On average GEO 6 m, IGSO 1 m Time-lag of the solutions

17.  Large RMS in Along- Tracking, 23 m  Constant Bias !  < 1 m in Cross-Tracking & Radial Orbit Comparison

18.  Systematic Bias Except C04  Orbit Related ?  STD 0.5 ns (15 cm) Clock Comparison

19. ZTD RW process with PD Better than 10 mm in Horizontal 4 cm bias in vertical, 1-2 cm STD Static PPP With Estimated Orb&CLK

20. MEAM GPS-COMPASS = -13 mm, STD=14 mm Both PCO&PCV for Sat. and Rec. not available ZTD Estimated vs GPS Derived

21.  Position: 100 m + 1 m per sqrt (minute)  Epoch not shown if nsat <=4  After 1-2 hour to 1 dm, Stay at cm-level  Fluctuation at 20:00, repeated daily (?) Kinematic PPP (Forward)

22.  Epoch not shown if nsat <=4  Bias 12, 6, -8 mm, STD 45, 27. 74 mm (ENU)  Fluctuation at 20:00 ? Kinematic PPP (+Backward)

23. EPOS-RT For Real-Time PPP Service RT Orbit RT Clock RT PPP GPS receivers SRIF(Orb) BNCBNC2SRIFSRIF(Clk)‏ SRIF2BNS BNC2SRIFSRIF(PPP)‏ Internet connection Control Unit IGS Hourly Data RT PPP GPS receivers BNC2SRIFSRIF(PPP)‏ OBS Streaming NTRIP Products ORB/CLK/UPD Hourly D a t a RT ORB Pos&Time ZTD/STD Control Unit IGS Real-Time Analysis Center at GFZ

24. Orbit Prediction  Three-Day Sliding Window With One-Day Step-size.  Orbit Integration To The Fourth Day (1D Pred.)  The Step-size Can Be To 1 h For A Faster Update depending on the data availability Prediction (Green with Data, Yelllow=Predicted

25.  Compared With Estimated Orbits  Major Bias in Along-track Direction, Especially for GEOs  STD Are Similar, Smallest in Radial. Quality of Predicted Orbits

26.  Clocks are estimated epoch-wise by fixing the predicted orbits.  Both clocks&orbits are used for simulated real-time positioning  URA should be compared Quality of Estimated Clocks

27. Simulated Real-Time PPP Very similar to that with estimated orbits&clocks Decimeter accuracy achievable Fluctuation at 20:00 ?

28. 3D-rms 16 m for GEOs and 2.4 m for IGSOs. Large bias in along-track, small and similar errors in radial of 1.8 m for GEO and IGSO. Static Daily PPP: 1 cm/3cm, Bias due to PCO/PCV Kinematic PPP: 5, 3 and 7 cm in ENU Simulated RTPPP service: 1-2 dm. To be improved with the full constellation of Phase II. Summary