Estimating COMPASS Orbits And Clocks And Applying To Real-Time Precise Positioning Services Maorong Hongping Zhang, Xiaolin Jia, Shuli Song, and Jens 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, March 2012, Munich, Germany

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

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

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.

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)

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

Tracking Network (Wuhan Uni)

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

Data Availability

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

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

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

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

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

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

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

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

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

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

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

 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)

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

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

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

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

 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

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

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