1. SP Swedish National Testing and Research Institute Real-Time GPS Processing with Carrier Phase FILTER PARAMETER INFLUENCE ON GPS CARRIER PHASE REAL-TIME TIME AND FREQUENCY TRANSFER FOR SHORT AND LONG BASELINES Carsten Rieck, Per Jarlemark, Kenneth Jaldehag and Jan Johansson SP Swedish National Testing and Research Institute Box 857, S-501 15 Borås Sweden 36 th PTTI December 7-9, 2004 Washington DC

2. SP Swedish National Testing and Research Institute Real-Time T&F GPS 1.Introduction 2.Real-time-GPS Filter 3.Station Position Correction Estimation 4.Satellite Orbits 5.Earth Tide Modeling 6.Long Baselines 7.Conclusions and Future Work

3. SP Swedish National Testing and Research Institute Real-Time T&F GPS: Principle Operation REC1 CLK1 REC2 CLK2 RECN CLKN...... InterNetwork TCP/IP Client/Server Data Streaming Real-Time Kalman Filter IGS-Orbits Broadcast EPH KF-States  CLK1-2, …  CLK1-N TROP1, … TROPN  STAPOS1, …  STAPOSN AMBIGUxy x – clockdiff y – satellite Residuals: Receiver Pair/Sat

4. SP Swedish National Testing and Research Institute Real-Time Kalman Filter Raw Data Modeling RT Filter  CLK STATROP STAPOS AMBIGU - common view differential phase observations, L3 ionospheric ”free” phase, P3 code support, - satellite orbits (broadcast, IGS predicted,P3) - earth tides (simple elastic) - continental drift, rebound - ocean loading (optional) - forward Kalman filter, Matlab/GNU Octave, purely L3 based, RW noise model non standard troposphere, RW noise model station position corrections, constant non-integer ambiguities, constant

5. SP Swedish National Testing and Research Institute Method & Result Verification “real-time” streaming of RINEX observation and navigation files to the filter software RT results compared to solutions based on TWSTFT, Circular-T, GPS post-processed PPP, GPS-P3 Real-Time

6. SP Swedish National Testing and Research Institute Results: UTC(SP)-UTC(PTB) 623km

7. SP Swedish National Testing and Research Institute Results: UTC(SP)-UTC(PTB) 623km

8. SP Swedish National Testing and Research Institute Results: UTC(SP)-UTC(PTB) 623km

9. SP Swedish National Testing and Research Institute Results: UTC(SP)-UTC(PTB) : RT-TWSTFT

10. SP Swedish National Testing and Research Institute Station Position Offsets assume: perfect orbits & atmosphere modeling, max range error  is initially absorbed by the respective (non-integer) satellite ambiguity parameter Several different filter state variables have to compensate for an absolute range error of 2  :  CLK STATROP residuals SAT AMB

11. SP Swedish National Testing and Research Institute West->East Dominance of Satellite Passes A majority of all satellite passes have a west-east orientation and thus dominantly influence the initial satellite ambiguities in one direction.

12. SP Swedish National Testing and Research Institute Station Position Offset Example SP-PTB East :10 mm offset  f  200 ps/day North :10 mm offset  f  35 ps/day Vertical :10 mm offset  f  2 ps/day

13. SP Swedish National Testing and Research Institute Station Position Correction If station positions are not properly known they can be estimated as constant offsets from an approximate position. Offsets do not necessarily reflect real positions but correct for wrong baseline geometry (local).

14. SP Swedish National Testing and Research Institute Orbit Position Modeling Broadcast Ephemerides have an uncertainty of about 2m (IGS). IGS ultra-rapid orbit predictions are available in real- time and can be used to correct broadcast orbits.

15. SP Swedish National Testing and Research Institute Earth Tide Modeling, Simple Elastic (VLBI)

16. SP Swedish National Testing and Research Institute Earth Tide Modeling – Complex & Ocean Loading http://www.oso.chalmers.se/~loading

17. SP Swedish National Testing and Research Institute Earth Tides – Differential Errors of Simple Model

18. SP Swedish National Testing and Research Institute AMC2 PTBB MDVJ ALGO support stations allow to estimate a better local troposphere  precise station positions and good orbits needed ! >3x 2361 km 786 km 622 km 1484 km Transatlantic Baselines : UTC(SP)-UTC(USNO) USNO SP01 1 common sat observation versus 3 states (  clk+2trop) 6184 km >1x

19. SP Swedish National Testing and Research Institute Transatlantic Baselines : UTC(SP)-UTC(USNO)

20. SP Swedish National Testing and Research Institute Conclusions and Future Work In good agreement with GIPSY, TWSTFT and Circular-T. UTC(SP) –UTC(PTB): 40ps/day frequency offset between TWSTFT and RT. RMS differences of 50ps between real-time processing and GIPSY PPP post-processing are achievable. To do … filter : –combination with code, steer the long term frequency, –loading models, correct short term frequency, –short smoothing, –KF code migration to a ”clean” POSIX environment. To do … real-time data handling: –support for raw data streams, NTRIP,… –encryption, authentication, –multicast mode.

21. SP Swedish National Testing and Research Institute Thanks and Contact Thanks to: IGS Open Source Community LMV, National Land Survey of Sweden OSO, Onsala Space Observatory Contact : Carsten Rieckcarsten.rieck@sp.se SP / Mtehttp://tempus.sp.se Box 857+46 33 165440 Borås / Sweden