CONVERGENCE TIME IMPROVEMENT OF PRECISE POINT POSITIONING

Transcription

1 CONVERGENCE TIME IMPROVEMENT OF PRECISE POINT POSITIONING Mohamed Elsobeiey and Ahmed El-Rabbany Department of Civil Engineering (Geomatics Option) Ryerson University, CANADA

2 Outline Introduction Impact of Second-order Ionospheric Delay: - GPS Satellite Orbit - GPS Satellite Clock Corrections - PPP solution Conclusions and Future Outlook 2

3 Introduction 3 Real-time and near real-time GPS precise point positioning (PPP) requires shorter convergence time for the estimated parameters Recent research has shown that not all errors and biases are rigorously modelled in PPP, which results in correlated residual errors Such unmodelled errors should be accounted for to achieve shorter convergence of the PPP solution Second-order ionospheric delays is considered one of the most important errors that should be considered in GPS PPP

4 Second-order Ionospheric Delay Factors Affecting Second-order Ionospheric Delay Z z' Satellite - Total electron content - Magnetic field at the ionospheric pierce point h ion B 0 z Receiver θ Pierce Point - Angle between magnetic field and propagation direction α R Y X 4

5 Second-order Ionospheric Delay (Cont d) Parameters of Geomagnetic Field Magnetic field parameters are estimated at the Ionospheric Pierce Point (IPP) using the 11 th generation of International Geomagnetic Reference Field model (IGRF) Slant Total Electron Content (STEC) P1-P2 is used and satellites and receiver differential hardware delays are applied 5

6 6 IGS Stations Used in Estimating orbit and Clock Corrections

7 Effect of Second-order Ionospheric Delay on Orbit Determination Radial Along-track Cross-track GPS Satellite 7 G02 G03 G04 G05 G06 G07 G08 G09 G10 G11 G12 G13 G14 G15 G16 G17 G18 G19 G20 G21 G22 G23 G24 G26 G27 G28 G29 G30 G31 G32 Orbit Difference (m)

8 Effect of Second-order Ionospheric Delay on Clock Corrections 50 IGS Clock RMS Estimated Clock RMS GPS Satellite 8 G02 G03 G04 G05 G06 G07 G08 G09 G10 G11 G12 G13 G14 G15 G16 G17 G18 G19 G20 G21 G22 G23 G24 G26 G27 G28 G29 G30 G31 G32 Clock RMS (ps) 10 0

9 Effect of Second-order Ionospheric Delay on PPP Solution NRCan GPS PPP software is modified to accept the second-order ionospheric delay correction The estimated satellite orbit and clock corrections are used to process the GPS data of several GPS stations First-order ionosphere-free linear combination of both code and carrier-phase are used and the correction for the second-order ionospheric delay is applied for both observables 9

10 IGS Stations Used to Verify the Estimated Orbit and Clock Corrections 10

11 Latitude Results for Station DRAG DOY125, First-Order IONO Only First+Second-order IONO Latitude Error (m) Time (Minutes) 11

12 Longitude Results for Station DRAG DOY125, Longitude Error (m) First-Order IONO Only First+Second-order IONO Time (Minutes) 12

13 Height Results for Station DRAG DOY125, Height Error (m) First-Order IONO Only First+Second-order IONO Time (Minutes) 13

14 Latitude Results for Station THA1 DOY125, First-Order IONO Only First+Second-order IONO Latitude Error (m) Time (Minutes) 14

15 Longitude Results for Station THA1 DOY125, Longitude Error (m) First-Order IONO Only First+Second-order IONO Time (Minutes) 15

16 Height Results for Station THA1 DOY125, First-Order IONO Only First+Second-order IONO Height Error (m) Time (Minutes) 16

17 Conclusions and Future Outlook The impact of the second-order ionospheric delay on GPS satellite orbit and clock corrections is investigated The results showed that an error in the GPS satellites orbits ranges from 1.5 to 24.7 mm in radial, 2.7 to 18.6 mm in along-track, and 3.2 to 15.9 mm in cross-track directions, respectively Second-order ionospheric-delay can cause satellite clock error up to ns (2 cm) 17

18 Conclusions and Future Outlook (Cont d) Accounting for the second-order ionospheric delay can improve the PPP coordinate solution by about 3 mm and the convergence time by about 15% Future research will develop between-satellite single-difference (BSSD) algorithm BSSD PPP with accounting for the second-order ionospheric delay will be the key for carrier-phase ambiguity resolution in PPP 18

19 19 Thank You!