Combined Processing of GPS GLONASS and SBAS Code
Combined Processing of GPS, GLONASS, and SBAS Code Phase and Carrier Phase Measurements Lambert Wanninger, Stephan Wallstab-Freitag Geodetic Institute, Dresden University of Technology, Germany ION GNSS 2007, Session D 2
GPS+GLONASS+SBAS Maxim: The more satellites the better. GPS (30) GPS+ GLONASS (30+11) GPS+ SBAS (30+4) GPS+ GLONASS+SBAS (30+11+4) # visible SV 8. 4 11. 7 12. 4 15. 7 Æ PDOP 1. 9 1. 7 1. 6 1. 4 but several differences: • reference systems (GLONASS) transformation • orbit accuracy (GLONASS, SBAS) weighting • observation quality (GLONASS, SBAS) weighting • inter-channel biases (GLONASS) algorithm, estimation
Orbit Accuracy GPS/GLONASS Broadcast orbit accuracy (source: JPL, IGS) Precise IGS orbits GPS (final): <5 cm GLONASS: 15 cm
Observation Quality GPS/GLONASS Code Observations: Elevation dependence of MP 1 Station 1 / Receiver 1 Station 2 / Receiver 2 Proper weighting required receiver dependence
GPS+GLONASS+SBAS Observation Equations for Single-Difference Carrier Phases GLONASS inter-channel bias difference [cm]:
GLONASS Inter-channel Bias Diff. Double-Difference Residuals L 1 GPS GLONASS inter-channel biases removed
GLONASS Inter-channel Bias Diff. Long-term Stability L 0 – iono. -free linear combination
GLONASS Interchannel Bias Diff. Temperature effects Chilling: 20° Celsius temperature difference no effect but change of antenna affects inter-channel bias difference L 0 – iono. -free linear combination
GLONASS Inter-channel Bias Diff. A priori values of [cm] Ashtech Z-18 JPS Legacy, TPS E_GGD, TPS Net-G 3 Leica GRX 1200 GG PRO Trimble Net. R 5 Ashtech Z-18 0. 0 2. 4 -0. 7 JPS Legacy, TPS E_GGD, TPS Net-G 3 0. 0 2. 4 -0. 7 Leica GRX 1200 GG PRO -2. 4 0. 0 -3. 1 Trimble Net. R 5 0. 7 3. 1 0. 0
Baseline Results GPS/GLONASS RTK-like processing: short baseline, 2 minutes of observations GPS + GLONASS 8. 0 11. 6 Combined Float/DGNSS Std. Dev. N/E/Up [cm] 18 / 20 / 25 15 / 19 / 20 Fixed solution # valid solutions (of 360) Std. Dev. N/E/Up [cm] 358 0. 54 / 0. 49 / 1. 00 359 0. 53 / 0. 48 / 0. 93 average # of SV
SBAS Code and carrier phase observations to GEO satellites presently • 10 SBAS satellites, • 4 over Europe, • just single-frequency EGNOS presently: poor broadcast orbits+clocks short baselines only
Observation Quality GPS/SBAS Code observations: elevation dependence of MP 1 dual-frequency GPS MP 1 single-frequency GPS MP 1´ single-frequency SBAS MP 1´
SBAS RTK-like processing: short baseline, 2 minutes of observations, dual-freq. GPS, single-freq. SBAS GPS + SBAS 8. 7 12. 7 Combined Float/DGNSS Std. Dev. N/E/Up [cm] 16/18/22 15/17/21 Fixed # valid solutions (of 720) Std. Dev. N/E/Up [cm] 713 0. 44 / 0. 35 / 0. 89 712 0. 27 / 0. 26 / 0. 74 average # of SV single-frequency SBAS improves dual-frequency GPS
SBAS Carrier Phase Multipath Double-difference residuals L 1: short static baseline, 2 SBAS satellites daily multipath pattern, but also changes in pattern: due to daily repetition of orbits, orbit maneuvers
Summary + Outlook GLONASS • lower orbit accuracy • some receivers: lower accuracy of code observations • inter-channel biases SBAS • presently + EGNOS only: very poor orbit accuracy • lower accuracy of code observations • single-frequency only Bright future • GPS L 5, dual-frequency SBAS • more GPS/GLONASS/SBAS satellites • Galileo / Compass / GLONASS CDMA A bird in the hand is worth two in the bush.
- Slides: 15