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ASHTECH Z18 (4) JPS EGGDT/E_GGD/LEGACY (16) LEICA GRX1200GGPRO (44) NOV OEMV3 (2) TPS EUROCARD/E_GGD/GB- 1000/ODYSSEY_E (18) TRIMBLE NETR5/NETR8 (18) LEICA GRX1200+GNSS (5) TPS NETG3 (2) LEIAT504GG (40) TPSCR3_GGD (14) NOV702GG (2) TPSCR.G3 (3) LEIAR25 (6) TRM55971.00 (22) TRM59800.00 (1) Moving the EPN from a GPS-only Network to a Multi-GNSS Network: Challenges and Pitfalls C. Bruyninx, N. Bergeot, J. Legrand, and E. Pottiaux Royal Observatory of Belgium, Av. Circulaire 3, Brussels, Belgium, [email protected] 2 nd Intern. Colloq. on Scientific and Fundamental Aspects of the Galileo Progamme EPN Data Analysis Conclusion Royal Observatory of Belgium Figure 1. EPN tracking network (status Oct. 2009). Stations indicated with red triangles observe GLONASS in addition to GPS. EPN Local Analysis Centre GNSS Software GLONASS capable Galileo capable GPS+GLONASS processing GPS+GLONASS+ GALILEO processing BEK Bernese V5.0 yes Yes, V5.1 update exp. 12/2010 yes planned BKG planned, 2010 planned GOP planned planned IGE TBD TBD IGN planned, 2010 planned NKG planned, 2010 TBD OLG planned planned ROB yes planned SGO planned, 2010 planned SUT planned, 2010 planned UPA planned, 2010 planned WUT planned, 2010 planned LPT Bernese 5.0 ext. yes yes yes planned COE Bernese V5.1 yes yes yes planned ASI MicroCosm software Vs. 2009.0 no no no TBD DEO GIPSY 4.0 yes no no TBD Modernization of EPN Tracking Network The large majority of the EPN LAC uses data analysis software from third parties and therefore depends on the multi-GNSS policy of these software providers: Satellite orbits and earth rotation parameters: ― IGS provides separate GPS & GLONASS products, multi-GNSS final IGS SP3 product in development (remaining consistency issues) ― The quality of the GLONASS orbits is not yet comparable with the quality of the GPS orbits. ― Taking the growing importance of PPP (Precise Point Positioning) into account, the availability of satellite clocks (as well as inter-channel hardware delays) for all GNSS is mandatory. At the moment the IGS is only providing high rate clock parameters for the GPS satellites. Despite EUREF recommendations, the majority of EPN LACs who do process GLONASS data use the fully consistent GPS/GLONASS orbit files from individual IGS ACs (CODE). Satellite and receiver antenna phase centre models: ― Best-available models not always used at IGS level to maintain consistency of reference frame ― GPS-only models are extrapolated for GLONASS ― Update foreseen in spring 2010 The EUREF Permanent Network (EPN) in a Nutshell 220+ continuously operating GPS and GPS+GLONASS (49%) stations, 38% also in IGS Maintained on a voluntary basis by EUREF members Daily, hourly RINEX, 15min high-rate RINEX and real-time data in raw or RTCM formats 2 Regional Data Centres, containing a copy of ALL hourly and daily data 1 Regional Broadcaster (www.euref-ip.net), streaming all real-time data using NTRIP EPN Central Bureau (CB), responsible for the day-to-day management of the EPN, http://epncb.oma.be is the gateway to all information about EPN 16 Local Analysis Centres (LAC), providing daily and weekly SINEX (some also hourly) and hourly zenith path delays Products: Weekly combined EPN SINEX solutions, station coordinates and velocities (ITRS/ETRS89), time series analysis, site zenith path delays Introduction of GLONASS & Galileo tracking capabilities GPS Modernization Stations not tracking unhealthy satellites (general problem) Stations not tracking PRN32 (ASHTECH Z-18, TRIMBLE NETR8/NETRS) L5 tracking: 31 EPN stations are equipped with an L5-capable receiver L2C tracking ― 50 EPN stations with L2C tracking capability; 18 capable of observing P2 and C2 (TRIMBLE NETRS/NETR5), others observe P2 or C2. Following IGS recommendation all should observe P2. ― ¼ cycle satellite-based phase shift (between different carrier components of the same frequency) of L2C w.r.t. P2: to be corrected in RINEX (V2.12 and 3.01, not yet implemented), not in RTCM. Careful with RTCM to RINEX converters (e.g. BNC)! Figure 6. Examples of reduced GLONASS tracking on L2. The majority of JPS and TPS receivers are not affected, while all LEICA, Novatel and Trimble GPS/GLONASS receivers suffer from this problem. 1999: first GPS+GLONASS tracking station, today: 49% GPS+GLONSS tracking stations, 15% increase in last year More than 90% of the new antennas installed are multi-GNSS antenna. From these, 75% observe GPS and GLONASS signals and 25% are in addition Galileo-ready. Remaining problems: ― with negative frequency channels (significantly reduced, only 4% of EPN stations still affected – ASHTECH-Z18 !) December 2006 Indiv. abs. calib 5 % Type abs.calib 64 % Calib. from field 14 % No calib. 17 % October 2009 Indiv. abs. calib 15 % Type abs. calib 68 % Calib. from field 8 % No calib. 9 % Figure 7. Calibration types used within the EPN. Left: Dec. 2006, Right: Oct. 2009 Figure 2. Multi-GNSS receivers used in the EPN (Oct. 2009) Figure 3. Multi-GNSS antenna used in the EPN (Oct. 2009) Antenna calibrations Since Dec. 2006, each antenna/radome introduced in the EPN (new stations or replacements at existing stations) must have absolute elevation and azimuth-dependent calibrations down to the horizon. 17% of antenna/radome combinations used within the EPN still do not have absolute elevation and azimuth- dependent calibrations down to the horizon. antenna/radome replacements continue to introduce jumps in the estimated station coordinates. EUREF strongly recommends, in the case an antenna has to be changed, to replace it with a multi-GNSS antenna. Table 1. Overview of the multi-GNSS analysis capabilities of the EPN analysis centres including future plans Almost half of the EPN stations are today already equipped with GPS+GLONASS tracking stations. A few of them allow to observe in addition the future Galileo signals. Several tracking problems where encountered with these receivers requiring frequent firmware upgrades and a close follow-up by the station managers as well as the EPN Central Bureau (who will need to develop additional tools for that). Height jumps have been reported after installing one of the new GPS+GLONASS+Galileo antenna suspecting that the absolute type calibrations values in use today are not optimal (possible change in antenna hardware for fine tuning?). How to reconcile the need to modernise the EPN tracking network in view of tracking new satellite signals without degrading the network stability? A careful introduction followed by an intensive monitoring of new equipment is mandatory. The availability of consistently combined GPS/GLONASS/Galileo orbits is an important pre-requisite for the EPN to be able to introduce all these GNSS in a consistent analysis. Some of the European IGS ACs will provide these products in the future, but it is preferable if the IGS, as a GNSS service, provides these consistent multi- GNSS orbits. Acknowledgement: Part of the statistics shown are based on EPN tracking information provided by CODE (see ftp://ftp.unibe.ch/aiub/epndata/) Several EPN station operators noticed considerable jumps in the station height after switching to the LEIAR25 antenna, although robot calibrations were available for the old and the new antenna. So while the installation of multi-GNSS antennas is recommended, extreme care is still necessary when using new antennas which could still have some child-diseases. LEIAT504GG NONE LEIAR25 NONE TRM29659.00 NONE LEIAR25 NONE TRM29659.00 NONE LEIAR25 NONE Figure 8. Residual position time series (RAW) for the EPN stations VALA, LEON , and SALA. A height jump of 1-2 cm is seen after the installation of the LEIAR25 (GPS+GLONASS+Galileo) antenna Figure 5. Number of GLONASS satellites and number of EPN stations tracking GLONASS GPS+ GLONASS GPS+ GLONASS+ Galileo Figure 8. WRMS individual AC orbit solutions with respect to the IGS Final products GPS+ GLONASS GPS+ GLONASS+ Galileo ― need for frequent receiver firmware upgrades (e.g. 6 firmware upgrades in 2009 for a specific GGG- receiver) ― Missing L2 (on R09), see Fig. 6 Figure 4. Example of GNSS tracking of new GPS+GLONASS+Galileo receivers used in EPN To guarantee consistency with the International GNSS Service (IGS), EUREF asks the EPN LACs to use IGS products (e.g. satellite orbits & clocks, antenna calibrations) within their data analysis. Consequently, the EPN analysis strongly depends on the availability of these IGS products: The usage of individual receiver antenna calibrations is allowed within the EPN.
