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. PottiauxRoyal Observatory of Belgium, Av. Circulaire 3, Brussels, Belgium, C.Bruyninx@oma.be

2nd Intern. Colloq. onScientific 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 yesYes, 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 themulti-GNSS policy of these software providers:

Satellite orbits and earth rotation parameters:

― IGS provides separate GPS & GLONASSproducts, multi-GNSS final IGS SP3 product indevelopment (remaining consistency issues)

― The quality of the GLONASS orbits is not yetcomparable with the quality of the GPS orbits.

― Taking the growing importance of PPP (PrecisePoint Positioning) into account, the availability ofsatellite clocks (as well as inter-channel hardwaredelays) for all GNSS is mandatory. At the momentthe IGS is only providing high rate clockparameters for the GPS satellites.

Despite EUREF recommendations, the majority of EPNLACs who do process GLONASS data use the fullyconsistent GPS/GLONASS orbit files from individualIGS ACs (CODE).

Satellite and receiver antenna phase centre models:

― Best-available models not always used at IGS levelto 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 andGPS+GLONASS (49%) stations, 38% also inIGS

Maintained on a voluntary basis by EUREFmembers

Daily, hourly RINEX, 15min high-rate RINEXand real-time data in raw or RTCM formats

2 Regional Data Centres, containing a copy ofALL hourly and daily data

1 Regional Broadcaster (www.euref-ip.net),streaming all real-time data using NTRIP

EPN Central Bureau (CB), responsible for theday-to-day management of the EPN,http://epncb.oma.be is the gateway to allinformation about EPN

16 Local Analysis Centres (LAC), providing daily and weekly SINEX (some also hourly) and hourly zenithpath delays

Products: Weekly combined EPN SINEX solutions, station coordinates and velocities (ITRS/ETRS89), timeseries 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 L2Cw.r.t. P2: to be corrected in RINEX (V2.12 and 3.01, not yet implemented), not in RTCM. Careful withRTCM to RINEX converters (e.g. BNC)!

Figure 6. Examples of reduced GLONASS tracking on L2. The majorityof JPS and TPS receivers are not affected, while all LEICA, Novateland 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-GNSSantenna. From these, 75% observe GPS and GLONASSsignals 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 2006Indiv. abs. calib 5 %Type abs.calib 64 % Calib. from field 14 %No calib. 17 %

October 2009Indiv. 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 existingstations) 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. EUREFstrongly 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 ofthem allow to observe in addition the future Galileo signals. Several tracking problems where encountered withthese receivers requiring frequent firmware upgrades and a close follow-up by the station managers as well asthe 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 suspectingthat the absolute type calibrations values in use today are not optimal (possible change in antenna hardware forfine tuning?).

How to reconcile the need to modernise the EPN tracking network in view of tracking new satellite signalswithout degrading the network stability? A careful introduction followed by an intensive monitoring of newequipment is mandatory.

The availability of consistently combined GPS/GLONASS/Galileo orbits is an important pre-requisite for the EPNto be able to introduce all these GNSS in a consistent analysis. Some of the European IGS ACs will providethese 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 LEIAR25antenna, although robot calibrations were available for the old and the new antenna. So while the installation ofmulti-GNSS antennas is recommended, extreme care is still necessary when using new antennas which couldstill have some child-diseases.

LEIAT504GG NONELEIAR25 NONE

TRM29659.00 NONELEIAR25 NONE

TRM29659.00 NONELEIAR25 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 tothe IGS Final products

GPS+GLONASS

GPS+GLONASS+Galileo

― need for frequent receiverfirmware upgrades (e.g. 6firmware upgrades in2009 for a specific GGG-receiver)

― Missing L2 (on R09), seeFig. 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 IGSproducts (e.g. satellite orbits & clocks, antenna calibrations) within their data analysis. Consequently, the EPNanalysis strongly depends on the availability of these IGS products:

The usage of individual receiver antenna calibrations is allowed within the EPN.