multi-gnss real-time precise point positioning: gps

Multi-GNSS Real-time Precise Point Positioning: GPS, GLONASS, BeiDou, and

Galileo Xingxing Li, Maorong Ge, Mathias Fritsche, Yang Liu, Zhiguo

Deng, Jens Wickert, and Harald Schuh

The German Research Centre for Geosciences (GFZ) Telegrafenberg, Potsdam, Germany. lixin@gfz-potsdam.de

1 Multi-GNSS status 2 Multi-GNSS data processing 3 Multi-GNSS orbit and clock 4 Multi-GNSS real-time PPP 5 Discussions

Content

1 Current multi-GNSS status

3

Figure 1. Ground tracks of four satellite navigation systems: BeiDou (14), Galileo (8+), GLONASS (24) and GPS (32).

1 Current multi-GNSS status

4

Figure 2. Satellite visibility of Galileo, BeiDou, GLONASS and GPS at the four-system station GMSD (Japan) on September 3, 2013 .

Li et al (2015), Precise positioning with current multi-constellation Globa l Naviga t ion Sa te l l i t e Systems: GPS, GLONASS, Galileo and BeiDou. Sci Rep., 5, 8328.

1 Current multi-GNSS status

5

Figure 3. Distribution of MGEX stations and their supported constellations (as of 2014, almost 90 stations); some IGS stations (the red circles, GPS-only) are also included.

1 2 30

2

4

6

8

180oW 120oW 60oW 0o 60oE 120oE 180oW

60oS

30oS

0o

30oN

60oN

180oW 120oW 60oW 0o 60oE 120oE 180oW

60oS

30oS

0o

30oN

60oN

BeiDou GPS GLONASS Galileo

1 Current multi-GNSS status

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Figure 4. BETN (WHU) and a local CORS network equipped with GPS+BeiDou capable dual-system receivers. The small map indicates the local CORS network and the

large one is for BETN.

7

2 Multi-GNSS data processing Initial Satellite Orbit

Multi-GNSS POD(Batch-processing, Every 3h)

Orbit Prediction Using Orbit Integrator

(6h Predicted Orbits)

Multi-GNSS Real-Time PCE(Sequential Processing,Every 5s)

Multi-GNSS PPP(Sequential Processing)

UPD Estimation(Sequential processing from PPP

float amb)

NTRIP Caster

Optional

Optional

Multi-GNSS OBS(MGEX+BETN+IGS)

Antenna & Receiver Info.

Site Coordinatese.g.SINEX

Inter-system BiasInter-frequency Bias

UncalibratedPhase Delays

UD Integer Ambiguity

Real-Time Orbit CorrectionsReal-Time Clock Corrections

Optional

Optional

Optional

R1 R2

R3

RnR4

Multi-GNSS Receiver

PPP Solution 1:Coord,clk,ZTD,iono, ISB&IFB,amb

PPP Solution 2:Coord,clk,ZTD,iono, ISB&IFB,amb

……PPP Solution n:Coord,clk,ZTD,iono, ISB&IFB,amb

Figure 5. The structure of the prototype multi-GNSS real-time PPP

service system at GFZ.

2 Multi-GNSS data processing

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Table 1. Multi-GNSS data processing strategy, observation models and estimated parameters for POD, PCE, and PPP

Item Models Satellites BeiDou+Galileo+GLONASS+GPS; about 74 satellites

Procedure Integrated processing, all the observations from different GNSS in one common parameter adjustment procedure

Estimator LSQ in batch mode for POD; LSQ in sequential mode for PCE & PPP

Observations Undifferenced phase and code observations

Combination mode Ionosphere-free combination for POD/PCE network solution; raw observations on individual frequencies for PPP

Signal selection GPS: L1/L2; GLONASS: L1/L2; BeiDou: B1/B2; Galileo: E1/E5a

Tracking data IGS+MGEX+BETN (about 120 stations) for POD and PCE; Local CORS and some MGEX stations are selected for PPP

Sampling rate 30s Elevation cutoff 7°

Observation weight Elevation dependent weight

Phase-windup effect Corrected

Earth rotation parameter Estimated with tight constraint (He et al., 2013b)

Tropospheric delay Initial model + random-walk process

Ionospheric delay Eliminated by IF combination in POD and PCE; estimated as parameters in PPP

Receiver clock Estimated, white noise

ISB and IFB Estimated as constant with zero mean conditions in post; introduced as known values in RT

Station displacement Solid Earth tide, pole tide, ocean tide loading, IERS Convention 2003 (McCarthy and Petit, 2003)

Satellite antenna phase center Corrected using MGEX and IGS values

Receiver antenna phase center Corrected using GPS values

Terrestrial frame ITRF2008 (Altamimi et al., 2011)

Satellite orbit Estimated in POD; Fixed in PCE&PPP using the products from POD

Satellite clock Estimated in POD and PCE, white noise; Fixed in PPP using the products from PCE

Station coordinate Fixed (or tightly constrained) in POD and PCE; Estimated in epoch-wise kinematic for PPP

Phase ambiguities Constant for each arc; DD AR for network solution, undifferenced AR if UPD

Li et al (2015), Accuracy and reliability of multi-GNSS real-time precise positioning: GPS, GLONASS, BeiDou, and Galileo. J. Geod., 2015, 89(6): 607-635.

2 Multi-GNSS data processing

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Table 2. Dynamical models involved for multi-GNSS POD.

Item Models Orbit arc 3-day solution Geopotential EGM96 model (12×12)

Tide Solid Earth tide, pole tide, ocean tide IERS Conventions 2003

M-body gravity Sun, Moon and all planets (JPL DE405)

Solar Radiation Pressure Bern five parameters with no initial value

Relativistic Effect Applied Velocity breaks Every other 12 hours

Attitude model

Nominal attitude for GPS/GLONASS/Galileo; Nominal attitude with yaw maneuver for MEO and IGSO satellites of BeiDou; Yaw-fixed attitude mode used for GEO satellites of BeiDou

3 Multi-GNSS orbit and clock

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Figure 6. Averaged RMS values of 48 h orbit and clock overlap differences in radial, cross, and along directions .

3 Real-time orbit and clock

Figure 7. Averaged RMS values of orbit and clock differences between the real-time and post-processed solutions

3 Real-time orbit and clock

Table 3. The averaged RMS values of predicted orbit differences in along- (A), cross-track (C) and radial (R) components.

Satellite R(cm) C(cm) A(cm) 3D(cm)

BeiDou IGSO 8.3 7.5 13.0 17.1

BeiDou MEO 6.3 6.2 12.0 14.9

BeiDou GEO 10.1 6.8 92.7 93.4

Galileo 2.9 6.8 9.8 12.2

GLONASS 2.2 3.1 5.9 7.0

GPS 1.8 3.0 3.2 4.7

4 Multi-GNSS real-time PPP

Figure 8．Comparisons of GPS, BeiDou and GPS/BeiDou kinematic PPP solutions at station CENT.

-0.5-0.3-0.10.10.30.5

(a) G

PS[m

]

Up East North

-0.5-0.3-0.10.10.30.5

(b) B

eiDo

u[m

]

-0.5-0.3-0.10.10.30.5

(c) G

/C[m

]

Hours

0 2 4 6 8 10 12 14 16 18 20 22 2405

1015202530

(d) N

um o

f Sat

Hours

G C G/C

4 Multi-GNSS real-time PPP

Figure 9．Kinematic PPP solutions of single-system, dual-system and four-system modes at station GMSD.

-0.5-0.3-0.10.10.30.5

(a) G

PS

[m]

Up East North

-0.5-0.3-0.10.10.30.5

(e) G

/R/E

/C[m

]

Up East North

-0.5-0.3-0.10.10.30.5

(b) G

LON

AS

S[m

]

-0.5-0.3-0.10.10.30.5

(f) G

/R[m

]

-0.5-0.3-0.10.10.30.5

(c) B

eiD

ou[m

]

-0.5-0.3-0.10.10.30.5

(g) G

/C[m

]

0 2 4 6 8 10 12 14 16 18 20 22 24-0.5-0.3-0.10.10.30.5

(d) G

alile

o[m

]

Hours0 2 4 6 8 10 12 14 16 18 20 22 24

-0.5-0.3-0.10.10.30.5

(h) G

/E[m

]

Hours

4 Multi-GNSS real-time PPP

Figure 10．Kinematic PPP solutions of single-system, dual-system and four-system modes at station CUT0.

4 Multi-GNSS real-time PPP

Figure 11. Comparisons of PPP results from different

single-system and combined solutions in the east, north

and up components, respectively at station CUT0.

-0.5-0.3-0.10.10.30.5

(a) E

[m]

C E R G G/C G/E G/R G/R/E/C

-0.5-0.3-0.10.10.30.5

(b) N

[m]

-0.5-0.3-0.10.10.30.5

(c) U

[m]

05

10152025303540

(d) N

um o

f Sat

G G/R/E/C

0 2 4 6 8 10 12 14 16 18 20 22 240

12345

(e) P

DO

P

Hours

G G/R/E/C

4 Multi-GNSS real-time PPP

Figure 12. Sky plots (azimuth vs elevation) of the four GNSS (BeiDou in pink, Galileo in red, GPS in blue and GLONASS in

green) for CUT0.

4 Multi-GNSS real-time PPP

Figure 13．The averaged RMS values of all the stations for kinematic PPP solutions in north, east and up components.

4 Multi-GNSS real-time PPP

Figure 14．Comparisons of PPP results in single- and multi-system modes under different elevation cutoffs (from 10° to 40°) at

station CUT0.

-0.4-0.2

00.20.4

East

[m]

G G/R/E/C

-0.4-0.2

00.20.4

North

[m]

-0.4-0.2

00.20.4

Up[m

]

0 4 8 12 16 20 2405

1015202530

Num

of S

at

0 4 8 12 16 20 24 0 4 8 12 16 20 24 0 4 8 12 16 20 24

0 4 8 12 16 20 240369

1215

PDO

P

CutOff 10°0 4 8 12 16 20 24

CutOff 20°0 4 8 12 16 20 24

CutOff 30°0 4 8 12 16 20 24

CutOff 40°

4 Multi-GNSS real-time PPP

Table 4. The empirical availability rates (in %) for the single- and

multi-GNSS under different elevation cutoffs (from 10° to 40°) .

Station GPS（%） G/R/E/C（%）

10° 20° 30° 40° 10° 20° 30° 40°  

CENT 100.0 99.6 89.2 41.5 100.0 100.0 100.0 100.0  

CHDU 99.7 98.3 84.7 46.0 100.0 100.0 100.0 100.0  

SIGP 94.8 93.7 72.1 39.2 100.0 100.0 99.9 99.5  

CUT0 96.8 95.0 89.3 57.6 100.0 100.0 100.0 100.0  

GMSD 98.1 97.6 79.5 30.2 100.0 100.0 100.0 99.8  

NNOR 99.2 93.8 78.6 37.8 100.0 100.0 100.0 100.0  

ONS1 96.1 93.3 62.5 30.6 100.0 100.0 99.9 99.6  

preciseavailability

total

Nf

N =

Discussions

u The performance of the multi-GNSS processing will be further improved in the next years along with the launch of more satellites and the setup of more multi-GNSS stations.

u The Multi-GNSS will bring many benefits for Geosciences applications: Li et al. (2015), Retrieving of atmospheric parameters from multi-GNSS in real-time: Validation with

water vapor radiometer and numerical weather model. JGR.

Li et al. (2015), Retrieving high-resolution tropospheric gradients from multi-constellation GNSS observations. GRL, DOI:10.1002/2015GL063856

Lu et al. (2015), Real-time retrieval of precipitable water vapor from GPS and BeiDou observations. Journal of Geodesy, DOI:10.1007/s00190-015-0818-0

Li et al. (2015), Multi-GNSS meteorology: Real-time retrieving of atmospheric water vapor from BeiDou, Galileo, GLONASS and GPS observations. IEEE Transactions on Geoscience and Remote Sensing, DOI:10.1109/TGRS.2015.2438395

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