phase bias product and open-source software for undifferenced … · 2018. 12. 6. · phase bias...
TRANSCRIPT
GNSS Research Center, Wuhan University, China
IGS Workshop 201831 Oct 2018
Wuhan China
GNSS Research Center Wuhan UniversityGNSS Research Center Wuhan University
Phase bias product and open-source software for undifferenced ambiguity resolution at
Wuhan University
Jianghui GENG (耿江辉), Xingyu CHEN
Slid
e 2
Wuh
an 2
018
GNSS biases and IGS Bias-SINEX file
l Code biases across GNSS systems, frequencies and observables.§ Align pseudorange to obey IGS “conventions”;§ Resolve Melbourne-Wübbena ambiguities.
l IGS has been standardizing bias products since 2012 (Schaer 2018)§ to address flourishing observables due to multi-GNSS;§ to formulate IGS conventions on bias products.
l However, phase biases are seldom discussed.
Slid
e 3
Wuh
an 2
018
Phase biases
l Phase biases are relevant§ not only in ambiguity resolution,§ but also in highly accurate positions.
l Uncalibrated phase delays/fractional-cycle biases (UPD/FCB)§ Satellite specific§ for undifferenced ambiguity resolution.
l Code-phase biases (CPB) for GLONASS (Sleewaegen et al. 2012; Geng et al. 2017)§ Station specific§ for double-difference/undifferenced ambiguity resolution§ See the poster by Pan et al. (PS06-04).
l Inter-system phase biases (ISPB) (Odijk et al. 2013; Geng et al. 2017)§ Station specific§ for double-difference/undifferenced ambiguity resolution.
l We focus on UPD/FCB, or simply phase bias for brevity, in this presentation.
Slid
e 4
Wuh
an 2
018
Problems with phase biases (UPDs/FCBs)
l Phase biases are not always stable over time.§ Wide-lane phase biases are quite stable over days or even months;§ But narrow-lane phase biases have significant subdaily signatures.
l In 2006, daily wide-lane and 15-min narrow-lane phase biases (Ge et al. 2006).
Wide-lane phase bias Narrow-lane phase bias
Can we make phase biases always stable?
Slid
e 5
Wuh
an 2
018
Solutions: “Better” clocks?
l Why unstable phase biases?§ Because legacy IGS clocks are aligned to pseudorange.
l Why not formulate clock products aligned to carrier-phase?§ We have, that’s “integer clock” (Laurichesse et al. 2010; Collins et al. 2010).
However, integer clocks are not compatible with legacy IGS code biases!
Slid
e 6
Wuh
an 2
018
New phase bias & phase clock products
l We derive§ stable phase biases (daily, instead of 15-min, calculations),§ phase clocks (like integer clocks),§ and compatibility with IGS code biases.
Slid
e 7
Wuh
an 2
018How do the new phase bias & phase clock work?
l 180-200 globally distributed stationsl Daily positions in 2006 & 2016 compared to IGS solutions
10-20% improvement after applying daily phase biases and code-compatible phase clocks
Slid
e 8
Wuh
an 2
018How do the new phase bias & phase clock work?
l 180-200 globally distributed stationsl Daily positions in 2006 & 2016 compared to IGS solutions
0.1 0.2 0.30.1
0.2
0.3East(2016)
15-min phase bias / cm
0.1 0.2 0.30.1
0.2
0.3North(2016)
0.45 0.60 0.75
0.45
0.60
0.75Up(2016)
0.2 0.3 0.4 0.5 0.6
0.2
0.3
0.4
0.5
0.6
East(2006)
Relative PCV daysAbsolute PCV days
15-min phase bias / cm
0.2 0.3 0.4
0.2
0.3
0.4
North(2006)
Relative PCV daysAbsolute PCV days
Daily phase bias / cm0.45 0.60 0.75 0.90 1.05 1.20
0.45
0.60
0.75
0.90
1.05
1.20
Up(2006)
Relative PCV daysAbsolute PCV days
10-20% improvement almost uniformly at all stations.
Slid
e 9
Wuh
an 2
018However, remaining problems with phase biases
l Discontinuity of our phase biases across days (Day-boundary jumps)
0 50 100 150 200 250 300 350
-0.9
-0.6
-0.3
0.0
0.3
0.6
0.9
1.2
G10
NL_FCB / cycle
day of year(2016)
Day-to-day phase bias variations are due to pseudorange again.
G03 G06 G09 G12 G15 G18 G21 G24 G27 G300.30
0.35
0.40
0.45
0.50
0.55
STD / cycle
Satellite PRN
2016
Slid
e 10
Wuh
an 2
018
Day-boundary jumps: leveling phase biases
l Calculate the jumps using integer clocks and legacy clocks
Slid
e 11
Wuh
an 2
018
How does the leveling work?
l Phase bias products in 2006 & 2016 without day-boundary jumps
0 50 100 150 200 250 300 350-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
IIR-B:G02 IIA:G04 IIR-A:G11 II:G15 IIR-M:G17
NL_FCB / cycle
day of year(2006)
0 50 100 150 200 250 300 350-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
IIR:G02 IIR:G11 IIR-M:G15 IIR-M:G17 IIF:G30
NL_FCB / cycle
day of year(2016)
Slid
e 12
Wuh
an 2
018
How does the leveling work?
l The yearly STDs of daily phase biases are reduced below 0.1 cycles
G03 G06 G09 G12 G15 G18 G21 G24 G27 G30
0.01
0.02
0.03
0.04
0.05
0.06
0.07
STD / cycle
Satallite PRN
2016 2006
The leveling does not impact the positioning performance
Slid
e 13
Wuh
an 2
018
Open-source software for undifferenced ambiguity resolution
l Package name: “PRIDE PPP-AR” in Fortran 95
Slid
e 14
Wuh
an 2
018
Summary and outlook
l 10-year (2006-2016) GPS phase bias and phase clock products at Wuhan§ In the form of L1 & L2 biases§ Under final validation using PRIDE PPP-AR software§ Preliminary release of products and software before 2019§ Also include GLONASS DCPBs, BeiDou, Galileo phase bias on the way§ News on http://pride.whu.edu.cn
l Phase bias products§ Daily values§ No day-boundary jumps
l Phase clocks§ Compatible with IGS code biases§ Identical performance to “integer clocks”
l Positioning differences from IGS solutions in terms of RMS§ 1.6mm, 1.8mm and 5.6mm for the east, north and up components
l Remaining questions: how to combine phase products from different ACs?§ New “PPP-AR WG” for phase biases/phase clocks
