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Fugro’sFugro’s StarfixStarfix HP and XPHP and XP
Decimeter accuracy, worldwideDecimeter accuracy, worldwide
KeesKees de de JongJongFugro Intersite B.V.Fugro Intersite B.V.
The Hydrographic Society in Scotland, October 20, 2005The Hydrographic Society in Scotland, October 20, 2005
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Contents
• Introduction
• Starfix HP
• Starfix XP
• Convergence and reconvergence
• Future
• Conclusion
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Mode Description Horizontal Exampleprecision (1σσσσ)
Absolute, code no external data 5 – 10 m
Absolute, carrier improved orbits 0.1 – 0.2 m Starfix XPand clocks
Differential, code single ref., < 25 km 0.5 – 1 m
single ref., < 250 km 2 – 3 m IALA
network, regional 1 – 2 m WAASEGNOS
Differential, carrier single ref., < 25 km 0.02 m
network, < 70 km 0.02 m
network, < 1000 km 0.1 m Starfix HP
GPS positioning modes
Ref: Jonkman & de Jong, The Hydrographic Journal, No. 117, July 2005
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Mode Limiting error source Additional limitation
Absolute, code ionosphere (single frequency),orbits/clocks
Absolute, carrier troposphere, long initializationorbits/clocks
Differential, code atmosphere (single ref.), baseline dependentcode multipath (single ref.)
Differential, carrier troposphere, integer ambiguity resolution,phase multipath long initialization (long
baseline)
Limiting factors
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Absolute positioning
Broadcast parameters- sparse tracking network- accuracy 1 – 3 m
Precise parameters- dense tracking network- accuracy 0.05 – 0.2 m
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
Broadcast Precise, predicted Precise, post-processed
Err
or (m
)
Real-time applications
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Relative positioning
Baseline error- linear function of
orbit error- linear function of
baseline length
ExampleOrbit error : 2 mBaseline length: 500 km
Baseline error: 0.05 m
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Troposphere
Troposphere- dry part well predictable
(2.3 m at zenith)- wet part poorly predictable
(0.2 – 0.3 m at zenith), low spatial and temporalcorrelation
-0.10
-0.08
-0.06
-0.04
-0.02
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0.10
5:00
:00.
05:
30:0
0.0
6:00
:00.
06:
30:0
0.0
7:00
:00.
07:
30:0
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:00.
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30:0
0.0
9:00
:00.
09:
30:0
0.0
10:0
0:00
.010
:30:
00.0
11:0
0:00
.011
:30:
00.0
12:0
0:00
.012
:30:
00.0
13:0
0:00
.013
:30:
00.0
14:0
0:00
.014
:30:
00.0
15:0
0:00
.015
:30:
00.0
16:0
0:00
.016
:30:
00.0
17:0
0:00
.0
Cor
rect
ion
to m
odel
(m)
Zenith 20° elevation
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Carrier noise and multipath
Measurement noise- dominated by multipath- dependent on satellite
elevation- actual noise < 0.0005 m (1σ)
-0.005
-0.004
-0.003
-0.002
-0.001
0.000
0.001
0.002
0.003
0.004
0.005
14:0
0:00
.0
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5:00
.0
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.0
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.0
15:0
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.0
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5:00
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.0
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.0
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.0
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.0
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.0
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.0
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.0
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5:00
.0
18:0
0:00
.0
Err
or (m
)
0
15
30
45
60
75
Ele
vatio
n (d
eg)
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0
1
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4
5
0:00
:00.
0
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:00.
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:00.
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:00.
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:00.
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:00.
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:00.
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:00.
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:00.
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:00.
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:00.
0
0:55
:00.
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1:00
:00.
0
Sta
ndar
d de
viat
ion
(m)
Convergence
Kinematic positioning
0.0
0.1
0.2
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0.4
0.5
0:15
:00.
0
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:00.
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:00.
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:00.
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:00.
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:00.
0
Sta
ndar
d de
viat
ion
(m)
5
6
7
8
9
10
Num
ber
of s
atel
lites
– north– east– up– number of satellites
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• Starfix HP/XP
• Global coverage
• Real-time accuracy 10 – 20 cm (after convergence period of 45 – 60 minutes)
High precision GPS services
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Starfix HP - Principle
• Relative positioning– Network of reference stations– Reference data transmitted to mobile user
via satellite link
• Dual frequency observations– Ionosphere-free
code and carrier
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Fugro reference network
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Estimated parameters
• 3D position
• Carrier ambiguities– No integer ambiguity resolution
• Troposphere
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HP - Lafayette, USA
Easting, standard deviation: 0.03 m
Northing, standard deviation: 0.03 m
Height, standard deviation: 0.07 m
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Why relative positioning?
• Reduction/elimination of error sources– Broadcast satellite orbits and clocks
– But precise orbits and clocks are available
– Troposphere– Can be estimated together with position
• Reduce convergence time– Integer ambiguity resolution
– Not applied in HP due to lengthof baselines
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Starfix XP
• Absolute positioning– Precise Point Positioning (PPP)
• External corrections– Satellite orbit and clock corrections from
NASA’s Jet Propulsion Laboratory (JPL)
• Dual frequency observations– Ionosphere-free code and carrier
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JPL reference network
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PPP – additional error sources
• Earth tides– Up to 30 cm
• Ocean loading– Up to 5 cm
• Polar motion– Up to 2.5 cm
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Earth tides, Aberdeen, Oct. 2005
-0.20
-0.15
-0.10
-0.05
0.00
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1 O
ct 2
005
2 O
ct 2
005
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ct 2
005
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ct 2
005
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ct 2
005
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ct 2
005
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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19 O
ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
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ct 2
005
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ct 2
005
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ct 2
005
30 O
ct 2
005
31 O
ct 2
005
Dis
plac
emen
t (m
)
North East Up
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-0.06-0.04
-0.020
0.020.04
0.06
-0.06
-0.04
-0.02
0
0.02-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
East (m)North (m)
Up
(m)
Earth tides, tonight
18:00: Up -0.14 m
21:00: Up -0.10 m
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XP - Lafayette, USA
Easting, standard deviation: 0.05 m
Northing, standard deviation: 0.04 m
Height, standard deviation: 0.09 m
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Comparison HP and XP
• Transmitted data– HP: reference station data
XP: orbit and clock data
• Convergence time– Comparable
• Accuracy– HP slightly more accurate
than XP for baselines up to about 1000 km
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Independent services
NASA/JPL reference stations
NASA/JPL reference stations
Orbits/clocks (Starfix XP) NCC/Hub
Orbits/clocks (Starfix XP) NCC/Hub
Multiple uplinks to low power channels
Multiple uplinks to low power channels
Fugro Starfixreference stations
Fugro Starfixreference stations
DGPS network (Starfix HP) NCC/Hub
DGPS network (Starfix HP) NCC/Hub
Multiple uplinks to high power channels
Multiple uplinks to high power channels
NCC: Network Control CenterJPL : Jet Propulsion Laboratory
Users
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Convergence and reconvergence
• Initial convergence– 45 – 60 minutes
• Reconvergence (after signal interruption)– 45 – 60 minutes?
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Reconvergence test
• Static receiver, kinematic positioning
• September 2003, Lafayette, USA
• 69 gaps of 20 s (average)
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Fast reconvergence
Success rate: 98.5%, average position error: 0.05 m
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67
Interruption
Pos
ition
err
or (m
)
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Future
• Support current and future systems/signals– GPS (USA, 28 satellites)– Glonass (Russia, 18 satellites in 2007)– Galileo (Europe, 30 satellites in 2010)
• Faster convergence
• More accurate positions– in particular height
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Conclusion
Starfix HP and XP offerglobal, real-time positioning with
decimeter accuracyon land, at sea and in the air