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

Contents

• Introduction

• Starfix HP

• Starfix XP

• Convergence and reconvergence

• Future

• Conclusion

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

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

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

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1.75

2.00

2.25

2.50

Broadcast Precise, predicted Precise, post-processed

Err

or (m

)

Real-time applications

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

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

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Cor

rect

ion

to m

odel

(m)

Zenith 20° elevation

Carrier noise and multipath

Measurement noise- dominated by multipath- dependent on satellite

elevation- actual noise < 0.0005 m (1σ)

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Err

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vatio

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eg)

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(m)

Convergence

Kinematic positioning

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10

Num

ber

of s

atel

lites

– north– east– up– number of satellites

• Starfix HP/XP

• Global coverage

• Real-time accuracy 10 – 20 cm (after convergence period of 45 – 60 minutes)

High precision GPS services

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

Fugro reference network

Estimated parameters

• 3D position

• Carrier ambiguities– No integer ambiguity resolution

• Troposphere

HP - Lafayette, USA

Easting, standard deviation: 0.03 m

Northing, standard deviation: 0.03 m

Height, standard deviation: 0.07 m

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

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

JPL reference network

PPP – additional error sources

• Earth tides– Up to 30 cm

• Ocean loading– Up to 5 cm

• Polar motion– Up to 2.5 cm

Earth tides, Aberdeen, Oct. 2005

-0.20

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1 O

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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Dis

plac

emen

t (m

)

North East Up

-0.06-0.04

-0.020

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0.15

East (m)North (m)

Up

(m)

Earth tides, tonight

18:00: Up -0.14 m

21:00: Up -0.10 m

XP - Lafayette, USA

Easting, standard deviation: 0.05 m

Northing, standard deviation: 0.04 m

Height, standard deviation: 0.09 m

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

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

Convergence and reconvergence

• Initial convergence– 45 – 60 minutes

• Reconvergence (after signal interruption)– 45 – 60 minutes?

Reconvergence test

• Static receiver, kinematic positioning

• September 2003, Lafayette, USA

• 69 gaps of 20 s (average)

Fast reconvergence

Success rate: 98.5%, average position error: 0.05 m

0.00

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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

)

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

Conclusion

Starfix HP and XP offerglobal, real-time positioning with

decimeter accuracyon land, at sea and in the air