Precise Science Orbits for the GOCE Satellite – …...GOCE Workshop at ESA LP Symposium, Bergen,...
Transcript of Precise Science Orbits for the GOCE Satellite – …...GOCE Workshop at ESA LP Symposium, Bergen,...
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
Precise Science Orbits for the GOCE Satellite –
Aiming at the cm-level
H. Bock1, A. Jäggi1, U. Meyer1, G. Beutler1, M. Heinze2
1Astronomical Institute, University of Bern, Switzerland2Institute of Astronomical and Physical Geodesy (IAPG),
TU München, Germany
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
GOCE-HPF: Orbit groupsGOCE-HPF: Orbit groups
Responsibilities:
• DEOS => RSO(Rapid Science Orbit)
• AIUB => PSO (Precise Science Orbit)
• IAPG => Validation
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
GOCE Precise Science OrbitsGOCE Precise Science Orbits
GOCE instruments data used:• 1 Hz GPS data of highest
quality• Star tracker measurements
Precise Science Orbit product
PSO is a Level 2 product consistingof two different orbit solutions:
• Kinematic• Reduced-dynamic
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
• A kinematic orbit is an ephemeris at discrete measurement epochs
• Kinematic positions are fully independent of the force models used for LEO orbit determination
• Kinematic orbits are well suited for gravity field recovery of the long- wavelength part
Kinematic orbit representationKinematic orbit representation
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
• Satellite trajectory is a particular solution of the equation of motion defined by the force models used. The strength of the force models is reduced, to some extent, by additional empirical parameters.
• Reduced-dynamic orbits heavily depend on the force models used, e.g., on the gravity field model (solving the equation of motion)
• Reduced-dynamic orbits are well suited to compute LEO orbits of highest quality
Reduced-dynamic orbit representationReduced-dynamic orbit representation
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
Special GOCE characteristic: Drag-free flightSpecial GOCE characteristic: Drag-free flight
Transition to first drag-free flight on 7 May 2009
Empirical accelerations from reduced-dynamic orbit determination
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
Special GOCE characteristic: Drag-free flightSpecial GOCE characteristic: Drag-free flight
• Non-gravitational forces in along-track direction are compensated by the IPA (Ion Propulsion Assembly)
• Empirical accelerations from reduced-dynamic orbit determination illustrate the effect
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
Special GOCE characteristics: Observation epochsSpecial GOCE characteristics: Observation epochs
• Internal clock is not steered to integer seconds
• This is no problem for the GPS data processing but
=> resulting kinematic positions are not truly equidistant
Fractional offsets of observation epochs at midnight (from RINEX)
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
GOCE PSO procedureGOCE PSO procedure
CODE products
GOCE GPS data
GOCE attitude data
Auxiliary data
Preparation of GPS orbits, clocks
and ERPs (30 hours)
Pseudorange:first a priori orbit
Receiver clock synchronization
Phase:Iterative data
screening
Reduced-dynamic orbit
solution (iterative)
Kinematic orbit solution
Data pre-processing
Piece-wise constant accelerations (6 min)
a priori10 sec
1 sec
• Tailored version of Bernese GPS Software used
• Un-differenced processing• 30 h batches
=> overlaps• CODE final products• Consequent use of antenna
phase center variation (PCV) map
• Final kinematic positions are only accepted, if five or more simultaneous observations were available=> on average only 0.5% positions missing
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
GOCE PSO procedure: ImprovementsGOCE PSO procedure: Improvements
• GOCE SLR residuals as a function of the azimuth of the SLR stations
• Significant improvement of SLR residuals due to use of the PCV map
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
GOCE PSO procedure: PCV mapGOCE PSO procedure: PCV map
• Azimuth-elevation diagram of antenna PCVs [mm] – ionosphere-free linear combination
• Azimuth of 0o => flight direction
• 154 days of data used for the generation of the PCV map
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
PSO: Comparison reduced-dynamic kinematic orbitsPSO: Comparison reduced-dynamic kinematic orbits
• Orbit differences between reduced-dynamic and kinematic PSO solutions
• Orbit differences > 1 m removed (only 60 positions for the whole period)
• Consistency of reduced-dynamic and kinematic PSO is at 2 cm level=> mean 3D-RMS 1.82 cm
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
PSO: Comparison reduced-dynamic kinematic orbitsPSO: Comparison reduced-dynamic kinematic orbits
Typical example fororbit differences betweenreduced-dynamic andkinematic PSO
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
PSO: Overlaps reduced-dynamic orbitsPSO: Overlaps reduced-dynamic orbits
• 5 h overlaps (21:30 – 02:30)• Mean 3D-RMS: 0.55 cm
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
Reduced-dynamic orbit Mean: 0.88 cm, RMS: 2.05 cm
Orbit validation with SLROrbit validation with SLR
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
Orbit validation with SLROrbit validation with SLR
Kinematic orbit Mean: 0.88 cm, RMS: 2.23 cm
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GOCE Workshop at ESA LP Symposium, Bergen, 29./30.June, 2010
SummarySummary
• GOCE PSO product consists of a kinematic and a reduced- dynamic orbit solution
• Both orbits are computed in one and the same processing chain
• Use of PCV map led to a significant improvement of the PSO product
• Validation with independent SLR measurements shows that precision requirements of 2 cm are amply met by the PSO