Astronomical Institute University of Bern
Astronomical Institute, University of Bern, Switzerland
G1.3
EGU General Assembly 2014
27 April -2 May 2014
Vienna, Austria
GOCE – Validation of last days’ orbits with kinematic PPP
H. Bock, A. Jäggi, U. Meyer
source: https://doi.org/10.7892/boris.53908 | downloaded: 9.6.2020
Slide 2 Astronomical Institute University of Bern
Background and Motivation
Copyright: Bill Chater
•The first ESA Earth Explorer core mission GOCE ended officially on 21 October 2013, because the satellite ran out of fuel.
•Three weeks later, on 11 November 2013, the satellite re-entered the Earth’s atmosphere near the Falkland Islands in the South Atlantic.
•GPS-based orbit determination was possible until few hours before re-entry.
Slide 3 Astronomical Institute University of Bern
Background and Motivation
GOCE orbit height derived from GPS
21 October 2013
10 November 2013
Last available GPS measurements: 10 November, 17:15:20 UTC
Slide 4 Astronomical Institute University of Bern
Background and Motivation In the frame of the European GOCE Gravity Consortium (EGG-C) AIUB
was responsible for the generation of the GOCE Precise Science Orbit (PSO) product.
The PSO product consists of a reduced-dynamic and a kinematic orbit (comparable to a kinematic PPP of a ground station).
Internal validation: Orbit overlap analysis and differences between reduced-dynamic and kinematic orbits for consistency checks.
External validation: Satellite Laser Ranging (SLR) measurements.
Reduced-dynamic orbits were generated with the same orbit parameterization for the entire mission.
Two main questions for this study:
Can the kinematic orbits/PPP be used for validation, because SLR measurements are no longer available (only three passes)?
Is the orbit parameterization of the reduced-dynamic orbit still reasonable for the last three weeks of GOCE?
Slide 5 Astronomical Institute University of Bern
Differences red.-dyn. kinematic orbits
−0.1
0
0.1
m
−0.1
0
0.1
m
0 6 12 18 24
−0.1
0
0.1
Hours
mradial
along-track
out-of-plane
29 December 2009
Differences between reduced-dynamic and kinematic orbit
show consistency between the two orbit types and
reveal data problems and gaps in the kinematic orbit
Slide 6 Astronomical Institute University of Bern
Differences red.-dyn. kinematic orbits
−0.5
0
0.5m
−0.5
0
0.5
m
0 6 12 18 24−0.5
0
0.5
Hours
mradial
along-track
out-of-plane
28 December 2012 and 29 December 2009
End of 2012 the data quality is worse than end of 2009
Kinematic orbit shows more “outliers” and systematic effects
It should, however, be possible to validate the reduced-dynamic orbit modeling
Slide 7 Astronomical Institute University of Bern
GOCE internal orbit validation
Jul Jan Jul Jan Jul Jan Jul Jan Jul0369
121518
RM
S (
cm)
Date in 2009−2013
radial +9cm along−track +6cm out−of−plane +3cm 3−D
RMS of differences between red.-dyn. and kinematic orbits for official mission
Bock et al. (2014)
285 290 295 300 305 310 3150
20
40
60
80
100
RM
S (
cm)
Day in 2013
radial along−track out−of−plane 3−D
21 October 2013
Larger RMS values for the last three weeks probably reveal that the parameterization of the reduced-dynamic orbit is not ideal at all
Slide 8 Astronomical Institute University of Bern
Differences red.-dyn. kinematic orbits
−0.5
0
0.5m
−0.5
0
0.5
m
0 6 12 18 24−0.5
0
0.5
Hours
mradial
along-track
out-of-plane
Original solution; 31 October 2013
Large once-per-revolution signal in radial and along-track componentshows that the orbit parameterization is not ideal for the reduced-dynamic orbit
Slide 9 Astronomical Institute University of Bern
Reduced-dynamic orbit determination
30 h processing batches (not for the last 10 days), 10 s sampling, undifferenced processing, ionosphere-free linear combination, CODE Final GNSS orbits and clocks (5 s) and Earth Rotation Parameters
Orbit models and parameterization: EIGEN5S 120x120, FES2004 50x50 (fixed by GOCE Standards) Six initial orbital elements Three constant accelerations in radial, along-track, out-of-plane 6-min piece-wise constant accelerations in radial, along-track,
out-of-plane (2*10-8 m/s2) Test solutions with weaker constraints:
2.5 x 2*10-8 m/s2
5 x 10 x 25 x 50 x
−2
0
2
μm/s
2
−15
−10
−5
0
μm/s
20 6 12 18 24
−2
0
2
μm/s
2
Hours of day 294/2013
Slide 10 Astronomical Institute University of Bern
Solutions with weaker constraints
Test solutions with weaker constraints show better consistency with kinematic orbits.
Differences between 5x and 50x weaker constraints are marginal.
Except the very last days, these solutions are acceptable.
295 300 305 310 3150
20
40
60
80
1003D
RM
S (
cm)
Day in 2013
orig 2.5x 5x 10x 25x 50x
3D RMS of differences between red.-dyn. and kinematic orbits
Slide 11 Astronomical Institute University of Bern
Differences red.-dyn. kinematic orbits
−0.5
0
0.5m
−0.5
0
0.5
m
0 6 12 18 24−0.5
0
0.5
Hours
mradial
along-track
out-of-plane Large once-per-revolution signal is
very much reduced
Original solution and 10x weaker constraints; 31 October 2013
Slide 12 Astronomical Institute University of Bern
Differences red.-dyn. kinematic orbits
−1
0
1m
−1
0
1
m
0 6 12 18 24
−1
0
1
Hours
mradial
along-track
out-of-plane
Orbit modeling and data screening for the very last hours need further investigations
The GPS data quality at this stage of the mission (150 – 130 km altitude) is still surprisingly good!!!
10x weaker constraints; 10 November 2013
Slide 13 Astronomical Institute University of Bern
Improved background modeling
No or only small improvements with respect to the old solutions can be noticed with the better gravity field model.
294 296 298 300 302 3040
10
20
30
3D R
MS
(cm
)
Day in 2013
orig 2.5x 5x 10x 25x 50x
In order to improve the background models the gravity field model EIGEN5S 120x120 is replaced by GOCO03S 200x200 for the first 11 days of the decay phase.
Test solutions with original and weaker constraints are repeated.Old solutions
Slide 14 Astronomical Institute University of Bern
Summary Can the kinematic orbits be used for validation? => Yes, except that
the very last hours/days are difficult because of data screening problems leading to larger data gaps.
Is the orbit parameterization of the reduced-dynamic orbit still reasonable for the last three weeks of GOCE? => No, the constraints are too tight; 10x weaker constraints are reasonable.
First updates in the background modeling of the reduced-dynamic orbit determination did not improve the results of the reduced-dynamic orbits.
Further work:
Detailed check of background modeling and sampling of piece-wise constant accelerations.
Improve data screening procedure for the very last days/hours.
Comparison with and possibly use of accelerometer data in the reduced-dynamic orbit determination (as long as they are available).