TOWARDS THE TIME-VARIABLE GRAVITY FIELD FROM CHAMP M. Weigelt, A. Jäggi, L. Prange, W. Keller, N. Sneeuw TexPoint fonts used in EMF. Read the TexPoint.
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TOWARDS THE TIME-VARIABLE GRAVITY FIELD FROM CHAMP
M. Weigelt, A. Jäggi, L. Prange, W. Keller, N. Sneeuw
Questions
• Did we get everything out of the CHAMP data?
• Is the time variable gravity field really out of
reach?
• What do we learn for future satellite missions?
2
Previous studies & limitations
• based on the energy balance approach
• two years of GPS-data with 30 s sampling
• no dealiasing products
• no covariance information
3
Degree RMS w.r.t. ITG-GRACE2010s
Processing refinements
Refinements5
r V = Äx ¡ f 3rdBody ¡ f T ides ¡ f Rel ¡ f Grav
Acceleration approach:
• three times the number of observations
• three dimensional observations
Improved GPS positioning:
• 10 s sampling• estimated absolute antenna phase
center model• new IGS standards• …
Prange 2010
Outliers vs. poor observations6
• Typically threshold based outlier detection based on residuals:
?? ?
?
• Localizing outlier detection necessary
• Consider (synthetical) covariance information
Results using outlier detection7
CHAMP vs. GRACE monthly solutions8
Monthly solutions
Pushing the limits – combination strategies10
Standard case:single month solution
Combining n-month with unit weight
Combining n-month with Bartlett weight
+ Grace A and Grace B
+ Grace A and Grace B
+ Grace A and Grace B
Comparison of combination strategies11
CHAMP-only solution with Bartlett option12
Adding GRACE …13
Results for CHAMP + GRACE14
Time series of coefficients15
C40
C44
Correlation
Single coefficients
comparison capabilityGRACE – GFZ Rl. 4CHAMP + GRACE
Spatial pattern16
Lat
itu
de
[deg
]Longitude [deg]
CHAMP
-180 -120 -60 0 60 120 180-90
-45
0
45
90
Lat
itu
de
[deg
]
Longitude [deg]
GRACE - GFZ Rl.4
-150 -90 -30 30 90 150-90
-45
0
45
90
[cm]
-20 -15 -10 -5 0 5 10 15 20
Lat
itu
de
[deg
]
Longitude [deg]
CHAMP
-180 -120 -60 0 60 120 180-90
-45
0
45
90
Lat
itu
de
[deg
]
Longitude [deg]
GRACE - GFZ Rl.4
-150 -90 -30 30 90 150-90
-45
0
45
90
[cm]
-20 -15 -10 -5 0 5 10 15 20
Lat
itu
de
[deg
]
Longitude [deg]
CHAMP
-180 -120 -60 0 60 120 180-90
-45
0
45
90
Lat
itu
de
[deg
]
Longitude [deg]
GRACE - GFZ Rl.4
-150 -90 -30 30 90 150-90
-45
0
45
90
[cm]
-20 -15 -10 -5 0 5 10 15 20
Lat
itu
de
[deg
]
Longitude [deg]
CHAMP
-180 -120 -60 0 60 120 180-90
-45
0
45
90
Lat
itu
de
[deg
]
Longitude [deg]
GRACE - GFZ Rl.4
-150 -90 -30 30 90 150-90
-45
0
45
90
[cm]
-20 -15 -10 -5 0 5 10 15 20
Lat
itu
de
[deg
]
Longitude [deg]
CHAMP
-180 -120 -60 0 60 120 180-90
-45
0
45
90
Lat
itu
de
[deg
]
Longitude [deg]
GRACE - GFZ Rl.4
-150 -90 -30 30 90 150-90
-45
0
45
90
[cm]
-20 -15 -10 -5 0 5 10 15 20
Lat
itu
de
[deg
]
Longitude [deg]
CHAMP
-180 -120 -60 0 60 120 180-90
-45
0
45
90
Lat
itu
de
[deg
]
Longitude [deg]
GRACE - GFZ Rl.4
-150 -90 -30 30 90 150-90
-45
0
45
90
[cm]
-20 -15 -10 -5 0 5 10 15 20
October 2003:
February 2004:
Conclusion
• Did we get everything out of the data of CHAMP?
CHAMP still offers a wealth of information
• Is the time variable gravity field really out of
reach?
No, but processing needs further improvements
• What do we learn for future satellite missions?
“Real” covariance information neededIncrease the number of observations
17
TOWARDS THE TIME-VARIABLE GRAVITY FIELD FROM CHAMP
M. Weigelt, A. Jäggi, L. Prange, W. Keller, N. Sneeuw
THANK YOU
Appendix
Time variable signal?20
GRACE – GFZ Rl. 4CHAMP + GRACE
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