M. Weigelt, A. Jäggi, L. Prange, W. Keller, N. Sneeuw
TOWARDS THE TIME-VARIABLE
GRAVITY FIELD FROM CHAMP
2
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?
3
Previous studies & limitations
Degree RMS w.r.t. ITG-GRACE2010s
• based on the energy
balance approach
• two years of GPS-data
with 30 s sampling
• no dealiasing products
• no covariance
information
Processing refinements
5
Refinements
Acceleration approach:
r V = xÄ¡ f 3rdBody ¡ f T ides ¡ f Rel ¡ f Grav
• 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
6
Outliers vs. poor observations
• Typically threshold based outlier detection based on residuals:
?
?
?
?
• Localizing outlier detection necessary
• Consider (synthetical) covariance information
7
Results using outlier detection
8
CHAMP vs. GRACE monthly solutions
Monthly solutions
10
Pushing the limits – combination strategies
Standard case:
single month solution
+ Grace A and Grace B
Combining n-month
with unit weight
+ Grace A and Grace B
Combining n-month
with Bartlett weight
+ Grace A and Grace B
11
Comparison of combination strategies
12
CHAMP-only solution with Bartlett option
13
Adding GRACE …
14
Results for CHAMP + GRACE
15
Time series of coefficients
C44
Correlation
C40
Single coefficients
comparison capability
GRACE – GFZ Rl. 4
CHAMP + GRACE
Spatial pattern
90
45
45
0
0
-45
-90
-180
-45
-120
-60
0
60
Longitude [deg]
120
180
-150
-90
CHAMP
-30
30
Longitude [deg]
90
-90
150
GRACE - GFZ Rl.4
[cm]
90
90
-20
February 2004:
-15
-10
-5
0
5
10
15
20
45
45
0
0
-45
-90
-180
-45
-120
-60
0
60
Longitude [deg]
120
180
-150
-90
-30
30
Longitude [deg]
90
-90
150
[cm]
-20
-15
-10
-5
0
5
10
15
20
Latitude [deg]
Latitude [deg]
October 2003:
GRACE - GFZ Rl.4
90
Latitude [deg]
CHAMP
Latitude [deg]
16
17
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 needed
Increase the number of observations
THANK YOU
M. Weigelt, A. Jäggi, L. Prange, W. Keller, N. Sneeuw
TOWARDS THE TIME-VARIABLE
GRAVITY FIELD FROM CHAMP
Appendix
20
Time variable signal?
GRACE – GFZ Rl. 4
CHAMP + GRACE