SLR analysis

For the 11-day period of the CHAMP orbit campaign the available orbit solutions have been used as fixed input orbit in a process to compute the SLR tracking data residuals. The software used at ESOC for this analysis is based on the system that is also used operationally for satellites like ERS and is completely independent of the POD systems that were used for any of the orbit solutions, including the ESA solution. These SLR residuals should therefore form a useful independent check of the orbit quality.

The three-dimensional orbit error at the time of the SLR observation will hardly ever be oriented along the line of sight between tracking station and satellite. This means that the SLR residuals form a lower limit to the 3D orbit error, assuming that the SLR residual is predominantly due to orbit error.

The following data editing has been applied:

  1. The data from stations 1873 and 7237 was excluded because of large resiudals in all solutions
  2. Two bad passes from other stations were identified and rejected
  3. The residuals from the three most precise orbit solutions (according to a first run) were used to compute a common sigma value of 7 cm (1-way range). A 1.5 sigma rejection window was subsequently applied to reject individual bad points. Only those observations that were excluded in all three solutions were rejected as bad points.
  4. The  remaining data set of 1686 SLR observations was used for all input orbit solutions. Any further rejections occurred due to gaps in the orbit files.
The temporal and spatial distribution of the SLR data is of course highly irregular, typically concentrated in a few overlapping passes over Europe, complemented with incidental passes over USA or Australia.

Table 1 below presents the overall SLR residual statistics for each included orbit solution.

The SLR residuals have been plotted in a single figure per contributed orbit solution. Please click on the icons below to obtain the larger Figures. Due to the 11-day time scale, the laser tracking passes are compressed into near-vertical lines in these Figures, which conveniently translates into a mean value with an error bar for each pass. The small images here already show that the SLR residuals increase from the currently most precise solution onwards.

 
 
centre
nr obs
RMS
MEAN
SIGMA
DEOS
1686
3.60
1.31
3.36
CSR
1686
4.43
0.04
4.43
TUM
1686
4.61
1.78
4.26
GFZ
1686
4.81
0.75
4.76
JPL
1686
5.31
2.51
4.68
GRGS
1686
6.80
3.35
5.92
NCL
1686
7.44
-0.59
7.42
ASI
1686
7.88
0.97
7.82
AIUB
1686
13.56
2.55
13.33
CNES
1686
13.58
0.31
13.58
ESA
1686
16.83
2.64
16.63
UCAR
1686
17.35
4.68
16.71
UNB
1403
27.37
0.81
27.37
Table 1: SLR statistics per contributed solution (1-way range)


DEOS CSR TUM GFZ
JPL GRGS NCL ASI
AIUB CNES ESA UCAR
UNB
Figure 2: SLR residuals per contributed orbit solution (2-way range)