IGS LEO CHAMP orbit campaign 2001

The campaign will continue for as long as new contributions are submitted. Updates may not always be immediate after submission of a new solution, but an attempt is made to ensure that these webpages always reflect the most recent contribution by each centre. Until now, the following Associate Analysis Centres have contributed to the CHAMP orbit campaign:

ASI        Agenzia Spaziale Italiana, Matera, Italy
AIUB    Astronomical Institute, University of Bern, Switzerland
CNES    Centre National d'Etudes Spatiales, Toulouse, France
CSR       Centre for Space Research, University of Texas, USA
DEOS    Delft institute for Earth Oriented Space Research, The Netherlands
ESOC    European Space Operation Centre, Darmstadt, Germany
GFZ       Geo Forschungs Zentrum, Potsdam, Germany
GRGS    Groupe de Recherche de Geodesie Spatiale, Toulouse, France
JPL         Jet Propulsion Laboratory, Pasadena, USA
NCL       Newcastle University, UK
TUM     Technical University of Munich, Germany
UCAR   University Corporation for Atmospheric Research, USA
UNB       University of New Brunswick, Canada

Campaign analysis

• Pairwise orbit comparisons between all solutions
• Independent computation of SLR tracking residuals to all input orbits

Conclusions

The main conclusions of the CHAMP orbit campaign have been as follows:

• The most promising POD approach for Low Earth Orbiters with continuous (GPS) tracking always seemed to be a kinematic approach. In kinematic orbit solutions, the tracking data is filtered e.g. with a Kalman filter. using characteristic times that are relatively short. As a consequence, the orbit solution tends to follow the short-term variations in the tracking data without being forced to remain consistent with longer-term dynamic orbit models. this approach seemed more adequate for the low orbiters, because the dynamic models (high degree gravity field, atmospheric drag) were not known very well. Surprisingly, the CHAMP Orbit Campaign has shown that the dynamic solutions rapidly gained on the kinematic solutions. The precision limit of the latter is set partially by the inherent noise of the tracking data, and partially by the diluting effect of the tracking geometry. Dynamic solutions are limited by the quality of the orbit models, which have improved continuously since the launch of CHAMP (in particular with the arrival of the CHAMP-based gravity field solutions). As a result, the most precise orbit solutions for CHAMP are dynamic solutions, although in many cases it is more realistic to speak of reduced dynamic solutions due to the heavy parametrisation of the orbit models.
• The centers that provide the best orbit solutions for CHAMP are not really involved in IGS product generation. The centers that are computing the IGS product family tend to be struggling with the LEO GPS data, in particular with the handling of the phase observations. Exceptions are GFZ and JPL, who have state-of-the-art CHAMP orbits while also being IGS Analysis Centers.
• The interest in orbit campaigns like these extends far beyond the IGS working groups. Various participating centers are mainly interested in CHAMP data processing, typically for geodetical purposes. This is encouraging for the upcoming orbit campaigns, in particular for JASON and GRACE.
• Dependencies between solutions tend to show up quite clearly from the combination of pairwise comparisons and SLR analysis. Dependent pairs of orbits show low RMS values in the comparisons because part of the systematic orbit error is common to both solutions. Nonetheless, their SLR residuals do not match the low pairwise difference values. This acknowledges the usefulness of the orbit campaign concept, and could lead to extensions of the performed analysis for applications outside the IGS LEO context. One could also state that the IGS LEO campaigns form part of the added value of the LEO data, even though this analysis is not aimed at enhancements of the IGS product family directly.