IGS Analysis Center Workshop - IGS - NASA

discussion, a question as to whether the weighted orbits satisfy the orbit dynamics was raised. Theposition paper was subsequently amended to answer the question. It is shown that indeed theweighted average orbits under some conditions also satisfy the orbit dynamics.The differences between using one or two radiation scale parameters (in the X- and Z- directions)were raised and left to discretion of individual Centers. The net effect, as pointed out duringdiscussions, is that the difference between one or two radiation scale orbits introduces significantRMS of about 10cm as compared to 3-5cm for comparable (one scale) orbit estimation. Since thecurrent orbit disagreements are still larger and to foster some diversity (e.g. avoiding failures by allat the same time) both one or two radiation scale estimations were considered as acceptable. Notethat orbit comparisons in Section 3 of the position paper favor the one scale orbit estimation.Further discussion of the position paper related to significant improvements for reprocessed resultsas compared to originally computed and submitted ones. It was poin”ted out that there were onlyslight improvements for some Centers (e.g. CODE and EMR) mainly due to improved coordinatesand additional data and some major improvements mainly due to significant improvements in orbitestimations (e.g. ESA and GFZ). Consequently one can also see (Figure 2.5b) that even L] normestimation fails when most orbits are of poor quality. Here the two precise orbits (CODE, EMR)are both biased on account of the large variation of the other two orbit series. Obviously the L2norm estimation with appropriate weighting would have performed here better than the L 1 norm.Finally it was felt that it would be desirable for the January orbit test reprocessing to be completedby all remaining Centers. For Centers which have already reprocessed the data set, thisreprocessing only makes sense when new, improved estimation strategies are used.58