Residuals between satellite observed positions, reduced from the four theories and from the multi-theory method, and computed positions derived from these four theories. Residuals are computed for all observations of calibration satellites given in Table 1 and are expressed in arcseconds Table 5.1. 0.0879 0.1030 Table 5.2. 0.0831 5.2 Analysis of differences between observations reduced from different theories We shall try to evaluate the bias pointed out above. We have determined, for each satellite, differences between the four successive positions, obtained from each theory in the CCD reduction, and positions derived from the multi-theory method, used as a reference method, described above in the introduction.
Ordinates are in arcseconds.
Ordinates are in arcseconds. Abscissas give the sequence of nights of observation From a preliminary analysis, all differences appearing in Figs. This confirms our preliminary evaluation of the consistency of reduction methods using satellite theories obtained above from residuals of Table 4 . However, some exceptions appear, especially in Fig. 1 . Such a bias can be confirmed from the analysis of Table 6 which presents mean values of differences visualized in Figs.