2 The residuals

 

 

Table 1: LLR residuals: time distribution of the rms (in centimeter). N is the number of normal points involved.

OBSERVATORY	Time	S1998	S2000	Time	S2001	N
and instruments	Interval	rms	rms	Interval	rms
McDONALD	1972-1986	34.7	34.5	1972-1975	43.5	1487
Telescope 2.70 m				1976-1979	27.7	1035
and MLRS1				1980-1986	29.1	990
CERGA Rubis	1984-1986	18.2	18.8	1984-1986	18.7	1165
HALEAKALA	1987-1990	11.1	8.0	1987-1990	6.3	451
McDONALD	1987-1998	5.0		1987-1991	5.8	232
MLRS2	1987-2000		3.8	1991-1995	4.6	586
				1995-2001	3.3	1669
CERGA Yag	1987-1998	4.8		1987-1991	5.3	1574
	1987-2000		3.8	1991-1995	3.9	2044
				1995-2001	3.0	3273

Table 1 shows the residuals in distance and illustrates the global precision of the solution S2001. As it was already mentioned for S2000, an important gain of precision has been obtained in our new solutions compared to S1998. Consequently the unknowns in S2001 are determined with a better accuracy than in S1998.

In order to estimate the evolution in the quality of the observations we illustrate in Fig. 1 the time distribution of rms obtained with S2001, for the data provided by the 2 modern instruments: MLRS2 for McDONALD and Yag for the CERGA.

Since 1991 we have observed smaller residuals for the CERGA except around 1997. It is worthwhile to note that this period corresponds to an offset in the CERGA measurements (Mangin 1998), which is taken into account in our analysis by a global correction of 0.7 ns for the observations from January 13, 1997 to June 24, 1998. During the same period, we also observe in the determination of various parameters a kind of "accidental jump'' (see, for example, in Fig. 4, the "jump'' occurring during this period for the correction to the IAU76 constant of precession).

Figure 1: Time evolution of rms for the 2 stations McDONALD and CERGA covering 14 years (solution S2001).