The contribution of LLR data to the estimation of the celestial pole coordinates

1. 2 3 1 Figure 4 (red : fitted parameters, blue : DX or DY) Figure 5 Figure 3 (red : fitted parameters, blue : DX or DY) (red : fitted parameters, blue : DX or DY) The contribution of LLR data to the estimation of the celestial pole coordinates Wassila Zerhouni (1), Nicole Capitaine (1), Gerard Francou (1) (1) Observatoire de Paris / SYRTE , 61 Avenue de l’Observatoire 75014 Paris Wassila.zerhouni@obspm.fr,Nicole.capitaine@obspm.fr,Gerard.francou@obspm.fr A Lunar Laser observation is, at a date t0 , the duration Δt between laser pulses from a telescope on the Earth toward a reflector on the Moon, and its detection on Earth by the same station. McDonald 1969 – 2006 LLR data Haleakala 1987 – 1990 Cerga 1984 – 2005 In this study, we focus on the determination of the Earth Orientation Parameters (EOP) especially, the direction towards the Celestial Intermediate Pole (CIP) in the Geocentric Celestial System. We have first calculated the LLR residuals over a period of more than 37 years, using IAU 2000A-2006 as a model of precession nutation and the CIO based procedure. Second, we have determined the corrections to the the IAU 2000A-2006 X and Y coordinates every 70 days, and analysed the signal. Time evolution of LLR data • First step : • Calculation of the LLR residuals using IAU 2006-2000A as a model of precession nutation (i.e MHB 2000 nutation of Mathews et al. 2002 and P03 precession of Capitaine et al. 2003) using the CIO based procedure. • Second step : • Fitting X andY coordinates of the Celestial Pole to the IAU2006-2000A modelevery 70 days (figure 1). Figure 2 represents the formal errors Correlation coefficients : The correlation coefficients between the parameters are given in Table 3 and Table 4. It should be noted that only correlations greater than 0.5 are provided. Table 3 Table 4 • Third case : the 18.6 term.The resulting fit is shown on figure 5 and the numerical estimates of the amplitudes in Table 5. Figure 1 Figure 2 Third step : • In order to analyse the signal we have obtained, we have made a new analysis with fitting : • First case : the long-term nutation parameters (18.6, 9.3 year, a secular term, and a constant term). The resulting fit is shown on figure 3 and the numerical estimates of the amplitudes in Table 1. Table 5 Comparison with VLBI : Table 1 Second case : the annual and semi annual terms. It should be noted that in this case we have removed the FCN (Free Core Nutation) using a model derived from VLBI analysis. The resulting fit is shown on figure 4 and the numerical estimates of the amplitudes in Table 2. IVS combined solution (ivse08q1.eops) Table 6 Discussion and Conclusion : From LLR observations, it is possible to determine the celestial pole coordinates. Due to the imperfect distribution of the data, the precision of the results is not at the same level as with VLBI. The next step will be to combine LLR results with VLBI celestial pole offsets in order to benefit from both techniques References : Capitaine et al. 2003, Astron. Astrophys., 412, 567-586.. Chapront et al.1999, Astron. Astrophys., 343, 624-633 Chapront et al. 2002, Astron. Astrophys., 387, 700-709 Mathews et al.2002, J.Geophys. Res, 107(B4), 10.1029/2001JB00390. , McCarthy, D. D. 1996, IERS technical Note 21: IERS Conventions (1996). IERS technical Note 32 : IERS Conventions (2003) SOFA : www.iau-sofa.rl.ac.uk Table 2