Celestial pole offsets from lunar laser ranging and comparison with VLBI

Abstract

Context. The analysis of lunar laser ranging (LLR) observations is based on determining the round-trip travel times of light pulses between stations on the Earth and reflectors on the surface of the Moon. Several works have demonstrated that this technique is powerful in various domains including astronomy, geodynamics and gravitational physics. Aims. In the field of geodynamics, LLR contributes to the realization of a dynamical celestial reference frame, in contrast to very long baseline interferometry (VLBI) that determines a kinematical celestial reference frame. In this paper, we have determined corrections to the celestial pole coordinates, denoted X, Y, using LLR observations. This determination is of particular interest for comparison with the one obtained from VLBI observations. The main purpose is to study the benefits of LLR for the determination of the celestial pole coordinates and second how to best combine the time series obtained from both techniques. Methods. For these determinations, data acquired by LLR tracking stations since 1969 were analyzed and corrections to the nutation terms estimated using a weighted least square fit. Finally, LLR data were combined with the IVS combined VLBI series of 23-year duration. Results. We have demonstrated the possibility of determining the celestial pole offsets from LLR data even though the results are not as accurate nor as dense as those obtained with VLBI. This work provides some external constraints to the celestial pole coordinates derived from VLBI observations. Moreover, the LLR determination of the long periodic nutation terms shows an improvement with respect to previous studies. The combination of LLR and VLBI series may indicate that the combined series reveal details that do not appear in the VLBI series alone.

Testing various facets of the equivalence principle using lunar laser ranging

“…• initial values of the lunar orbit and rotation, which are used for the calculation of lunar ephemeris with highest accuracy (Williams et al 2008, Fienga et Müller 2009, Zerhouni andCapitaine 2009), • the tidal bulge lag angle, indicating the lunar tidal acceleration and • parameters of the lunar interior .…”

Lunar laser ranging test of the Nordtvedt parameter and a possible variation in the gravitational constant

“…Up to now, approximately 17 000 NPs were collected and serve as observations for the analysis. Various components of the EarthMoon system dynamics can be addressed, e.g., initial conditions for the lunar orbit and rotation, reflector and station coordinates, Earth orientation parameters Zerhouni & Capitaine 2009), nutation coefficients , and also studies of the lunar interior ). In addition, LLR is used to test general relativity ), e.g., the strong equivalence principle (EP) (Müller & Nordtvedt 1998;Nordtvedt et al 1995), temporal variation in the gravitational constant G (Müller & Biskupek 2007;Williams & Folkner 2009), metric parameters, and preferred frame effects (Soffel et al 2008).…”

Commission 19: Rotation of the Earth

“…The IVS center managed by Sébastien Lambert (and Anne-Marie Gontier, deceased in 2010) delivers SINEX normal equations that are included in the IVS EOP combined solution. The department also gives attention to Lunar Laser Ranging observations, which may improve the knowledge of multi-year variations of the celestial pole offsets (Zerhouni and Capitaine 2009). …”