Estimation of Earth Rotation Parameter UT from Lunar Laser Ranging Observations

Abstract

Since 1969, Lunar Laser Ranging (LLR) data have been collected by different observatories and analysed by different analysis groups. In recent years, observations have been made with larger telescopes (APOLLO) and at infrared wavelengths, resulting in a better distribution of precise LLR data over the lunar orbit and the observed retro-reflectors on the Moon. In Germany, beginning in the early 1980s, the LUNAR software package was developed to study the Earth-Moon system and determine various related model parameters. Our research includes the physical libration and orbit of the Moon, the coordinates of observatories and retroreflectors, and, with special modifications, tests of Einstein´s theory of relativity such as parameters related to the equivalence principle, the time variation of the gravitational constant, and for a selection of PPN (Parametrized Post-Newtonian) parameters. Providing the longest time series of any space geodetic technique for studying the Earth-Moon dynamics, LLR can also support the estimation of Earth Orientation Parameters (EOP), such as UT1. The increased number of high-accuracy LLR observations allows for more accurate determination of EOP compared to previous years. Here, we focus on ∆UT results from different constellations such as single or multi-station results and on results for a different number of normal points per night. The mean uncertainty of the determined corrections to the IERS C04 series are about 18 µs. The findings are discussed in comparison to results from VLBI measurements. The ∆UT results of VLBI can be verified by LLR for selected nights.