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Published online by Cambridge University Press: 12 April 2016
A comparison of polar motion results from three sources [Bureau International de l’Heure (BIH), Defense Mapping Agency Hydrographic/Topographic Center (DMAHTC-Doppler), the International Polar Motion Service (IPMS)] was performed using lunar laser ranging (LLR) data. The rms errors, both of the LLR data and of the determinations of polar motion by the three services, decreased in recent times. The BIH and Doppler polar motion are comparable in quality (12 ± 6 cm for BIH values taken from August 1976 through May 1980, 14 ± 7 cm for Doppler results taken from June 1977 through May 1980). The IPMS errors were substantially larger (33 ± 7 cm for data taken from August 1976 through May 1980). All three analyses give 13 ± 3 cm as an estimate for the combined LLR modeling, fitting, and instrumental error (noise) for the last four years.