| The multiple taper method is optimal for bias control, and yields consistent estimates without section or band averaging. We apply this method to various length-of-day ({dollar}Delta{dollar}lod) and polar motion data sets from optical, satellite laser ranging (SLR), and very-long-baseline interferometry (VLBI) techniques.; We use the power spectrum to compare {dollar}Delta{dollar}lod data sets sampled at different times. The NGS and GSFC reductions of IRIS VLBI data, the IRIS intensive VLBI data (filtered and decimated to 5 day samples), and the CSR SLR data (filtered and decimated to 6 day samples) are consistent with the same model power spectrum. However, the GSFC SLR and CDP VLBI data are not consistent with this model. When the CDP observations are removed from GSFC's data, coherence between the NGS and GSFC data improves and is 0.8 or higher for all frequencies.; Lunar occultation {dollar}Delta{dollar}lod must be smoothed. The version of McCarthy and Babcock (1986) appears valid because its power spectrum and that of JPL's combined data fall off similarly.; For data after 1984, the power spectra of SLR and VLBI data fall off similarly. However, signals from the two systems are not coherent for frequencies above about 20 cycles per year.; We use several data sets to construct a composite power spectrum for {dollar}Delta{dollar}lod. This spectrum bends between 1 and 5 cycles per year. The power spectrum of NMC atmospheric data has similar structure. Coherence between {dollar}Delta{dollar}lod and the NMC atmospheric data is very low below the seasonal band. This is not true for coherence between {dollar}Delta{dollar}lod and EC atmospheric data; however, these estimates are based on record lengths of less than 3 years. The results suggest that the transition between core and atmospheric excitation of changes in {dollar}Delta{dollar}lod occurs between 1 and 5 cycles per year.; For polar motion, the power spectrum of IRIS VLBI data lies about 15 dB below the ILS power spectrum at high frequencies. There is no evidence that the Chandler band is split. The retrograde annual wobble is much smaller in the space geodetic data, suggesting that the optical data is contaminated with an annual systematic error. |
