Study of the high-frequency structure of polar motion derived from LAGEOS ranging data

摘要: The spectrum of polar motion at or near 1 cycle per day contains very valuable information. For example, the celestial ephemeris pole International Astronomical Union (IAU) 1980 nutation theory has, by definition, no body fixed nor space motions. But is also known to be affected a nonnegligible error annual frequency, so that one expects visible in coordinates as (nearly) diurnal motion. In addition, if are determined from satellite tracking data, absence dirurnal changes direct consequence use correct dynamical model orbit. There reason search for nearly free wobble associated core nutation, due stringent upper limits recently set long baseline interferometry (VLBI) observations. requirements dense and uniform data distribution, both temporally geographically, constructing meaningful spectra have been, past, incompatible with available data. uniformily sets now obtained laser ranging LAGEOS satellite. To investigate frequencies, we selected six arcs criteria temporal spatial distribution range possible enough provide an acceptable spectral resolution. each these accurate has been using reduced version NASA GEM T1 IAU theory. Station three Earth rotation parameters 1-day interval were least squares adjusted simultaneously Keplerian parameters, along-track acceleration, solar radiation coefficient. Then orbit station constrained previously found values estimated hourly intervals. resulting time series, when compared independent VLBI determination 5-day intervals, show excellent agreement stability. They indicate presence signal. Spectral analysis yields amplitudes signal 3.8 milliarc seconds (mas) (1 mas = 0.001″) 1.4 mas, exception 12.8 mas. positive frequency all cases, sense recovered counterrotating relative Chandler wobble. We examine causes signal, such nonuniform and/or mismodeling Earth/ocean tides, incorrect choice initial vector state orbit, adopted Our indicates being repeatable maintaining phase coherence between contiguous unlikely originate but more probably due, perhaps different proportions arc arc, combination errors. two are, principle, separable: amplitude satellite, while varies orbital inclination node. should disappear form repeated corrected coefficients consistent