Geocentre motion measured with DORIS and SLR, and predicted by geophysical models

Abstract

Geocentre motion signals measured by satellite geodesy and those predicted from the observed mass redistribution in the ocean, atmosphere and terrestrial waters over 1993.1–2003.0 are analysed and compared under two viewpoints: the amplitudes and phases of the seasonal components, and the spectral signature of the non-seasonal components. The geodetic signals partly match the geophysical variations in the seasonal band, with possible remaining annual and semi-annual errors in both techniques, at the millimetre level in the equatorial plane for Satellite laser ranging (SLR) and Doppler Orbitography and radiopositioning integrated on Satellite (DORIS), and at the centimetre level in T z (Z-axis translation) for DORIS. Unlike SLR, the DORIS annual signatures in all three geocentre components have strongly varying amplitudes after 1996. The amplitude of the annual geophysical signal in T y is slowly growing with time. All three geophysical fluids contribute to this effect. The magnitude of the geophysically derived long-term geocentre motion is of the same magnitude in the T x , T y and T z directions, with a 0.5–1.0 mm Allan standard deviation for the 1-year sampling time, while the geodetic values are 2 mm in the equatorial plane for both SLR and DORIS, 4 mm for SLR and 9 mm for DORIS in the T z direction. The mismatch of the geodetic signal with the geophysical one in the inter-annual band is suggested to be due partly to excessive geodetic noise and partly to underestimated geophysical signal.