Analysis of Systematic Errors in Geocenter Coordinates Determined From GNSS, SLR, DORIS, and GRACE

Abstract

Abstract The goal of this paper is to determine and analyze the common geocenter signal from the geocenter coordinates based on four independent techniques: Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Global Navigation Satellite System (GNSS), Gravity Recovery And Climate Experiment with the ocean bottom pressure model, and Satellite Laser Ranging, and to analyze the residuals as the differences between these geocenter coordinates and their common signal. Another objective of this paper is to compute variable amplitudes and phases of the annual and semi-annual oscillations in the geocenter coordinates of these techniques by the combination of the Fourier Transform Band Pass Filter (FTBPF) with the Hilbert Transform (FTBPF + HT) and to compare their mean values with those obtained by other authors. It was assumed that the geocenter time series of individual techniques consist of the common signal of geocenter motion, systematic errors resulting from orbital modeling and noise. Generally, the annual oscillation amplitudes in these techniques computed by the FTBPF + HT vary in time and their mean values are of the order of 2 mm for the X coordinate, 2.4–3.6 mm for the Y coordinate and 2.8–5.6 mm for the Z coordinate and the semi-annual oscillation amplitude is variable and about two times smaller than the annual one. The phases of these two oscillations are also variable, there are differences in their mean values for different techniques and the semi-annual oscillation phases changes throughout the entire phase range. To detect the common geocenter signal the wavelet-based semblance filtering (WBSF) method was applied. The weighted mean model was computed from all geocenter coordinate pairs from individual techniques assuming weights as inversely proportional to the variances of differences between the geocenter coordinates and their corresponding WBSF outputs. The average and median models computed from these outputs show a good agreement with the weighted mean model and generally, the average amplitudes of the annual signal in these models are of the order of 2 mm in each geocenter coordinate. The FTBPF amplitude spectra of these models reveals the retrograde annual oscillation in the XY equatorial plane. The FTBPF and FTBPF + HT amplitude spectra of geocenter time series and their residuals show mainly the maxima of different heights in the annual frequency band. The annual oscillations left in all residuals and oscillations with period less than ~ 120 days in DORIS and GNSS amplitude spectra may be caused by systematic errors of techniques resulting from mis-modeling of satellite orbits.