A New Strategy on Precise Clock Combination of IGS Analysis Centers
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Precise clock correction is the important basic data for estimating troposphere parameters, precise point positioning (PPP) and satellite precise orbit determination. In this paper, a strict and reliable clock combination approach is proposed. The main idea is as follows: the compatibility corrections of satellite orbit, station coordinates and geocenter offset are applied to Analysis Center (AC) clock solutions firstly. It aims at maintaining the consistency of all IGS combined products. The individual AC clock solutions’ offset and drift parameters with respect to the broadcast clock solutions are estimated using robust least square method. Then individual AC solutions are aligned to a common reference time-frame. The initial weights of clock combination are determined by posteriori mean square error of parameters estimate. Using robust estimation with high-breakpoint of pollution rate resists gross error. At last the final clock combination is obtained based on the weighted average method by iteratively calculating equivalent weights. The results show that combined clock solution obtained by the proposed method has commendable consistency with IGS final clock solution. The RMS of the discrepancy between combination clock and IGS final clock is about 0.03–0.05 ns, which is significantly better than the results of AC clock solutions. Combination clock correction is also more stable and reliable. Finally, static PPP test proves that the combination clock maintains the consistency of orbit and clock at millimeter level.
KeywordsClock combination Reference time-frame Robust estimation High-breakpoint of pollution rate
This work was supported by the State key laboratory of geodesy and geodynamics open funded projects (SKLGED2013-4-2-EZ) and the national natural science fund project (41174008) and the Open Foundation of State Key Laboratory of Astronautic and Dynamics (2014ADL-DW0101).
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